Patent Publication Number: US-2012042390-A1

Title: Method and apparatus for secure revocable location sharing

Description:
BACKGROUND 
     Service providers and device manufacturers (e.g., wireless, cellular, etc.) are continually challenged to deliver value and convenience to consumers by, for example, providing compelling network services. A widely popular class of network services includes social networking services in which subscribers identify each other as members of a circle of friends and share posted text, audio, photographs, video, World Wide Web links and other information. Some of the shared information includes geospatial location data, such as a home, school or work address or some meeting place and time for a subscriber. As more subscribers carry mobile devices with global positioning system (GPS) receivers, the subscribers&#39; current and past locations can also be tracked and shared by a location sharing service (LSS) of the social networking service. As intriguing and useful as location-sharing services may be, they pose a privacy problem to users. A user&#39;s current or recent location can be exposed to employers or clients or antagonists or creditors or government agencies as a result of the practices of the LSS or from a breach into the LSS system. Such exposure might sometimes be undesirable. Some systems prevent a subscriber&#39;s location from being revealed to the LSS by encrypting the subscriber&#39;s location. However such systems require the subscriber to send a decryption key to each friend who is privileged to share the location data; and do not provide for revocation of location sharing privileges. 
     SOME EXAMPLE EMBODIMENTS 
     Therefore, there is a need for an approach for a secure revocable location sharing network service. 
     According to one embodiment, a method comprises determining a first identifier for a subscriber at a first service. The method also comprises determining a location access key stored at a second service in association with a second identifier for the subscriber. The method further comprises determining at least one ciphered location based on the location access key and at least one location associated with the subscriber. The method still further comprises determining to send the at least one ciphered location to the first service in association with the first identifier. 
     According to another embodiment, a method comprises receiving at least one location sharing invitation message indicating a first identifier for a corresponding subscriber at a first service and a second identifier for the subscriber at a second service. The method further comprises determining to send, to the second service, a request for an access key associated with the second identifier. The method further comprises receiving a contact access key in response to sending the request. 
     In some embodiments, the second identifier for the subscriber is identical to the first identifier for the subscriber. 
     According to another embodiment, a method comprises determining to associate a first identifier for a subscriber with an access key and at least one second identifier at a first service for at least one contact of the subscriber. However, the access key is not associated with the first identifier at the first service. 
     According to another embodiment, an apparatus comprises at least one processor, and at least one memory including computer program code, the at least one memory and the computer program code configured to, with the at least one processor, cause, at least in part, the apparatus to determine a first identifier for a subscriber at a first service. The apparatus is also caused to determine a location access key stored at a second service in association with a second identifier for the subscriber. The apparatus is further caused to determine at least one ciphered location based on the location access key and at least one location associated with the subscriber. The apparatus is also caused to determining to send the at least one ciphered location to the first service in association with the first identifier. 
     According to another embodiment, an apparatus comprises at least one processor, and at least one memory including computer program code, the at least one memory and the computer program code configured to, with the at least one processor, cause, at least in part, the apparatus to receive at least one location sharing invitation message indicating a first identifier for a corresponding subscriber at a first service and a second identifier for the subscriber at a second service. The apparatus is further caused to determine to send, to the second service, a request for an access key associated with the second identifier. The apparatus is further caused to receive a contact access key in response to sending the request. 
     According to another embodiment, an apparatus comprises at least one processor, and at least one memory including computer program code, the at least one memory and the computer program code configured to, with the at least one processor, cause, at least in part, the apparatus to determine to associate a first identifier for a subscriber with an access key and at least one second identifier at a first service for a contact of the subscriber. The access key is not associated with the first identifier at the first service. 
     According to another embodiment, a method comprises facilitating access to at least one interface configured to allow access to at least one service, the at least one service configured to perform at least one of the above methods. 
     According to another embodiment, a computer-readable storage medium carries one or more sequences of one or more instructions which, when executed by one or more processors, cause, at least in part, an apparatus to perform at least one of the above methods. 
     According to another embodiment, a computer program product includes one or more sequences of one or more instructions which, when executed by one or more processors, cause an apparatus to at least perform one of the above methods. 
     According to another embodiment, an apparatus comprises means for performing steps of one of the above methods. 
     Still other aspects, features, and advantages of the invention are readily apparent from the following detailed description, simply by illustrating a number of particular embodiments and implementations, including the best mode contemplated for carrying out the invention. The invention is also capable of other and different embodiments, and its several details can be modified in various obvious respects, all without departing from the spirit and scope of the invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The embodiments of the invention are illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings: 
         FIG. 1  is a diagram of a system capable of secure revocable location sharing, according to one embodiment; 
         FIG. 2A  is a diagram of a subscriber profiles data structure, according to one embodiment; 
         FIG. 2B  is a diagram of a location access keys data structure, according to one embodiment; 
         FIG. 2C  is a diagram of a cached access keys data structure, according to one embodiment; 
         FIG. 2D  is a diagram of a location share invitation message, according to one embodiment; 
         FIG. 3  is a time sequence diagram of messages exchanged to provide secure revocable location sharing, according to an embodiment; 
         FIG. 4  is a flowchart of a process for location key service, according to one embodiment; 
         FIG. 5  is a flowchart of a process for location privacy management, according to one embodiment; 
         FIGS. 6A-6B  are diagrams of user interfaces utilized in the processes of  FIG. 5 , according to various embodiments; 
         FIG. 7  is a diagram of hardware that can be used to implement an embodiment of the invention; 
         FIG. 8  is a diagram of a chip set that can be used to implement an embodiment of the invention; and 
         FIG. 9  is a diagram of a mobile terminal (e.g., handset) that can be used to implement an embodiment of the invention. 
     
    
    
     DESCRIPTION OF SOME EMBODIMENTS 
     Examples of a method, apparatus, and computer program are disclosed for secure revocable location sharing. In the following description, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the embodiments of the invention. It is apparent, however, to one skilled in the art that the embodiments of the invention may be practiced without these specific details or with an equivalent arrangement. In other instances, well-known structures and devices are shown in block diagram form in order to avoid unnecessarily obscuring the embodiments of the invention. 
     As used herein, the term location refers to geospatial location data, unless otherwise evident from the context. A subscriber refers to an entity or person who has registered with a network subscription service to receive a service based on information provided to the service by the subscriber. The information provided by the subscriber is stored by the subscription service in one or more subscriber profiles data structures. Although various embodiments are described with respect to sharing a subscriber&#39;s current location, it is contemplated that the approach described herein may be used with other locations associated with a subscriber, such as an office, home, school, place of worship, or other location regardless of the subscriber&#39;s current location. 
     As used herein a cipher refers to a value that contains a message in hidden form. In the illustrated embodiments, the message is a subscriber&#39;s location. The process of the changing the message to the cipher is called enciphering. When the message is a location, the cipher can be called a ciphered location. The process of changing the cipher back to the message is called deciphering. A location recovered from a ciphered location is therefore often called a deciphered location. The terms encrypt and decrypt are often used in the art as synonyms for encipher and decipher, respectively. Because a crypt also refers to an enclosure for a dead body, the forms encipher and decipher are preferred and used herein. 
       FIG. 1  is a diagram of a system capable of secure revocable location sharing, according to one embodiment. The general architecture of a location-sharing service (LSS) includes a LSS  118  on subscription service  110   a  which is accessed by a subscriber with a browser process  107  or service client process  116  on user equipment (UE), e.g., UE  101   a . Backend functions of the subscription service  110   a  can be reached through an application programming interface (API)  114   a . A subscriber Alice, operating user equipment (UE)  101   a  designates subscriber Bob, operating UE  101   b , as a “friend,” and this information is stored in a subscriber profiles data structure  112  for both Alice and Bob. A location sharing client  117  on Alice&#39;s UE  101   a  submits her location to the LSS  118  which stores the location in the subscriber profiles data structure  112 . A location sharing client  117  on Bob&#39;s UE  101   b  makes a request to the LSS  118  to retrieve the locations of all his “friends”. The LSS  118  checks the subscriber profiles data structure  112  to determine that Alice is a friend of Bob. The LSS  118  sends Alice&#39;s location to the location sharing client  117  on Bob&#39;s UE  101   b . As a result, the LSS  118  and subscriptions service  110   a  are fully aware of Alice&#39;s location information, exposing her location to anyone who misuses the subscription service  110   a  or the API  114   a . Furthermore, subscribers who make use of more than one of these network services  110   a  through  110   n  simultaneously increase the chances that they will suffer from a loss of privacy. 
     To address this problem, a system  100  of  FIG. 1  introduces a location privacy manager module  150  and a location key service  152  separate from the LSS  118 . Therefore, the location key service  152  is different from the location sharing network service LSS  118 . The location privacy manager module  150  enciphers Alice&#39;s location using a key stored at the location key service  152  before sending the ciphered location to the LSS  118 . The ciphered location is stored in the subscriber profiles data structure  112 , but neither the LSS  118  nor the subscription service  110   a  has the key. That is, the access key is not associated with a first identifier for the subscriber at the location sharing network service. The LSS  118  sends Alice&#39;s ciphered location to Bob&#39;s UE  101   b . The location privacy manager module  150  on Bob&#39;s UE  101   b  requests Alice&#39;s key from the location key service  152  and uses that key to decipher Alice&#39;s location and pass the deciphered location to the location sharing client  117  on Bob/s UE  101   b . The location key service  152  stores, in location access keys data structure  154 , data indicating Alice&#39;s identity and data indicating her location access key and data indicating a list of subscribers, such as Bob, who are privileged to obtain the key to decipher her location. Alice can tailor the list of those who have access to her location to differ from the complete friends list known to the subscription service  110   a . Alice can revoke privileges by changing the key and removing the subscriber&#39;s identifier from the list in data structure  154 . For example, Alice can stop sharing her location with Bob by removing an identifier for Bob from the location access keys data structure  154  and changing the value of her access key. 
