Patent Publication Number: US-10791196-B2

Title: Directory lookup for federated messaging with a user from a different secure communication network

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is related to co-pending applications U.S. Ser. No. 15/689,239, entitled “Federated Messaging,” U.S. Ser. No. 15/689,250, entitled “Transmitting an Encrypted Communication to a User in a Second Secure Communication Network,” and U.S. Ser. No. 15/689,253, entitled “Receiving an Encrypted Communication from a User in a Second Secure Communication Network,” all filed concurrently herewith, the entireties of which are incorporated by reference herein. 
     BACKGROUND OF THE INVENTION 
     Most corporations today provide a communication platform to their employees to send and receive instant messages, share files, and video conference. However, these communication platforms are often limited in that users are only allowed to communicate with users within their own corporation network. That is, a first user, on a first corporate network, is unable to send a communication to a second user on a second corporate network, and vice versa. Even if a communication platform allows for cross-network communication exchanges, most corporate networks block communications from outside networks because communications from external networks could introduce malware, such as viruses, spyware, adware, phishing attempts, Trojan horses, etc., into the network since the sender cannot be authenticated. Those communication platforms that do allow users to communicate with people from different networks, often do so at the expense of security. Thus, there is need to provide a communication platform that allows users from different networks to communicate securely. 
     BACKGROUND OF THE INVENTION 
     The present disclosure describes a federated messaging system that allows a first user belonging to a first secure communication network to communicate with a second user belonging to a second secure communication network. 
     According to one aspect of the disclosure a method for determining whether the first device and the second device are permitted to communicate is disclosed. The method includes receiving a first communication for a second device on a second secure communication network at a server. The first communication includes a first security group identifier associated with a first device and a second security group identifier associated with the second device. Next, the server uses a first set of permissions associated with the first security group identifier to determine if the first device is permitted to communicate with the second secure communication network. When the first device is permitted to communicate with the second secure communication network, the server then determines whether the second device is allowed to communicate with the first secure communication network according to a second set of permissions associated with the second security group identifier. When the first device and the second device are permitted to communicate, the server provides the first communication to the second device on the second secure communication network. However, when either the first set of permissions or the second set of permissions do not permit communications between the networks of the first device and second devices, the server discards the first communication. 
     In some examples, the first communication includes encrypted routing data and an encrypted payload and the server decrypts the encrypted routing data, using a private key, to obtain the first security group identifier and the second security group identifier. In further examples, the server determines whether the first device and the second device are on the same secure communication network and provides the first communication to the second device when they are. 
     Another aspect of the disclosure describes a system method for determining whether the first device and the second device are permitted to communicate that includes an interface, a processor, and a memory. The interface is configured to receive a first communication from a first device, on a first network, for a second device, on a second network. The first communication includes a first security group identifier associated with the first device and a second security group identifier associated with the second device. The processor is configured to determine whether a first set of permissions associated with the first security group identifier permit the first device to communicate with the second secure communication network, determine whether a second set of permissions associated with the second security group identifier permit the second device to communication with the first secure communication network, and provide the first communication to the second device on the second secure communication network when the first device and the second device are permitted to communicate with each other. The processor is also configured to discard the first communication when either the first set of permissions or the second set of permissions do not permit communications between the networks of the first device and second devices. The memory is coupled to the processor and configured to store the first set of permissions and second set of permissions and to provide the processor with instructions for determining whether the first device and the second device are permitted to communicate. 
     In some aspects of the disclosure, the first communication includes encrypted routing data and an encrypted payload and the processor is configured to decrypt the encrypted routing data using a first key, such as a private key, to obtain the first security group identifier and the second security group identifier. Another example describes that the processor is configured to determine whether the first network and the second network are the same network and provide the first communication to the second device when they are. 
     According to another aspect of the disclosure, a non-transitory computer-readable medium that includes instructions for determining whether the first device and the second device are permitted to communicate is disclosed. The instructions include receiving a first communication for a second device on a second secure communication network at a server. The first communication includes a first security group identifier associated with a first device and a second security group identifier associated with the second device. Next, the instructions determine whether the first device is permitted to communicate with the second secure communication network using a first set of permissions associated with the first security group identifier. When the first device is permitted to communicate with the second secure communication network, the instructions then determine whether the second device is allowed to communicate with the first secure communication network according to a second set of permissions associated with the second security group identifier. When the first device and the second device are permitted to communicate, the instructions provide the first communication to the second device on the second secure communication network. However, when either the first set of permissions or the second set of permissions do not permit communications between the networks of the first device and second devices, the instructions discards the first communication. 
     In some examples, the first communication includes encrypted routing data and an encrypted payload and the instructions include decrypting the encrypted routing data, using a private key, to obtain the first security group identifier and the second security group identifier. In further examples, the instructions determine whether the first device and the second device are on the same secure communication network and provide the first communication to the second device when they are. 
     Another example of the disclosure describes a method for performing a directory lookup to determine if a first user in a first secure communication network can communication with a second user in a second secure communication network. The method includes receiving, at a server, a first identifier, such as a phone number, an email address, and a native identifier, for a second user belonging to a second network from a first device belonging to a first network. Next, the server determines whether the first device is permitted to communicate with the second network. When the first device is permitted to communicate with the second network, the server determines whether the second user is permitted communicate with the first secure communication network. The first server provides profile information of the second user to the first user device when the second user is permitted to communicate with the first network. 
     In some examples, the first device is associated with a first security group identifier which is used to determine whether the first device is permitted to communicate with the second network. This determination includes determining whether a first set of permissions associated with the first security group identifier allows the first device to communicate with the second secure communication network. Similarly, the second user is associated with a second security group identifier that is used to determine whether the second user is permitted to communicate with the first secure communication network. This determination includes determining whether a second set of permissions associated with the second security group identifier allows the second user to communicate with the first secure communication network. If these determinations fail and the first device is not permitted to communicate with the second network, the server provides an indication to the first device that the second user is unavailable. A similar indication may be provided when the first device is not permitted to communicate with the second communication network. 
     An additional example of the disclosure describes a system that includes an interface, a processor and a memory. The interface is configured to receive a first identifier for a second user belonging to a second secure communication network from a first device belonging to a first secure communication network. The processor is configured to determine whether the first device is permitted to communicate with the second secure communication network, determine whether the second user is permitted to communicate with the first secure communication network, and provide profile information of the second user to the first device when the first device and the second user are permitted to communicate. When the first device or second device are not permitted to communicate with the other&#39;s network, the processor provides an indication to the first device that the second user is unavailable. The memory is coupled to the processor and configured to provide the processor with instructions for determining whether to provide the second user&#39;s profile to the first device. 
