Patent Publication Number: US-9892584-B1

Title: Managing electronic keys

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation (and claims the benefit of priority under 35 USC 120) of U.S. application Ser. No. 14/605,788, filed Jan. 26, 2015, now allowed, which is a continuation of U.S. application Ser. No. 13/735,102, filed Jan. 7, 2013, now U.S. Pat. No. 8,943,187, issued Jan. 27, 2015, which claims the benefit of U.S. Patent Application Ser. No. 61/694,992, filed on Aug. 30, 2012. All of the prior applications are incorporated herein by reference in their entirety. 
    
    
     TECHNICAL FIELD 
     This disclosure relates to managing electronic keys. 
     BACKGROUND 
     Locks are used to control access to many items and areas, such as buildings, vehicles, and storage containers. Frequently, a lock is opened with a physical key shaped for the lock. Typically, different locks are opened with different keys. Consequently, many people carry several physical keys in order to be able to open different locks. 
     SUMMARY 
     This disclosure relates to managing electronic keys. 
     The details of one or more implementations are set forth in the accompanying drawings and the description, below. Other potential features and advantages of the disclosure will be apparent from the description and drawings, and from the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a diagram illustrating an example of a user interface for transferring an electronic key using a social networking platform. 
         FIG. 1B  is a diagram illustrating an example of a user interface for setting conditions on use of an electronic key. 
         FIGS. 1C and 1D  are diagrams illustrating examples of user interfaces for notifying a recipient of a transfer of an electronic key. 
         FIG. 1E  is a schematic diagram illustrating an example of a system for using an electronic key. 
         FIGS. 2A and 2B  are schematic diagrams illustrating examples of electronic social networking platforms. 
         FIG. 3  is a block diagram illustrating an example of a communications system. 
         FIG. 4  is a schematic diagram illustrating an example of a system for managing electronic keys. 
         FIGS. 5A-5E  are schematic diagrams illustrating examples of techniques for using electronic keys. 
         FIG. 6  is a flow diagram illustrating an example of a process for transferring an electronic key using a social networking platform. 
         FIG. 7  is a flow diagram illustrating an example of a process for using an electronic key. 
         FIG. 8  is a table illustrating example key data. 
         FIG. 9  is a diagram illustrating an example of a user interface for approving use of an electronic key. 
         FIG. 10  is a diagram illustrating an example of a user interface for providing information about electronic keys. 
         FIG. 11  is a flow diagram illustrating an example process for modifying an electronic key based on actions of a recipient of the electronic key. 
         FIG. 12  is a diagram illustrating an example of a user interface for providing an alert about an electronic key 
     
    
    
     DETAILED DESCRIPTION 
     Techniques are described for enabling users to distribute electronic keys to other users. For example, techniques are described for enabling users of a social networking platform to distribute electronic keys to other users of the social networking platform. In some implementations, a user of the social networking platform selects a lock that the user controls, such as a lock for a door to the user&#39;s house or lock for the user&#39;s vehicle. The user also selects a member of the user&#39;s social network as a recipient for a key to the lock. For example, the user may select the recipient of the key from among users designated as friends of the user in a social networking platform. A key management server issues to the recipient an electronic key that opens the lock. The recipient can then use an electronic device, such as a mobile phone, to activate the electronic key, thereby opening the lock. For example, the recipient&#39;s electronic device can receive access data from the key management system, and the electronic device can provide the access data to the lock to open the lock. 
     The user that issues the electronic key may impose one or more conditions on the use of the electronic key by the recipient. For example, the issuer may limit a number of times the electronic key may be used, limit a window of time during which the electronic key may be used, require the recipient to possess certain qualifications to use the electronic key, and/or place other restrictions or constraints on use of the electronic key. In some implementations, when one or more conditions are imposed on the use of an electronic key, the key management server determines whether the one or more conditions are satisfied each time use of the electronic key is attempted. When all of the one or more conditions are determined to be satisfied, the key management server permits the lock to be opened. When the one or more conditions are not satisfied, the key management server does not permit the lock to open. 
     In some implementations, managing electronic keys using social networking platforms allows users to quickly and conveniently provide keys to other users. By selecting the recipient for an electronic key from among the user&#39;s social networking connections, a user can quickly select recipients whom the user trusts. Using social networking connections to transfer the electronic key can also help ensure that the intended recipient, instead of someone else, actually receives the electronic key. Selecting a recipient with whom the issuer has a relationship in a social networking platform can help avoid a transfer to an incorrect user due to, for example, mistyping an electronic address or designating a user with a name that is confusingly similar to the name of the desired recipient. 
     In some implementations, issuing an electronic key rather than a physical key may provide a number of other advantages. Electronic keys can be transferred through remote action of the issuer, while physical keys must be physically transported from one location to another. When a user issues an electronic key, the user&#39;s own ability to open the corresponding lock is not diminished. By contrast, a person that transfers a physical key must give up use of the physical key to complete the transfer. A user may issue multiple electronic keys without affecting the user&#39;s own access, and without incurring the expense of duplicating a physical key. Further, after an electronic key has been issued, the user may revoke or temporarily disable the electronic key quickly and remotely. 
     In some implementations, electronic keys relieve the recipient of the electronic keys of the need to carry multiple keys. Rather than carry multiple physical keys each of which is dedicated to opening a particular lock, a single electronic device, such as a mobile phone, can act as the key to open any lock for which an electronic key has been granted. In addition, electronic keys can be linked to a user identity rather than being limited to a single physical device. For example, if a user&#39;s personal mobile phone is unavailable, the user may log in to his user identity using another electronic device to use electronic keys granted to him. When electronic keys are linked to a user identity, the electronic keys may be less likely to be misplaced or stolen than physical keys. 
     In some implementations, by setting conditions on the use of electronic keys, users can specify the type of access permitted to particular recipients of an electronic key. Different recipients of an electronic key can be given different levels of access selected by the key issuer. In addition, the issuer of an electronic key can also change the conditions for use of an electronic key quickly and remotely, for example, through interaction with a server system over a network. The issuer may thus retain a degree of control over electronic keys, through conditions on the use of the electronic keys and/or through the ability to revoke the electronic keys. 
     As an example, a parent may issue to a teenage child an electronic key to an automobile. The parent may place conditions that allow unrestricted use of the electronic key during designated times, such as on weekdays between 7:00 am and 9:00 am and 3:00 pm and 6:00 pm, to allow the child to travel to and from school. The conditions can specify that, at other times, each use of the electronic key to start the ignition for the automobile requires approval from the parent, which the parent can provide remotely using his or her mobile phone. In addition, the electronic key issued by the parent may be a “valet key” that, for example, permits entry to the vehicle and ignition, but does not provide access to storage compartments or other functionality of the automobile. 
     As another example, an executive may grant to his assistant an electronic key that unlocks the executive&#39;s office door. However, the executive can impose the condition that the electronic key may only be used when the executive is not present in the office. The executive may also grant, to each of the information technology staff and cleaning staff in the company, an electronic key that unlocks the office. The conditions on the electronic key can require that, for these recipients, the electronic key can only be used when the executive is not present in the office and one of a designated set of supervisors is present at the office. 
     In some implementations, a system receives data identifying a recipient for an electronic key to a physical lock, where the recipient is connected to the user in a social networking platform. The system also receives data identifying the physical lock to which the user desires to provide the electronic key. The physical lock may be selected from a set of locks to which the user has authority to grant access. The system receives data indicating one or more conditions on use of the electronic key. The system stores, in electronic storage, key data that identifies the recipient of the electronic key, the lock for which the electronic key is granted, and the one or more conditions on use of the electronic key. The system accesses, from profile data for the recipient from the social networking platform, an electronic address for the recipient. The system transmits, to the electronic address for the recipient, data that indicates that the electronic key is transferred to the recipient. The system transmits, to the electronic address for the recipient, data that enables the recipient to use the electronic key in accordance with the one or more conditions on use of the electronic key. 
     Thereafter, the system may receive, from an electronic device, use data indicating an attempted use of the electronic key. The request may identify the electronic key and include description information that describes the attempted use of the electronic key. The system accesses the stored key data, and evaluates the description information against the key data. Based on the evaluation, the system determines that the attempted use of the electronic key satisfies the one or more conditions on use of the electronic key. In response to determining that the attempted use of the electronic key satisfies the one or more conditions, the system transmits, to the electronic device, an access code that unlocks the lock. 
       FIGS. 1A-1E  illustrate an example of transferring an electronic key from a user, referred to as a key issuer, to a recipient. The key issuer selects the recipient for the electronic key and the lock that the electronic key will open ( FIG. 1A ). The key issuer also selects one or more conditions that limit use of the electronic key ( FIG. 1B ). The recipient is notified that the electronic key has been issued ( FIGS. 1C and 1D ), and the recipient then uses the electronic key to open the lock ( FIG. 1E ). 
       FIG. 1A  illustrates an example of a user interface  100  for transferring an electronic key using a social networking platform. The user interface  100  may be displayed on a phone or other electronic device  102 . In some implementations, the user interface  100  is provided by an application running on the electronic device  102 . In other implementations, the user interface  100  is a rendering of a web page or other document. 
     The user interface  100  enables the key issuer to select one or more recipients to receive an electronic key. In particular, the user interface  100  identifies members of the key issuer&#39;s social network in a social networking platform. Examples of social networking platforms include Facebook, Twitter, LinkedIn, Google+, MySpace, and Orkut, to name a few. Electronic social networking platforms may permit human users of the social networking platform to create user identities within the social networking platform and establish connections with the user identities of other users. The members of the key issuer&#39;s social network include, for example, users whose social networking user identities are connected to the social networking user identity for the key issuer within the social networking platform. 
     Electronic social networking platforms may indicate a variety of relationships between human users of the social network. Examples of these relationships include social friendships, family relationships, professional relationships, and affiliations with groups or organizations. Relationships are often represented by connections between user identities corresponding to the respective human users. When a connection exists between user identities, and thus a relationship also exists between the associated human users, one user may be termed a “friend,” a “connection,” a “follower,” or a “subscriber” of another user, or the relationship may have another designation. 
     In the illustrated example, the user interface  100  includes user interface elements  105   a - 105   e  that identify users who are connected to the key issuer in a social networking platform (e.g., users designated in a social networking platform as friends of the key issuer, family members of the key issuer, etc.). Also in the illustrated example, each of the user interface elements  105   a - 105   e  includes a name and photo from the social networking profile for the corresponding user. Other information from the social networking profile of a user (e.g., current status, hometown, current location, etc.) may additionally or alternatively be displayed. In addition, or as an alternative, data indicating the relationship of the social networking contact to the user in a social networking platform can be provided (e.g., whether a social networking contact is designated as a friend, a close friend, a family member, a co-worker, etc. in one or more social networking platforms). 
     By interacting with the user interface elements  105   a - 105   e , the key issuer may select a set of users to designate as recipients for the electronic key. For example, the key issuer may tap or otherwise interact with the user interface elements  105   a - 105   e  on a touchscreen of the electronic device  102  to select the users as recipients of the electronic key. Additionally or alternatively, the key issuer may utilize another input mechanism (e.g., a pointing device like a computer mouse or a keyboard) to interact with the user interface elements  105 ( a )- 105 ( e ). 
     In some implementations, the user interface  100  identifies users who are connected to the key issuer in different social networks. For example, multiple lists of friends of the key issuer can be included, where each of the multiple lists identifies friends of the key issuer in a different social networking platform. As another example, data from multiple social networking platforms may be combined so that users connected to the key issuer in different social networking platforms may be listed together in a single list or interface. 
     In some implementations, a set of multiple users can be identified on the user interface  100 , and the key issuer can select the entire set to provide the same electronic key to each member of the set. For example, a subset of a user&#39;s friends (e.g., co-workers) can be defined in the social networking platform. The key issuer may be able to select a user interface element representing the subset to select all of the users in the subset to receive the electronic key. 
     The user interface  100  also enables the key issuer to select one or more locks that the electronic key will open. By selecting one or more locks, the key issuer can designate the type of electronic key that will be issued (e.g., a key to the key issuer&#39;s car, home, office, boat, etc.). The locks can be physical locks that control access to a physical device or physical space. For example, the locks can secure the door of a room or building, the ignition of a vehicle, entry to a file cabinet or safe, and so on. 
     In the illustrated example, the user interface  100  includes user interface elements  106   a - 106   d  that indicate locks for which the key issuer is authorized to grant keys (e.g., locks for which the key issuer owns access control). For example, the locks identified by the user interface elements  106   a - 106   d  can be locks that the key issuer or another user has previously registered as being under the key issuer&#39;s control. In some implementations, a key management system verifies the key issuer&#39;s authority to grant access to locks, and indicates only locks that have been successfully verified. In some implementations, if the key issuer has received an electronic key from another user and is permitted to share the key with others, the corresponding lock can be included in the list of locks to which the key issuer has been granted access. 
     After selecting one or more recipients for the electronic key and selecting one or more locks that the electronic key will open, the key issuer may interact with one or more controls  108  to submit the data indicating the selections to a key management system. The key management system may provide an electronic key to the selected recipients. In some implementations, transferring the electronic key does not affect the key issuer&#39;s access to the lock, but extends access to the recipient that the recipient did not previously enjoy. The key issuer may also set one or more conditions for use of the electronic key, as described further below. 