     Using the separate location key service  152  is an advantage because when Alice&#39;s key is changed, her UE  101   a  only communicates the change to the location key service  152  and not to every privileged friend. Only when a privileged friend asks for Alice&#39;s location does the UE of that privileged friend request the key from the location key service  152 . Bandwidth is saved on a communications network  105  and computational resources are saved on a host of the location key service  152  because the key change is passed on demand and not pushed to every privileged user with every key change. 
     In some embodiments, if the same entity controls, or has access to, both the subscription service  110   a  and location key service  152 , the key can still be kept secure by using different identifiers for Alice on the key service  152  than on the subscription service  110   a , as described in more detail below. In an invitation message, Alice informs the privileged subscribers of her different identifier at the location key service to be used for multiple key changes. Thereafter the location key service  152  propagates key changes to the privileged users on demand. 
     As shown in  FIG. 1 , the system  100  comprises user equipment (UE)  101   a  and UE  101   b  (collectively referenced hereinafter as UE  101 ) having connectivity to one or more network services including map service  120 , subscription service  110   a  through network service  110   n  (collectively referenced hereinafter as network services  110 ) as well as a location key service  152 , via a communication network  105 . By way of example, the communication network  105  of system  100  includes one or more networks such as a data network (not shown), a wireless network (not shown), a telephony network (not shown), or any combination thereof. It is contemplated that the data network may be any local area network (LAN), metropolitan area network (MAN), wide area network (WAN), a public data network (e.g., the Internet), short range wireless network, or any other suitable packet-switched network, such as a commercially owned, proprietary packet-switched network, e.g., a proprietary cable or fiber-optic network, and the like, or any combination thereof. In addition, the wireless network may be, for example, a cellular network and may employ various technologies including enhanced data rates for global evolution (EDGE), general packet radio service (GPRS), global system for mobile communications (GSM), Internet protocol multimedia subsystem (IMS), universal mobile telecommunications system (UMTS), etc., as well as any other suitable wireless medium, e.g., worldwide interoperability for microwave access (WiMAX), Long Term Evolution (LTE) networks, code division multiple access (CDMA), wideband code division multiple access (WCDMA), wireless fidelity (WiFi), wireless LAN (WLAN), Bluetooth®, Internet Protocol (IP) data casting, satellite, mobile ad-hoc network (MANET), and the like, or any combination thereof. 
     The network services  110  include one or more with API, such as API  114   a  in subscription service  110   a  and API  114   n  in network service  110   n . The subscription service  110   a  includes subscriber profiles data structure  112  and a location sharing service (LSS)  118 , as described above. 
     The location key service  152  maintains the location access keys data structure  154  and distributes location access keys of one or more subscribers to one or more privileged contacts of each subscriber. The location key service  152  thus manages the location access keys for a subscriber. A subscriber creates a location access key at the location key service  152  to enable “friends” to decipher the user&#39;s location. The location key service  152  is preferably a separate entity from the location-sharing service (e.g., LSS  118 ), e.g., they are not under the control of the same organization. 
     The UE  101  is any type of mobile terminal, fixed terminal, or portable terminal including a mobile handset, station, unit, device, multimedia computer, multimedia tablet, Internet node, communicator, desktop computer, laptop computer, notebook computer, netbook computer, tablet computer, Personal Digital Assistants (PDAs), audio/video player, digital camera/camcorder, positioning device, television receiver, radio broadcast receiver, electronic book device, game device, or any combination thereof, including the accessories and peripherals of these devices, or any combination thereof. It is also contemplated that the UE  101  can support any type of interface to the user (such as “wearable” circuitry, etc.). 
     By way of example, the UE  101 , network services  110  and location key service  152  communicate with each other and other components of the communication network  105  using well known, new or still developing protocols. In this context, a protocol includes a set of rules defining how the network nodes within the communication network  105  interact with each other based on information sent over the communication links. The protocols are effective at different layers of operation within each node, from generating and receiving physical signals of various types, to selecting a link for transferring those signals, to the format of information indicated by those signals, to identifying which software application executing on a computer system sends or receives the information. The conceptually different layers of protocols for exchanging information over a network are described in the Open Systems Interconnection (OSI) Reference Model. 
     Communications between the network nodes are typically effected by exchanging discrete packets of data. Each packet typically comprises (1) header information associated with a particular protocol, and (2) payload information that follows the header information and contains information that may be processed independently of that particular protocol. In some protocols, the packet includes (3) trailer information following the payload and indicating the end of the payload information. The header includes information such as the source of the packet, its destination, the length of the payload, and other properties used by the protocol. Often, the data in the payload for the particular protocol includes a header and payload for a different protocol associated with a different, often higher layer of the OSI Reference Model. The header for a particular protocol typically indicates a type for the next protocol contained in its payload. The payload protocol is said to be encapsulated in the header protocol. The headers included in a packet traversing multiple heterogeneous networks, such as the Internet, typically include a physical (layer 1) header, a data-link (layer 2) header, an internetwork (layer 3) header and a transport (layer 4) header, and various application headers (layer 5, layer 6 and layer 7) as defined by the OSI Reference Model. 
     Processes executing on various devices, often communicate using the client-server model of network communications, widely known and used. According to the client-server model, a client process sends a message including a request to a server process, and the server process responds by providing a service. The server process may also return a message with a response to the client process. Often the client process and server process execute on different computer devices, called hosts, and communicate via a network using one or more protocols for network communications. The term “server” is conventionally used to refer to the process that provides the service, or the host on which the process operates. Similarly, the term “client” is conventionally used to refer to the process that makes the request, or the host on which the process operates. As used herein, the terms “client” and “server” refer to the processes, rather than the hosts, unless otherwise clear from the context. In addition, the process performed by a server can be broken up to run as multiple processes on multiple hosts (sometimes called tiers) for reasons that include reliability, scalability, and redundancy, among others. A well known client process available on most devices (called nodes) connected to a communications network is a World Wide Web client (called a “web browser,” or simply “browser”) that interacts through messages formatted according to the hypertext transfer protocol (HTTP) with any of a large number of servers called World Wide Web (WWW) servers that provide web pages. 
     In the illustrated embodiment, the UE  101  include a browser  107 , a service client  116  for one or more of the network services  110 , and a location privacy manager module  150 . In some embodiments, one or more of services  110  interact with a user of UE  101  though a browser  107 , and the service client  116  is a script or form within the browser  107 . In some embodiments, a separate service client  116  employs the graphics and forms of the browser  107  as a user interface for prompting and detecting user input at UE  101 . The service client  116  includes a location sharing client  117  that interacts across communications network  105  with the LSS  118 . 
     According to the illustrated embodiment, the location privacy manager module  150  exchanges actual locations with the location sharing client  117  and exchanges only ciphered locations with the LSS  118 . In the illustrated embodiment, the location privacy manager module  150  on UE  101   a  and  101   b  also caches access keys already exchanged with the location key service  152  in cached access keys data structures  157   a  and  157   b , respectively (collectively referenced hereinafter as cached access keys data structure  157 ). In some embodiments, cached access keys data structure  157  is omitted on one or more UE  101 . Thus, location privacy manager module  150  is the layer through which subscribers access a location-sharing service (LSS) or the location key service  152 . When a subscriber initiates a location upload to the LSS  118 , the location privacy manager module  150  performs the appropriate actions to protect the subscriber&#39;s privacy by enciphering the subscriber&#39;s location with a key equal or related to the subscriber&#39;s location access key, and by sending the ciphered location to the LSS  118 . Thus, enciphering and deciphering are performed locally on the user&#39;s device UE  101 . That is, a user&#39;s location is enciphered on the user&#39;s device (UE  101 ) before upload and “friends” locations are deciphered on the user&#39;s device (UE  101 ) for viewing. Hence the locations of any subscriber cannot be viewed in their clear (deciphered) form outside of the user&#39;s device (UE  101 ). 
     Although processes and data structures are shown in  FIG. 1  as integral blocks in a particular order on particular nodes of the communication network for purposes of illustration, in other embodiments, one or more processes or data structure or portions thereof are arranged in a different order on the same, more or fewer nodes of the network or in one or more databases or are omitted or one or more additional processes or data structures are included. 
       FIG. 2A  is a diagram of a subscriber profiles data structure  200 , according to one embodiment. Data structure  200  is a particular embodiment of subscriber profiles data structure  112  depicted in  FIG. 1 . Although fields, entries and data structures are depicted in  FIG. 2A  through  FIG. 2D  as integral blocks in a particular arrangement for purposes of illustration, in other embodiments, one or more fields, entries, data structures, or portions thereof, are arranged in a different order or in one or more databases on one or more nodes of the communications network, or are omitted, or one or more additional fields, entries or data structures are included. 
     The subscriber profiles data structure  200  includes a subscriber entry field  201  for each of one or more subscribers as indicated by ellipsis. Each subscriber entry field  201  includes a subscriber service identifier (ID) field  203 , a subscriber information field  205 , a subscriber contacts field  207 , and a location field  209 . 
     The subscriber service ID field  203  holds data that indicates an identifier for the subscriber at the subscription service. For example, at a social networking service, Alice is identified as “Alice 123 ” and data indicating “Alice 123 ” is stored in field  203 . Alice may have other identifiers at other subscriber services, such as Alice 567 ” or “AllyZ”. Furthermore, in some embodiments, Alice may use a different identifier at the location key service  152 , as described in more detail below. The subscriber&#39;s identifier at the location key service is called the key identifier (ID) and the subscriber&#39;s identifier at the location sharing service (LSS  118 ) or subscription service  110   a  is called the service identifier (ID), hereinafter. Thus the service ID in field  203  is used to refer to an identifier for Alice at subscription service  110   a.    
     The subscriber information field  205  holds data that indicates information about the subscriber, such as actual name, birth date, gender, relationship status, city and province and country of residence, an email address, a telephone number, a postal address, and billing information, if any, among others. 