     In these examples, the first device is associated with a first security group identifier that is used to determine whether a first set of permissions associated with the first security group identifier permits the first device to transmit communications to the second secure communication network. Like the first device, the second device is also associated with a second security group identifier and the processor is configured to determine whether a second set of permissions associated with the second security group identifier permits the second device to receive communications from the first secure communication network. 
     Another aspect of the disclosure provides for a non-transitory computer-readable medium comprising instructions that when, executed by at least one processor, perform a directory lookup. The instructions include receiving, at a server from a first device belonging to a first network, a first identifier for a second user belonging to a second secure communication network. Next, the instructions determine whether the first device is permitted to communicate with the second secure communication network. When the first device is permitted to communicate with the second communication network, the instructions determine whether the second user is permitted to receive communications from the first secure communication network. When the second user is permitted to communicate with the first communication network, the instructions provide profile information of the second user to the first device. However, when either user is not allowed to communicate with the other&#39;s network, the instructions provide an indication to the first device that the second user is unavailable. 
     As with previous examples, the first device is associated with a first security group identifier, and the instructions determine whether a first set of permissions associated with the first security group identifier permits the first device to communicate with the second secure communication network. Additionally, the second user is associated with a second security group identifier which the instructions use to determine whether a second set of permissions associated with the second security group identifier permits the second device to receive communications from the first secure communication network. 
     Another aspect of the disclosure provides for method for transmitting a federated message. The method includes a first device transmitting a first identifier for a second user that belongs to a second secure communication network to a secure communication platform. The first device receives a response from the secure communication platform that includes a user profile. The user profile includes at least one of a first security group identifier, a first network identifier, a first ephemeral public key, and a first key identifier. Next, the first device generates a first encryption key, derives a key-encrypting key using at least the first ephemeral public key, and then encrypts a first communication to the first user using the first encryption key and the first encryption key using the key-encrypting key. The first device then transmits the first encrypted communication, the key identifier, and the encrypted first encryption key to the second user on the second secure communication network. 
     In preferred examples, the first device belongs to a first secure communication network and the first secure communication network and the second secure communication network are different networks. The first encryption key is calculated by inputting a first set of pseudorandom bytes into a key derivation function. Further, the first device generates a second ephemeral key pair to derive the key-encrypting key according to a key agreement protocol. For example, the key agreement protocol uses the first ephemeral public key and the second ephemeral private key generated by the first device. Accordingly, the second ephemeral public key is transmitted to the first user with the first encrypted communication, the key identifier, and the encrypted first encryption key. 
     One example of the present disclosure describes a system that includes an interface, a processor, and a memory. The interface is configured to transmit a first identifier for a second user that belongs to a second secure communication network to a secure communication platform and receive response from the secure communication platform that includes a user profile for the second user. The user profile includes at least one of a first security group identifier, a first network identifier, a first ephemeral public key, and a first key identifier. The processor is configured to generate a first encryption key, derive a key-encrypting key using at least the first ephemeral public key, encrypt a first communication to the first user using the first encryption key, encrypt the first encryption key using the key-encrypting key; and transmit the first encrypted communication, the key identifier, and the encrypted first encryption key to the second user on the second secure communication network. The memory is coupled to the processor and configured to provide the processor with instructions for generating the first encryption key, deriving the key-encrypting key, encrypting the first communication, and encrypting the first encryption key. 
     In the example described above, the first device belongs to a first secure communication network and the first secure communication network and the second secure communication network are different networks. Additionally, the processor may be configured to generate a second ephemeral key pair. The second ephemeral private key is used to generate the key-encrypting key along with the first ephemeral public key. Accordingly, the processor is configured to transmit the second ephemeral public key to the first user with the first encrypted communication, the key identifier, and the encrypted first encryption key. 
     Another example of the present disclosure provide for a non-transitory computer-readable medium comprising instructions that when, executed by at least one processor, transmit an encrypted communication to a user of a different secure network. The instructions include transmitting a first identifier for a second user to a secure communication platform. The instructions receive a response from the secure communication platform that includes the user profile for the second user. The user profile includes at least a first security group identifier, a first network identifier, a first ephemeral public key, and a first key identifier. The instructions generate a first encryption key, derive a key-encrypting key using at least the first ephemeral public key, and encrypting a first communication using the first encryption key and the first encryption key using the key-encrypting key. The instructions transmit the first encrypted communication, the key identifier, and the encrypted first encryption key to the second user on the second secure communication network. 
     In further examples, the first device belongs to a first secure communication network and the first secure communication network and the second secure communication network are different networks. In some examples, the instructions calculate the first encryption key by inputting a first set of pseudorandom bytes into a key derivation function. Additionally, the instructions generate a second ephemeral key pair, and the second ephemeral private key, along with the first ephemeral public key, is used to generate the key-encrypting key. The instructions transmit the second ephemeral public key to the first user with the first encrypted communication, the key identifier, and the encrypted first encryption key. 
     Another example of the disclosure describes a method for receiving encrypted communications from a user in a different network. The method includes a first device receiving a first encrypted communication from a second device. Next, the first device decrypts the first encrypted communication received from the second device and provides the first decrypted communication to a user of the first device. In order to decrypt the communication, the first device derives a key-encrypting key using at least one ephemeral key, decrypts a first encrypted communication encryption key using the derived key-encrypting key, and decrypts the first encrypted communication using the first decrypted communication encryption key. 
     In some examples, the first encrypted communication includes a time-to-live value that is used to calculate an expiry time of the first encrypted communication. The first device determines whether a current time is greater than the expiry time. Determining the current time includes requesting a master clock time from a server, receiving the master clock time and comparing the master clock time to the local device time. When the current time is greater than the expiry time, the first device revokes the first user&#39;s access to the first communication by either deleting the first communication from the first device or revoking one or more keys required to access the first communication. 
     One example of the disclosure provides for a system for receiving an encrypted communication from a user of a different network. The system includes an interface configured to receive the encrypted communication from a second device. The system also includes a processor that is configured to decrypt the first encrypted communication received from the second device and provide the first decrypted communication to a user of the device. The system has a memory coupled to the processor that is configured to provide the processor with instructions for decrypting and providing the first communication to the user. In some examples, the processor is configured to derive a key-encrypting key using at least one ephemeral key, decrypt a first encrypted communication encryption key using the derived key-encrypting key, and decrypt the first encrypted communication using the first decrypted communication encryption key. 