       FIG. 1B  illustrates an example of a user interface  110  for setting conditions on use of an electronic key. The user interface  110  may be displayed on the electronic device  102 , for example, during the process of initially transferring an electronic key or when modifying an electronic key that has already been transferred. In some implementations, the user interface  100  is provided by an application running on the electronic device  102 . In other implementations, the user interface  100  is a rendering of a web page or other document. 
     The user interface  110  enables the key issuer to set the properties of an electronic key. In the illustrated example, the user interface  110  includes user interface elements  112   a ,  112   b  that identify the electronic key being modified. For example, the user interface element  112   a  identifies the user that is the recipient of the electronic key, and the user interface element  112   b  identifies the lock that the electronic key opens. 
     The user interface  110  enables the key issuer to select one or more conditions on the use of the electronic key. The conditions may specify limits to the use of the key by the recipient and/or limits to the ability of the recipient to transfer the key to others. In the illustrated example, the user interface  110  includes user interface elements  115   a - 115   g  that specify various conditions, which the key issuer may select to apply to the electronic key. 
     The key issuer may set time conditions that regulate the time that the electronic key may be used by the recipient. For example, the key issuer may specify a range of time during which the electronic key can be used by indicating a start time and/or end time that the electronic key is operable. In the illustrated example, the user interface element  115   a  specifies a condition that the electronic key will expire, and thus not be operable, after a particular date. A time condition may specify a recurring range of time during which the electronic key can be used (e.g., on weekends; nightly from 6:00-9:00 pm; etc.). 
     Some conditions on use of the electronic key may require that the recipient possess particular credentials or qualifications to use the electronic key. For example, the user interface element  115   b  specifies a condition that the electronic key for the vehicle is operable only when the recipient possesses a valid driver&#39;s license. Other examples of qualifications that may be required include meeting an age requirement (e.g., recipient must be at least a minimum age), holding a particular position in a company, and having no criminal record. 
     Conditions on use of the electronic key may require approval from the key issuer for actions requiring use of the electronic key. For example, the user interface element  115   c  specifies that each use of the electronic key requires approval of the key issuer. In some implementations, when the recipient attempts to use the electronic key, a key management system provides information about the attempted use to an application running on an electronic device associated with the key issuer. The application asks whether the key issuer approves the attempted use, and the key issuer can grant or deny approval. The input from the key issuer is transmitted to the key management system, which permits the electronic key to be used only if the attempted use was approved. 
     Conditions on use of the electronic key may limit the number of uses of the electronic key, as indicated by the user interface element  115   d . For example, a key issuer may grant an electronic key that permits only a single use, or a predetermined number of uses (e.g., 3 uses, 10 uses, 20 uses, etc.). 
     Conditions on use of the electronic key may require the presence of the key issuer, the recipient, or others at the lock, or may require their absence, when the electronic key is used. The presence of a user can be determined based on the location of an electronic device associated with a user, near-field communication (NFC) between the electronic device and the lock, passwords, biometric input, and other techniques. As an example, a condition may specify that the electronic key is operable only when the key issuer is not present at the site of the lock. With this condition, the key issuer can avoid being disturbed by the entry of an unannounced visitor. The key issuer can be determined to be present near a lock when, for example, GPS data or other location data indicates that a phone or other electronic device associated with the key issuer is located within a threshold distance of the lock, or that the key issuer has opened the lock within a predetermined amount of time (e.g., 2 hours, 6 hours, 1 day, 3 days, etc.). 
     As another example, a condition can specify that the electronic key is only operable when the identity of the recipient is confirmed at the time the electronic key is used. Conditions may require multi-factor authentication of the recipient for an electronic key to be operable. For example, in addition to providing data identifying the recipient&#39;s phone or other electronic device, the recipient may be required to enter a password, provide a biometric input (e.g., through a fingerprint scan, retina scan, iris scan, facial image, speech sample, etc.), or provide another identifying input. 
     Conditions may also require the presence of a person at the site of the lock in addition to the recipient. For example, the electronic key may be operational only when the recipient is accompanied by one of a designated set of individuals, or by an individual that satisfies one or more criteria. For example, a teenager with a new driver&#39;s license may be issued an electronic key for a vehicle, with the condition that another person at least 21 years old that holds a driver&#39;s license must also be present. As another example, an employee may be granted an electronic key that opens a safe, but the electronic key is operational only when a manager or security guard is present with the employee. The presence of a particular person can be verified based on the presence of an electronic device associated with the particular person at the site of the lock, entry of a password, biometric input, and/or other techniques. 
     Conditions can also specify to what extent, if any, the recipient is permitted to transfer the received electronic key to other users. The user interface  110  includes user interface elements  115   e - 115   g  that indicate various conditions that affect transferability of an electronic key. The key issuer may specify that an electronic key is not transferrable, as shown by the user interface element  115   e . The key issuer may specify that the electronic key may be transferred to only a limited set of users, for example, users who have a particular relationship with the key issuer in one or more social networks. As indicated by the user interface element  115   f , transfers may be limited to friends of the key issuer. In a similar manner, transfer of the electronic key can be limited to users who are connected to both the key issuer and the recipient in one or more social networks. In addition, or as an alternative, the key issuer may specify that each transfer of the electronic key requires approval from the key issuer. 
     In some implementations, when a first recipient transfers a received electronic key to a second recipient, the conditions on use of the electronic key for the first recipient are also applied to the electronic key received by the second recipient. In some implementations, additional or different conditions may be placed on the electronic key after the transfer. 
     After the key issuer selects the conditions, if any, that the key issuer desires to impose for the electronic key, the key issuer may interact with one or more controls  118  to save or confirm the selections. The key management system receives data indicating the conditions, and saves data identifying the conditions. The key management system then notifies the recipient of the newly issued key. 
       FIG. 1C  illustrates an example of a user interface  120  for notifying a recipient of a transfer of an electronic key. The user interface  120  may be displayed on a phone or other electronic device  122 , for example, the mobile phone of the recipient or another electronic device associated with the recipient. In some implementations, the user interface  120  is provided by an application running on the electronic device  122 . In other implementations, the user interface  120  is a rendering of a web page, electronic mail message, or anther document. 
     In some implementations, the key management system notifies a recipient when an electronic key is issued to the recipient or when conditions on the recipient&#39;s electronic key are modified. In the illustrated example, the user interface  120  notifies a recipient that a new electronic key has been issued to the recipient. The user interface  120  includes one or more indicators  124  that identify the lock that the electronic key opens, for example, with an identifier (e.g., address, room number, license plate number, etc.), image, and/or description. The user interface  120  also includes one or more user interface elements  126  that identify the conditions that limit use of the electronic key. The user interface  120  can provide identifying information  128  that identifies the key issuer, for example, a name, a social networking identifier, a photo, an electronic address, or other identifying information. 
       FIG. 1D  illustrates an example of a user interface  130  for notifying a recipient of a transfer of an electronic key. The user interface  130  may be displayed on a phone or other electronic device  122 , for example, the mobile phone of the recipient or another electronic device associated with the recipient. In some implementations, the user interface  120  is provided by an application running on the electronic device  122 . In other implementations, the user interface  130  is a rendering of a web page, electronic mail message, or anther document. 
     In some implementations, notifications about electronic keys can be provided through a social networking platform, in addition to, or as an alternative to, the notification shown in  FIG. 1C  and notifications through other channels (e.g., an SMS text message, an electronic mail message, etc.). In the illustrated example, the key management system distributes information about the electronic key in a user interface used to access a social networking platform, such as a “home page” or “wall” of the recipient. For example, when the recipient logs into the social networking platform, information about the electronic key may be provided as a status update, post, item in a news feed, or other social networking message or notice. Like the user interface  120  of  FIG. 1C , the user interface  130  includes one or more user interface elements  132  that describe the electronic key by identifying, for example, the key issuer, the lock that the electronic key opens, and conditions on use of the electronic key. 
     In some implementations, the electronic device  122  receives access data that permits the electronic device  122  to open the lock. The key management system may provide the access data when the recipient logs into a key management application (e.g., executing on the electronic device and/or on a remote server) after the electronic key has been issued. The access data may be, for example, a numeric code, a text sequence, or data encoded in another form. For example, the access data may include data from which a Quick Response (QR) code, a bar code, or another image may be rendered. The electronic device  122  may display the image, and a scanner on the lock may read the image to confirm that access is permitted. As another example, the access data can describe a signal, such as a radio-frequency signal, infrared signal, or an ultrasonic signal (e.g., a sound wave with a frequency of approximately 20 kHz or more). The electronic device  122  can output the signal to the lock to transmit the access code, for example, using near-field communication (NFC) techniques, an electromagnetic radiation source, and/or a loudspeaker. 
     In some implementations, the access data may be stored on the electronic device  122 , permitting the electronic device  122  to act as a key to open the lock. In some implementations, however, additional data, or other data, is required to open a lock. For example, data from the key management system may be required to verify that conditions on use of the electronic key are satisfied, as described further below. When an electronic key is revoked or disabled, the key management application on the electronic device  122  may delete or otherwise disallow access to the stored access data. 
       FIG. 1E  is illustrates an example of a system  150  for using an electronic key. The recipient  152  of the electronic key uses the electronic device  122 , such as a mobile phone, to apply the electronic key to a lock  158 . The electronic key enables the recipient  152  to gain access to a resource  156  secured by the lock  158 . The resource  156  can be a physical resource (e.g., such as a physical object or area). The lock can be a physical lock, such as a device that mechanically limits entry or access to, or operation of, a physical resource. In the illustrated example, the recipient  152  uses the electronic key to gain entry to a vehicle and start the ignition of the vehicle. The electronic device  122  communicates with a key management system  160  over a network  162  to open the lock  158 . 
     The lock  158  may be attached to, be controlled by, or include control logic (implemented as hardware, software, or a combination thereof) that determines when the lock  158  should be unlocked. For example, the lock  158  may determine whether a received code is valid to open the lock  158  (e.g., whether the code matches a predetermined code). Mechanical locking mechanisms may be manipulated by electronics that operate responsive to outputs from the control logic. 
     The lock  158  may include one or more mechanisms for communicating with persons and other devices. The input mechanisms may include, one or more of, for example, a camera, a microphone, a keypad, a touchpad, a touchscreen, a proximity sensor, an infrared receiver, an ultrasound receiver (e.g., a microphone), a fingerprint scanner, an iris scanner, a retina scanner, an RFID reader, a bar code reader, and a QR code reader. The input mechanisms can also include sensors, antennas, transceivers, and/or other components that enable direct communication with other devices, such as the electronic device  122 . For example, the lock  158  may include a camera with which to capture an image of a QR code displayed on the electronic device  122 . As another example, the lock  158  may include a Bluetooth module to communicate with the electronic device  122 . Modules to permit communication over Wi-Fi, direct wired connections, or other communications channels may additionally or alternatively be included in the lock  158  or electronics associated with the lock  158 . The lock  158  may include sensors permitting communication using ultrasound signals, infrared signals, electromagnetic signals, and other data carriers. The lock  158  can include one or more near-field communication (NFC) modules. The lock  158  may include communications modules that permit communication over the network  162 . 
     To use the electronic key, the recipient  152  initiates an unlocking action using the electronic device  122 . The unlocking action can be, for example, entry of a user input on a touchscreen or other user interface of the electronic device  122 , a tap of the electronic device  122  against the lock  158  (e.g., to enable NFC-based transfer of information from the electronic device  122  to the lock  158 ), positioning the electronic device  122  near the lock  158  (e.g., to enable the transfer of information from the electronic device  122  to the lock  158  via an IR and/or ultrasonic signal), or another action using the electronic device  122 . 
     In some implementations, the electronic device  122  may store or provide access to multiple different electronic keys. The recipient  152  may select, from among the multiple different keys, a particular electronic key that is needed. As an example, the electronic device  122  may display a list of electronic keys issued to the recipient  152 , based on data stored on the electronic device  122  or data received from the key management system  160 . The recipient  152  provides user input indicating the particular key that the recipient intends to use, for example, the key to the car owned by Sam, the key issuer. In response, the electronic device  122  performs a process to make the selected key available to be used to unlock the lock  158 . As shown, the electronic device  122  may indicate, on a user interface, a visual representation of the electronic key that is being used. 
     In some implementations, the recipient  152  may unlock the lock  158  without designating a particular electronic key that should be used. When the recipient  152  initiates the unlocking action, the application may determine whether the recipient  152  has been issued an electronic key that opens the lock  158 . When the application determines that an appropriate electronic key has been issued, the application may select the electronic key and automatically use the electronic key to unlock the lock  158 , without receiving user input that selects the electronic key. 
     As an example, as a result of the unlocking action, the electronic device  122  may receive an identifier for the lock  158  through communication with the lock  158 . The electronic device  122  and/or the key management system  160  may compare the lock identifier with lock identifiers stored in key data for the various electronic keys issued to the recipient. The electronic device  122  and/or the key management system  160  may determine that a lock identifier in key data for a particular electronic key matches the lock identifier for the lock  158 . In response, the electronic device  122  and/or the key management system  160  engage in an unlocking process using the particular electronic key. In this manner, the electronic device  122  and/or key management system  160  may automatically select the electronic key corresponding to any of multiple different locks when the recipient  152  performs an unlocking action. 