     The subscriber contacts field  207  holds data that indicates one or more contacts of the subscriber within the subscription service, e.g., the service IDs of other subscribers with whom the subscriber has established a relationship. In some embodiments in which different relationships are supported, e.g., family, close friends, acquaintances, the relationship is included with the service ID of each contact of the subscriber. 
     The location field  209  holds data that indicates one or more locations of the subscriber, such as the most recent location or the location of home or work or school or place of worship or other context sensitive location. The information in the location field  209  is shared with one or more other subscribers, such as one or more subscriber contacts indicated in field  207 , through the LSS  118 . According to various embodiments, the location field  209  holds data that indicates only ciphers of the one or more locations, so that the subscription service  110   a  and LSS  118  are unable to determine the actual location or locations associated with the subscriber. Storing ciphers of the location in field  209  is an example means to achieve the advantage of protecting the privacy of the subscriber&#39;s location information from the subscription service or other users thereof, without express privilege from the subscriber. 
     The subscriber contact who receives the location data from field  209  should decipher the data using an access key for the subscriber indicated in the subscriber service ID field  203 . That access key is maintained separately by the location key service  152 . Maintaining access keys at a separate service is an example means to achieve the advantage of protecting the privacy of the subscriber&#39;s location information from the subscription service or other users thereof, without express privilege from the subscriber. 
     Some LSS  118  associate the subscriber&#39;s location with one or more related items as determined, for example, by the map service  120  or other network service  110 . When the location field  209  contains only a cipher of the subscriber&#39;s location, the LSS  118  and subscription service  110   a  are unable to promote items related to the subscriber&#39;s spatial context. A technique to resurrect this capability, at least temporarily, in some embodiments is described in more detail below. 
       FIG. 2B  is a diagram of a location access keys data structure  220 , according to one embodiment. Data structure  220  is a particular embodiment of location access keys data structure  154  depicted in  FIG. 1 . The location access keys data structure  220  includes a subscriber entry field  221  for each of one or more subscribers as indicated by ellipsis. Each subscriber entry field  221  includes a subscriber key identifier (ID) field  223 , an access key field  225 , and a privileged subscribers field  227 . 
     The subscriber key ID field  223  holds data that indicates an identifier for the subscriber at the location key service  152 . In some embodiments, the same value, e.g., “Alice 123 ,” is used for both the service ID and key ID. However, in some embodiments, the same entity controls, or has access to, both the subscription service  110   a  and the location key service  152 , e.g., through one or more API. To prevent such an indirect disclosure of the subscriber&#39;s access key to the LSS  118  or subscriptions service  110   a , in some embodiments the subscriber uses a different value in the key ID field  223 . For example, Alice uses “LookingGlassXYZ” as the key ID indicated by data stored in the subscriber key ID field  223 . 
     The access key field  225  holds data that indicates a secret key used to decipher a cipher of a location associated with the subscriber identified in key ID field  223 . Any secret key may be used that deciphers a location from a cipher of the location. For example, in some embodiments, the secret key is a symmetric key that is used to both encipher a message and decipher it. Several algorithms using symmetric keys are well known, such as a N-bit key used in an exclusive logical OR (XOR) binary operation on N bits at a time, or an N-bit key used in a Data Encryption Standard (DES) algorithm. In some embodiments, the secret key is used just for deciphering; and a different key, known to the subscriber identified in field  223 , is used to generate a ciphered message, e.g., a ciphered location. In such cases the enciphering key is associated with the access key at least at the location privacy manager module  150 . An advantage of the symmetric key is that only one key needs to be saved by the subscriber. An advantage of a non-symmetric key is that only the subscriber can encipher the locations, even though all the privileged contacts can decipher the locations. 
     The privileged subscribers field  227  holds data that indicates one or more contacts of the subscriber who are allowed to receive the access key. In some embodiments, the privileged subscribers are indicated by a list of their servicer IDs. For example, if Bob subscribes to the subscription service as “Bob 456 ” and Bob is to be granted the privilege of accessing Alice&#39;s location, then data indicating “Bob 456 ” is included in the privileged subscribers field  227 . Thus the field  227  holds data used to determine who is permitted to “view” a given subscriber&#39;s locations. When subscriber A accepts a “friend” request from another subscriber B via the LSS  118 , the location privacy manager module  150  issues a corresponding update message that indicates “add subscriber B to subscriber A&#39;s privileged subscribers list” to the location key service  152 . Subscriber B is thus allowed to retrieve subscriber A&#39;s location access key from the location key service  152 . This enables subscriber B to “view” subscriber A&#39;s locations on subscriber B&#39;s local device. 
       FIG. 2C  is a diagram of a cached access keys data structure  240 , according to one embodiment. Data structure  240  is a particular embodiment of cached access keys data structure  157  maintained on the UE  101 , as depicted in  FIG. 1 . The cached access keys data structure  240  includes a subscriber key identifier (ID) field  243 , a subscriber access key  245 , a privileged subscribers field  247 , and a contact entry field  250  for each of one or more contacts of the subscriber, as indicated by ellipsis. Each contact entry field  250  includes a contact service identifier (ID) field  251 , a contact key identifier (ID) field  253 , a location key service address field  255 , and an access key field  257 . 
     The subscriber key ID field  243  holds data that indicates the identifier for the subscriber in the location access keys data structure  220  of the location key service  152 . In some embodiments, if the subscriber&#39;s service ID is also used at the location key service, field  243  is omitted. 
     The access key field  245  holds data that indicates the access key stored in the location access keys data structure  220  at the location key service  152 . In some embodiments that use an asymmetric key, i.e., a different key to turn the location into a cipher (encipher) than is used to turn the cipher into the location (decipher), the access key field  245  also includes data that indicates the key used to encipher the location. 
     The privileged subscribers ID field  247  holds data that indicates the service identifiers for the subscribers who are allowed to share the location of the subscriber indicated in field  243 . 
     The contact service ID field  251  holds data that indicates an identifier for the contact at the subscription service  110   a  or LSS  118 . The contact key ID field  253  holds data that indicates an identifier for the contact at the location key service  152 . If the same value is used for both a service ID and a key ID, then in some embodiments one of field  251  or  253  is omitted and the other indicates both the service ID and the key ID of the contact. 
     The location key service address field  255  holds data that indicates the network address of the location key service  152 , e.g., the universal resource locator (URL) name. In some embodiments that use a single location key service  152  for all subscribers to the subscription service  110   a , field  255  is omitted. 
     The access key field  257  holds data that indicates the access key, if any, last retrieved from the location key service  152  for the contact identified in field  251  and  253 . The access key field  257  is an example means to achieve the advantage of reducing message traffic over the communications network and computational resources at the host of the location key service if a previously retrieved access key still suffices to decipher the locations of the contact. 
       FIG. 2D  is a diagram of a location share invitation message  260 , according to one embodiment. As described in more detail below, the message  260  is sent from a subscriber to one or more contacts to invite the one or more contacts to decipher the subscriber&#39;s locations. Because the message  260  sends only a notice that the subscriber will share the location but not the access key, the message is sent only once no matter how often the access key is changed. This saves computational resources on the UE. The use of the separate location key service is an example means to achieve the advantage of saving these computational resources on the UE. In some embodiments that use only one location key service  152  and that use the same value for both the service ID and the key ID, the invitation message  260  is omitted. The location share invitation message  260  includes a subscriber service identifier (ID) field  261 , a subscriber key identifier (ID) field  263  and a location key service address field  265 . 
     The subscriber service ID field  261  holds data that indicates an identifier for the subscriber at the subscription service  110   a  or LSS  118 . The subscriber key ID field  263  holds data that indicates an identifier for the subscriber at the location key service  152 . If the same identifier is used for both, then in some embodiments one of field  261  or  263  is omitted and the other indicates both the service ID and the key ID of the subscriber. 
     The location key service address field  265  holds data that indicates the network address of the location key service  152 , e.g., the universal resource locator (URL) name. In some embodiments that use a single location key service for all subscribers to the subscription service  110   a , field  265  is omitted. 
       FIG. 3  is a time sequence diagram  300  of messages exchanged to provide secure revocable location sharing, according to an embodiment. In  FIG. 3  time increases downward (not to scale), an individual network process is represented by vertically elongated boxes labeled by rectangles at the top. A message sent from one process to another is indicated by a horizontal arrow pointing from the sending process to the receiving process. A step at a single process is indicated by a segmented arrow looping back on the process at a vertical position indicative of the relative time when the step occurs. The processes represented in  FIG. 3  include the location sharing client  117 , the location privacy manager module  150 , the location key service  152 , and the subscription service  110   a  (including LSS  118 ). 
     In one or more messages  303 , the location sharing client  117  of the service client  116  sends the subscriber service ID and contacts to the location privacy manager module  150  on the UE  101 . In this manner the privacy manager module  150  determines the subscriber ID for the user of UE  101  and the contacts from which to select the contacts privileged to share locations with the subscriber. 
     In step  311  the location privacy manager module  150  generates a key ID for the subscriber to use at the location key service and a list of privileged contacts. For example, the user of UE  101  is prompted to provide a key ID and to select one or more privileged contacts from the list of contacts provided by the subscription service through the service client  116  and location sharing client  117 . For example, a share location graphical user interface is presented on a display of the UE  101  as described below with reference to  FIG. 6B . The contacts can be indicated in any manner. In the illustrated embodiment, the contacts are indicated by their service identifiers, as stored in subscriber profiles  112 . In some embodiments that use the same value for both service ID and key ID, the generation of the key ID is trivial and no prompt is presented on UE  101  to the subscriber. 