     Another example has the processor configured to determine whether a time-to-live value associated with the first encrypted communication has expired. The processor determines an expiry time of the encrypted communication based in part on the time-to-live value. In this regard, the processor is configured to determine whether a current time is greater than the expiry time by requesting a master clock time from a server and receiving a response that includes the master clock time. The processor compares the received master clock time to a local device time to determine the current time. When the current time is greater than the expiry time, the processor revokes the user&#39;s access to the first communication by either deleting the first communication from first device or revoking one or more keys required to access the first communication. 
     Another example of the disclosure describes a non-transitory computer-readable medium that includes instructions for receiving encrypted communications from a user in a different network. The instructions include receiving a first encrypted communication from a second device. Next, the instructions decrypt the first encrypted communication received from the second device and provide the first decrypted communication to a user of the first device. In order to decrypt the communication, the instructions derive a key-encrypting key using at least one ephemeral key, decrypt a first encrypted communication encryption key using the derived key-encrypting key, and decrypt the first encrypted communication using the first decrypted communication encryption key. 
     In some examples, the first encrypted communication includes a time-to-live value that is used to calculate an expiry time of the first encrypted communication. The first device whether a current time is greater than the expiry time. Determining the current time includes requesting a master clock time from a server, receiving the master clock time and comparing the master clock time to the local device time. When the current time is greater than the expiry time, the instructions revoke the first user&#39;s access to the first communication by either deleting the first communication from the first device or revoking one or more keys required to access the first communication. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various examples of the invention are disclosed in the following detailed description and the accompanying drawings. 
         FIGS. 1A and 1B  illustrates a secure communication platform according to one 
         FIG. 2  shows a process for creating a secure communication network according to an example of the present disclosure. 
         FIG. 3  illustrates a process for performing a directory search for a user of a second secure communication network. 
         FIG. 4  shows an example of an interface for performing a directory search. 
         FIGS. 5A and 5B  illustrate a process for transmitting an encrypted communication according to another aspect of the disclosure. 
         FIG. 6  shows a process for routing a secure communication from a first secure communication network to a second secure communication network. 
         FIG. 7  illustrates a process for receiving and decrypting an encrypted communication according to one example of the disclosure. 
         FIG. 8  shows an example of an interface for an end-to-end encrypted communication between two users 
         FIG. 9  shows an example of a mobile interface for end-to-end encrypted communications between a first and second user. 
         FIG. 10  illustrates a process for enforcing a time-to-live value (TTL) on a second secure communication network on a secure communication received from a first secure communication network. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure describes a system, a method, and a non-transitory computer readable medium that includes instructions for permitting users of different secure communication networks to exchange encrypted communications. As noted above, prior art communication platforms would not permit users from different networks to communicate securely. In this regard, the technical problems arise when a sender attempts to provide a recipient with an encryption key used to encrypt the communication. Specifically, a sender could not provide the encryption key in a plaintext message, since any unauthorized user who intercepted the plaintext message containing the encryption key would be able to decrypt the communication, defeating the purpose of the encryption. Alternative methods for distributing an encryption key, such as encrypting it with a key obtained from a key distribution center or a key derived according to a key agreement protocol, suffer from vulnerabilities, as well. Namely, there is no way to authenticate the person providing the key and state-actors have been known to pre-calculate the most commonly used keys in key agreement protocols. Thus, key distribution and authenticating a sender represent technical problems in enabling a first user, on a first communication network, to transmit and receive encrypted communications from a second user, on a second communication network. 
     To address the technical problems in the art, the present disclosure provides a secure communication platform that includes a unified user database. The unified user database allows the secure communication platform to provide recipients&#39; keys to senders outside of the recipients&#39; networks. Moreover, only authorized users may access the unified user database. Therefore, the receiving network has a high degree of assurance regarding of sender&#39;s identity. 
     The present disclosure can be implemented in numerous ways, including as a process; an apparatus; a system; a composition of matter; a computer program product embodied on a non-transitory computer readable storage medium; and/or a processor, such as a processor configured to execute instructions stored on and/or provided by a memory coupled to the processor. These implementations, or any other form that the present disclosure may take, may be referred to as techniques. In general, the order of the steps of disclosed processes may be altered within the scope of the present disclosure. Unless stated otherwise, a component such as a processor or a memory described as being configured to perform a task may be implemented as a general component that is temporarily configured to perform the task at a given time or a specific component that is manufactured to perform the task. As used herein, the term ‘processor’ refers to one or more devices, circuits, and/or processing cores configured to process data, such as computer program instructions. 
     A detailed description of one or more examples of the present disclosure is provided below along with accompanying figures that illustrate the principles of the present disclosure. The present disclosure is described in connection with such examples, but the present disclosure is not limited to any example. The scope of the present disclosure is limited only by the claims and the present disclosure encompasses numerous alternatives, modifications, and equivalents. Numerous specific details are set forth in the following description in order to provide a thorough understanding of the present disclosure. These details are provided for the purpose of example and the present disclosure may be practiced according to the claims without some or all of these specific details. For the purpose of clarity, technical material that is known in the technical fields related to the present disclosure has not been described in detail so that the present disclosure is not unnecessarily obscured. 
     The present disclosure describes a secure communication platform that permits a first user, belonging to a first secure communication network, to send encrypted communications to a second user, belonging to second secure communication network that is separate and distinct from the first secure communication network.  FIGS. 1A and 1B  illustrate examples of the secure communication platform and the logical hierarchy of maintaining a plurality of secure communication networks, respectively, that enable the first user and the second user to exchange encrypted communications. As used herein, “communications” and “messages” may be used interchangeably to describe a variety of interactions, including: text messages, chat room messages, control messages, commands, e-mails, documents, audiovisual files, Short Message Service messages (SMSes), audio calls, voice calls (i.e., VOIP), and video calls. The exchange of messages and/or communications is explained in further detail below. 
       FIG. 1A  shows a server  100 , that includes processor  110  and memory  120 , connected to unified user database  1500 .  FIG. 1A  also shows secure communication platform  1000  located in memory  120 . 
     Server  100  may be a stand-alone server, a corporate server, a virtual machine, a server located in a server farm or cloud-computing environment, or any combination thereof. In some examples, the server  100  may be a cloud service provider running one or more virtual machines configured to provide secure communication platform  1000  to one or more enterprises. As used herein, enterprises may include companies, corporations, partnerships, firms, organizations, and universities, and the secure communication platform may provide a secure communication application to one or more users of the one or more enterprises. According to some examples, the secure communication platform to the one or more enterprises as a Software as a Service (SaaS). In other examples, the secure communication platform may be provided to companies as an on-premise solution that is installed and maintained by the company&#39;s IT staff on servers or cloud computing devices operated by the company. In these examples, the secure communication platform  1000  and an enterprise user database (not shown) would be maintained on the enterprise&#39;s servers. In order to enable federated messaging (as defined below), the enterprise user database may be replicated to the unified user database maintained at the secure communication platform. Alternatively, the unified user database may be in communication with the enterprise user database. Accordingly, the enterprise user database would perform key management and the unified user database may perform as a pass through—providing the requesting user with the requested user&#39;s profile information. 