     After the recipient  154  performs the unlocking action, the electronic device  122  detects the unlocking action and sends use data  164  indicating the attempted use of the electronic key to the key management system  160 . The use data  164  identifies the electronic key and includes description information about the attempted use. For example, the electronic device  122  may send an identifier for the electronic key. In addition, or as an alternative, the electronic device  122  may send data that permits the electronic key to be identified, such information identifying the recipient  152  (e.g., a phone number, username, or electronic address for the recipient  152 ) and data identifying the lock  158  or the resource  156 . 
     The description information included in the use data  164  can indicate various aspects of the circumstances or context of the attempted use. The description information can enable the key management server to determine whether one or more conditions on use of the electronic key are satisfied. Examples of description information include, for example, a time of the attempted use, information about persons accompanying the recipient  152 , and information about the current state of the lock  158  or the resource  156 . 
     In some implementations, the computing device  154  selects the description information to send based on the conditions on the electronic key being used. The description information can include information relevant to determining whether the conditions are met. In the illustrated example, the conditions on use of the electronic key require the recipient  152  to have a driver&#39;s license. Accordingly, the electronic device  122  may include in the description information evidence that the recipient  152  has a driver&#39;s license, for example, by sending a driver&#39;s license number, a photograph of the driver&#39;s license, or a code extracted from the physical license. Such information about the recipient&#39;s driver&#39;s license may be stored within or otherwise accessible via the electronic device  122 . For example, a credential management application that stores or otherwise makes accessible information about various credentials that have been issued to the recipient  152 , including, for example, a driver&#39;s license, may be executing on the electronic device  122 . In such cases, information about the recipient&#39;s driver&#39;s license may be accessed from or by the credential management application. In some implementations, the key management application and the credential management application may be the same or components of a single application. 
     The key management system  160  receives the use data  164  over the network  162 , and determines whether the attempted use described by the use data  164  satisfies the one or more conditions for the electronic key. In the illustrated example, the key management system  160  determines that the recipient  152  has a driver&#39;s license, for example, by looking up the recipient&#39;s license status in a database. The key management system  160  also determines that the electronic key has not expired, for example, by comparing the time of the attempted use with the expiration data specified by the conditions. 
     The key management system  160  determines that the conditions on use of the electronic key are satisfied. In response, the key management system  160  provides an access code  166  capable of unlocking the lock. The access code  166  can be provided to the electronic device  122  over the network  162 . The electronic device  122  then provides the access code  166  to the lock  158 . The lock  158  determines that the access code  166  is valid and the lock  158  opens to permit access to the resource  156 . In some implementations, the key management system  160  provides the access code  166  to the lock  158  in addition to, or instead of, access data stored on the electronic device  122  before the attempt to use the electronic key. 
     The access code  166  may be transmitted as, for example, a numeric code, a text sequence, or data encoded in another form. For example, the access code  166  may be provided to the electronic device  122  encoded as data that describes an image of a Quick Response (QR) code, a bar code, or another image. The electronic device  122  may display the image, and a scanner on the lock  158  may read the image to obtain the access code  166 . As another example, the access code  166  can be provided to the computing device  154  as data that describes a signal, such as a radio-frequency signal, infrared signal, or an ultrasonic signal. The electronic device  122  can output the signal to the lock  158  to transmit the access code  166 , for example, using near-field communication (NFC) techniques, an electromagnetic radiation source, and/or a loudspeaker. 
     In some implementations, as described further below, the key management system  160  provides the access code to the lock  158  over the network  162 . In this manner, the key management system  160  may open the lock  158  directly, without relaying the access code  166  to the electronic device  122 . Further, the lock  158  may detect the unlocking action of the recipient  152 , and the lock  158  may transmit use data to the key management system  160  in response to detecting the unlocking action. Use data from the lock  158  may be used by the key management system  160  in addition to, or instead of, the use data  164  from the electronic device  122 . 
     In some implementations, the conditions imposed on an electronic key may be enforced by logic executing on the electronic device  122 . For example, the electronic device  122  may determine whether conditions on use of the electronic key are satisfied, and may prevent the electronic key from being used if the electronic device determines that the conditions are not satisfied, or if the electronic device  122  cannot determine that the conditions are satisfied. When the electronic device  122  does not determine the conditions to be satisfied, the electronic device  122  may, for example, exclude the electronic key from being included in a list of electronic keys accessible by the recipient  152 , prevent transmission of an access code to the lock  158 , and/or indicate to the recipient  152  that access to the lock  158  or use of the electronic key is denied. 
     In some implementations, during an unlocking sequence involving an electronic key, the key management system  160  and the electronic device  122  each determine whether one or more conditions on the electronic key are satisfied. For example, the key management system  160  and the electronic device  122  may determine whether different conditions are satisfied. In addition, or as an alternative, the lock  158  may determine whether one or more conditions on use of the electronic key are satisfied. Unlocking may be disallowed when any of the key management system  160 , the electronic device  122 , and the lock  158  determine that any condition on use of the electronic key is not satisfied. 
       FIG. 2A  illustrates an example of an electronic social networking platform. As illustrated in  FIG. 2A , the electronic social networking platform is represented as a graph  200  of nodes  202  connected by edges  204 . In some implementations, each node  202  of graph  200  represents an individual user identity of the electronic social networking platform. In such implementations, an edge  204  that connects two nodes  202  represents a connection that has been formed between the two user identities that are represented by the connected nodes  202 . For example, the edges  204  that connect node  202 ( a ) to nodes  202 ( b ) represent connections that have been formed within the electronic social networking platform between the user identity represented by node  202 ( a ) and the other user identities represented by nodes  202 ( b ). 
     There are many different examples of electronic social networking platforms. As described above, Facebook, Twitter, LinkedIn, Google+, MySpace, and Orkut are a few examples. But, there are many others, and it is reasonable to expect many more to be developed in the future. 
     Electronic social networking platforms frequently enable individual user identities (e.g., users who have registered with a platform and/or who have been assigned a unique or otherwise identifying identifier by the platform) to establish connections with other user identities. These connections between user identities may reflect relationships between the underlying human users who correspond to the user identities. For example, a connection between two user identities within an electronic social networking platform may reflect a social friendship (e.g., developed through physical interaction in the real-world and/or through on-line interaction in the cyber-world) or a professional relationship between the underlying human users who correspond to the user identities. 
     In some electronic social networking platforms, a user identity may be able to unilaterally form a connection with another user identity. For example, an electronic social networking platform may enable a first user identity to form a connection to a second user identity simply by specifying a desire to form a connection to the second user identity and without requiring approval of the connection by the second user identity. Alternatively, in other electronic social networking platforms, the formation of connections between two user identities may be a bilateral process. For example, in such electronic social networking platforms, when a first user identity specifies a desire to form a connection to a second user identity, the electronic social networking platform may establish the connection only after the second user identity approves the formation of the connection between the first user identity and the second user identity. 
     The connections formed between individual user identities within an electronic social networking platform may be represented in the form of a graph, where user identities are represented by nodes and connections between user identities are represented by edges connecting the nodes. Such a graph of interconnected user identities may change dynamically in time as new user identities join and old user identities quit the electronic social networking platform and/or as new connections are formed and old connections are dissolved. Proximity between two user identities of an electronic social networking platform may be measured in terms of degrees of separation between the two user identities. For example, proximity between two user identities of an electronic social networking platform may be calculated as the fewest number of edges required to form a path between the two user identities within the graph representing the connections between user identities of the electronic social networking platform. 
     A user identity of an electronic social networking platform may form connections to other user identities of the electronic social networking platform, thus forming a personal social network defined within the overall social networking platform. As used herein, the social network of a particular entity refers to the connections and entities for the particular entity, which form a subset of the entities and connections in the broader social networking platform, which encompasses the user identities for all entities and the connections among them. In some cases, the social network of a particular user identity of an electronic social networking platform may be defined as the group of other user identities to whom the particular user identity is directly connected. Alternatively, in other cases, the social network of a particular user identity of an electronic social networking platform may be defined to include a group of other user identities that are within a threshold number of degrees of separation of the particular user identity within the graph. 
     Electronic social networking platforms commonly facilitate sharing of information and the exchange of electronic communications between user identities and other user identities who are part of their social networks. In some implementations, an electronic social networking platform may allow a particular user identity to access more detailed profile information about the other user identities who are part of the particular user identity&#39;s social network than the electronic social networking platform allows the particular user identity to access about user identities who are not part of the particular user identity&#39;s social network. For example, an electronic social networking platform may allow a particular user identity to access information that identifies user identities who are part of the particular user identity&#39;s social network, but the electronic social networking platform may not allow the particular user identity to access this same information for user identities who are not part of the particular user identity&#39;s social network. 
     Additionally or alternatively, an electronic social networking platform may provide communication conduits between a particular user identity and the other user identities who are part of the particular user identity&#39;s social network that the electronic social networking platform does not otherwise provide between the particular user identity and other user identities who are not part of the particular user identity&#39;s social network. In some implementations, these communication conduits are used to transfer electronic key information, such as data that enables an electronic key to operate, or data notifying issuers and recipients of electronic keys about the status and usage of the electronic keys. 
     As discussed above, in some cases, an electronic social networking platform may define a particular user identity&#39;s social network as the group of other user identities to whom the user identity is directly connected. If this definition is applied within the electronic social networking platform illustrated in  FIG. 2A , the social network for the user identity represented by node  202 ( a ) would be defined as the group of other user identities represented by nodes  202 ( b ). 
     In addition to enabling a user identity to establish connections to other user identities and thereby form a social network, some electronic social networking platforms may enable a particular user identity to divide the user identity&#39;s social network into one or more subsets of user identities who may, for example, share one or more characteristics of significance to the particular user identity. For example, a particular user identity of an electronic social networking platform may wish to define subsets of user identities within the particular user identity&#39;s social network that reflect other user identities with whom the particular user identity has a familial relationship, a professional relationship, or a social relationship. For ease of reference, such defined subsets of a particular user&#39;s social network may be referred to herein as “Friendlists.” 
     In some implementations, a user that issues an electronic key may select a Friendlist in order to issue the electronic key to each of multiple other users in the Friendlist. As an example, a user may interact with a user interface element representing a Frendlist for family members to designate all of the user identities in the “family members” Friendlist to receive a particular electronic key. 
     In some implementations, the key management system uses social network data to determine that a key issuer and key recipient have a particular relationship in the social networking platform. For example, each time a key recipient attempts to use an electronic key, the key management system may access data from the social networking platform to determine whether the key recipient and the key issuer currently have a required relationship, such as a relationship that was in effect when the electronic key was issued. In some implementations, if the connection between the key issuer and the key recipient in the social networking platform is severed or altered, the electronic key may be automatically revoked or disabled. Data indicating connections in the social networking platform can also be used to determine whether conditions on an electronic key are satisfied. As another example, a condition may require the key recipient to be designated in the social networking platform as one of a particular subset of the key issuer&#39;s friends in order to use an electronic key. 
     In addition to enabling user identities to establish connections to other user identities, some electronic social networking platforms enable user identities to establish connections with other types of objects, such as locations and events. For example, some social networking platforms may enable user identities to record information about their hometowns, current places of residence, or places they have visited (including geographic locations (e.g., such as cities, states, or countries) as well as commercial venues, local businesses, or places (e.g., such as restaurants, retail stores, parks, train or bus stations, airports, etc.)) by establishing connections to location objects within the electronic social networking platforms. In some implementations, connections with various objects can be used by a key management system (such as the key management system  160  of  FIG. 1E ) to evaluate whether one or more conditions on use of an electronic key are satisfied. As an example, a condition on an electronic key may permit use of the electronic key only while the recipient resides in a particular city. The key management system may obtain data about a connection indicating the residence of the recipient when use of the electronic key is attempted to determine whether the residence location satisfies the condition. 
     Furthermore, some social networking platforms may enable user identities to establish connections with independent applications that leverage the social networking platforms, for example, by granting the independent applications authorization to access or extract data from the electronic social networking platform on their behalf. In some implementations, users access key management functionality provided by an application that communicates with the social networking platform but that is distinct from the social networking platform. For example, the application may be web-based, or may run locally on a client electronic device and be supported by an application server or other system (e.g., a computing system that is not part of the social networking platform and is operated independently from the social networking platform). With authorization from users, the key management system access data from the social networking platform to enable key management functionality for the users. 
       FIG. 2B  illustrates an example of an electronic social networking platform. The example of  FIG. 2B  illustrates a social networking platform that enables user identities to form connections with multiple different types of objects including, for example, other user identity objects, location objects, event objects, and interest objects. As illustrated in  FIG. 2B , the electronic social networking platform is represented as a graph  250  of nodes  252  connected by edges  254 . Each node  252  in the graph  250  represents a particular type of object in the electronic social networking platform. For example, nodes  252 ( a ) and  252 ( b ) represent user identity objects, while node  252 ( c ) represents an interest object, nodes  252 ( d ) represent location objects, and node  252 ( e ) represents an event object. 
