1. A method comprising:
- receiving, at a first device, a communication, wherein the communication comprises a time-to-live value;
determining an expiration time of the communication by adding the time-to-live value to a first current time;
obtaining, based on a request to access the communication, a second current time;
comparing the second current time to the expiration time; and
allowing, based on a determination that the second current time is less than the expiration time, access to the communication.
Determining whether to allow access to a message is disclosed. A message is received from a sender. The message is associated with a first time-to-live (TTL) value. A determination is made that the first time-to-live value has not been exceeded. The determination is made at least in part by obtaining an external master clock time. In response to the determination, access is allowed to the message.
- 1. A method comprising:
receiving, at a first device, a communication, wherein the communication comprises a time-to-live value; determining an expiration time of the communication by adding the time-to-live value to a first current time; obtaining, based on a request to access the communication, a second current time; comparing the second current time to the expiration time; and allowing, based on a determination that the second current time is less than the expiration time, access to the communication.
- View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
- 9. The method of claim 9, further comprising:
deny, based on a determination that a third current time is less than the embargo time, access to the communication.
- 10. A computing device comprising:
an interface configured to receive a communication, wherein the communication comprises a time-to-live value; one or more processors; memory storing instructions that, when executed by the one or more processors, cause the computing device to; determine an expiration time of the communication by adding the time-to-live value to a first current time; obtain, based on a request to access the communication, a second current time; compare the second current time the expiration time; and allow, based on a determination that the second current time is less than the expiration time, access to the communication.
- View Dependent Claims (11, 12, 13, 14)
- 15. A computer program product embodied in a non-transitory tangible computer readable storage medium and comprising computer instructions for:
receiving a communication, wherein the communication comprises a time-to-live value; obtaining, based on a request to access the communication, a second current time; comparing the second current time to the expiration time; and
- View Dependent Claims (16, 17, 18, 19, 20)
This application is a continuation of co-pending application U.S. Ser. No. 14/314,018, filed on Jun. 24, 2014 and entitled “Secure Time-to-Live”, which claims priority to U.S. Provisional Patent Application No. 61/839,307, entitled “SECURE TIME TO LIVE” filed Jun. 25, 2013; U.S. Provisional Patent Application No. 61/846,568, entitled “DIGITAL SECURITY BUBBLE” filed Jul. 15, 2013; and U.S. Provisional Patent Application No. 61/943,826 entitled ENHANCED PERFECT FORWARD SECRECY FOR MULTI-SYNCHRONOUS COMMUNICATION filed Feb. 24, 2014, all of which are incorporated herein by reference for all purposes.
This application is also related to U.S. Ser. No. 15/964,848, filed on Apr. 27, 2018 and entitled “Secure Time-to-Live” and issued as U.S. Pat. No. 10,263,964 on Apr. 16, 2019, the entirety of which is incorporated herein by reference for all purposes.
Users of electronic devices increasingly desire to communicate privately and securely with one another. Unfortunately, existing approaches to securing communications can be difficult and/or cumbersome to use. As one example, some approaches to data security make use of digital certificates or keys, or pre-shared passwords, which can be tedious to manage. Further, existing approaches are often susceptible to interception (e.g., eavesdropping and man-in-the middle attacks), forensic analysis, and impersonation. Improvements to digital communication techniques are therefore desirable.
Various embodiments of the invention are disclosed in the following detailed description and the accompanying drawings.
The invention 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 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. In this specification, these implementations, or any other form that the invention 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 invention. 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 embodiments of the invention is provided below along with accompanying figures that illustrate the principles of the invention. The invention is described in connection with such embodiments, but the invention is not limited to any embodiment. The scope of the invention is limited only by the claims and the invention 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 invention. These details are provided for the purpose of example and the invention 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 invention has not been described in detail so that the invention is not unnecessarily obscured.
Users of client devices, such as client devices 106-114 communicate securely with one another using techniques described herein. As shown in
Communications are exchanged via one or more networks (depicted collectively in
As will be described in more detail below, a variety of entities can operate embodiments of platform 102. Further, multiple embodiments of platform 102 can exist simultaneously in an environment (with those multiple embodiments operated by a single entity, or different entities) with the techniques described herein adapted as applicable. For example, platform 102 can be operated by a non-profit organization (or an individual, a company, or any other appropriate type of entity or set of entities) for use by the general public (e.g., with arbitrary members of the public able to use platform 102 to exchange communications). As another example, an enterprise organization can operate an embodiment of platform 102 exclusively for use by the employees of the enterprise (and, as applicable, other individuals, such as vendors). As yet another example, a company (or other entity or entities) can operate one or multiple instances of platform 102 on behalf of multiple organizations, such as small business or companies, schools, charitable organizations, etc.