     Processor  110  may be any conventional processor capable of interacting with memory  120  and executing secure communication platform  1000 . In this regard, processor  110  may include at least one processor, multiprocessor, multicore processor, or any combination thereof. Alternatively, processor  110  may be a dedicated controller, such as an Application Specific Integrated Circuit (ASIC) or Field Programmable Gate Array (FPGA). Processor  110  may perform a plurality of tasks on behalf of secure communication platform  1000 , such as determining whether a first user and a second user are permitted to communicate, routing encrypted communications between users, and performing directory lookups. Furthermore, whenever secure communication platform  1000  is described as performing a task, either a single component or a subset of components or all components of secure communication platform  1000  or server  100  may cooperate to perform the task. 
     Memory  120  stores information accessible by processor  110 , including instructions and data that may be executed or otherwise used by the processor  110 . Memory  120  may be any type of media capable of storing information accessible by the processor, including a non-transitory computer-readable medium or any other suitable medium that stores data that may be read with the aid of an electronic device, such as a hard-drive, solid state drive, memory card, flash drive, ROM, RAM, DVD, or other optical disks, as well as other write-capable and read-only memories. Memory  120  may include short term or temporary storage as well as long term or persistent storage. According to some embodiments, memory  120  may include a storage area network (SAN) accessible by the processor  110 . 
     Secure communication platform  1000  may be configured to facilitate the exchange of communications for users of a secure communication application. The secure communication application may be obtained from a website, an internal enterprise computer, or a third-party distributor, such as Google® Play or the Apple® App Store. Once a user has obtained the secure communication application, the user will be able to send and receive encrypted communications with other users of the secure communication platform as discussed in greater detail below. In addition to facilitating the exchange of encrypted communications, secure communication platform  1000  may perform additional functions to enforce security and restrictions on the encrypted communications. For example, secure communication platform  1000  make available a master clock time available to enforce a time-to-live (TTL) value. The TTL values can be used to enforce time constraints on how long a recipient can access an encrypted communication received from the sender. 
     Secure communication platform  1000  may access unified user database  1500 . Unified user database  1500  may be a relational database that stores information in a variety of tables. Alternatively, unified user database  1500  may be a Storage Area Network (SAN) accessible by the secure communication platform  1000 . In this regard, unified user database  1500  may include a record for each user of secure communication platform  1000 , including each user on every secure communication network. By maintaining all users in a single, unified database, a first user on a first secure communication network may be able to search and find a second user on a second secure communication network. Accordingly, unified user database  1500  may include an entry for each user. The entry may include a username, a network identifier (network ID), a security group identifier, an application identifier (app ID), a plurality of ephemeral public keys, an application public signing key, and a user public signing key. In some examples, a user may have the secure communication application installed on multiple devices, such as a first instance on a mobile device and a second instance on a desktop device. Accordingly, the user&#39;s entry in unified user database  1500  will include a first application identifier, a first plurality of ephemeral public keys, and a first application public signing key for the first instance of the secure communication application and a second application identifier, a second plurality of ephemeral public keys, and a second application public signing key for the second instance of the secure communication application. The username, network identifier, security group, and user public signing key will be the same for both the first instance and the second instance of the secure communication application. Additionally, unified user database  1500  may include a table of communications (not shown). That is, the secure communication platform may store communications for a predetermined time in unified user database  1500 . For example, when a communication is received, the secure communication platform may store the communication in the table of communications and provide an alert, such as a push notification, to the recipient. Accordingly, a recipient may access the secure communication platform to obtain his or her stored communications. In some examples, communications may be stored for a predetermined amount of time, such as 30 days; however, this may be adjusted, as needed, based on industry standards and/or to comply with regulatory schemes. 
     As noted above, secure communication platform  1000  may support a plurality of secure communication networks. As used herein, a secure communication network is a logical network that provides a service to an enterprise. The service includes a secure communication application that allows users to exchange encrypted communications, encrypted files, and collaborate securely.  FIG. 1B  illustrates an example of a logical hierarchy of secure communication platform  1000  supporting a plurality of secure communication networks. 
     As shown in  FIG. 1B , secure communication platform  1000  includes a first secure communication network  1100 , a second secure communication network  1200 , and a third secure communication network  1300 . While only three secure communication networks are shown, secure communication platform  1000  may include any number of secure communication networks. In preferred examples, each secure communication network is associated with a different enterprise. For example, first secure communication network  1100  may be a communication platform for a first enterprise, second secure communication network  1200  may be a communication platform for a second enterprise, and third secure communication network  1300  may be a communication platform for a third enterprise. 
     First secure communication network  1100  includes first security group  1110  and second security group  1120 . First security group  1110  and second security group  1120  may correspond to organizations or teams within the enterprise that configured first secure communication network  1100 . Alternatively, first security group  1110  and second security group  1120  may be configured by an administrator of first secure communication network  1100 . In this regard, first secure communication network may have more security groups than first security group  1110  and second security group  1120 . 
     As illustrated in  FIG. 1B , first security group  1110  includes first device  1112  and second device  1114 . Similarly, second security group  1120  includes third device  1122  and fourth device  1124 . First device  1112 , second device  1114 , third device  1122 , and fourth device  1124  may make use of the secure communication platform  1000  and the techniques described herein via first secure communication network  1100  and a secure communication application installed on each of the devices. First device  1112 , second device  1114 , third device  1122 , and fourth device  1124  may be mobile devices, such as a laptops, smart phones, or tablets, or computing devices, such as desktop computers or servers. As noted above, the secure communication application described herein allows cross-platform communications, thereby allowing users of various devices to communicate seamlessly. For example, a first user on an iPhone® may transmit an encrypted communication to a second user on an Android® device. Further, each user may have different instances of the secure communication application installed on multiple devices. That is, the user of first device  1112  may be able to receive messages on both device  1112  as well as on any other devices that the user may have that includes a copy of the secure communication application, such as a laptop. In some embodiments, first device  1112  and second device  1114  may be a user&#39;s personal device (i.e. a bring your own device (BYOD) scenario) and an enterprise asset, respectively. Because security groups may correspond to organizations or teams within an enterprise, first security group  1110  and second security group  1120  may include more than first device  1112 , second device  1114 , third device  1122 , and fourth device  1124 . 