     An edge  254  that connects two nodes  252  represents a connection that has been formed between the two objects that are represented by the connected nodes  252 . For example, the edges  254  that connect node  252 ( a ) to nodes  252 ( b ) represent connections that have been formed between the user identity represented by node  202 ( a ) and the user identities represented by nodes  252 ( b ). (For ease of reference, such a connection between two user identity objects in an electronic social networking platform may be referred to herein as a “friend” connection.) Similarly, the edge  254  that connects node  252 ( a ) to node  252 ( c ) represents a connection, such an endorsement, between the user identity represented by node  252 ( a ) and the interest object represented by node  252 ( c ). The edge  254  that connects node  252 ( a ) to node  252 ( e ) represents a connection that has been formed between the user identity represented by node  252 ( a ) and the event represented by event object node  252 ( e ). 
     Furthermore, the edges  254  that connect node  252 ( a ) to nodes  252 ( d ) represent connections that have been formed between the user identity represented by node  252 ( a ) and the location objects represented by nodes  252 ( d ). Depending on the electronic social networking platform, a user identity may be able to establish various different types of connections to location objects. For example, in order to store a record of the user identity&#39;s hometown, the user identity may establish what may be referred to herein as a “hometown” connection to a location object that represents the user identity&#39;s hometown. Additionally or alternatively, in order to store a record of the user identity&#39;s current residence, the user identity may establish what may be referred to herein as a “current city” connection to a location object that represents the user identity&#39;s current residence. 
     Moreover, in order to store a record of a place the user identity visited (including geographic locations (e.g., such as cities, states, or countries) as well as commercial venues, local businesses or places (e.g., such as restaurants, retail stores, parks, train or bus stations, airports, etc.)), the user identity may establish what may be referred to herein as a “check-in” connection to a location object that represents a place that the user identity visited. In some cases, an electronic social networking platform may provide mechanisms that enable a user identity to manually “check-in” at a location. For instance, a social networking platform may provide mechanisms that enable a user identity to “check-in” at a location using a mobile computing device (e.g., a smartphone or tablet computer) using global positioning system (GPS) and/or map data available to the mobile computing device. As with other data stored by a social networking platform, “check-in” records can be accessed by key management systems to validate the use of an electronic key in accordance with the corresponding conditions on use of the electronic key, if any have been imposed. 
     Electronic social networking platforms often enable user identities to maintain user profiles or other collections of data that include information about the user identities to whom they correspond. Such a profile for an individual user identity of an electronic social networking platform may include, among other information, information about the user identity&#39;s hometown, current residence, age, gender, relationship status, educational background, and/or professional background. The key management system may use profile data (e.g., a name, a photograph, etc.) to identify potential recipients for an electronic key, assisting key issuers to select appropriate recipients. Similarly, the key management system may provide profile data of key issuers to key recipients, assisting the key recipients to identify the user identities that issued the received keys. In addition, the key management system can use profile data to determine whether conditions on an electronic key are satisfied. As an example, a condition may require the key recipient to be a member of a particular community organization, be above a particular age, or have a particular educational background to use an electronic key. In some implementations, the key management system obtains social networking profile data for the key recipient and evaluates the profile data to determine whether the condition is satisfied. 
     In some implementations, a profile for a user identity may include one or more phone numbers, electronic communication addresses (e.g., electronic mail addresses, Twitter feed address, etc.), or other identifiers. The key management system can obtain one or more electronic addresses or other identifiers from the profile of a key issuer or key recipient to communicate regarding an electronic key. For example, the key management system may access an electronic address from a key recipient&#39;s profile, and send to the electronic address a notification of transfer of an electronic key, an access code that opens the corresponding lock, and/or other data that enables the recipient to use the electronic key. As another example, the key management system may access an electronic address from a key issuer&#39;s profile, and may send to the electronic address access data requesting the key issuer&#39;s approval for use or transfer an electronic key issued by the key issuer. 
       FIG. 3  illustrates an example of a communications system  300 . For illustrative purposes, several elements illustrated in  FIG. 3  and described below are represented as monolithic entities. However, these elements each may include and/or be implemented on numerous interconnected computing devices and other components that are designed to perform a set of specified operations. 
     As illustrated in  FIG. 3 , the communications system  300  includes an electronic social networking platform  302  that is accessible to a number of computing devices or other electronic devices  304 ( a )- 304 ( n ), including, for example, a laptop computer  304 ( a ), a tablet computer  304 ( b ), and a smartphone  304 ( n ), over a network  306 . In addition, the communications system  300  also includes a computing system  308 . The computing system  308  may be external to the electronic social networking platform  302 . As such, the electronic social networking platform  302  may be accessible to the computing system  308  over the network  306 . Additionally, the computing system  308  may be accessible to the electronic devices  304 ( a )- 304 ( n ) over the network  306 . 
     The electronic social networking platform  302  may be implemented using one or more computing devices (e.g., servers) configured to provide a service to one or more client devices (e.g., electronic devices  304 ( a )- 304 ( n )) connected to electronic social networking platform  302  over network  306 . The one or more computing devices on which electronic social networking platform  302  is implemented may have internal or external storage components storing data and programs such as an operating system and one or more application programs. The one or more application programs may be implemented as instructions that are stored in the storage components and that, when executed, cause the one or more computing devices to provide the features of an electronic social networking platform  302 . Furthermore, the one or more computing devices on which the electronic social networking platform  302  is implemented each may include one or more processors for executing instructions stored in storage and/or received from one or more other electronic devices, for example over the network  306 . In addition, these computing devices also typically may include network interfaces and communication devices for sending and receiving data. The electronic social networking platform  302  also may provide an application programming interface (API)  310  that enables other applications to interact with and extract data from the electronic social networking platform  302 . 
     The electronic devices  304 ( a )- 304 ( n ) may be any of a number of different types of computing devices including, for example, mobile phones; smartphones; personal digital assistants; navigation devices; laptop, tablet, and netbook computers; wearable computers; and desktop computers including personal computers, special purpose computers, general purpose computers, and/or combinations of special purpose and general purpose computers. Each of the electronic devices  304 ( a )- 304 ( n ) typically may have internal or external storage components for storing data and programs such as an operating system and one or more application programs. In particular, the internal or external storage components for each of the electronic devices  304 ( a )- 304 ( n ) may store a client application for interfacing with the electronic social networking platform  302  and/or a client application for interfacing with the computing system  308 . Additionally or alternatively, the electronic devices  304 ( a )- 304 ( n ) may be configured to interface with the electronic social networking platform  302  or the computing system  308  without a specific client application, using, for example, a web browser. 
     Each of the electronic devices  304 ( a )- 304 ( n ) also typically may include a central processing unit (CPU) for executing instructions stored in storage and/or received from one or more other electronic devices, for example over the network  306 . Each of the electronic devices  304 ( a )- 304 ( n ) also usually may include one or more communication devices for sending and receiving data. One example of such communications devices is a modem. Other examples include antennas, transceivers, communications cards, and other network adapters capable of transmitting and receiving data over a network (e.g., the network  306 ) through a wired or wireless data pathway. 
     The network  306  may provide direct or indirect communication links between the electronic social networking platform  302 , the electronic devices  304 ( a )- 304 ( n ), and the computing system  308 . Examples of the network  306  include the Internet, the World Wide Web, wide area networks (WANs), local area networks (LANs) including wireless LANs (WLANs), analog or digital wired and wireless telephone networks, radio, television, cable, satellite, and/or any other delivery mechanisms for carrying data. 
     The computing system  308  may be implemented using one or more computing devices (e.g., servers). The one or more computing devices on which computing system  308  is implemented may have internal or external storage components storing data and programs such as an operating system and one or more application programs. The one or more application programs may be implemented as instructions that are stored in the storage components and that, when executed, cause the one or more computing devices to provide the features ascribed herein to the computing system  308 . Furthermore, the one or more computing devices on which the computing system  308  is implemented each may include one or more processors for executing instructions stored in storage and/or received from one or more other electronic devices, for example, over the network  306 . In addition, these computing devices also typically may include network interfaces and communication devices for sending and receiving data. 
     The computing system  308  may host an application (e.g., a key management application) that leverages electronic social networking platform  302 . As such, the computing system  308  may be configured to extract and process data from electronic social networking platform  302 . For example, the computing system  308  may be configured to exploit the API  310  to extract data from the electronic social networking platform  302 . Among other features, the computing system  308  may be configured to extract data about multiple different user identities&#39; social networks including information identifying the members of each user identity&#39;s social network and profile data for the members of each user identity&#39;s social network, including electronic addresses with which to contact the members of the social network. 
     In some implementations, the electronic social networking platform  302  may enable individual user identities to grant the computing system  308  a token that defines permission levels related to data about the user identities&#39; social networks that computing system  308  may access and extract from electronic social networking platform  302 . For each individual user identity for which the computing system  308  has a token, the computing system  308  may extract information about the user identity and the other user identities who are members of the user identity&#39;s social network. This information may include identifying information for the user identity and each member of the user identity&#39;s social network as well as profile data for the user identity and each member of the user identity&#39;s social network (e.g., hometown, current residence, age (or date of birth), gender, relationship status, etc.). In addition, or as an alternative, the computing system  308  may access any other data from the social networking platform, associated with the user identity and each member of the user identity&#39;s social network, for which access permission is granted, including communications sent or received, endorsements, and other activities occurring within or described within the social networking platform. 
     In  FIG. 3 , the computing system  308  may represent the key management system  160  of  FIGS. 1A-1E  that receives user input, issues electronic keys, evaluates attempted uses of electronic keys, approves uses that satisfy appropriate conditions, and/or sends access codes that open locks. The electronic devices  304 ( a )- 304 ( n ) may each perform the functions of the electronic devices  102 ,  122  of  FIGS. 1A-1E . That is, any of the electronic devices  304 ( a )- 304 ( n ) may interact with a server system to issue or modify an electronic key, as described for the electronic device  102 ,  122 . Further, any of the electronic devices  304 ( a )- 304 ( n ) may receive electronic key data and access codes to open a lock with an electronic key, as described above for the electronic device  102 ,  122 . 
       FIG. 4  illustrates an example of a system  400  for providing an electronic key using a social networking platform. The system  400  includes electronic devices  410 ,  420 , a lock  450 , the computing system  308  of  FIG. 3 , the social networking platform  302  of  FIG. 3 , and a data server  460 , each of which communicates over the network  306  of  FIG. 3 . The electronic devices  410 ,  420  can be any type of electronic device, for example, including any of the types of electronic devices  304 ( a )- 304 ( n ) described above. The lock  450  can be a physical lock, such as a lock that secures access to a physical space or secures the function of a physical device, even though the physical lock may function using electrical or software processes. 
     The electronic device  410  is associated with an issuer  411  of an electronic key. The electronic device  420  is associated with a recipient  421  of the electronic key. In the example of  FIG. 4 , the issuer  411  uses the electronic device  410  to interact with the computing system  308  and provide an electronic key to the recipient  421 . The computing system  308  acts as a key management server by carrying out transfer of the electronic key and storing data that permits the electronic key to operate. Thereafter, the recipient  421  may use the electronic key to open a lock  450  (or multiple different locks). 
     The issuer  411  may place conditions on use of the electronic key by the recipient  421 . When conditions are imposed on the electronic key, the computing system  308  evaluates each attempted use of the electronic key, and permits the lock  450  to open only when the conditions are satisfied. When the conditions for use of the electronic key are not satisfied, the computing system  308  may prevent the lock  450  from opening. 
     In further detail, the issuer  411  uses the electronic device  410  to issue an electronic key to a user to which the issuer  411  is connected in the social networking platform  302 . The electronic device  410  runs an application (e.g., a key management application) that enables the issuer  411  to provide the electronic key, for example, through interactions with the computing system  308 . In some implementations, a web page or other interface is used to establish an electronic key rather than an application running on the electronic device  410 . 
     In some implementations, the issuer  411  may use any of multiple different electronic devices to manage electronic keys. For example, the issuer  411  may access the application through a mobile phone, desktop computer, tablet computer, and/or other electronic device by interacting with the application through the devices. 
     The computing system  308  provides data to support the application running on the electronic device  410 . As illustrated in  FIG. 4 , the computing system  308  is a third-party system separate from the social networking platform  302 . In some implementations, the computing system  308  is part of the social networking platform  302 . 
     The computing system  308  may extract information about the social networking connections of the issuer  411  in the social networking platform  302 . The computing system  308  may provide the extracted social network data  415  to the electronic device  410 . For example, the social network data  415  may identify users who are connected to the issuer  411  in the social networking platform  302 . 
     The computing system  308  may provide data identifying locks for which the issuer  411  has authority to extend access permissions to others. In some implementations, the computing system  308  maintains records identifying locks controlled by various different users. For example, users may register locks with the computing system  308  and may validate ownership of or another form of right to control a particular lock. 
     In the example of  FIG. 4 , the electronic device  410  receives the social network data  415  from the computing system  308  and also receives lock data  418  that identifies locks controlled by the issuer  411 . The electronic device  410  displays a list of members of the social network of the issuer  411 . The electronic device  410  also displays a list of locks controlled by the issuer  411 . For example, the electronic device  410  may indicate members of the social network of the issuer  411  and indicate locks controlled by the issuer  411  using a user interface similar to the user interface  100  of  FIG. 1A . 