     In one or more update messages  313 , the subscriber is registered with the location key service  152  and associated with an access key for deciphering enciphered locations. In some embodiments, the location key service  152  generates the key. In some embodiments, the location privacy manager module  150  generates the key. In some embodiments, the key is generated based, at least in part, on a seed value provided by the user of UE  101 , e.g., in response to a prompt presented in a graphical user interface as described below with reference to  FIG. 6B . The list of privileged contacts is also provided in the one or more update messages  313 . The location key service  152  stores the key and list of privileged contacts in association with the subscriber&#39;s key ID, e.g., in subscriber entry field  221  of the location access keys data structure  220 . During registration, in some embodiments, the subscriber is also prompted to present credentials (such as a password) to be used to authenticate the subscriber in subsequent messages to the location key service  152 . In some embodiments the access key is generated by the location key service  152  and returned to the location privacy manager module  150  in one or more messages, not shown. 
     In step  321 , one or more location share invitation messages  260  are sent to the location privacy manager modules on the UE  101  of the privileged contacts, either directly, or indirectly through the LSS  118  or subscription service  110   a . In some embodiments in which the service ID and the key ID are identical and the location key service network address is known by all subscribers, step  321  is omitted. 
     In one or more messages  331 , the location sharing client  117  sends a location to share, e.g., based on the current location of the UE  101  as determined from a global positioning system (GPS) or based on user input indicating a location to be associated with the subscriber. In prior approaches, messages  331  would be directed to the LSS  118  in the subscriptions service  110   a . However, according to the illustrated embodiment, the message goes to the location privacy manager module  150  to encipher the location in step  333 . In one or more messages  335 , the cipher with the subscriber&#39;s service ID is sent to the LSS  118  of the subscription service  110   a  to share with other contacts. 
     In step  341 , one or more location share invitation messages  260  are received from the location privacy manager modules on the UE  101  of one or more contacts of the subscriber, either directly, or indirectly through the LSS  118  or subscription service  110   a . Each message indicates the subscriber is privileged to decipher the locations of the sending contact. In some embodiments in which the service ID and the key ID are identical and the location key service network address is known by all subscribers, step  341  is omitted. 
     In one or more messages  343 , the LSS  118  of the subscription service  110   a  sends a cipher of a location to share, e.g., based on the current location of the UE of a contact as determined from a global positioning system (GPS) or based on user input indicating a location to be associated with the contact. The contact is identified by the contact&#39;s service ID. In prior approaches, messages  343  would be directed to the location sharing client  117  in the service client  116 . However, according to the illustrated embodiment, the message goes to the location privacy manager module  150  to decipher the location. 
     If the access key for the contact is already cached in data structure  157 , the cipher for the location is deciphered using the cached key to provide the actual location. If the key is not cached, or if the deciphered location is faulty, then the location privacy manager module  150  sends a request message  345  to the location key service for the access key for the contact. The ID for the contact at the location key service (e.g., the key ID) and the service ID of the requesting subscriber are used in the request message  345 . In some embodiments, the service credentials of the requestor are also included in the one or more request messages  345 . 
     The location key service determines whether the subscriber is included in the list of privileged contacts associated with the contact. In some embodiments, the location key service  152  also authenticates the requesting subscriber based on the credentials. If the subscriber is authenticated and privileged to share the contact&#39;s location, then one or more messages  347  are sent with the access key for the contact. In some embodiments, the request messages  345  and response messages  347  are encapsulated using a network security protocol such as HTTP secure (HTTPS). The contact&#39;s key ID and access key are cached in cached access keys data structure  157  on the local UE  101  by the location privacy manager module  150 . 
     In step  349 , the location privacy manager module  150  deciphers the cipher for the location and provides the actual location to be shared. In one or more messages  351 , the deciphered location is sent to the location sharing client  117  of the service client  116  to share with the subscriber, e.g., by plotting contact locations on a graphic depicting a map. 
     At some later time, in one or more messages  361 , the access key of the subscriber and the list of privileged contacts is updated. During the update in some embodiments, a new contact can be granted the privilege, which does not require a change of the access key. In some of these embodiments, an invitation message  260  is sent to each of the added contacts. During updates in some embodiments, a former privileged client is removed which should involve a change of the access key. No new invitation messages  260  are sent when a contact is removed. When the remaining privileged contacts attempt to decipher an enciphered location of the subscriber, any cached access key should fail and a request message  345  should be sent by the location privacy manager module  150  on the contact&#39;s UE (e.g., Bob&#39;s UE  101   b ) to the location key service  152  to obtain the new access key. By updating the location key service  152  instead of all the subscriber&#39;s contacts, the system  100  scales well for subscribers with many contacts. The location key service  152  just send the new access key to the contacts who send a request, thus saving computational resources and bandwidth updating contacts who are not attempting to share the subscriber&#39;s location. The separate location key service  152  is an example means to achieve the advantage of these reductions in the consumption of computational resources and bandwidth. 
     The system  100  ensures that a mobile user&#39;s location privacy is protected while taking part in location-sharing services. The system  100  makes no assumption of trust. A goal of the system  100  is to ensure that no external party is allowed to “view” the user&#39;s locations. Only those that have been authorized by a user can “view” the user&#39;s location. So while a location sharing service may serve as the location data management system, where users constantly “upload” their current location information such as GPS information and where users retrieve location information of their “friends”, the system  100  prevents the location data management system (e.g., LSS  118  and subscription service  110   a ) from gaining any knowledge of the subscribers&#39; actual locations. 
     In some embodiments, the subscriber may allow the LSS provider to decipher the subscriber&#39;s location. For example, providers can use subscribers&#39; locations to supply other services such as location-based advertising that involve knowledge of the subscribers&#39; locations. A subscriber may designate a LSS provider as a “contact” and include the provider in the list of privileged contacts in field  227  on the location key service  152 . The privilege can be revoked at any time using the same procedure described above for revoking the privilege of any other contact, e.g., by removing the contact from field  227  and changing the access key in field  225 . 
       FIG. 4  is a flowchart of a process  400  for location key service, according to one embodiment. In one embodiment, the location key service  152  performs the process  400  and is implemented in, for instance, a chip set including a processor and a memory as shown in  FIG. 8  or general purpose computer  700  as depicted in  FIG. 7 . Although steps are depicted in  FIG. 4  and  FIG. 5  as integral blocks in a particular order for purposes of illustration, in other embodiments one or more steps or portions thereof are performed in a different order, or overlapping in time, in series or in parallel, or are omitted or one or more steps are added, or the process is changed in some combination of ways. 
     In step  401 , it is determined whether an access key update message is received. For example, one or more messages are received at the location key service with one or more fields to be stored in a subscriber entry field  221  of the location access keys data structure  220 . For example, one or more messages are received from Alice&#39;s UE  101   a  that indicate a subscriber “LookingGlassXYZ”, and a list of one or more privileged subscribers including “Bob 456 .” If not, control passes to step  421  described below. 
     If it is determined, in step  401  that an access key update message is received, then in step  403  it is determined whether the update message indicates a new subscriber. For example, it is determined whether the subscriber ID in the update message (e.g., “LookingGlassXYZ”) is different from any subscriber ID in field  223  of any entry field  221  in the data structure  220 . If so, then the update message is treated as a registration message  313 ; and in step  405  the new subscriber is registered. In some embodiments the access key update message is also enciphered, e.g., using the HTTPS protocol. 
     Step  405  to register a new subscriber includes adding a new subscriber entry field  221  to the location access keys data structure  220  based on the update message. Data indicating the subscriber ID is stored in field  223 . The subscriber ID is the key ID for the subscriber, which is used as the subscriber ID at the location key service  152 . In some embodiments, the key ID for the subscriber is the same as the service ID for the subscriber at the LSS  118  or subscription service  110   a . For example, in some embodiments, the subscriber key ID in the update message is the same as the service ID “Alice 123 ” instead of the different key ID “LookingGlassXYZ.” 
     An access key is also determined during step  405 , either based on a value sent in the update message or by the location key service  152 . Any method to generate a secret key may be used to determine the access key, such as using a key exchange protocol, hashing an arbitrary seed string provided by the subscriber, or using a random number generator or selecting the next value in a sequence of random numbers stored in a data structure (not shown) at the location key service, among others, or some combination. 
     An initial list of privileged subscribers is also determined during step  405  and data indicating the list is stored in field  227 . Any method may be used to determine the initial list. For example, in some embodiments, the list is included in the one or more update messages sent by the new subscriber. In embodiments that use different subscriber IDs for the subscriber key ID at the location key service  152 , the privileged subscribers IDs in field  227  indicate the contacts&#39; service IDs, because the request for location access keys will be associated with the requestor&#39;s service ID. For example the update message from Alice&#39;s UE  101   a  that indicates a subscriber key ID of “LookingGlassXYZ” specifically lists “Bob 456 ”, which is Bob&#39;s service ID. 
     In some embodiments that use the same value for the subscriber key ID as in the subscriber service ID, the initial list is requested from subscription service  110   a  based on the contents of the subscriber contacts field  207  in the subscriber entry field  201  for the subscriber service ID field  203  that matches the subscriber key ID field  223 . For example, in embodiments that use the same ID, the update message from Alice&#39;s UE  101   a  indicates the subscriber is “Alice 123 .” The location key service  152  then requests from the subscriptions service  110   a , e.g., using API  114   a , the contact list in field  207  of the subscriber entry field  201  that indicates “Alice 123 ” in field  203 . 
     In some embodiments, step  405  includes determining one or more credentials to authenticate the new subscriber in future messages, such as a password or answer to a security question with or without a text recognition test to rule out machine attempts, or some combination. Control then passes to step  407 , described below to update the location access keys data structure, e.g., data structure  220 . 
     If it is determined, in step  403  that the update message does not indicate a new subscriber, then in step  409  the subscriber is authenticated to indicate that the update message is from the same person who registered the subscriber ID. For example, a password is demanded and checked against the credentials obtained during step  405 . In step  411 , it is determined whether the authentication is successful. If so, then in step  407  the location access keys data structure  154  is updated, as described next. If not, control passes to step  421 . 