Suppose a user of client device 106 (hereinafter referred to as “Alice”) would like to send a secure message to her friend, Bob (a user of client device 114) in accordance with techniques described herein. In some embodiments, in order to send a message Bob, Alice first obtains a copy of a messaging application suitable for her device. For example, if Alice'"'"'s tablet device runs iOS, she could obtain an “app” for her tablet from the Apple App Store (an example of software distribution server 106). Bob similarly obtains an appropriate application suitable for his client device 114 (e.g., an Android-based smartphone) from an appropriate location (e.g., the Google Play store or Amazon Appstore). In some embodiments, client devices make use of a web-based application (e.g., made available by platform 102 through interface 118), instead of, or in addition to, a dedicated installed application.
In embodiments where platform 102 is operated on behalf of specific groups of individuals (e.g., on behalf of employees of a company, students/teachers at a school, company stockholders, members of a club, premium customers, etc.), the app can be obtained from a publicly accessible software distribution server as Alice and Bob do above (e.g., from the Google Play store), can be obtained from a privately operated software distribution server (e.g., made available only to company-issued devices or devices otherwise authorized to communicate with the private server), can be provisioned by support personnel associated with the group (e.g., by being directly installed by the support personnel or included in a device image), etc., as applicable. For example, suppose an embodiment of platform 102 is operated by ACME University on behalf of its students and faculty/staff. As mentioned above, the university can itself operate an embodiment of platform 102, or can contract with a third party to make available the embodiment of platform 102 for university users. Freshmen (and other new students/employees, as applicable) at ACME University can be provided with instructions for downloading and installing an ACME University-specific embodiment of the secure messaging application from a university server in conjunction with their new student orientation. As another example, new employees of Beta Corporation can be issued company phones (and/or other devices such as laptops) with an embodiment of the secure messaging application pre-installed and pre-configured by support personnel for Beta Corporation (e.g., where Beta Corporation operates an embodiment of platform 102 on behalf of its employees and business partners). As yet another example, business partners of Beta Corporation (e.g., vendors) can be provided with instructions for provisioning a Beta Corporation-specific embodiment of the secure messaging application via email, or via a website. And, the Beta Corporation-specific embodiment of the secure messaging application can be made available via email, a website, or any other appropriate mechanism.
Returning to the example of Alice (a member of the public, using an embodiment of platform 102 made available to the public), once Alice'"'"'s tablet 106 has obtained a copy of the secure messaging app, the app is installed, and Alice is able to register for an account. An instance of a messaging app usable in conjunction with the techniques described herein is depicted in
In some embodiments, process 200 is performed on a client device, such as Alice'"'"'s client device 106. The process begins at 202 when a pool of public/private keypairs for the application is generated, on client device 106 (e.g., using RSA, ECDH, or any other appropriate asymmetric encryption algorithms). As one example, the keypairs can be generated using Eliptic Curve Algorithm with Diffie Helman Key Exchange (ECDH). Other cryptographic standards can also be used, such as RSA. In some embodiments, the keypairs are randomly seeded. As will be described in more detail below, each message Alice sends (whether to Bob or anyone else) can be encrypted with a unique, random key that is used only once then destroyed forensically by Alice (the sender'"'"'s) device. The forensic destruction ensures that the deleted keys cannot be recovered from Alice'"'"'s device, even via digital forensics methods.
At 254, a pool of keys (i.e., a number of keypairs equal to the size initialized at 252) is generated on client device 106. As mentioned above, the keypairs can be generated using Eliptic Curve Algorithm with Diffie Helman Key Exchange (ECDH). Other cryptographic standards can also be used, such as RSA.
At 256, a reference value is assigned for each of the respective keypairs. As one example, suppose fifty keypairs are generated at portion 254 of process 250. At 256, fifty respective reference values are assigned to each of the respective keypairs. The reference values will be used to distinguish the various keys in the pool of keys from one another and can be assigned to the keypairs in a variety of ways. As one example, a six digit random number can be generated by device 106 as the first reference value for the first keypair, and each subsequent reference value can be selected as an increment of the first reference value. As another example, every reference value can be randomly selected. Other schemes for selecting/assigning reference values can be employed at 256 as applicable.