     The issuer  411  provides user input indicating selection of one or more members of the social network who should receive the electronic key. In some implementations, only users who are connected to the issuer  411  in the social networking platform  302  are permitted to receive the electronic key from the issuer  411 . In the illustrated example, the recipient  421  is connected to the issuer  411  in the social networking platform  302 . When selecting from among the users who are connected to the recipient  421  in the social networking platform  302 , the issuer  411  selects the recipient  421  to receive the electronic key. 
     The issuer  411  also provides user input indicating selection of one or more locks that the electronic key should open. In the example, the issuer  411  indicates that that the electronic key should open the lock  450 , which controls entry to the house of the issuer  411 . 
     The application on the electronic device  410  also enables the issuer  411  to impose conditions on use of the electronic key. For example, the electronic device  410  may permit the issuer  411  to select conditions for the electronic key using a user interface similar to the user interface  110  of  FIG. 1B . Conditions may be defined to limit use to only a set of approved uses (e.g., designating a “whitelist” of allowed uses). Conditions may additionally or alternatively be defined to allow all uses except a set of excluded uses (e.g., designating a “blacklist” of excluded uses). 
     Examples of conditions on use of an electronic key include conditions that: (1) limit a time during which the electronic key may be used; (2) require the recipient to possess a particular credential or qualification; (3) require approval from the key issuer for each use of the electronic key; (4) limit a number of times that the electronic key may be used; (5) require the recipient to be accompanied by another person (e.g., a person selected from a defined list of persons, or a person that has a particular qualification); (6) require that, when the electronic key is used, the key issuer must be outside of, or be located beyond a predetermined distance from, a space to which the electronic key provides access; (7) require that, when the electronic key is used, the key issuer must be within, or be located within a predetermined distance from, a space to which the electronic key provides access; and (8) require the identity of the recipient to be confirmed at the time the electronic key is used (e.g., through a password, a biometric input, or another form of authentication). 
     Based on the user input from the issuer  411 , the electronic device  410  provides, to the computing system  308 , data  412  that identifies the recipient  421 , the lock  450 , and the one or more conditions on use of the electronic key. The computing system  308  receives the data  412  and issues the electronic key as requested by the issuer  411 . 
     The computing system  308  stores key data that identifies the recipient  421 , the lock  450 , the one or more conditions on use of the electronic key. The key data may be stored in electronic storage, such as a database or other data storage system. Various examples of key data are shown in  FIG. 8  and described below. 
     The computing system  308  may also store, in the key data, data that indicates access codes which are effective to open the lock  450  or data from which the access codes may be generated. For example, when the lock  450  is registered with the application and determined to be under the control of the issuer  411 , the computing system  308  may obtain a serial number or other lock identifier for the lock  450 . Using the lock identifier, the computing system  308  may obtain access data indicating input data, interactions, and or communication formats that may be used to open the lock  450 . The access data may be obtained from a manufacturer of the lock, from the electronic device  410 , from communication with the lock  450  directly over the network  306  or through another device, or through one or more other devices. As an example, the lock  450  may use encrypted communication, a rolling code scheme, and/or other security measures. In this example, the computing system  308  may store an encryption key, synchronization data for the rolling code scheme, and one or more access codes accepted by the lock  450 , which permit the computing system  308  to determine, at any given time, an access code that is effective to open the lock  450 . 
     The computing system  308  obtains an electronic address (e.g., an electronic mail address, a phone number, a social networking username, etc.) for the recipient  421 . For example, the computing system  308  may obtain the electronic address from a social networking user profile of the recipient  421  in the social networking platform  302 . 
     The computing system  308  sends notification data  424  to the electronic address for the recipient  421 . The notification data  424  indicates that the electronic key has been issued, and may indicate the lock  450  and conditions corresponding to the electronic key. For example, the notification data  424  may be received at the electronic device  420 , and the electronic device  420  can display a user interface similar to the user interface  120  of  FIG. 1C  or user interface  130  of  FIG. 1D . 
     In some implementations, the notification data  424  includes data that enables the recipient to use the electronic key in accordance with the one or more conditions on use of the electronic key. For example, the notification data  424  can include data that the electronic device  420  can use to communicate with the lock  450  and initiate an unlocking sequence. As described further below, additional data from the computing system  308  may be required to complete the unlocking sequence successfully. Each time the electronic key is used to unlock the lock  450 , the computing system  308  may provide the additional data only when the computing system  308  determines that the conditions on use of the electronic key are satisfied. 
     In some implementations, the electronic key is revocable by the issuer  411 . For example, the issuer  411  may use the application running on the electronic device  410  to revoke the electronic key at any time. The issuer  411  may temporarily disable the electronic key, for example, causing the electronic key to be unusable by the recipient  421  (e.g., ineffective to open the lock  450 ) for a specified amount of time or until the issuer  411  re-enables the electronic key. When the electronic key is disabled or revoked, the computing system  308  may transmit, to the electronic address for the recipient  421 , data that indicates that the electronic key is not available for use. For example, when the key has been disabled or revoked and the recipient  421  attempts to use the electronic key to open the lock  450 , the computing system  308  may indicate that access is denied, and may indicate the status of the electronic key. 
     After the electronic key has been issued to the recipient  421 , the recipient  421  may use the electronic device  420  (or another electronic device) to open the lock  450 . In some implementations, the recipient  421  may open the lock using any electronic device running the application that manages electronic keys. 
     Various interactions can occur among the electronic device  420 , the lock  450 , the computing system  308 , and other systems when opening the lock  450 . Different interactions may occur for different electronic keys, for example, when different conditions are imposed on use of the electronic keys, or when different locks are opened. One example of interactions for unlocking the lock  450  is described below with respect to  FIG. 4 . Other examples of interactions for opening locks are described below with respect to  FIGS. 5A-5E . 
     The electronic device  420  sends, to the computing system  308 , use data  452  about the attempted use of the electronic key by the recipient  421 . The electronic device  420  may send the use data  452  in response to detecting an action of the user or receiving a communication from another device. For example, transmission of use data may be triggered by: receipt of a user input, such as a user input selecting the electronic key from among a set of electronic keys issued to the recipient  421 ; detection of a gesture made with the electronic device  420 , such as a tap, twist, or shake of the electronic device; and/or receipt of data from the lock  450 , such as receiving a lock identifier through direct communication with the lock  450 . 
     The use data  452  includes description information that describes the circumstances in which use of the electronic key is attempted. For example, the use data  452  may indicate an identifier for the recipient  421  and/or the electronic device  420 , data obtained from the lock  450  by the electronic device  420  (e.g., via NFC data transfer techniques, IR data transfer, and/or ultrasonic data transfer), data indicating a time of the attempted use, data identifying persons accompanying the recipient, data confirming the identity of the recipient  421 , and other data. The use data  452  may further include other data which enables the computing system  308  to determine (e.g., to select or generate) an access code that is effective to open the lock  450 . 
     In response to the use data  452 , the computing system  308  accesses the stored key data for the electronic key. From the key data, the computing system  308  determines which conditions have been imposed on the electronic key, if any. The computing system  308  then determines whether the conditions are satisfied by the attempted use described by the use data  452 . 
     The computing system  308  may extract data from the social networking platform  302  and use extracted social network data to determine whether the lock  450  should be opened for the recipient  421 . For example, the computing system  308  may access data indicating social networking connections in the social networking platform  302 , and determine whether the issuer  411  and the recipient  421  are still connected within the social networking platform. In some implementations, the computing system  308  permits the lock  450  to be opened only when the social networking connection between the issuer  411  and the recipient  421  is still in force within the social networking platform. 
     The computing system  308  may also use social network data to determine whether one or more conditions on use of the electronic key are satisfied. For example, when a condition for use of the electronic key requires the recipient  421  to be at least a certain age, the computing system  308  may obtain the age of the recipient  421  from social networking profile data of the recipient  421 . As another example, a condition for use of the electronic key may require the recipient  421  to be accompanied by a family member. The computing system  308  may determine, based on the social network data, whether a person that accompanies the recipient  421  is designated in the social networking platform  302  as being a family member of the recipient  421 . Other social network data may be obtained and evaluated to determine whether conditions are satisfied. 
     The computing system  308  may communicate with one or more other systems, such as a data server  460 , to obtain additional data used to determine whether conditions on use of the electronic key are satisfied. For example, a condition for use of the electronic key may require the recipient  421  to have a valid driver&#39;s license. The computing system  308  may provide an identifier for the recipient  421  to the data server  460 , and obtain from the data server  460  data indicating whether or not the recipient  421  has a valid driver&#39;s license. 
     The computing system  308  may communicate with the electronic device  410  to determine whether conditions on use of the electronic key are satisfied. For example, a condition for use of the electronic key may require approval of each use of the electronic key by the issuer  411 . The computing system  308  may send a request to the electronic device  410  (e.g., to an electronic address or account for the issuer  411 ) requesting approval for the attempted use of the electronic key. After the issuer  411  provides input indicating whether the attempted use is approved, the electronic device  410  sends, to the computing system  308 , data indicating the approval or denial of authorization of the particular instance of use of the electronic key attempted by the recipient  421 . 
     The computing system  308  evaluates the use data  452  against the key data. The computing system  308  compares the information about the attempted use of the electronic key with the one or more conditions designated for the electronic key by the issuer  411 . In some implementations, the computing system  308  uses extracted social network data, data from the electronic device  410 , and data from other systems such as the data server  460  to evaluate the attempted use of the electronic key and determine whether the conditions are satisfied. 
     In the illustrated example, the computing system  308  determines that the attempted use of the electronic key satisfies the associated conditions. As a result, the computing system  308  selects an access code  432  that will open the lock  450 . To select the access code  432 , the computing system  308  may, for example, select a particular code from among a set of codes used in a rolling code scheme. The computing system  308  may store or obtain data to synchronize access code usage in the rolling code scheme with the lock  450 . Additionally or alternatively, the computing system  308  may generate, as the access code, an encrypted message using encryption decodable by the lock  450 . In some implementations, the access code may be valid only for a defined period of time. 
     In some implementations, the computing system  308  encodes the access code  432  in a QR code, a bar code, an image, or in in another form. The access code  432  is provided to the electronic device  122  in the encoded form. The electronic device  420  then provides the access code  432  to the lock  450 . In some implementations, the lock  450  includes a scanner or reader that can read a QR code, bar code, or other data displayed on the electronic device  420 . The electronic device  420  displays an image encoding the access code  432 , and the lock  450  reads the access code  432  from the displayed image. In some implementations, the electronic device  420  provides the access code to the lock  450  through a WiFi connection, a Bluetooth connection, a wired connection, or another means of communication. The electronic device  420  may provide the access code to the lock  450  through near field communication (NFC) techniques, infrared transmission, radio-frequency transmission, ultrasonic transmission, or other outputs of the electronic device  420 . 
     The lock  450  obtains the access code  432  from the electronic device  420 , and the lock  450  evaluates the access code  432 . The lock  450  determines that the access code  432  is valid, and the lock  450  opens in response. In some implementations, as discussed below, the lock  450  receives the access code  432  from the computing system  308  over the network  306  rather than through communication with the electronic device  420 . 
     If the computing system  308  determines that the conditions on use of the electronic key are not satisfied, or if the computing system  308  cannot verify that the conditions are satisfied, the computing system  308  does not send the access code  432 . Instead, the computing system  308  may send a message indicating that the access to the lock  450  is denied. Without the access code  432 , the recipient  421  is unable to open the lock  450 . To open the lock  450 , the recipient  421  may be required to initiate the unlocking process again, in a manner that satisfies the conditions imposed on the electronic key. 
     In some implementations, the computing system  308  identifies the electronic device  420  and transmits the access code  432  in response to determining that the electronic device  420  is associated with the recipient  421 . For example, the use data  452  may include a device identifier for the electronic device  420 , such as a phone number for a mobile phone, device serial number, media access control (MAC) address. The computing system  308  compares the received device identifier with one or more stored device identifiers that have been registered with the application or the social networking platform  302 . The computing system  308  provides the access code  432  to unlock the lock  450  only when the electronic device  420  is one of a set of devices registered as associated with the recipient  421 . In this manner, the recipient&#39;s mobile phone, watch, music player, etc., may each act as a key to open any of the locks for which the recipient  421  has been issued an electronic key. 
     In some implementations, the computing system  308  transmits the access code  432  in response to verifying that the electronic device  420  is controlled by the recipient  421 , in addition to or as an alternative to determining that the electronic device  420  is associated with the recipient  421 . For example, the recipient  421  may be required to provide a password for the application or the social networking platform  302 , and the password may be transmitted in the use data  452 . An electronic cookie or session identifier may be provided to indicate that the recipient  421  is logged in to the application or the social networking platform  302 . In addition, or as an alternative, the electronic device  420  or the lock  450  may acquire biometric information from the recipient  421 , for example, through a fingerprint scan, a retina scan, an iris scan, voice analysis, handwriting analysis, a facial photograph, or other techniques. With a password or biometric input, the recipient  421  may be authenticated and be permitted to use the electronic key using any suitable electronic device, not only electronic devices previously registered with the application or the social networking platform  302 . 