     In step  407 , the location access keys data structure  154 , e.g., data structure  220 , is updated based on the one or more update messages. For example, a new subscriber entry field  221  is added based on a registration update message  313 , and an existing subscriber entry field  221  is modified based on other update messages, e.g.,  361 . During the update, the access key may be changed or one or more privileged subscribers may be added to or deleted from the privileged subscribers field  227 , or some combination, based on the update message. Thus, step  407  includes determining to associate a first (key) identifier for a subscriber with an access key and at least one second (service) identifier at a location sharing network service for a contact of the subscriber. 
     In step  421 , it is determined whether a request message is received for the access key of a subscriber. A request message, e.g., request message  345 , includes data that indicates the requestor using the requestor&#39;s service ID. The request message also indicates a subscriber&#39;s key ID. Thus, step  421  includes receiving a request message for the access key, wherein the request message indicates the first identifier at the location key service, i.e., the key ID. For example, a request message  345  is received from the location privacy manager module  150  on Bob&#39;s UE  101   b . The request message indicates the requestor is “Bob 456 ” for the access code of “LookingGlassXYZ.” In some embodiments, the request message also includes a code that indicates the message is a request message. Any protocol may be used to send the request message. In some embodiments, a request message includes one or more credentials for authenticating the requestor. If a request message is not received, then control passes to step  431 . In step  431 , it is determined whether end conditions are satisfied, e.g., to shut down or replace the location key service  152 . If so, the process ends. Otherwise, the process continues with step  401  described above. 
     If it is determined, in step  421 , that a request message is received for the access key of a subscriber, then in step  423 , the requestor is authenticated. Any method may be used to authenticate the requestor. For example, in some embodiments, the request message includes one or more credentials for the requestor as used at the LSS  118  or subscription service  110   a . In some of these embodiments, during step  423 , the requestor ID and one or more credentials are sent to the subscription service  110   a , e.g., using API  114   a . For example, the requestor ID “Bob 456 ” and credentials are sent to the subscription service  110   a  to authenticate Bob. A response message is received from the subscription service  110   a . The response message indicates success or failure of the authentication. 
     In step  425 , it is determined whether the requestor was successfully authenticated. If not, control passes to step  431  to determine if end conditions are satisfied, as described above. 
     If it is determined, in step  425 , that the requestor was successfully authenticated, then in step  427  it is determined whether the requestor is a privileged subscriber for the access key of the other subscriber based on the service IDs in field  227 . Thus, step  427  includes determining whether a service identifier for a sender of the request message is included in the at least one second service identifier associated with the first key identifier. For example, it is determined whether “Bob 456 ” is included in field  227  for “LookingGlassXYZ.” If not, control passes to step  431 , described above. 
     If it is determined, in step  427 , that the requestor is a privileged subscriber, then in step  429  the access key of the subscriber is sent to the requestor. Thus, step  429  includes determining to send the access key associated with the first key identifier in response to the request message, if the service identifier for the sender is included in the at least one second service identifier. For example, message  347  with Alice&#39;s access key from field  225  (of the subscriber entry field  221  with “LookingGlassXYZ” in subscriber key ID field  223 ) is sent to the location privacy manager module  150  on Bob&#39;s UE  101   b . Control passes to step  431 , described above. 
       FIG. 5  is a flowchart of a process  500  for location privacy management, according to one embodiment. In one embodiment, the location privacy manager module  150  performs the process  500  and is implemented in, for instance, a chip set including a processor and a memory as shown in  FIG. 8  or a mobile terminal  900  as depicted in  FIG. 9 . 
     In step  501 , the subscriber service ID and contacts are determined. Any method may be used to determine these values. In various embodiments, the service ID and contacts are received from the subscription service  110   a  or LSS  118 , either directly or indirectly through the service client  116  or location sharing client  117 , e.g., in one or more messages  303 . Thus method  500  includes determining a first identifier for a subscriber at a location sharing network service. 
     In step  503 , a key ID is determined along with a list of privileged subscribers allowed to share the subscriber&#39;s location. Any method may be used to determine the key ID. In some embodiments, the key ID is the same as the service ID. In such embodiments, a second identifier for the subscriber is identical to the first identifier for the subscriber. In some embodiments, a different key ID is generated by the location privacy manager module  150  automatically. In some embodiments, the location privacy manager module  150  prompts the user of UE  101  to enter a different key ID. In both such embodiments, the second identifier for the subscriber is different from the first identifier for the subscriber. 
     Any method may be used to determine the list of privileged subscribers. For example, in some embodiments, the list is entered directly by the subscriber. In some embodiments, one or more privileged subscribers are selected from the list of contacts of the subscriber in the subscriber&#39;s profile as obtained from the subscription service  110   a . In some embodiments, all the subscriber&#39;s contacts are automatically included in the list of privileged subscribers. In embodiments that use different service IDs and key IDs, the privileged subscribers IDs in field  227  indicate the service IDs. In some embodiments that use the same ID for the service ID and the key ID, an initial list is determined automatically by the location key service as described above. In these embodiments, during step  503 , it is determined to utilize the automatic initial list from the location key service  152 . 
       FIGS. 6A-6B  are diagrams of user interfaces utilized in the processes of  FIG. 5 , according to various embodiments.  FIG. 6A  is a diagram that illustrates a client graphical user interface (GUI)  601  for a location sharing application, e.g., location sharing client  117  of service client  116  on UE  101  or browser  107  interacting with subscription  110   a  or map service  120 , according to an embodiment. The GUI  601  includes one or more active areas in which a user selection is detected to determine user input. For example, user input is determined based on positioning a pointing device, such as a controller for a cursor and a key to indicate a selection, or a touch screen. The GUI  601  includes a map portion area  620  that presents a portion of a map, e.g., a map portion obtained from map service  120 . The map portion  620  includes roads  622 , points of interest (POI)  624   a ,  624   b ,  624   c , among others, collectively referenced hereinafter as POI  624 . A pointer  611  indicates a selected position in the map portion area  620 , such as the subscriber&#39;s current position or the position of the subscriber&#39;s home, school, work or place of worship. The GUI  601  also includes buttons  613   a  and  613   b  (collectively referenced hereinafter as buttons  613 ) that are active areas that perform a particular function indicated by a button label upon selection by a user. For example, in response to detecting a touch on button  613   a , the map portion in the map area is zoomed in to expand distances. Similarly, in response to detecting a touch on button  613   b , the map portion in the map area is zoomed out to shrink distances. In the illustrated embodiment, in response to detecting a touch on button  613   c , the share settings are determined. 
       FIG. 6B  is a diagram that illustrates a client graphical user interface (GUI)  602  for inputting location sharing settings, according to an embodiment. The GUI  602  includes the map portion area  620  and buttons  613  as described above. The selected location is indicated in map portion area  620  by pointer  611 . The user is prompted to input setting for sharing selected location by presenting the window  630  that includes text prompting the user to share location information. For example, in the illustrated embodiment, the text in window  630  recites the words “share your locations.” The window  630  is presented in any manner. For example, window  630  is presented by a user interface module of the location sharing client  117  or service client  116 , the browser  107  or directly using the UE operating system, or some combination. 
     The window  630  includes a key ID and password text box  631 , an access key seed text box  633  and a change contact pull down menu  635 . The user of the UE  101  is prompted to add a key ID in the text box  631 . In some embodiments, the text box automatically includes the service ID or an automatically generated random key ID which the subscriber can accept or over-write. For example, the text box  631  on UE  101   a  is presented pre-filled with “Alice 123 ,” the service ID of the subscriber, Alice, who uses UE  101   a . Alice is then able to type in a different key ID if desired; e.g., Alice types in “LookingGlassXYZ.” In some embodiments, the text box  631  includes a prompt for the user of UE  101  to enter one or more security credentials, such as a password, to be used to authenticate future messages from the subscriber. The text box  631  is an example means to achieve the advantage of indicating a key ID and password with reduced consumption of computational resources and idle time on the UE  101 . 
     The user of the UE  101  is prompted to add a seed for the access key in the text box  633 . In some embodiments, the text box automatically includes an automatically generated random access key or seed which the subscriber can accept or over-write. For example, the text box  633  on UE  101   a  is presented pre-filled with the date and time as a seed, e.g., “20100203141312,” Alice is then able to type in a different seed if desired. In some embodiments, the text box  633  prompts for an access key directly, instead of a seed used to generate the access key. In some embodiments, the access key is determined automatically, without input from the subscriber; and text box  633  is omitted. For example, in some embodiments, the key is obtained from a service or device, such as an electronic wallet, a radio frequency identifier (RFID) tag, secure storage, or a SIM card, among others, alone or in some combination. The text box  633  is an example means to achieve the advantage of indicating an access key with reduced consumption of computational resources and idle time on the UE  101 . 
     The user of the UE  101  is prompted to indicate the contacts to include among the privileged subscribers for sharing the user&#39;s location by means of the change contact pull down menu  635 . By selecting the pull down menu  635 , the service IDs of all the subscriber&#39;s contacts from the subscriber profiles data structure  112  are listed. The user selects each one to add. In some embodiments, an option in the pull down menu is “ALL CONTACTS” to reduce time and effort in selecting all contacts. In some embodiments, an option in the pull down menu is “NO CONTACTS” to reduce time and effort to unselect all contacts. In some embodiments, an option in the pull down menu is “DELETE CONTACTS” to reduce time and effort to unselect one or more contacts already or previously added to the list of privileged subscribers. In some embodiments, the subscriber&#39;s contacts are grouped by an application, such as the social network service, (e.g., into family, work, friends, etc.) and one or more groups are included in the pull down menu. In some embodiments the contacts include contacts from the local telephone directory on the UE  101 . For example, the pull down menu, when selected, lists: ALL CONTACTS; NO CONTACTS, DELETE CONTACTS; BOB 456 ; . . . where the ellipsis indicates other contacts in field  207  from Alice&#39;s entry field  201  in the profiles data structure  200 . The pull down menu  635  is an example means to achieve the advantage of indicating privileged subscribers with reduced consumption of computational resources and idle time on the UE  101 . 