At 258, the private keys and reference values are stored (e.g., in a secure database residing on device 106). As will be described in more detail below, the corresponding public keys will be transmitted to platform 102 (along with the associated reference values) and platform 102 will designate one of the public keys in the pool as a reserve key.
At 208, a device identifier (“deviceID”) is created from captured hardware information. Examples of captured hardware information include: hard drive identifiers, motherboard identifiers, CPU identifiers, and MAC addresses for wireless, LAN, Bluetooth, and optical cards. Combinations of information pertaining to device characteristics, such as RAM, CACHE, controller cards, etc., can also be used to uniquely identify the device. Some, or all, of the captured hardware information is run through a cryptographic hash algorithm such as SHA-256, to create a unique deviceID for the device. The captured hardware information can also be used for other purposes, such as to seed cryptographic functions.
At 210, Alice is asked, via an interface provided by app 116, to supply a desired username. Alice enters “Alice” into the interface. A determination is made as to whether the username is available. As one example, app 116 can supply a cryptographic hash of “Alice” to platform 102 for checking. If platform 102 does not already have a record for that hash, the username “Alice” is available for Alice to use. If platform 102 already has a record of that hash, Alice is instructed by the interface to pick an alternate username. Once Alice has selected an available username, she is asked to supply a password. As mentioned above, in some embodiments, portions of process 200 may be omitted (or performed by other entities, as applicable). For example, where a university student at ACME University is getting set up to use an ACME University-specific embodiment of platform 102, the user'"'"'s name may be preselected or otherwise issued by the University, rather than being selected by the user.
At 212, an application identifier (“appID”) is created. The appID is a unique identifier for the particular installation of the messaging app. If Alice installs the messaging app on multiple devices, each of her devices will have its own unique appID. (And, each of her devices will also have its own unique deviceID.) In some embodiments, the appID is created by hashing Alice'"'"'s selected password and other information such as device information.
Finally, at 214 Alice'"'"'s public keys (and reference values), deviceID, and appID are sent to platform 102 in a secure manner. As one example, in some embodiments app 116 is configured to communicate with platform 102 via TLS.
At the conclusion of process 200, Alice is ready to send and receive secure communications.
As mentioned above, alternate versions of processes 200 and/or 250 can be used in accordance with the techniques described herein. As one example, username/password selection (210) can be performed prior to other portions of process 200 (and can be performed by an entity other than the end user of the messaging application, e.g., where an employer determines a username for an employee). As another example, the random server seed generation (204) and random local seed generation (206) can be performed prior to the keypair generation (202), e.g., with the local seed being used in conjunction with the generating of the keypairs. As yet another example, portions of processes 200 and/or 250 can be combined and/or omitted as applicable. For example, instead of generating a pool of fifty key pairs (254), assigning reference values to the pool as a batch operation (256) and storing the keys/values as a batch operation (258), fifty iterations of a process that generates a key pair, assigns a reference value, and stores the information can be performed.
As mentioned above, security platform 102 is configured to facilitate the exchange of communications (e.g., among any/all of client devices 106-114). Also as mentioned above, platform 102 can be operated by a variety of entities on behalf of a variety of end users. For example, one embodiment of platform 102 can be made available to members of the public, whether as a public service, or for a fee. As another example, another embodiment of platform 102 can be made available by a business, by a school, by a charitable organization, etc., and its use limited to its employees/students/members, etc., as applicable. Additional detail regarding various aspects of embodiments of platform 102 will now be provided.
Security platform 102 includes one or more interface(s) 118 for communicating with client devices, such as client devices 106-114. As one example, platform 102 provides an application programming interface (API) configured to communicate with apps installed on client devices, such as app 116 and app 138. Platform 102 can also provide other types of interfaces, such as a web interface, or stand alone software programs for desktops and laptops, running on various Operating Systems (OSes). The web interface can allow users of client devices such as client devices 108 and 110 to exchange messages securely (whether with one another or other users), without the need for a separately installed messaging application. The stand alone software program allows users to exchange secure messages via software that is downloaded by each user. As will be discussed in more detail below (e.g., in Section G), in various embodiments, platform 102 makes available (e.g., via one or more interface(s) 118) a master clock time. The master clock time can be used, in various embodiments, to enforce secure time-to-live (TTL) values of messages. The TTL values can be used to enforce (e.g., on behalf of a message sender) time constraints on message access (e.g., by a recipient).