     Multi-factor authentication may be used to verify that the recipient  421  to which the electronic key is issued is the person opening the lock  450 . The computing system  308  may require a combination of at least two different forms of authentication, such as a password and a fingerprint scan, or the use of a registered electronic device  420  and a password. The two or more forms of authentication can be selected from among biometric data, other user inputs or interactions (such as passwords or answers to security questions), and device identifiers. Authentication requirements, for recipients of electronic keys or for associated electronic devices, may be implemented as conditions on particular keys or as general conditions for all electronic keys. 
     The same authentication procedures used to authenticate the recipient  421  may be used to authenticate a person accompanying the recipient  421 . For example, when a condition requires that a designated person accompany the recipient  421  in order for the electronic key to be used, the designated person can be authenticated through a device identifier (e.g., indicating the presence of the designated person&#39;s mobile phone or other device), a user input (e.g., a password for the designated person&#39;s social networking user identity in the social networking platform  302 ), or biometric data for the designated person. 
     Authentication data (e.g., user input, fingerprint scan data, device identifiers, etc.) that indicates the presence of a companion may be communicated to the computing system  308  in various ways. Authentication data for the companion may be entered into the electronic device  420  by the companion, and the authentication data may be transmitted to the computing system  308  by the electronic device  420 . In addition, or as an alternative, the authentication data for the companion may be entered by the companion into a device different from the electronic device  420 , such as the companion&#39;s mobile phone or another device associated with the companion. The authentication data may be transmitted from the companion&#39;s mobile phone to the computing system  308  over the network  162  (e.g., and not through the electronic device  420 ). In addition, or as an alternative, authentication data may be transmitted from the companion&#39;s mobile phone or other electronic device to the electronic device  420 , and the electronic device  420  may send the authentication data to the computing system  308 . The companion&#39;s mobile phone or other electronic device may communicate with the electronic device  420  using near-field communication techniques, infrared transmissions, ultrasonic transmissions, Bluetooth, and/or other communication channels. 
     In addition, or as an alternative, authentication data for the companion may be entered into the lock  450  (e.g., through a fingerprint scanner of the lock  450 , a microphone of the lock, a keypad of the lock, etc.), and the lock  450  may transmit the authentication data to the computing system  308  over the network  306 , without the authentication data being relayed through the electronic device  420  or the companion&#39;s mobile phone or other electronic device. 
     In some implementations, rather than the computing system  308  sending an access code  432 , the computing system  308  sends data that indicates approval for the electronic device  420  to provide to the lock  450  an access code that was stored on the electronic device  420  before the use data  452  was sent. In such implementations, the use data  452  may be a request for authorization to use (e.g., transmit to the lock  450 ) one or more access codes already stored on the electronic device  420 . For example, one or more access codes that open the lock  450  (or data from which the electronic device  420  may generate such access codes) may have been downloaded to the electronic device  420  previously, such as when the recipient  421  was first notified that the electronic key was issued. The application that manages electronic keys, running on the electronic device  420 , may limit use of the stored access codes, disallowing transmission of the access codes to the lock  450  unless approval is received from the computing system  308  for each attempt to open the lock  450 . 
       FIG. 5A  illustrates another example of interactions that open the lock  450 . In the example, the recipient  421  performs an unlocking action with the electronic device  420 . The unlocking action can be achieved by a tap of the electronic device  420  against the lock  450  or by otherwise initiating near-field communication between the electronic device  420  and the lock  450 . Additionally or alternatively, the unlocking action can be achieved by other data transfer mechanisms between the electronic device  420  and the lock  450 , including, for example, IR data transfer or ultrasonic data transfer. Irrespective of the data transfer mechanism employed, the electronic device  420  may send a request or other message  470  to the lock  450 . The lock  450  may have, or be associated with, various different sensors that enable various different forms of communication between the electronic device  420  and the lock  450  (e.g., a NFC sensor, an IR sensor, a microphone for ultrasonic data transfer, a camera, etc.). 
     The lock  450  responds to the message  470  by sending a lock code  474 . In some implementations, the lock  450  provides different lock codes  474  at different times, for example, using a rolling code system. In some implementations, the lock code  474  includes data that uniquely identifies the lock  450 . 
     In some implementations, use of the electronic key is permitted only when the recipient  421  is in proximity of the lock  450  (e.g., when the recipient  421  is within a threshold distance of the lock  450 ). To enforce the proximity requirement, the computing system  308  can require the lock code  474  to be obtained from the lock  450 , at the physical location or site of the lock  450 , at the time the use of the electronic key is attempted. Since various different lock codes  474  can be used by a single lock  450 , the electronic device  420  must obtain the lock code  474  that is current at the time that use of the electronic key is attempted. The lock code  474  may be obtainable only through short-range communication with the lock  450  that requires proximity to the lock  450  (e.g., communication via radio-frequency electromagnetic waves, infrared, ultrasonic waves, visible light, etc.). As a result, the electronic device  420  obtains the lock code  474  only when at least a minimum proximity to the lock  450  has been achieved (e.g., sufficient proximity to effect the short-range communication). In some implementations, the short-range communication channel permits the electronic device  420  to communicate with the lock  450 , and consequently permits use of the electronic key, only when the electronic device  420  is located within some distance of the lock (e.g., within approximately 5 feet, approximately 10 feet, approximately 15 feet, approximately 30 feet, approximately 50 feet, approximately 100, etc.). 
     The electronic device  420  receives the lock code  474  from the lock  450  through proximity-dependent communication. The electronic device  420  sends the lock code  474  to the computing system  308  with the use data  452 . The computing device  430  determines that the lock code  474  is valid, and thus that the electronic device  420  is in proximity to the lock  450 . Based on determining that the electronic device  420  is in proximity to the lock  450 , the computing device  430  sends the access code  432  to the electronic device  420 . The electronic device  420  transmits the access code  432  to the lock  450 , and the lock  450  opens. 
     If the computing system  308  determines that the lock code  474  is not valid, or if the lock code  474  is not provided by the electronic device  420 , the computing system  308  may determine that the electronic device  420  is not currently in proximity to the lock  450 . Accordingly, the computing system  308  may not provide the access code  432 , which denies the recipient  421  the ability to open the lock  450 . 
     In some implementations, other forms of verifying the proximity of the electronic device  420  to the lock  450 , and thus the proximity of the recipient  421  associated with the electronic device  420 , may be used. For example, the electronic device  420  can capture an image of the lock  450  with a camera, the electronic device  420  can obtain global positioning system (GPS) or other location data, the position of the electronic device  420  can be triangulated with WiFi or cellular network access stations, and so on. 
     In some implementations, proximity to the lock  450  is not required, and the recipient  421  may open the lock remotely, through interactions with the computing device  430  and the lock  450  over the network  306 . 
       FIG. 5B  illustrates another example of interactions that open the lock  450 . The example of  FIG. 5B  includes the interactions described for  FIG. 5A . In addition, the lock  450  also communicates with the computing system  308  by sending use data  475  that describes the attempted use of the electronic key. The use data  475  may be sent by the lock  450 , and not by or through the electronic device  420 , to reduce the risk of tampering by other systems. The use data  475  may include data to which the electronic device  420  generally does not have access, such as usage logs stored by the lock  450 . In some implementations, the use data  475  is relayed through the electronic device  420  to the computing system  308 . In some implementations, the use data  452  is relayed through the lock  450  to the computing system  308 . 
     The lock  450  may send the use data  475  in response to receiving the message  470  and/or in response to receiving the access code  432  from the electronic device  420 . The computing system  308  may evaluate the use data  475  from the lock  450 , as well as the use data  452  from the electronic device  420 , to determine whether the conditions on use of the electronic key are satisfied. In response to evaluating the use data  452 , the computing system  308  may send a message  477  confirming that the lock  450  should open in response to the access code  432 . In some implementations, the lock  450  opens only when the message  477  from the computing system  308  is received. 
       FIG. 5C  illustrates another example of interactions that open the lock  450 . As described above with respect to  FIG. 5A , the electronic device  420  sends the message  470  to the lock  450 , and receives the lock code  474  in response. The electronic device  420  sends the use data  452 , including the lock code  474 , to the computing system  308 . 
     The computing system  308  evaluates the use data  452  and the lock code  474 , and determines whether the conditions on use of the electronic key are satisfied. Unlike the example of  FIG. 5A , responsive to a determination that the conditions on use of the electronic key are satisfied, the computing system  308  sends the access code  432  to the lock  450  over the network  306  (e.g., without sending the access code  432  to the electronic device  420 ), thereby causing the lock to open. In the event that the computing system  308  determines that the conditions on use of the electronic key are not satisfied, the computing system  308  may not send the access code  432  to the lock  450 . 
       FIG. 5D  illustrates another example of interactions that open the lock  450 . In the example, the electronic device  420  interacts with the lock  450  (e.g., using any one or more of the techniques described above), and provides data  480  that identifies the electronic key (e.g., an identifier for the recipient  421 , an identifier for the electronic key itself, an identifier for the electronic device  420 , etc.) The data  480  may include other information, such as, for example, data authenticating the recipient  421 , data indicating the presence of others accompanying the recipient  421 , or other data that indicates whether conditions on use of the electronic key are satisfied. 
     Based on the data  480 , the lock  450  sends use data  485  to the computing system  308  over the network  306 , thereby enabling the computing system  308  to determine whether the conditions on use of the electronic key have been satisfied. After determining that the conditions have been satisfied, the computing system  308  sends the access code  432  to the lock  450  over the network  306 , thereby causing the lock to open. In some implementations, no direct interaction between the electronic device  420  and the computing system  308  may be required at the time the electronic key is used. In the event that the computing system  308  determines that the conditions have not been satisfied, the computing system  308  may not send the access code  432  to the lock  450 . 
       FIG. 5E  illustrates another example of interactions that open the lock  450 . In the example, the electronic device  420  opens the lock  450  without interacting with the computing system  308 . The electronic device  420  stores the access code  432  in local electronic storage before the recipient  421  initiates unlocking of the lock  450 . For example, the access code  432  that opens the lock  450  may be downloaded to the electronic device  430  when the electronic key is issued to the recipient  421 . The access code  432  may continue to be stored on the electronic device  420  until, for example, the electronic key expires or is revoked. 
     In response to detecting that the recipient  421  performed an unlocking action, the electronic device  420  determines whether any conditions have been imposed on use of the electronic key. For each of the electronic keys issued to the recipient  421 , the electronic device  420  may store key data that identifies (i) the lock corresponding to the electronic key, (ii) the conditions on use of the electronic key, if any, and (iii) access codes that open the lock. The electronic device  420  accesses the locally stored key data for the electronic key that opens the lock  450 . The electronic device  420  may receive user input from the recipient  421  indicating that this electronic key should be used. In addition, or as an alternative, the electronic device  420  may receive a lock identifier from the lock  450 , and may identify, based on the lock identifier, the electronic key that corresponds to the lock  450  (e.g., by selecting the electronic key from among multiple electronic keys for which key data is stored on the electronic device). The key data for the electronic key indicates whether any conditions are imposed on use of the electronic key, and what those conditions are, if any. 
     If no conditions have been imposed on use of the electronic key, the electronic device  420  transmits the access code  432  to the lock  450  in response to detecting the unlocking action performed by the recipient  421 . If one or more conditions have been imposed on use of the electronic key, the electronic device  420  determines whether the conditions on the electronic key are satisfied, without communicating with the computing system  308 . For many conditions, the electronic device  420  may store or have access to data that indicates whether the conditions are satisfied. For example, for a condition requiring use during a particular time period, the electronic device  420  can determine whether the current time (e.g., the time of the unlocking action by the recipient  421 ) is within the particular time period. Similarly, for a condition requiring a valid driver&#39;s license, a credential management application, a credential file, or other data may permit the electronic device  420  to determine, without communication with the computing system  308  or even any other device, whether the recipient  421  possesses the credential. 
     In the example, the electronic device  420  determines that conditions on use of the electronic key are satisfied, and the electronic device  420  transmits the access code  432  to the lock  450 . 
     In the examples of  FIGS. 4 and 5A-5E , other interactions between the lock  450 , the electronic device  420 , and the computing system  308  may also occur. In addition, interactions with other devices may occur. For example, to indicate the presence of a companion accompanying the recipient, the companion may enter a password directly to the electronic device  420 . In addition, or as an alternative, the companion may enter the password directly to a different electronic device, such as the companion&#39;s mobile phone, and the companion&#39;s mobile phone may transmit the password to the computing system  308 . In addition, or as an alternative, the companion&#39;s mobile phone may transmit the password to the electronic device  420 , which then sends the password to the computing system  308 . 
     In some implementations, multiple electronic keys may be required to be used together to open the lock  450 . For example, the recipient  421  and another person may be required to both use their electronic keys (using interactions as shown in any of the examples of  4  and  5 A- 5 E) within a defined period of time of each other (e.g., within 1 minute, 5 minutes, 30 minutes, or 1 hour) in order for the access code  432  to be provided and the lock  450  to be opened. Two or more users may interact with the same lock using the same electronic device, or using different devices. For example, two users may each tap the same lock with a different mobile phone, where the mobile phones are registered to their respective social networking user identities. Based on identifiers for the mobile phones, the identity and presence of both users at the lock can be verified. 