     Second secure communication network  1200  and third secure communication network  1300  may be similar to first secure communication network  1100 . For example, second secure communication network  1200  includes third security group  1210  with fifth device  1212  and sixth device  1214  and fourth security group  1220  with seventh device  1222  and eighth device  1224 . Third secure communication  1300  includes fifth security group  1310  and sixth security group  1320 . Ninth device  1312  and tenth device  1314  may be assigned to fifth security group  1310 , while eleventh device  1322  and twelfth device  1324  may be assigned to sixth security group  1320 . Like with first security group  1110  and second security group  1220 , third security group  1210 , fourth security group  1220 , fifth security group  1310 , and sixth security group  1320  may correspond to organizations or teams within the enterprise or be configured by an administrator. Similarly, fifth device  1212 , sixth device  1214 , seventh device  1222 , eighth device  1224 , ninth device  1312 , tenth device  1314 , eleventh device  1322 , and twelfth device  1324  may be any of the devices described above with respect to first device  1112 , second device  1114 , third device  1122 , and fourth device  1124 . Further, a skilled artisan would recognize that the number of security groups and devices are merely illustrative and that secure communication networks may contain any number of security groups, and each security group may include any number of devices. 
       FIG. 1B  also shows unified user database  1500  in communication with secure communication platform  1000 . In this regard, unified user database  1500  maintains user information for each user of secure communication platform  1000 . That is, unified user database  1500  includes user information for every user of first secure communication network  1100 , second secure communication network  1200 , and third secure communication network  1300 . In preferred examples, the user information maintained in unified user database is encrypted. Because unified user database  1500  stores user information for each user of the secure communication platform, a first user of first device  1112  may contact the secure communication platform  1000  for user information for a second user of third device  1212 . In this example, the first user may obtain profile information from unified user database  1500  for the second user because both the first user and the second user are in the same secure communication network. Moreover, a user&#39;s ability to access user information from unified user database  1500  provides a solution to the technical problem of being unable to send encrypted communications from a first secure communication network to a second secure communication network. In this regard, unified user database  1500  may act as a central repository to provide a first user device on a first secure communication network with information that allows the first user device to transmit an encrypted communication to a second user on a second secure communication network. Furthermore, the second secure communication network has a high-level of assurance that the encrypted communication can be trusted since the sender is using the secure communication application associated with the secure communication platform  1000  and, therefore, has been verified by secure communication platform  1000 . 
     To make use of the secure communication platform, a user must first provision a secure communication network for his or her enterprise.  FIG. 2  shows a process  200  for provisioning a secure communications network. 
     Process  200  begins in block  210  when a secure communication network is created. A secure communication network is created when a user registers with secure communication platform  1000 . In preferred examples, an administrator, or another authorized user, may contact secure communication platform and complete a registration process to create the secure communication network for the enterprise. Once the registration process is complete, secure communication platform creates the secure communication network. Creation of the secure communication network includes generating a network identifier (“network ID”). According to some examples, the network identifier may be the name of the enterprise or some other information entered by the user during the registration process. Alternatively, the network identifier may be a random identifier generated by secure communication platform. In block  220 , the network identifier may be provided to the user for his or her records. Additionally, the network identifier may be stored in unified user database  1500 . 
     In block  230 , the newly created secure communication network may be configured. Configuring the secure communication network may include importing user information. For example, the administrator may import user information from a directory service, such as LDAP or active directory. Additionally, configuring the secure communication network may include defining whether users of the secure communication network may receive communications from other secure communication networks. That is, a user may configure whether users of the secure communication network are able to receive communications from users outside their secure communication network. According to some examples, configuring the secure communication may include defining a time-to-live (TTL) value and enabling a burn-on-read (BOR) feature for communications. As noted above, the TTL value defines how long a recipient may access a communication. In some examples, the TTL value may be set by a sender at the time a communication is sent. In other examples, however, an administrator may set a maximum or minimum limit on the TTL value for all communications on the secure communication network. Alternatively, the administrator may define the TTL value for all communications, removing a sender&#39;s ability to control how long a recipient has access to a received communication. The BOR feature may be enabled by an administrator during configuration of the secure communication network. By enabling the BOR feature, a sender may define that access to a communication will be revoked after the recipient has read the communication. If the administrator disables the BOR feature, senders will not have this option. 
     In block  240 , one or more security groups may be defined. By default, the secure communication network includes one security group. However, additional security groups may be defined by the user, either during registration or some time thereafter. For example, security groups may be defined by department, permissions, access control lists, teams, or projects. Once security groups have been defined, each security group may be configured in block  250 . Configuring each security group may also include defining the TTL value and enabling/disabling the BOR feature. Additionally, configuring a security group may include defining whether the security group is federated. Federated, in this context, means a security group&#39;s ability to communicate with users in different secure communication networks. Federated messaging may be disabled, restricted or enabled. Disabled, in this sense, means that users would only be allowed to communicate with other users in their secure communication network. Restricted would restrict which secure communication networks users could send to and receive from. For example, a user in a security group with restricted federation may be able to receive from and transmit to first and second secure communication network, but the user may not be able to send or receive any communications from a third secure communication network. In another example of restricted federation, the user may be able to send to and receive from a first secure communication network, but not to second and third secure communication networks. When federated messaging is enabled, users are permitted to send to and receive from any secure communication network. 
     If the secure communication network and security groups are not defined by the administrator at the time the secure communication network is created, then default values may be used. For example, a maximum TTL value of 30 days, BOR off, and disabled federated messaging may be the default values for a secure communication network. The administrator may change these values at any time after the secure communication network has been created. 
     After the secure communication network and security groups are defined, enterprise users may be enabled to communicate via the newly configured secure communication network in block  260 . This may include providing the enterprise users with an email, or other communication, inviting them to download the secure communication application. In some examples, enabling enterprise users may include sending them a code to enter when registering the secure communication application on their device. This code may be used by the secure communication platform  1000  to associate the user with a specific secure communication network. 
     Once enterprise users have downloaded the secure communication application, they may begin exchanging encrypted communications with other users. As noted above, exchanging encrypted communications may include sending and receiving encrypted communications with users outside of the user&#39;s secure communication network. In order to exchange encrypted communications with a user outside their secure communication network, a user may perform a directory lookup on the secure communication platform. In turn, the secure communication platform may determine whether the sending user is able to send encrypted communications off their secure communication network and whether the receiving user is able to receive encrypted communications from users external to their secure communication network.  FIG. 3  shows an exemplary process  300  for performing a directory lookup on a user from a different secure communication network. 