     When finished, the user of UE  101  activates the OK button  637  or the cancel button  639  to accept or reject the changes, respectively. The user choices are stored locally in the cached access keys data structure  157 , e.g., in fields  243 ,  245  and  247  of data structure  240 . 
     In step  505 , the subscriber is registered with the location key service  152 . For example, one or more update messages  313  are prepared to send to the location key service  152  with the key ID and list of privileged subscribers. In some embodiment in which the location privacy manager module  150  determines the access key, the messages  313  include the access key so determined. In some embodiment in which the location key service determines the access key, the access key is omitted from message  313  but included in a message (not shown) returned from the location key service  152  to the location privacy manager module  150 . In some embodiment in which the location key service determines the access key based on a user provided seed value, the access key seed value is included in the message  313 ; and the access key is included in a message (not shown) returned from the location key service  152  to the location privacy manager module  150 . In some embodiments, step  505  includes generating or prompting the user of UE  101  for one or more credentials, such as a password, to authenticate future messages from the subscriber. The credentials are included in the update messages prepared. 
     In step  507  the one or more location key access update messages, e.g., register update messages  313  or follow on update message  361 , are sent from the location privacy manager module  150  to the location key service  152 . In some embodiments, the update messages  313  or  361  include the subscriber&#39;s credentials. In some embodiments, a return message with the access key is returned during step  507  and stored in the access key field  245  in the cached access keys data structure  240 . Thus, method  500  includes determining a location access key stored at a location key service in association with a second (key) identifier for the subscriber. Step  509  includes determining to send to the location key service a third identifier (contact service ID) indicating at least one contact of the subscriber. 
     In step  509 , one or more location share invitation messages  260  are sent to the UE  101  of new privileged subscribers, e.g., privileged subscribers who have not yet received an invitation message. The message  260  informs the recipient of the subscriber key ID associated with the service ID, if different, and location key service address on the communications network. In some embodiments, the message  260  is sent directly to the UE  101  of the privileged subscribers, e.g., using a network address for the UE  101  of the privileged subscriber obtained from the privileged subscriber or from the subscription service  110   a  using API  114   a . For example a location share invitation message  260  that indicates service ID “Alice 123 ” and key ID “LookingGlassXYZ” is sent from the location privacy manager module  150  on Alice&#39;s UE  101   a  to the location privacy manager module  150  on Bob&#39;s UE  101   b . In some embodiments, the message  260  is sent indirectly through the location sharing client  117  or service client  116 . Thus, step  509  includes determining to send a location sharing invitation message to at least one contact of the subscriber, wherein the location sharing invitation message comprises data that indicates the first (service) identifier for the subscriber and the second (key) identifier for the subscriber. In some embodiments that use the same value for both the service ID and key ID only on field that indicates both is included in the invitation message. In some embodiments that use the same value for both the service ID and key ID and that use a common known location key service  152 , step  509  is omitted. 
     In step  511 , it is determined whether a location share invitation message  260  is received. For example, a location share invitation message  260  that indicates service ID “Bob 456 ” and key ID “AndWeaveABC” is received on the location privacy manager module  150  on Alice&#39;s UE  101   a , directly or indirectly, from the location privacy manager module  150  on Bob&#39;s UE  101   b . If so, then in step  513  the information is cached in the local cached access keys data structure  157 . For example, “Bob 456 ” is stored in contact service ID field  251 , “AndWeaveABC” is stored in contact key ID field  253  in data structure  240 . The access key is not included in the invitation message and is not available for storage in the access key field  255  during step  513 . Thus, step  513  includes receiving at least one location sharing invitation message indicating a corresponding contact of the subscriber, wherein the at least one location sharing invitation message comprises data that indicates a third identifier (contact service ID) for the contact at the location sharing network service and a fourth identifier (contact key ID) for the contact at the location key service. 
     In step  515 , it is determined whether a location of the subscriber is received from the local location sharing client  117 . For example, a message  331  from the location sharing client  117  is intercepted by the location privacy manager. Thus, step  515  includes receiving the at least one location associated with the subscriber from a location sharing client process different from the location sharing network service. If so, then in step  517  the location is enciphered (turned into a cipher) based on the subscriber&#39;s location access key. If the enciphering and deciphering procedures are symmetric, then the enciphering key is the same as the location access key. If not, then the enciphering key is a different value associated with the location access key, and therefore based on the chosen location access key. Thus, method  500  includes determining at least one ciphered location based on the location access key and at least one location associated with the subscriber. For example, on Alice&#39;s UE  101   a , Alice&#39;s current location, received from the local location sharing client  117 , is turned into a cipher using the DES algorithm and Alice&#39;s access key stored in the local cached access keys data structure  157 , e.g., stored in access key field  245  of data structure  240  on UE  101   a . The cipher is sent as the location to the LSS  118  in association with the subscriber&#39;s service ID, e.g., in association with Alice&#39;s service ID, “Alice 123 .” Thus, method  500  includes determining to send the at least one ciphered location to the location sharing network service in association with the first identifier. 
     Alice&#39;s contacts listed in field  207  of her entry field  201  in the subscriber profiles data structure  200  are then allowed to receive the cipher of her location, as is typical for existing location sharing services. Unlike typical sharing services, however, only her privileged subscribers can decipher her location. Similarly, Alice can only decipher locations of subscribers who have listed her as a privileged subscriber. 
     In step  521 , it is determined whether a ciphered location of another subscriber is received from the remote location sharing service  118 . For example, a message  343  from the LSS  118  of service  110   a  directed to the local location sharing client  117  is intercepted by the location privacy manager module  150 . Thus, step  521  includes receiving, from the location sharing network service, at least one ciphered contact location associated with the third identifier. If so, then in step  523  it is determined whether the location is deciphered based on the other subscriber&#39;s location access key. The other subscriber&#39;s key ID is stored in field  253 , if different from the service ID. Thus, in some embodiments, the fourth identifier for the contact is different from the third identifier for the contact. Otherwise the other subscriber&#39;s key ID is the same as the service ID associated with the cipher of the location. Thus in some embodiments, the fourth identifier for the contact is identical to the third identifier for the contact. 
     If the access key field  255  is empty, or the deciphered location is not in a valid range, then the location is not deciphered, and control passes to step  525  to request the access key of the other subscriber from the location key service  152 , using the other subscriber&#39;s key ID. 
     For example, on Alice&#39;s UE  101   a , a cipher associated with subscriber service ID “Bob 123 ” is received from the remote LSS  118 . It is assumed for purposes of illustration that different values are used for the service ID and the key ID. The value “Bob 123 ” matches the value already stored in contact service ID  251 ; and is associated with contact key ID “AndWeaveABC.” Bob&#39;s access key is not yet stored in the associated access key field  255  of data structure  240  on UE  101   a . Thus, in step  525 , a request message  345  that indicates the key ID “AndWeaveABC” is sent to the location key service  152  from Alice&#39;s UE  101   a . Alice indicates that she is the requestor using her service ID “Alice 123 ” in the request message. For purposes of illustration, it is assumed that Alice&#39;s request is authenticated, e.g., by obtaining her password for the subscription service  110   a  in one or more prompts in a graphical user interface (not shown). The password is included in the request message. If the location key server authenticates Alice based on her password and if Alice is listed among the privileged subscribers associated with the key ID value “AndWeaveABC” in the location access keys data structure  220 , then a return message  347  indicates a success and includes the access key for Bob&#39;s locations. Step  525  includes storing the access key in the cached access keys data structure, e.g., in access key field  255  associated with Bob&#39;s entry field  250 . Otherwise, the return message indicates a failure. Thus step  525  includes determining to send to the location key service a request for an access key associated with the fourth identifier; and receiving a contact access key in response to sending the request. 
     In step  527 , it is determined if the result of the request is a success. If so, then control passes back to step  523  to determine if the location is deciphered using the access key, as described above. If the location is deciphered in step  523 , then in step  529  the deciphered location is sent to the local location sharing client  117  of the service client  116 , e.g., to plot Bob&#39;s location on the map portion  620  of the GUI  601 . Thus, step  523  includes determining at least one deciphered contact location based on the at least one ciphered contact location and the contact access key. Step  529  includes determining to send the at least one deciphered contact location associated with the contact to a location sharing client process different from the location sharing network service. 
     After sending the deciphered location in step  529 , or if it is determined in step  527  that the request for the access key was not successful, control passes to step  531 . In step  531 , it is determined whether the subscriber wants to update the access key or list of privileged subscribers. For example, it is determined if the user of UE  101  has activated button  613   c  and accepted new entries into window  630 . As another example, a user Edgar (service ID “Ed 789 ”) wishes to retrieve Alice&#39;s location access key and initiates a request for Alice&#39;s permission. This step will be triggered by an operation such as a “friend request” on a LSS  118  and client  117 . If Alice accepts Edgar&#39;s request, the location privacy manager module  150  issues a corresponding update message indicating “add user Ed 789  to privileged subscribers list for LookingGlassXYZ” to the location key service  152 . Alice&#39;s new privileged subscribers list will be “Bob 456 ” and “Ed 789 .” Edgar may then retrieve Alice&#39;s location access key from the location key service  152 . If an update is desired, then control passes back to step  507  to send an update message to the location key service  152 . If not, then control passes to step  533 . 
     In step  533 , it is determined whether end conditions are satisfied. For example it is determined if the UE  101  is turned off, or the location sharing client  117  or service client  116  are closed. If so, the process ends. Otherwise, control passes back to step  511  and following to determine whether an invitation message, or location or ciphered location is received, as described above. 
     The processes described herein for secure revocable location sharing may be advantageously implemented via software, hardware, firmware or a combination of software and/or firmware and/or hardware. For example, the processes described herein, may be advantageously implemented via processor(s), Digital Signal Processing (DSP) chip, an Application Specific Integrated Circuit (ASIC), Field Programmable Gate Arrays (FPGAs), etc. Such exemplary hardware for performing the described functions is detailed below. 