Security platform 102 also includes a database 120. Included in database 120 is a record for each user of platform 102. Each record has associated with it information such as the user'"'"'s public key pool and associated reference values, deviceID(s), appID(s), and messages. As shown in
Finally, security platform 102 includes a processing engine 134 which performs a variety of tasks, including interacting with database 120 on behalf of interface(s) 118. As will be described in more detail below, one task performed by platform 102 (e.g., by processing engine 134) is to designate one of the keys in the pool of public keys (e.g., received from Alice at the conclusion of portion 214 of process 200) as a “reserve” key. Another task performed by platform 102 (e.g., processing engine 134) is to facilitate the addition of new keys to a user'"'"'s key pool as the keys are used. Yet another task performed by platform 102 (e.g., processing engine 134) is to dynamically adjust the size of a user'"'"'s key pool as needed.
The embodiment of platform 102 depicted in
Whenever platform 102 is described as performing a task, either a single component or a subset of components or all components of platform 102 may cooperate to perform the task. Similarly, whenever a component of platform 102 is described as performing a task, a subcomponent may perform the task and/or the component may perform the task in conjunction with other components.
Returning back to Alice'"'"'s desire to send a message to Bob: at the conclusion of Section A above, Alice has successfully registered her username (“Alice”) with security platform 102. And, Bob is also a user of platform 102. Suppose Alice would like to send a message to Bob. She starts app 116 and is presented with an interface that includes a “compose” option. Alice selects the compose option and is presented with a message composition interface.
An example message composition interface is shown in
If Alice is satisfied with her message, she can send it to Bob by clicking the send button (314). If she wishes to cancel out of composing the message, she can click the cancel button (312). Suppose Alice clicks send button (314) after composing the message shown in interface 300. An example of the events that occur, in some embodiments, in conjunction with Alice sending a message is illustrated as process 400 in
At 404, a random symmetric encryption key is generated (e.g., by app 116 on device 106). As one example, the symmetric key is an AES 256 bit key. At 406, the symmetric encryption key is used to encrypt the message body, any attachments, and any message control options. In some embodiments, Alice'"'"'s own information (e.g., public key(s) and associated reference value(s), deviceID(s), and appID(s) are included in the DSB as well. Finally, at 408, the symmetric key is encrypted with the particular public key of each recipient (obtained from the pool of public keys). A DSB encapsulation is then generated, and contains the aforementioned components and reference values of the public keys used to encrypt the symmetric key. Examples of the DSB format are provided in Section D below.
In some cases, a user may own multiple devices. For example, Bob may be the owner of device 114 and 112, both of which are configured with secure messaging apps. Each of Bob'"'"'s installations will have its own deviceID and appID. When the DSB is created, each of Bob'"'"'s devices will be considered a separate device under the same username account.
The generated DSB is securely transmitted to platform 102 (e.g., by being encrypted with a symmetric key shared by the app and platform 102, and also encapsulated by TLS as an additional security layer). Irrespective of how many recipients Alice designates for her message (and, e.g., how many recipients there are or how many devices Bob has), only one DSB will be created and transmitted to platform 102. Upon receipt of the DSB, processing engine 134 opens the DSB and determines the recipients of the message. Specifically, the processing engine 134 performs a match against the deviceIDs (in a cryptographic hash and camouflaged representation) included in the DSB and the deviceIDs stored in database 120 as well as the username (in a cryptographic hash and camouflaged representation) in the DSB and the ones stored in the database 120. A cryptographic hash and camouflaged representation means that the hash algorithm (i.e. SHA256) that is used for the deviceID, username, and appID values, is further camouflaged, in some embodiments, by taking multiple hashes of the result values (i.e. multiple rounds of SHA256 of the previous SHA256 value—i.e. SHA(SHA(SHA(SHA . . . ))). Processing engine 134 also creates an entry for the received DSB in message table 132 and notifies the recipient(s) that a new message is available. In various embodiments, other actions are also performed by platform 102 with respect to the DSB. As one example, platform 102 can be configured to remove the DSB as soon as the recipient successfully downloads it. As another example, platform 102 can enforce an expiration time (e.g., seven days) by which, if the DSB has not been accessed by the recipient, the DSB is deleted. Where multiple recipients are included in a DSB, platform 102 can be configured to keep track of which recipients have downloaded a copy of the DSB, and remove it once all recipients have successfully downloaded it (or an expiration event has occurred).