     In block  310 , the secure communication platform  1000  receives a first identifier for a second user of a second secure communication network from a first device on a first secure communication network. According to this example, the first secure communication network and second secure communication network are distinct networks that are logically separated from each other. The first identifier may be an email address, phone number, or username of the second user. In block  320 , secure communication platform  1000  determines whether the first device is permitted to transmit to the second secure communication network. In preferred examples, determining whether the first device is permitted to communicate with users from the second secure communication network includes checking a first set of permissions associated with the sender&#39;s security group. In this regard, secure communication platform  1000  may review the first set of permissions to determine whether the sender&#39;s security group is permitted to communicate with users from the second secure communication network. If the first set of permissions do not allow the sender to transmit encrypted communications to the second secure communication network, the process  300  proceeds to block  330 , where secure communication platform  1000  notifies the first device that the second user is unavailable. 
     On the other hand, when the first set of permissions indicate that the sender is allowed to transmit encrypted communications to the second secure communication network, process  300  proceeds to block  340 . In block  340 , secure communication platform  1000  determines whether the second user is permitted to receive encrypted communications from the first secure communication network. Determining whether the second user is permitted to receive from the first secure communication network may include checking a second set of permissions associated with the second user&#39;s security group to determine whether the second user&#39;s security group is permitted to communicate with users from the first secure communication network. If the second set of permissions do not allow the second user to communicate with users from the first secure communication network, the process  300  proceeds to block  350 , where secure communication platform  1000  notifies the first device that the second user is unavailable. 
     However, when the second set of permissions indicate that the second user is able to communicate with users from the first secure communication network, process  300  proceeds to block  360 . In block  360 , secure communication platform  1000  provides the first device with profile information of the second user. Receiving the second user&#39;s profile information may occur in the background of the first device, and the secure communication application may open a window that allows the user of the first device to proceed with composing an encrypted communication to the second user. 
     Turning to  FIG. 4 , an example of an interface  400  for performing a directory lookup is shown. Interface  400  includes an icon  410  for initiating a new communication to a second user. In response to a first user selecting icon  410 , a “Start Message” window  420  may be displayed. Window  420  may include a variety of options, such as setting a TTL value for the communication or enabling the BOR feature. Additionally, window  420  may have a directory that the user can search through to select another person with which to communicate. Window  420  may also include a search field  430 , where the first identifier may be entered to search for users of different secure communication networks. As noted above, window  420  may change into a message composition interface (illustrated below) when the user is permitted to communicate with a second user. However, if either user is unable to communicate with someone external to their secure communication network, an additional window  440  may be displayed indicating that the second user is unavailable. Additional information may be conveyed in window  440 . For example, window  440  may indicate which user does not have the requisite permissions. 
     After performing the directory lookup, the user is ready to send and receive encrypted communications. The encrypted communications provided by the secure communication platform  1000  can be best understood as providing node-to-node communication rather than user-to-user communication. As suggested above, a single user may have secure communication applications executing on multiple devices. For the purposes of transmitting an encrypted communication, each instance of the secure communication application on each device would be considered a node. For example, a first user with two devices that sends a message to a second user with three devices is sending an encrypted message to four nodes—the three devices associated with the second user, and the first user&#39;s second device.  FIGS. 5A and 5B  illustrate a process  500  for transmitting an encrypted communication based on this principle. 
     In block  505 , the sending device&#39;s secure communication application retrieves one or more receiving users&#39; profile information from the secure communication platform  1000 . In this regard, the sending secure communication application may request the receiving users&#39; profile information from the secure communication platform  1000  when the sending user begins composing the communication. Alternatively, the secure communication platform  1000  may provide the receiving user&#39;s profile information in response to the directory lookup performed in  FIG. 3 . The user profile information includes the user&#39;s username, a network identifier, a security group identifier, a list of the recipient user&#39;s devices, the second public key for each device, and the signature of the second public key for each device. Next, the sending secure communication application builds a list of recipient devices based on a union of the receiving user devices and the sender&#39;s devices in block  510 . In block  515 , the sending secure communication application retrieves a signed ephemeral public key, and its associated unique identifier, from the secure communication platform  1000  for each of the recipient devices. According to some examples, the signed ephemeral public key and the associated unique identifier may be obtained along with the receiving users&#39; profile information. In block  520 , the sending secure communication application validates the signature chain for each ephemeral public key received from the secure communication platform. In this regard, the signature of the ephemeral public key is authenticated according to a signature verification algorithm, such as ECDSA, using an application public signing key. Next, a signature of the application public signing key is verified using the user public signing key; finally, the username corresponds to an expected user identity. If the signature chain is invalid, the secure communication application may request the one or more receiving users&#39; profile information from the secure communication platform. Alternatively, the secure communication application may discard the communication and refuse to communicate with the one or more recipient devices with the invalid signature chain. If the signature chain is valid, then the secure communication application continues preparing the communication to send to the one or more receiver devices. 
     In block  525 , the sending secure communication application generates a random communication encryption key. In preferred examples, the random communication encryption key is a 256-bit key derived from a first set of pseudorandom bytes derived from a sending client&#39;s device. In alternative examples, the random communication encryption key is generated by applying a key derivation function (e.g. HKDF) to the first set of pseudorandom bytes derived from a sending client&#39;s device. The first set of pseudorandom bytes may be derived from ephemeral environmental noise obtained from device drivers and other kernel operations. For example, data from the one or more sensors (e.g., an accelerometer, a Global Positioning Satellite (GPS) system, a magnetometer, a proximity sensor, an ambient light sensor, a moisture sensor, and a gyroscope) may be used as the first set of pseudorandom bytes. 
     In block  530 , the sending secure communication application generates an ephemeral key pair. Preferably, the ephemeral key pair is generated according to ECC. In block  535 , the sending secure communication application calculates a key-encrypting key (KEK) for each receiver device. The key-encrypting key is calculated by deriving a shared secret using the ephemeral private key the sending secure communication application generated in block  525  and the receiving node&#39;s ephemeral public key received from the secure communication platform  1000 . In preferred examples, the shared secret is derived according to Diffie-Hellman. The shared secret and the recipient device&#39;s application identifier are inputted into a key derivation function to derive the key-encrypting key. By encrypting the random communication encryption key with the key-encrypting key, the encrypted communication is effectively bound to the receiver&#39;s secure communication application and device. This improves security by allowing only the recipient device to access the communication. That is, a receiver would not be able to transfer the communication from one device to another and still be able to decrypt the message since the keys used to generate the key-encrypting key are unique to the specific installation of the secure communication application. Block  535  may be repeated for each of the one or more receivers&#39; devices. 