       FIG. 7  illustrates a computer system  700  upon which an embodiment of the invention may be implemented. Although computer system  700  is depicted with respect to a particular device or equipment, it is contemplated that other devices or equipment (e.g., network elements, servers, etc.) within  FIG. 7  can deploy the illustrated hardware and components of system  700 . Computer system  700  is programmed (e.g., via computer program code or instructions) to provide secure revocable location sharing as described herein and includes a communication mechanism such as a bus  710  for passing information between other internal and external components of the computer system  700 . Information (also called data) is represented as a physical expression of a measurable phenomenon, typically electric voltages, but including, in other embodiments, such phenomena as magnetic, electromagnetic, pressure, chemical, biological, molecular, atomic, sub-atomic and quantum interactions. For example, north and south magnetic fields, or a zero and non-zero electric voltage, represent two states (0, 1) of a binary digit (bit). Other phenomena can represent digits of a higher base. A superposition of multiple simultaneous quantum states before measurement represents a quantum bit (qubit). A sequence of one or more digits constitutes digital data that is used to represent a number or code for a character. In some embodiments, information called analog data is represented by a near continuum of measurable values within a particular range. Computer system  700 , or a portion thereof, constitutes a means for performing one or more steps of secure revocable location sharing. 
     A bus  710  includes one or more parallel conductors of information so that information is transferred quickly among devices coupled to the bus  710 . One or more processors  702  for processing information are coupled with the bus  710 . 
     A processor (or multiple processors)  702  performs a set of operations on information as specified by computer program code related to secure revocable location sharing. The computer program code is a set of instructions or statements providing instructions for the operation of the processor and/or the computer system to perform specified functions. The code, for example, may be written in a computer programming language that is compiled into a native instruction set of the processor. The code may also be written directly using the native instruction set (e.g., machine language). The set of operations include bringing information in from the bus  710  and placing information on the bus  710 . The set of operations also typically include comparing two or more units of information, shifting positions of units of information, and combining two or more units of information, such as by addition or multiplication or logical operations like OR, exclusive OR (XOR), and AND. Each operation of the set of operations that can be performed by the processor is represented to the processor by information called instructions, such as an operation code of one or more digits. A sequence of operations to be executed by the processor  702 , such as a sequence of operation codes, constitute processor instructions, also called computer system instructions or, simply, computer instructions. Processors may be implemented as mechanical, electrical, magnetic, optical, chemical or quantum components, among others, alone or in combination. 
     Computer system  700  also includes a memory  704  coupled to bus  710 . The memory  704 , such as a random access memory (RAM) or other dynamic storage device, stores information including processor instructions for secure revocable location sharing. Dynamic memory allows information stored therein to be changed by the computer system  700 . RAM allows a unit of information stored at a location called a memory address to be stored and retrieved independently of information at neighboring addresses. The memory  704  is also used by the processor  702  to store temporary values during execution of processor instructions. The computer system  700  also includes a read only memory (ROM)  706  or other static storage device coupled to the bus  710  for storing static information, including instructions, that is not changed by the computer system  700 . Some memory is composed of volatile storage that loses the information stored thereon when power is lost. Also coupled to bus  710  is a non-volatile (persistent) storage device  708 , such as a magnetic disk, optical disk or flash card, for storing information, including instructions, that persists even when the computer system  700  is turned off or otherwise loses power. 
     Information, including instructions for secure revocable location sharing, is provided to the bus  710  for use by the processor from an external input device  712 , such as a keyboard containing alphanumeric keys operated by a human user, or a sensor. A sensor detects conditions in its vicinity and transforms those detections into physical expression compatible with the measurable phenomenon used to represent information in computer system  700 . Other external devices coupled to bus  710 , used primarily for interacting with humans, include a display device  714 , such as a cathode ray tube (CRT) or a liquid crystal display (LCD), or plasma screen or printer for presenting text or images, and a pointing device  716 , such as a mouse or a trackball or cursor direction keys, or motion sensor, for controlling a position of a small cursor image presented on the display  714  and issuing commands associated with graphical elements presented on the display  714 . In some embodiments, for example, in embodiments in which the computer system  700  performs all functions automatically without human input, one or more of external input device  712 , display device  714  and pointing device  716  is omitted. 
     In the illustrated embodiment, special purpose hardware, such as an application specific integrated circuit (ASIC)  720 , is coupled to bus  710 . The special purpose hardware is configured to perform operations not performed by processor  702  quickly enough for special purposes. Examples of application specific ICs include graphics accelerator cards for generating images for display  714 , cipherographic boards for enciphering and deciphering messages sent over a network, speech recognition, and interfaces to special external devices, such as robotic arms and medical scanning equipment that repeatedly perform some complex sequence of operations that are more efficiently implemented in hardware. 
     Computer system  700  also includes one or more instances of a communications interface  770  coupled to bus  710 . Communication interface  770  provides a one-way or two-way communication coupling to a variety of external devices that operate with their own processors, such as printers, scanners and external disks. In general the coupling is with a network link  778  that is connected to a local network  780  to which a variety of external devices with their own processors are connected. For example, communication interface  770  may be a parallel port or a serial port or a universal serial bus (USB) port on a personal computer. In some embodiments, communications interface  770  is an integrated services digital network (ISDN) card or a digital subscriber line (DSL) card or a telephone modem that provides an information communication connection to a corresponding type of telephone line. In some embodiments, a communication interface  770  is a cable modem that converts signals on bus  710  into signals for a communication connection over a coaxial cable or into optical signals for a communication connection over a fiber optic cable. As another example, communications interface  770  may be a local area network (LAN) card to provide a data communication connection to a compatible LAN, such as Ethernet. Wireless links may also be implemented. For wireless links, the communications interface  770  sends or receives or both sends and receives electrical, acoustic or electromagnetic signals, including infrared and optical signals, that carry information streams, such as digital data. For example, in wireless handheld devices, such as mobile telephones like cell phones, the communications interface  770  includes a radio band electromagnetic transmitter and receiver called a radio transceiver. In certain embodiments, the communications interface  770  enables connection to the communication network  105  for secure revocable location sharing with the UE  101 . 
     The term “computer-readable medium” as used herein refers to any medium that participates in providing information to processor  702 , including instructions for execution. Such a medium may take many forms, including, but not limited to computer-readable storage medium (e.g., non-volatile media, volatile media), and transmission media. Non-transitory media, such as non-volatile media, include, for example, optical or magnetic disks, such as storage device  708 . Volatile media include, for example, dynamic memory  704 . Transmission media include, for example, coaxial cables, copper wire, fiber optic cables, and carrier waves that travel through space without wires or cables, such as acoustic waves and electromagnetic waves, including radio, optical and infrared waves. Signals include man-made transient variations in amplitude, frequency, phase, polarization or other physical properties transmitted through the transmission media. Common forms of computer-readable media include, for example, a floppy disk, a flexible disk, hard disk, magnetic tape, any other magnetic medium, a CD-ROM, CDRW, DVD, any other optical medium, punch cards, paper tape, optical mark sheets, any other physical medium with patterns of holes or other optically recognizable indicia, a RAM, a PROM, an EPROM, a FLASH-EPROM, any other memory chip or cartridge, a carrier wave, or any other medium from which a computer can read. The term computer-readable storage medium is used herein to refer to any computer-readable medium except transmission media. 
     Logic encoded in one or more tangible media includes one or both of processor instructions on a computer-readable storage media and special purpose hardware, such as ASIC  720 . 
     Network link  778  typically provides information communication using transmission media through one or more networks to other devices that use or process the information. For example, network link  778  may provide a connection through local network  780  to a host computer  782  or to equipment  784  operated by an Internet Service Provider (ISP). ISP equipment  784  in turn provides data communication services through the public, world-wide packet-switching communication network of networks now commonly referred to as the Internet  790 . 
     A computer called a server host  792  connected to the Internet hosts a process that provides a service in response to information received over the Internet. For example, server host  792  hosts a process that provides information representing video data for presentation at display  714 . It is contemplated that the components of system  700  can be deployed in various configurations within other computer systems, e.g., host  782  and server  792 . 
     At least some embodiments of the invention are related to the use of computer system  700  for implementing some or all of the techniques described herein. According to one embodiment of the invention, those techniques are performed by computer system  700  in response to processor  702  executing one or more sequences of one or more processor instructions contained in memory  704 . Such instructions, also called computer instructions, software and program code, may be read into memory  704  from another computer-readable medium such as storage device  708  or network link  778 . Execution of the sequences of instructions contained in memory  704  causes processor  702  to perform one or more of the method steps described herein. In alternative embodiments, hardware, such as ASIC  720 , may be used in place of or in combination with software to implement the invention. Thus, embodiments of the invention are not limited to any specific combination of hardware and software, unless otherwise explicitly stated herein. 
     The signals transmitted over network link  778  and other networks through communications interface  770 , carry information to and from computer system  700 . Computer system  700  can send and receive information, including program code, through the networks  780 ,  790  among others, through network link  778  and communications interface  770 . In an example using the Internet  790 , a server host  792  transmits program code for a particular application, requested by a message sent from computer  700 , through Internet  790 , ISP equipment  784 , local network  780  and communications interface  770 . The received code may be executed by processor  702  as it is received, or may be stored in memory  704  or in storage device  708  or other non-volatile storage for later execution, or both. In this manner, computer system  700  may obtain application program code in the form of signals on a carrier wave. 
     Various forms of computer readable media may be involved in carrying one or more sequence of instructions or data or both to processor  702  for execution. For example, instructions and data may initially be carried on a magnetic disk of a remote computer such as host  782 . The remote computer loads the instructions and data into its dynamic memory and sends the instructions and data over a telephone line using a modem. A modem local to the computer system  700  receives the instructions and data on a telephone line and uses an infra-red transmitter to convert the instructions and data to a signal on an infra-red carrier wave serving as the network link  778 . An infrared detector serving as communications interface  770  receives the instructions and data carried in the infrared signal and places information representing the instructions and data onto bus  710 . Bus  710  carries the information to memory  704  from which processor  702  retrieves and executes the instructions using some of the data sent with the instructions. The instructions and data received in memory  704  may optionally be stored on storage device  708 , either before or after execution by the processor  702 . 