DSB 500 also includes, for each message recipient 1-n, the key Ek1,1 encrypted by each of the recipient'"'"'s respective particular public keys (as shown in region 508). Further, DSB 500 includes a combination of each recipient'"'"'s respective deviceID, hashed username, appID, and the reference value associated with the particular public key (collectively denoted HWk11-n) in region 510. These constituent parts are also referred to herein as “parameters.” Additional detail regarding the parameters is shown in
In some embodiments (e.g., as is shown in
As mentioned above, Bob is also a user of platform 102. When Bob loads his copy of the messaging app on his smartphone (i.e., app 138 on device 114), the app communicates with platform 102 (e.g., via interface 118) to determine whether Bob has any new messages. As will be described in more detail below, platform 102 will also determine how many additional keypairs Bob'"'"'s device should generate to replenish his pool, and facilitate the generation of those keypairs. Since Alice has sent a message to Bob since he last used app 138, a flag is set in database 120, indicating to app 138 that one or messages are available for download.
At 1004 (i.e., assuming the decryption was successful), hardware binding parameters are checked. As one example, a determination is made as to whether device information (i.e., collected from device 114) can be used to construct an identical hash to the one included in the received DSB. If the hardware binding parameters fail the check (i.e., an attempt is being made to access Alice'"'"'s message using Bob'"'"'s keys on a device that is not Bob'"'"'s), contents of the DSB will be inaccessible, preventing the decryption of Alice'"'"'s message. If the hardware binding parameter check is successful, the device is authorized to decrypt the symmetric key (i.e., using Bob'"'"'s private key generated at 202) which can in turn be used to decrypt Alice'"'"'s message (1006). As will be described in more detail below (e.g., in Section G), additional controls can be applied (e.g., by Bob'"'"'s app 138) to Bob'"'"'s ability to access Alice'"'"'s mes sage.
The following are examples of processes that can be performed by various entities present in environment 100, such as platform 102 and devices 106 and 114 in various embodiments (whether as alternate versions of or additional processes to those described above). The processes can also be performed outside of environment 100, e.g., by other types of platforms and/or devices.
At 1104, a number of keypairs is generated. In this example, a number of asymmetric keypairs equal to the initialization value received at 1102 (e.g., fifty) is generated. In some embodiments, the keypairs are randomly seeded.
At 1106, reference values (e.g., usable to uniquely identify each of the key pairs and described in more detail above) are assigned for each of the keypairs generated at 1104.
At 1108, the private key portion of the key pairs (i.e., the fifty private keys) and associated reference values are securely stored locally (e.g., on device 106). As one example, the private keys are inserted into a database resident on device 106 and secured using an AES key derived from the password selected by Alice at portion 210 in process 200.
Finally, at 1110, the public key portion of the key pairs (i.e., the fifty public keys) and associated reference values are securely transmitted to platform 102. As mentioned above, platform 102 will designate one of the fifty keys as a reserve key (e.g., by setting a flag associated with that particular key).
At 1204, a public key is received (e.g., by device 114 from platform 102) along with the reference value associated with the key.
At 1206, the received public key is used to encrypt information, such as a message, or other information (e.g., a symmetric key which in turn is used to encrypt the message). The key reference value associated with the received public key is included in the message metadata or otherwise incorporated into the message payload.
Finally, at 1208, device 114 sends the message (e.g., to platform 102 for retrieval by Alice). Note that using techniques described, Alice'"'"'s device(s) need not be online (e.g., connected to platform 102) at the time Bob composes and/or sends messages to her.
For each retrieved message (at 1304), read the respective key reference value (e.g., included in the respective message as metadata), retrieve the appropriate private key (i.e., having the key reference value) from local storage on device 106, and decrypt the message(s).
At 1306, device 106 generates additional keypairs (i.e., to replenish public keys used from the pool on platform 102 by Bob). The number of keys to be generated can be determined in a variety of ways. As one example, device 106 can generate a number of new keypairs equal to the number of messages she received at 1302. As another example, device 106 can be instructed (whether by platform 102 or local instructions) to generate the lesser of: A: (the number of messages downloaded at 1302 * V), where (V) is a variable impacting the desired expansion rate of the server cache size (e.g. 0.9); or B: the initialization value (e.g., 50 keys, as discussed at 1102 in process 1100).
At 1308 (similar to 1106), reference values (e.g., usable to uniquely identify each of the key pairs and described in more detail above) are assigned for each of the keypairs generated at 1308.
At 1310 (similar to 1108), the private key portion of the key pairs (i.e., the new private keys) and associated reference values are securely stored locally (e.g., on device 106). As one example, the private keys are inserted into a database resident on device 106 and secured using the password selected by Alice at 210 in process 200.