     After calculating the key-encrypting key for each of the one or more receivers&#39; devices, the sending secure communication application may create metadata for the communication in block  540 . The metadata includes at least one of a content type and ephemerality configuration. Content type may identify whether the communication is a text message, file transfer, voice call, video call, etc. Ephemerality configuration includes the TTL value and the BOR feature (e.g. enabled/disabled). In block  545 , the sending secure communication application encrypts the communication and metadata using the random communication encryption key. In preferred examples, the communication is encrypted via a symmetric encryption algorithm using the random communication encryption key. In block  550 , the communication key is encrypted using the derived KEK for each of the recipient devices. In block  555 , the sending secure communication application encrypts routing data with a public key belonging to secure communication platform  1000 . In this regard, the public key may be embedded in the secure communication application. Alternatively, the secure communication platform  1000  may provide a public key to the secure communication application. In this context, routing data includes at least one of the username for each of the one or more receiver devices, a network identifier for each of the usernames, and a security group identifier for each of the usernames. In block  560 , the sending secure communication application creates a serialized packet that includes the encrypted communication, the encrypted routing data, the ephemeral public key that the sender&#39;s secure communication application generated in block  530 , the one or more unique identifiers for the receiver&#39;s public key(s) received from secure communication platform, and the one or more encrypted communication encryption keys. In block  570 , the sending secure communication application transmits the serialized packet to the secure communication platform  1000  for distribution to the one or more receiver devices. In this way, the secure communication platform  1000  receives a single packet and distributes the single packet to the one or more receiver devices. 
     Upon receiving an encrypted communication, secure communication platform  1000  must determine to whom to route the message.  FIG. 6  illustrates a process  600  according to one aspect of the disclosure for routing the received encrypted communication to a recipient. 
     In block  610 , process  600  begins with secure communication platform  1000  receiving a serialized packet from a sender device. In block  620 , secure communication platform decrypts the routing data contained in the serialized packet received from the sender device. In preferred examples, secure communication platform  1000  decrypts the routing data with a private key to obtain the sender&#39;s username, the sender&#39;s security group identifier, the sender&#39;s network identifier, a first recipient&#39;s username, a first recipient&#39;s security group identifier, and a first recipient&#39;s network identifier. 
     In block  630 , secure communication platform  1000  determines if the sender&#39;s network identifier and the first recipient&#39;s network identifier are equivalent. If the sender&#39;s network identifier and the first recipient&#39;s network identifier are the same, then secure communication platform determines that the first sender and the first recipient are in the same secure communication network and the serialized packet is provided to the first recipient in block  640 . Providing the serialized packet may include transmitting an alert, such as a push notification, to the first recipient. In alternative examples, providing the packet to the first recipient may include pushing the serialized packet to the first recipient&#39;s device. If, however, the recipient&#39;s network identifier is different than the sender&#39;s network identifier, process  600  proceeds to block  650 . 
     In block  650 , secure communication platform  1000  determines if the sender is permitted to transmit to the first recipient&#39;s network. In preferred examples, determining whether the sender is permitted to transmit to the first recipient includes checking a first set of permissions associated with the sender&#39;s security group. For example, the first set of permissions may be reviewed to determine whether the sender&#39;s security group is permitted to transmit to the network identifier associated with the recipient. In another example, the first set of permissions may be reviewed to determine whether the sender&#39;s security group is permitted to transmit encrypted communications off network. That is, the secure communication platform determines whether the sender is allowed to transmit encrypted communications to the second secure communication networks based on the first set of permissions. If the first set of permissions do not allow the sender to transmit encrypted communications to the second secure communication network, secure communication platform  1000  discards the serialized packet in block  660 . In some examples, secure communication platform may notify the sender that he or she is not permitted to transmit to other networks. For example, secure communication platform may provide a message to the sender&#39;s secure communication application to indicate that the sender does not have permission to transmit to users on other networks. 
     When the first set of permissions permits the sender to transmit encrypted communications to other networks, secure communication platform  1000  determines whether the first recipient is permitted to receive encrypted communications from the other secure communication networks in block  670 . This may include checking a second set of permissions to determine whether the first recipient&#39;s security group is permitted to receive encrypted communications from first secure communication network. For example, the second set of permissions may indicate that the recipient is permitted to receive communications originating from the network identifier associated with the sender. Alternatively, the second set of permissions may not permit the recipient to receive communications from other secure communication networks. When the second set of permissions do not permit the recipient to receive encrypted communications from the sender&#39;s network, secure communication platform  1000  discards the serialized packet. Additionally, secure communication platform  1000  may provide an indication to the sender that the first recipient is unavailable. 
     However, when the second set of permissions allow the second user to receive encrypted communications from secure communication network with a different network identifier, secure communication platform  1000  provides the serialized packet to the first recipient in block  680 . Providing the serialized packet to the first recipient may include placing the serialized packet in the first recipient&#39;s queue and providing a push notification, or some other indication, to the first recipient that a new communication has been received. In other examples, secure communication platform may push the serialized packet directly to the first recipient. 
     As noted above, a sender may address a serialized packet to one or more recipients. Accordingly, process  600  may be repeated by the secure communication platform for each of the one or more recipients included in serialized packet. 
     After the secure communication platform has provided each of the one or more recipient devices with a notification of the new communication, each of the one or more recipient devices&#39; secure communication applications may contact the secure communication platform to obtain the new communication.  FIG. 7  illustrates a method  700  for decrypting an encrypted communication on a recipient device. 
     In block  710 , a recipient device receives a serialized packet from a sending device. As noted above, this may include retrieving the serialized packet from the secure communication platform in response to receiving an alert or notification. Alternatively, retrieving the serialized packet may include receiving the serialized packet directly from the sending device, for example, via a peer-to-peer protocol. In order to decrypt the received communication, the recipient must identify the appropriate key material in the serialized packet. The first time a recipient device receives a communication from a sender, the recipient device may obtain information about the sender from the secure communication platform. This information may include an application identifier of the sending device, a username, and user profile information of the sender. The recipient device may store this information locally, preferably encrypted, for subsequent communication exchanges. 
     After obtaining the communication and information about the sender, the recipient&#39;s secure communication application uses its application identifier to retrieve the encrypted communication key from the serialized packet in block  720 . Also in block  720 , the recipient&#39;s secure communication application may also recover the unique identifier of the recipient device&#39;s ephemeral key pair from the received serialized packet. In block  730 , the receiving node&#39;s secure communication application uses the unique identifier to identify and retrieve the ephemeral private key from a local storage that corresponds to the ephemeral public key used by the sending device to derive the KEK. According to some examples, the receiving device&#39;s secure communication application may decrypt the ephemeral private key retrieved from local storage using the receiving device&#39;s local storage device key. Next, the secure communication application on the receiving device derives the key-encrypting key in block  740 . Specifically, the receiving device calculates a shared secret using the recipient device&#39;s ephemeral private key and the sending device&#39;s ephemeral public key. The shared secret and the receiving device&#39;s application identifier are inputted to a key derivation function to derive the key-encrypting key. In block  750 , the recipient device&#39;s secure communication application decrypts the encrypted communication encryption key. In block  760 , the decrypted communication encryption key is used to decrypt the message and the metadata. As noted above, metadata may include a TTL or BOR value, which the recipient&#39;s secure communication application will enforce as discussed in greater detail below. In block  770 , the recipient device&#39;s secure communication application provides the decrypted communication to the user. Providing the decrypted message to the user may include, for example, displaying a text message, reproducing a call (e.g. audio or video), and/or downloading a file. In block  780 , the communication may be encrypted with the receiving device&#39;s local storage device key and stored in a local storage on the receiving device. 