       FIG. 8  illustrates a chip set or chip  800  upon which an embodiment of the invention may be implemented. Chip set  800  is programmed to provide secure revocable location sharing as described herein and includes, for instance, the processor and memory components described with respect to  FIG. 7  incorporated in one or more physical packages (e.g., chips). By way of example, a physical package includes an arrangement of one or more materials, components, and/or wires on a structural assembly (e.g., a baseboard) to provide one or more characteristics such as physical strength, conservation of size, and/or limitation of electrical interaction. It is contemplated that in certain embodiments the chip set  800  can be implemented in a single chip. It is further contemplated that in certain embodiments the chip set or chip  800  can be implemented as a single “system on a chip.” It is further contemplated that in certain embodiments a separate ASIC would not be used, for example, and that all relevant functions as disclosed herein would be performed by a processor or processors. Chip set or chip  800 , or a portion thereof, constitutes a means for performing one or more steps of providing user interface navigation information associated with the availability of functions. Chip set or chip  800 , or a portion thereof, constitutes a means for performing one or more steps of secure revocable location sharing. 
     In one embodiment, the chip set or chip  800  includes a communication mechanism such as a bus  801  for passing information among the components of the chip set  800 . A processor  803  has connectivity to the bus  801  to execute instructions and process information stored in, for example, a memory  805 . The processor  803  may include one or more processing cores with each core configured to perform independently. A multi-core processor enables multiprocessing within a single physical package. Examples of a multi-core processor include two, four, eight, or greater numbers of processing cores. Alternatively or in addition, the processor  803  may include one or more microprocessors configured in tandem via the bus  801  to enable independent execution of instructions, pipelining, and multithreading. The processor  803  may also be accompanied with one or more specialized components to perform certain processing functions and tasks such as one or more digital signal processors (DSP)  807 , or one or more application-specific integrated circuits (ASIC)  809 . A DSP  807  typically is configured to process real-world signals (e.g., sound) in real time independently of the processor  803 . Similarly, an ASIC  809  can be configured to performed specialized functions not easily performed by a more general purpose processor. Other specialized components to aid in performing the inventive functions described herein may include one or more field programmable gate arrays (FPGA) (not shown), one or more controllers (not shown), or one or more other special-purpose computer chips. 
     In one embodiment, the chip set or chip  800  includes merely one or more processors and some software and/or firmware supporting and/or relating to and/or for the one or more processors. 
     The processor  803  and accompanying components have connectivity to the memory  805  via the bus  801 . The memory  805  includes both dynamic memory (e.g., RAM, magnetic disk, writable optical disk, etc.) and static memory (e.g., ROM, CD-ROM, etc.) for storing executable instructions that when executed perform the inventive steps described herein to provide secure revocable location sharing. The memory  805  also stores the data associated with or generated by the execution of the inventive steps. 
       FIG. 9  is a diagram of exemplary components of a mobile terminal (e.g., handset) for communications, which is capable of operating in the system of  FIG. 1 , according to one embodiment. In some embodiments, mobile terminal  901 , or a portion thereof, constitutes a means for performing one or more steps of secure revocable location sharing. Generally, a radio receiver is often defined in terms of front-end and back-end characteristics. The front-end of the receiver encompasses all of the Radio Frequency (RF) circuitry whereas the back-end encompasses all of the base-band processing circuitry. As used in this application, the term “circuitry” refers to both: (1) hardware-only implementations (such as implementations in only analog and/or digital circuitry), and (2) to combinations of circuitry and software (and/or firmware) (such as, if applicable to the particular context, to a combination of processor(s), including digital signal processor(s), software, and memory(ies) that work together to cause an apparatus, such as a mobile phone or server, to perform various functions). This definition of “circuitry” applies to all uses of this term in this application, including in any claims. As a further example, as used in this application and if applicable to the particular context, the term “circuitry” would also cover an implementation of merely a processor (or multiple processors) and its (or their) accompanying software/or firmware. The term “circuitry” would also cover if applicable to the particular context, for example, a baseband integrated circuit or applications processor integrated circuit in a mobile phone or a similar integrated circuit in a cellular network device or other network devices. 
     Pertinent internal components of the telephone include a Main Control Unit (MCU)  903 , a Digital Signal Processor (DSP)  905 , and a receiver/transmitter unit including a microphone gain control unit and a speaker gain control unit. A main display unit  907  provides a display to the user in support of various applications and mobile terminal functions that perform or support the steps of secure revocable location sharing. The display  907  includes display circuitry configured to display at least a portion of a user interface of the mobile terminal (e.g., mobile telephone). Additionally, the display  907  and display circuitry are configured to facilitate user control of at least some functions of the mobile terminal. An audio function circuitry  909  includes a microphone  911  and microphone amplifier that amplifies the speech signal output from the microphone  911 . The amplified speech signal output from the microphone  911  is fed to a coder/decoder (CODEC)  913 . 
     A radio section  915  amplifies power and converts frequency in order to communicate with a base station, which is included in a mobile communication system, via antenna  917 . The power amplifier (PA)  919  and the transmitter/modulation circuitry are operationally responsive to the MCU  903 , with an output from the PA  919  coupled to the duplexer  921  or circulator or antenna switch. The PA  919  also couples to a battery interface and power control unit  920 . 
     In use, a user of mobile terminal  901  speaks into the microphone  911  and his or her voice along with any detected background noise is converted into an analog voltage. The analog voltage is then converted into a digital signal through the Analog to Digital Converter (ADC)  923 . The control unit  903  routes the digital signal into the DSP  905  for processing therein, such as speech encoding, channel encoding, enciphering, and interleaving. In one embodiment, the processed voice signals are encoded, by units not separately shown, using a cellular transmission protocol such as global evolution (EDGE), general packet radio service (GPRS), global system for mobile communications (GSM), Internet protocol multimedia subsystem (IMS), universal mobile telecommunications system (UMTS), etc., as well as any other suitable wireless medium, e.g., microwave access (WiMAX), Long Term Evolution (LTE) networks, code division multiple access (CDMA), wideband code division multiple access (WCDMA), wireless fidelity (WiFi), satellite, and the like. 
     The encoded signals are then routed to an equalizer  925  for compensation of any frequency-dependent impairments that occur during transmission though the air such as phase and amplitude distortion. After equalizing the bit stream, the modulator  927  combines the signal with a RF signal generated in the RF interface  929 . The modulator  927  generates a sine wave by way of frequency or phase modulation. In order to prepare the signal for transmission, an up-converter  931  combines the sine wave output from the modulator  927  with another sine wave generated by a synthesizer  933  to achieve the desired frequency of transmission. The signal is then sent through a PA  919  to increase the signal to an appropriate power level. In practical systems, the PA  919  acts as a variable gain amplifier whose gain is controlled by the DSP  905  from information received from a network base station. The signal is then filtered within the duplexer  921  and optionally sent to an antenna coupler  935  to match impedances to provide maximum power transfer. Finally, the signal is transmitted via antenna  917  to a local base station. An automatic gain control (AGC) can be supplied to control the gain of the final stages of the receiver. The signals may be forwarded from there to a remote telephone which may be another cellular telephone, other mobile phone or a land-line connected to a Public Switched Telephone Network (PSTN), or other telephony networks. 
     Voice signals transmitted to the mobile terminal  901  are received via antenna  917  and immediately amplified by a low noise amplifier (LNA)  937 . A down-converter  939  lowers the carrier frequency while the demodulator  941  strips away the RF leaving only a digital bit stream. The signal then goes through the equalizer  925  and is processed by the DSP  905 . A Digital to Analog Converter (DAC)  943  converts the signal and the resulting output is transmitted to the user through the speaker  945 , all under control of a Main Control Unit (MCU)  903 —which can be implemented as a Central Processing Unit (CPU) (not shown). 
     The MCU  903  receives various signals including input signals from the keyboard  947 . The keyboard  947  and/or the MCU  903  in combination with other user input components (e.g., the microphone  911 ) comprise a user interface circuitry for managing user input. The MCU  903  runs a user interface software to facilitate user control of at least some functions of the mobile terminal  901  to provide secure revocable location sharing. The MCU  903  also delivers a display command and a switch command to the display  907  and to the speech output switching controller, respectively. Further, the MCU  903  exchanges information with the DSP  905  and can access an optionally incorporated SIM card  949  and a memory  951 . In addition, the MCU  903  executes various control functions required of the terminal. The DSP  905  may, depending upon the implementation, perform any of a variety of conventional digital processing functions on the voice signals. Additionally, DSP  905  determines the background noise level of the local environment from the signals detected by microphone  911  and sets the gain of microphone  911  to a level selected to compensate for the natural tendency of the user of the mobile terminal  901 . 
     The CODEC  913  includes the ADC  923  and DAC  943 . The memory  951  stores various data including call incoming tone data and is capable of storing other data including music data received via, e.g., the global Internet. The software module could reside in RAM memory, flash memory, registers, or any other form of writable storage medium. The memory device  951  may be, but not limited to, a single memory, CD, DVD, ROM, RAM, EEPROM, optical storage, or any other non-volatile storage medium capable of storing digital data. 
     An optionally incorporated SIM card  949  carries, for instance, important information, such as the cellular phone number, the carrier supplying service, subscription details, and security information. The SIM card  949  serves primarily to identify the mobile terminal  901  on a radio network. The card  949  also contains a memory for storing a personal telephone number registry, text messages, and user specific mobile terminal settings. 
     While the invention has been described in connection with a number of embodiments and implementations, the invention is not so limited but covers various obvious modifications and equivalent arrangements, which fall within the purview of the appended claims. Although features of the invention are expressed in certain combinations among the claims, it is contemplated that these features can be arranged in any combination and order.