       FIG. 6  illustrates an example of a process  600  for issuing an electronic key leveraging a social networking platform. For convenience, operations of the process  600  are described as being performed by the computing system  308 . However, the operations of the process  600  may be performed by other computer systems described throughout this disclosure or an electronic device that includes a processor. 
     The computing system  308  receives data identifying a recipient for an electronic key provided by a user ( 602 ). The recipient is connected to the user in a social networking platform. In some implementations, the computing system  308  accesses, from the social networking platform, data identifying a set of multiple users that are connected to the user in the social networking platform. The computing system  308  provides information (e.g., a list) identifying the set of users that are connected to the user. Based on input provided by the user, the computing system  308  receives data identifying one or more users, selected from among the set of multiple users connected to the user in the social networking platform, that should be recipients of the electronic key. 
     The data identifying the recipient may be based on input provided by a user through a social networking service. The social networking service may be an application or interface through which the user receives data from, or provides data to, the social networking platform. The social networking service may be provided by the computing system  308 , the social networking platform, or another device, or combinations thereof. 
     In some implementations, the data identifies multiple users of the social networking platform as recipients for the electronic key. For example, the user may individually select multiple users as recipients for an electronic key. As another example, the user may designate a group of users defined within the social networking platform as a group of recipients for an electronic key. Recipients of the electronic key may be selected from among, and may include, users that are connected to the user in different (e.g., separate or independent) social networking platforms. 
     The computing system  308  receives data identifying a lock that the electronic key opens ( 604 ). The data identifying the lock may be based on input provided by a user through a social networking service, for example, through an application or the social networking platform. In some implementations, the computing system  308  provides data indicating a set of locks for which the user has been determined to have access control. The computing system  308  receives data identifying one or more locks, selected from the set of locks for which the user has access control, that the electronic key should open. 
     The lock can be a physical lock. For example, the lock can have one or more physical elements that control physical access to a resource. The lock can secure a physical space, such as a building, a room, the interior of a vehicle, or a storage compartment. The lock can secure the function of a physical device, for example, limiting ignition of a vehicle&#39;s engine, or mechanically limiting other functionality. 
     The computing system  308  receives data indicating one or more conditions on use of the electronic key ( 606 ). The data indicating the one or more conditions may be based on input provided by a user through a social networking service. 
     Examples of conditions on use of an electronic key include conditions that: (1) limit a time during which the electronic key may be used; (2) require the recipient to possess a particular credential or qualification; (3) require approval from the key issuer for each use of the electronic key; (4) limit a number of times that the electronic key may be used; (5) require the recipient to be accompanied by another person (e.g., a person selected from a defined list of persons, or a person that has a particular qualification); (6) require the key issuer to be outside of, or be located beyond a predetermined distance from, a space to which the electronic key provides access when the key is used; and (7) require the identity of the recipient to be confirmed at the time the electronic key is used (e.g., through a password, a biometric input, or another form of authentication). 
     As an example, a grandparent may issue an electronic key a grandchild that permits entry to the grandparent&#39;s house. To avoid potential mischief that the grandchild may cause when alone, the grandparent may set a condition that grandchild must be accompanied by someone who has the qualification of being over age 18, and who has the additional qualification of being designated as a family member of the grandparent in the social networking platform. 
     As another example, when a user goes on vacation, the user may enlist the help of a neighbor to water his plants and feed his cat. To allow the neighbor to perform these tasks, the user may issue to a neighbor an electronic key that opens the user&#39;s house. The user may specify the condition that the key may only be used during the vacation, e.g., from August 2 to August 9. In addition, in case the user comes home early and the neighbor&#39;s help is no longer needed, the user may specify the condition that the electronic key may not be used when the user is home. 
     As another example, a user who left something important at home may ask a friend to go pick it up. The user may issue to the friend an electronic key that unlocks the door to his home. Since entry to the home is needed for only a specific incident, the user may specify the condition that the key is only valid for one use. Further, the user may specify that the electronic key expires at the end of the day, whether or not the electronic key has been used. 
     As another example, a boss may issue an employee a key to an office or conference room. The boss may set the condition that the electronic key may be used at any time between 7:00 am and 6:00 pm on weekdays, but that any use of the electronic key at other times requires specific approval from the boss. 
     The computing system  308  determines that the user has authority to issue an electronic key to the lock ( 608 ). For example, the computing system  308  may determine that the lock is included in a list of locks registered to the user as being controlled by the user. As another example, the computing system  308  may determine that the lock and/or a resource secured by the lock are owned by the user. As another example, the computing system may determine that the owner of the lock and/or a resource secured by the lock has delegated access control authority to the user. 
     The computing system  308  stores key data that identifies the recipient of the electronic key, the lock, and the one or more conditions on use of the electronic key ( 610 ). In some implementations, the computing system  308  stores the key data in response to determining that the user has authority to issue the electronic key. The key data may be stored in electronic storage, for example, a table, a database, or another data structure. In some implementations, the key data includes additional information about the lock, for example, one or more access codes that open the lock. 
     The computing system  308  accesses an electronic address for the recipient ( 612 ). For example, the computing system  308  accesses the electronic address from profile data for the recipient from the social networking platform. The electronic address may be, for example, an e-mail address, a phone number, a username for the recipient in the social networking platform, or another address. Additionally or alternatively, in some implementations, the electronic address may be an account that the user has registered with a key management application executing on the computing system  308 . 
     The computing system  308  transmits data that indicates that the electronic key is transferred ( 614 ). The data may be transmitted to the electronic address for the recipient. For example, the data may be transmitted by e-mail, short message service (SMS) text message, social networking post, or by another communication channel, for example, as an in-application communication within a key management application. 
     The computing system  308  transmits that data may enable the recipient to use the electronic key in accordance with the one or more conditions imposed by the user. The data may include configuration data that enables an electronic device associated with the recipient to communicate with the lock and initiate an unlocking sequence. In some implementations, the computing system  308  transmits an access code that may be used to open the lock (e.g., successfully complete the unlocking sequence). The access code may be stored on an electronic device (e.g., such as a mobile phone) and used to open the lock, either with or without further communication with the computing system  308 . The data that enables use of the electronic key can indicate the one or more conditions on use of the electronic key. 
     In some implementations, the computing system  308  identifies a recipient based on the recipient&#39;s log-in information when the recipient logs in to an application or to the social networking platform using an electronic device. The computing system  308  determines that an electronic key has been issued to the recipient, and in response, transfers to the electronic device the data enabling the recipient to use the electronic key. Thereafter, the electronic device may be used to open the lock. 
     In some implementations, the electronic key may be revoked at any time by the user that owns control of the lock (e.g., by the user that issues the electronic key). After the electronic key is issued, the computing system  308  may receive revocation data that indicates that the recipient should no longer have access to the electronic key. As a result, the computing system  308  can store key data that indicates that the electronic key is revoked. Or, the computing system  308  can delete the stored key data that indicated that the electronic key provided access to the lock. The computing system  308  may also transmit, to the electronic address of the recipient, data indicating that access to the electronic key is terminated. Thereafter, when the computing system  308  receives use data indicating an attempted use of the electronic key, the computing system  308  may transmit notification data indicating that access to the lock is denied. The notification data may be transmitted to the electronic address for the recipient. 
       FIG. 7  illustrates an example of a process  700  for enabling use of an electronic key. For convenience, operations of the process  700  are described as being performed by the computing system  308 . However, the operations of the process  700  may be performed by other computer systems described throughout this disclosure or an electronic device that includes a processor. 
     The computing system  308  receives use data indicating an attempted use of the electronic key ( 702 ). The use data identifies the electronic key and includes description information that describes the attempted use. To identify the electronic key, an identifier for the electronic key may be provided. In addition, or as an alternative, the use data can identify the recipient of the electronic key and the lock. In some implementations, the use data is received from an electronic device, for example, from a mobile phone or other device associated with the recipient. In some implementations, the use data is received from another electronic device, such as the lock or a device connected to or otherwise associated the lock. 
     The description information can indicate, for example, the context or circumstances of the attempted use. For example, the description information can indicate social networking user identities of users accompanying the recipient. The description information can include data authenticating the recipient and/or the electronic device, for example, biometric data for the recipient, a password of the recipient, and/or a device identifier for the electronic device. 
     The computing system  308  accesses the stored key data ( 704 ). For example, the computing system  308  determines the conditions associated with use of the electronic key. The computing system  308  evaluates the description information that describes the attempted use of the electronic key against the stored key data ( 706 ). Based on the evaluation, the computing system  308  determines if the attempted use satisfies the one or more conditions on use of the electronic key ( 708 ). In response to a determination that the attempted use satisfies the one or more conditions, the computing system  308  transmits to the electronic device an access code that unlocks the lock ( 710 ). If, however, the computing device determines that the attempted use does not satisfy the one or more conditions on use of the electronic key, the computing system transmits data indicating that access to the lock is denied. 
     In some implementations, the electronic device is a mobile phone associated with the recipient. The access code that unlocks the lock can be transmitted to the mobile phone associated with the recipient over a network, and the mobile phone may transmit the access code to the lock directly (e.g., according to techniques described above). 
     In some implementations, the electronic device is the lock or a device in communication with the lock. When the recipient presents a key code to the lock, the lock can provide the use data to query the computing system  308  about whether the conditions on use of the key code are satisfied. 
     The evaluation performed by the computing system  308  can include various operations, depending on the conditions imposed on the electronic key. In some implementations, the use data includes authentication data, and the authentication data is compared with stored reference data (e.g., previously stored information identifying information). The identity of the recipient may be confirmed based on the comparison, satisfying an authentication condition. 
     In some implementations, the computing system  308  determines a time of the attempted use of the electronic key, and compares the time to a time period indicated in the key data. When the attempted use is determined to be within the time period, the computing system  308  determines that a time condition is satisfied. 
     In some implementations, the lock controls access to a physical space, and the computing system  308  determines whether the user that issued the electronic key is in a location other than the physical space. For example, the computing system  308  may obtain access logs for the lock and determine whether the user has opened the lock within a defined period of time, such as 6 hours, 1 day, or 1 week. Additionally or alternatively, the computing system  308  may maintain its own access logs for the lock and determine whether the user has opened the lock within a defined period of time. If the user has not opened the lock within the defined period of time, the user may be considered to be outside the physical space. As another example, the computing system  308  may obtain location information indicating the user&#39;s location from a check-in, status update, post, or other social network data from the social networking platform, or from GPS data for the user. When the location information indicates that the user is away from the physical space, the computing system  308  may determine that a condition requiring the absence of the user is satisfied. 
     In some implementations, the computing system  308  determines that the recipient has a particular qualification (e.g., a qualification other than having been issued the electronic key and being connected to the user in the social networking platform). The qualification may be a credential issued by a third-party, such as a driver&#39;s license issued by a government agency, a degree issued by an educational institution, or a job title given by an employer. The qualification may be a characteristic of a person, such as age or height, or a skill or an ability of a person, such as an ability to speak a language. The computing system  308  may access data indicating the recipient&#39;s qualifications from the social networking platform or other sources. In some implementations, the computing system  308  may access data indicating the recipient&#39;s qualifications from one or more electronic credentials maintained on the same electronic device on which the electronic key is maintained. When the recipient possesses the required qualification, the computing system  308  may determine that a qualification condition is satisfied. 
     In some implementations, the computing system  308  sends a request for approval of an attempted use to the user that issued the electronic key. When the computing system  308  receives approval data indicating approval of the attempted use of the electronic key, the computing system  308  may determine that an approval condition is satisfied. 
     In some implementations, the computing system  308  determines a number of previous uses of the electronic key. The computing system  308  may compare the number of previous uses with a predetermined maximum number of times that the recipient is permitted to use the electronic key, as indicated by the stored key data. When the number of uses is less than the predetermined maximum number, the computing system  308  may determine that a limited use condition is satisfied. 
     In some implementations, the computing system  308  receives, in the use data or in connection with the use data, presence data that indicates the identity of a person who accompanies the recipient when use of the electronic key is attempted. The presence data may include a password of the person, biometric input from the person, a device identifier for a device associated with the person, and/or other authentication data for the person. The presence data may be entered directly into an electronic device associated with the recipient (e.g., the recipient&#39;s mobile phone), an electronic device associated with the person (e.g., the person&#39;s mobile phone, which is different from the recipient&#39;s mobile phone), the lock, or another device. Any of the devices to which the presence data is entered may transmit the presence data to the computing system  308 . In addition, or as an alternative, the presence data may be passed between two or more of these devices and then to the computing system  308 . For example, the person&#39;s mobile phone may transmit the presence data to the recipient&#39;s mobile phone, and the recipient&#39;s mobile phone may transmit the presence data to the computing device. As another example, the person&#39;s mobile phone may transmit the presence data to lock, and the lock may transmit the presence data to the computing device. The computing system  308  determines whether the person satisfies one or more criteria for a companion required to accompany the recipient when using the electronic key. For example, the computing system  308  determines whether the person possesses one or more qualifications indicated in the key data, or whether the person is one of a predetermined set of persons designated in the key data. When the person meets the one or more criteria, the computing system may determine that a companion condition is satisfied. 