     Turning to  FIG. 8 , an example of a desktop interface  800  for the secure communication application provided by the secure communication platform is illustrated. The interface  800  displays user information in field  805 . In this regard, interface  800  belongs to Vernicious Knids as indicated by field  805 . Field  810  displays the secure chat rooms that the user is participating in, while field  815  illustrates the one-to-one communications of the user. As illustrated, the Arthur Slugworth name is highlighted, indicating that a one-to-one communication with Arthur Slugworth is displayed. This is also displayed in the header field  830 , which displays the name of the other user. If a secure chat room was selected, header field  830  may display the name of the secure chat room. Additionally, interface  800  may include a search field  835 , the TTL status in field  840 , and a telephone icon  845  for voice and video calling. Search field  835  provides users with the ability to perform a text search for communications made in interface  800 . The TTL status field  840  allows a user to change the expiration time for messages before they are sent. The telephone icon  845  permits the user to participate in an encrypted audio or video call. Interface  800  also includes a text field  850 , which displays incoming and outgoing communications. Text field  850  may also include a timestamp of the message and a countdown time until a message will disappear in field  855 . Finally, interface  800  includes an input  860  to allow the user to enter text and/or upload files. 
     As noted above, a user may have the secure communication application installed on more than one device. As  FIG. 8  shows an example of a desktop interface,  FIG. 9  shows an example of a mobile interface  900  of a secure communication application. Similar to the desktop interface, mobile interface  900  includes a header field  910 . When the user is participating in a secure chat room, the title of the secure chat room will be displayed. Similarly, the name of the other participant will be shown when the user is participating in a one-to-one communication. Interface  900  may also include a search field  920  to provide the user with the ability to perform a text search. Additionally, mobile interface  900  may also include a telephone icon  930  that allows the user to participate in an encrypted voice or video call. Mobile interface  900  includes a text field  940 , which displays incoming and outgoing communications. Like the text field for the desktop interface, text field  940  also displays a timestamp and an expiration timer for each communication in field  947 . Lastly, mobile interface  900  may include an input  950  for a user to enter text and/or upload files. 
     As noted above, the secure communication platform may allow senders to control how long a recipient can access a communication by including a TTL value with the encrypted communication. This includes communications received on a second secure communication network from a user on a first secure communication network.  FIG. 10  shows a process  1000  for enforcing a TTL value on an encrypted communication. 
     In block  1010 , an encrypted communication with at least one TTL value is received on a recipient device from a sender. After decrypting the communication and metadata, which includes the TTL value, in accordance with the techniques described above, the secure communication application on the recipient device requests a master clock value in block  1020 . The request for the master clock value may be made to secure communication platform  1000 . Alternatively, the request for the master clock value may be transmitted to a trusted time server. In block  1030 , the secure communication application receives a response that includes the master clock value. The response may include a signature, a hash, or some other value for the secure communication application to validate the response. Accordingly, the recipient&#39;s secure communication application may verify the signature to ensure that the master clock value has not been tampered with. In block  1040 , the secure communication application determines whether the master clock value is substantially equal to the local device time. In this regard, determining whether the master clock value is substantially equal to the local device time accounts for differences in time zones between the local device and the source of the master clock value, as well as any delays in network transmission. If the master clock value and the local device time are substantially equal, the secure communication application determines an expiry time by adding the TTL value to the local clock value. Alternatively, the expiry time may be determined by adding the TTL value to a timestamp of when the encrypted communication was received at the secure communication application. When the master clock value and the local device time are significantly different, the secure communication application sets an expiry time by adding the TTL value to the received master clock value. Significantly different in this context means a difference between the times that cannot be attributed to a reasonable delay. For example, a difference of a few hours would be considered a significant difference and could be considered an attempt to circumvent the TTL value. Once the expiry time is calculated, it may be encrypted and stored locally on the recipient&#39;s device. 
     Regardless of how the expiry time is calculated, the secure communication application determines whether the current time is greater than the expiry time in block  1070 . Again, the secure communication application may request the master clock value from the secure communication platform or a trusted time server to determine the current time. A comparison may be made between the master clock value and the local device time. When the two values are substantially the same, the secure communication application will use the local device time as the current time value. However, if there is a significant difference between the master clock value and the local device time, the master clock value will be used to determine whether the current time is greater than the expiry time. If the current time is greater than the expiry time, access to the encrypted communication is revoked in block  1080 . Revoking access to the encrypted communication may include revoking the keys necessary to decrypt the communication, deleting the communication, or a combination thereof. 
     When the current time is less than the expiry time, the secure communication application provides the recipient with access to the encrypted communication in block  1090 . Providing access to the communication may include decrypting the communication and providing the communication to the recipient. Periodically, the secure communication application may request a master clock value to determine whether the communication has expired. In this regard, the actions in blocks  1020 ,  1030 ,  1040 , and  1070  may be repeated as necessary. Since the expiry time has already been calculated, the steps of blocks  1050  and  1060  may be skipped. Using the techniques described above, the secure communication platform can enforce TTL values on communications as they travel between different networks. 
     The above-described examples provide a technical solution that provides users on different secure communication networks with the ability to exchange encrypted communications with a high degree of trust. In particular, the unified user database distributes recipients&#39; keys and authenticates the identity of the sender to the recipient secure communication network. 
     Unless otherwise stated, the foregoing alternative examples are not mutually exclusive, but may be implemented in various combinations to achieve unique advantages. As these and other variations and combinations of the features discussed above can be utilized without departing from the subject matter defined by the claims, the foregoing description of the embodiments should be taken by way of illustration rather than by way of limitation of the subject matter defined by the claims. In addition, the provision of the examples described herein, as well as clauses phrased as “such as,” “including” and the like, should not be interpreted as limiting the subject matter of the claims to the specific examples; rather, the examples are intended to illustrate only one of many possible embodiments. Further, the same reference numbers in different drawings can identify the same or similar elements.