     As described above, when the conditions on use of an electronic key are not met, the computing system  308  withholds the access code that opens the lock and transmits data indicating that access to the lock is denied. This may occur when the computing system  308  determines that, for example, the attempted use is outside a time period designated in the key data, authentication data does not match reference data for the recipient, the recipient does not have a required qualification, a maximum number of uses of the electronic key is exceeded, the user that issued the key denies or fails to grant a required approval of use, or the recipient is not accompanied by a required person. 
       FIG. 8  illustrates an example of key data that may be stored by the computing system  308  in electronic storage. The key data is illustrated in a table  800 , in which each row  801   a - 801   e  represents data for a different key. The columns  806   a - 806   g  indicate various types of information about the electronic keys. The key data may additionally or alternatively be stored in formats and data structures other than those illustrated. 
     The table  800  includes an ID column  802   a  that includes an identifier for each electronic key, distinguishing the key from the other electronic keys. The table  800  includes a recipient column  802   b  that identifies the recipient of the electronic key. The electronic keys can be linked to the social networking user identities for the recipients. For example, the social networking username or profile identifier may be stored in the recipient column  802   b . The table  800  includes a lock column  802   c  that identifies the lock or locks to which the various electronic keys provide access (e.g., to open, close, or otherwise manipulate). The lock column  802   c  may identify locks with any appropriate identifiers, such as, for example, identification (ID) numbers or other unique identifiers assigned to the locks, addresses for buildings, room and floor numbers for rooms within a building, or license plates numbers or VIN numbers for vehicles. 
     The table  800  also includes columns  802   d - 802   g  that specify conditions on use of the electronic keys. A time conditions column  802   d  indicates conditions that limit the time during which an electronic key can be used. A credential conditions column  802   e  indicates credentials that the recipient must possess in order to use the electronic key. An authentication conditions column  802   f  indicates measures required to authenticate the user in order to use the electronic key. An “other conditions” column  802   g  indicates additional conditions that limit use of the electronic keys. A variety of additional or alternative conditions may be imposed on electronic keys, as described above. 
       FIG. 9  is an example of a user interface  900  that may be presented to a key issuer to request approval of use of an electronic key by a key recipient. For example, a key issuer may place a condition on an electronic key that each use of the electronic key must be approved by the key issuer. When use of the electronic key is attempted, the computing system  308  may indicate the attempted use to an electronic device associated with the key issuer, such as the electronic device  410  of  FIG. 4 . In response, the application on the electronic device  410  that manages the electronic keys may present the user interface  900 . 
     The user interface  900  includes an approve control  910  that the key issuer may interact with to approve the attempted use of the electronic key. When the approve control  910  is selected, the electronic device  410  sends data indicating the approval to the computing system  308 , and, in response, the computing system  308  transmits an approval code to the recipient, enabling the recipient to open the lock. The user interface  900  includes a deny control  920  that the key issuer may select to deny access to the recipient. When the deny control  920  is selected, the electronic device  410  sends data indicating the denial to the computing system  308 . The computing system  308  sends data to the recipient indicating that access is denied. 
       FIG. 10  illustrates an example report  1000  provided by the computing system  308 . The report  1000  presents information about electronic keys issued by a particular user. As shown, the report  1000  includes an identity column  1010  that shows a social networking user identity to which the corresponding electronic key has been issued by the user. The report  1000  also includes a key type column  1020  that identifies the lock or locked resource to which the corresponding electronic key provides access. The report  1000  further includes a last used column  1030  that indicates when the last use of the corresponding electronic key was used. The report  1000  may additionally or alternatively provide other information, such as, for example, information about unsuccessful attempted uses of the electronic keys, logs of attempted uses, and indications of the conditions currently imposed on the electronic keys. 
     As indicated by the report  1000 , the user issued an electronic key to John that unlocks the user&#39;s car, the electronic key was last used yesterday, and the electronic key is still active. Also as indicated by the report  1000 , the user issued an electronic key to Sandra that unlocks the user&#39;s office, the electronic key was last used at 11:23 am on the day the report was provided, and the electronic key is still active. In addition, the user issued an electronic key to Todd that unlocks the user&#39;s house, the electronic key was last used three weeks ago, and the electronic key is currently disabled. Finally, the user issued a key to Lisa that unlocks the user&#39;s car, the electronic key was never used, and the electronic key has expired. 
     The report  1000  includes an update control  1050  and an exit control  1060 . The update control  1050  causes display of an interface that enables the user to update one or more of the electronic keys, for example, by adding, removing, or modifying conditions on use of one or more of the electronic keys. For instance, viewing the report  1000  may cause the user to desire to increase or reduce the conditions imposed on the electronic keys. Invocation of update control  1050  may enable the user to do so. The exit control  1060  removes the report  1000  from display. 
       FIG. 11  illustrates an example process  1100  for modifying an electronic key based on actions of a recipient of the electronic key. For convenience, operations of the process  1100  are described as being performed by the computing system  308 . However, the operations of the process  1100  may be performed by other computer systems described throughout this disclosure or an electronic device that includes a processor. 
     The computing system  308  monitors actions of the recipient of the electronic key ( 1102 ). For example, the computing system  308  monitors any types of actions of the recipient that are possible to monitor using the computing system  308 . In this example, the computing system  308  may monitor attempts to use the electronic key and may monitor social networking actions of the recipient within the social networking platform. In monitoring attempted uses of the electronic key, the computing system  308  may monitor the frequency of use, time of use, number of uses, and the particular circumstances of each use. In monitoring social networking actions of the recipient within the social networking platform, the computing system  308  may monitor connections made or broken by the recipient, posts within the social networking platform, or any other type action within the social networking platform. 
     The computing system  308  compares the actions of the recipient of the electronic key with one or more rules that define at least one ramification for the electronic key that results from one or more specific actions of the recipient ( 1104 ). For instance, when the computing system  308  monitors attempted uses of the electronic key by the recipient, the computing system  308  compares parameters of the use with the conditions on use of the electronic key to determine whether the recipient violated the conditions. When the computing system  308  monitors social networking actions of the recipient within the social networking platform, the computing system  308  compares the social networking actions with rules that define when electronic keys should be modified based on social networking actions. The social networking actions may include actions related to connections within the social networking platform, messages exchanged within the social networking platform (e.g., posts), and/or any other types of actions that provide meaningful information relevant to an electronic key. 
     The computing system  308  determines that the actions of the recipient of the electronic key have violated at least one of the one or more rules ( 1106 ). For example, when the computing system  308  monitors attempted uses of the electronic key, the computing system  308  determines that the recipient violated the conditions of the transaction specified by the rule. In addition, when the computing system  308  monitors social networking actions of the recipient within the social networking platform, the computing system  308  determines that the recipient violated rules defining appropriate conduct for users who have received the electronic key. The rules may be generally applicable to all electronic keys, or may be designated by the key issuer to apply to a particular electronic key. 
     Based on the determination that the actions of the recipient of the electronic key have violated at least one of the one or more rules, the computing system  308  determines a ramification for the electronic key defined by the at least one of the one or more rules ( 1108 ). For instance, the computing system  308  determines a ramification that revokes the electronic key or modifies the electronic key. The electronic key can be modified by adding or modifying a condition on use of the electronic key. The ramification may be selected from a record in a database pertaining to the rule violated. 
     The computing system  308  modifies the electronic key in accordance with the determined ramification ( 1110 ). For example, the computing system  308  revokes the electronic key, temporarily disables the electronic key (e.g., disables the electronic key for a predetermined period of time), reduces level of access attainable using the electronic key, adds or modifies one or more conditions limiting use of the electronic key, and/or places other restrictions on the electronic key. The electronic key may still be available for use, but with the ramification applied. 
     As an example, the computing system  308  may monitor actions of the recipient and determine that a number of unsuccessful attempts to use the electronic key have occurred during a time period. The computing system  308  may compare the number of unsuccessful attempts to a threshold number of unsuccessful attempts indicated in a rule, and determine that the number exceeds the threshold number. Based on the comparison, the computing system  308  may determine that the actions have violated the rule, and the computing system  308  may determine that the ramification associated with violating the rule is for the electronic key to be disabled for seven days. The computing system  308  may also determine that the ramification includes applying a new condition on use of the electronic key, requiring that the key issuer subsequently approve each use of the electronic key. The computing system  308  may then modify stored key data to cause the electronic key to be disabled for seven days and for the new condition to be applied. 
       FIG. 12  illustrates an example alert  1200  that alerts the issuer of an electronic key and/or the recipient of the electronic key that the electronic key has been revoked (e.g., cancelled or disabled) based on actions taken by the recipient of the electronic key. As shown, the alert  1200  indicates that the electronic key extended from a Father User to a Daughter User has been revoked because the Daughter User removed the Father User as a connection within the social networking platform. In this regard, the computing system  308  detected that the Daughter User removed the Father User as a connection within the social networking platform. Based on the detection that the Daughter User removed the Father User as a connection within the social networking platform, the computing system  308  determines whether the Father User had previously extended an electronic key to the Daughter User through the social network service. In this example, the computing system  308  determines that the Father User had previously extended an electronic key to the Daughter User through the social network service and determines to revoke the electronic key based on the Daughter User removing the Father User as a connection within the social networking platform. The computing system  308  sends the alert  1200  to the Father User and/or the Daughter User in response to the determination to revoke the electronic key. 
     The alert  1200  also includes a reconnect control  1210 , a reinstate request control  1220 , and an exit control  1230 . The reconnect control  1210  causes a connection request message to be sent from the Daughter User to the Father User. If the Father User accepts the connection request, the Father User and the Daughter User become reconnected within the social networking platform and the electronic key from the Father User to the Daughter User is restored by the computing system  308 . 
     The reinstate request control  1220  causes a message to be sent to the Father User asking the Father User to reinstate the electronic key, despite the connection between the Father User and the Daughter User being severed in the social networking platform. The Father User may agree to reinstate the electronic key, which causes the computing system  308  to reactivate the electronic key shared by the Father User with the Daughter User. The Father User may decline to reinstate the electronic key, which causes the computing system  308  to maintain the electronic key previously shared by the Father User with the Daughter User in a revoked or disabled state. The exit control  1230  removes the alert  1200  from display and allows the electronic key previously shared by the Father User with the Daughter User to remain in a revoked or disabled state. 
     While the electronic keys have been described as providing access to physical locks, the techniques described may be used to provide access to any appropriate security or authentication measure. For example, the techniques can be used to issue electronic keys to access computer systems, computer network resources, software systems, particular files, or any other secured resource. 
     Further, while emphasis has been placed on using electronic keys to open corresponding locks, the electronic keys may equally be configured to lock the corresponding locks. Locking a lock, or otherwise changing the status of a lock using an electronic key, may be limited in accordance with the conditions set by the issuer of the electronic key. 
     The features described can be implemented in digital electronic circuitry, or in computer hardware, firmware, software, or in combinations of them. The apparatus can be implemented in a computer program product tangibly embodied in an information carrier, e.g., in a machine-readable storage device, for execution by a programmable processor; and method steps can be performed by a programmable processor executing a program of instructions to perform functions of the described implementations by operating on input data and generating output. The described features can be implemented advantageously in one or more computer programs that are executable on a programmable system including at least one programmable processor coupled to receive data and instructions from, and to transmit data and instructions to, a data storage system, at least one input device, and at least one output device. A computer program is a set of instructions that can be used, directly or indirectly, in a computer to perform a certain activity or bring about a certain result. A computer program can be written in any form of programming language, including compiled or interpreted languages, and it can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. 
     Suitable processors for the execution of a program of instructions include, by way of example, both general and special purpose microprocessors, and the sole processor or one of multiple processors of any kind of computer. Generally, a processor will receive instructions and data from a read-only memory or a random access memory or both. Elements of a computer include a processor for executing instructions and one or more memories for storing instructions and data. Generally, a computer will also include, or be operatively coupled to communicate with, one or more mass storage devices for storing data files; such devices include magnetic disks, such as internal hard disks and removable disks; magneto-optical disks; and optical disks. Storage devices suitable for tangibly embodying computer program instructions and data include all forms of non-volatile memory, including by way of example semiconductor memory devices, such as EPROM, EEPROM, and flash memory devices; magnetic disks such as internal hard disks and removable disks; magneto-optical disks; and CD-ROM and DVD-ROM disks. The processor and the memory can be supplemented by, or incorporated in, ASICs (application-specific integrated circuits). 
     To provide for interaction with a user, the features can be implemented on a computer having a display device such as a CRT (cathode ray tube) or LCD (liquid crystal display) monitor for displaying information to the user and a touchscreen and/or a keyboard and a pointing device such as a mouse or a trackball by which the user can provide input to the computer. 
     The features can be implemented in a computer system that includes a back-end component, such as a data server, or that includes a middleware component, such as an application server or an Internet server, or that includes a front-end component, such as a client computer having a graphical user interface or an Internet browser, or any combination of them. The components of the system can be connected by any form or medium of digital data communication such as a communication network. Examples of communication networks include, e.g., a LAN, a WAN, and the computers and networks forming the Internet. 
     The computer system can include clients and servers. A client and server are generally remote from each other and typically interact through a network, such as the described one. The relationship of client and server arises by virtue of computer programs running on the respective computers and having a client-server relationship to each other. 
     A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the disclosure. Accordingly, other implementations are within the scope of the following claims.