Finally, at 1312 (similar to 1110), the public key portion of the key pairs (i.e., the new public keys) and associated reference values are securely transmitted to platform 102. In this example, suppose Alice'"'"'s reserve key was not depleted. The key originally designated as her reserve key remains present on platform 102 and remains designated as the reserve key. Now suppose Alice'"'"'s reserve key was depleted (e.g., because Bob and/or other users of platform 102 sent Alice more than fifty messages prior to her connecting to platform 102). The first 49 messages addressed to Alice would make use of those public keys in her pool not designated as the reserve key. Any additional messages sent to Alice before she can replenish her pool will all make use of her reserve public key (i.e., messages 50, 51, and 52—whether from Bob or others, will all make use of the same public key for Alice—her reserve key). As will be explained below, when Alice'"'"'s pool has been deleted (i.e., her reserve key is being used), a flag will be set on platform 102 indicating that, in conjunction with her next execution of process 1300 (or portions thereof, as applicable), a new key should be designated as the reserve key, and the existing reserve key be destroyed. Additional actions can also be taken (e.g., by platform 102) in response to Alice depleting her key pool, such as by increasing the size of her pool.
At 1404, the device receives the current server key cache count (i.e., the number of keys presently in the platform'"'"'s pool for the user). At 1406, the device generates an appropriate number of keypairs (and reference values) and stores/transmits them in accordance with the techniques described above. Further, in the event the server key cache count is zero (i.e., the reserve key is being used by platform 102 due to key pool depletion), one of the newly generated keys will be designated by the server as a replacement reserve key and the old reserve key will be destroyed.
As mentioned above, one example of a message control a sender can specify for a message is a limit on the time period (also referred to herein as a “time-to-live” or “TTL”) during which a recipient is able to access the message (e.g., to view, listen to, or otherwise interact with the message and any attachments). In scenarios such as where the sender is using an embodiment of platform 102 operated by an enterprise on behalf of its employees, the TTL may be selected by an entity other than the sender (e.g., based on a default corporate policy, or based on administrator configurable rules implemented by an enterprise-specific version of the secure messaging application). For example, messages sent by employees to one another can have a first default TTL, and messages sent by employees to vendors (also using the enterprise-specific application) can have a second default TTL. As another example, messages sent by certain employees (e.g., within a particular department such as the legal department, or having certain titles or positions) can be given different default TTLs. In various embodiments, the default TTL can be overridden, if permitted by an administrator configuration.
The TTL is encrypted and sent together with the secure message. When the recipient opens the message (e.g., taps or clicks on the message in an app), the message is decrypted and displayed on the recipient'"'"'s device. The corresponding TTL is decrypted, and in some embodiments converted into a message expiry time by adding the TTL (e.g., expressed in seconds) to the current time. In various embodiments, the TTL is stored in the recipient'"'"'s device'"'"'s secure database and encrypted to prevent tampering with the secure TTL by the device'"'"'s user. As will be described in more detail below, the current time can also be secured (e.g., against attempts by the recipient to thwart the TTL by adjusting a clock on the recipient'"'"'s device). Once the TTL has expired, the message is no longer accessible to the recipient (e.g., is removed from the recipient'"'"'s viewing interface and deleted from the recipient'"'"'s device'"'"'s secure database, along with any associated decryption keys).
The sender (or sender'"'"'s application, as applicable, e.g., where configured by an enterprise administrator) can specify time limits in a variety of ways. As one example, the sender can set a maximum duration (e.g., a one day limit), with the time limit countdown commencing when the recipient first opens the message. The time limit countdown can also be commenced when the sender sends the message. As another example, the sender can specify a fixed start time (e.g., for embargo purposes) before which the recipient is unable to access the message, even if the recipient is already in possession of the message. Once the embargo period ends, as with above, a TTL value can control how long the recipient is able to view the message once opened. This allows, for example, a company to release company news to multiple shareholders in a secure, time-controlled manner, with each shareholder having the same opportunity to open the message at the same start time. This also allows an enterprise to implement rules (e.g., via an enterprise-specific version of the secure messaging application/platform 102) that only allow employees to open messages during certain periods of the day. (E.g., hourly workers can only read messages during business hours; salaried workers have no such prohibition.) As yet another example, the sender can specify a fixed end time after which the recipient is unable to access the message (irrespective of whether the message was also given an “upon opening” TTL, e.g., of ten minutes). Further, in various embodiments, a sender of the message can shorten a limit on an already sent message. For example, if Bob sends Alice a message with a one day limit, and Alice opens that message, Bob can subsequently revoke Alice'"'"'s ability to continue to read the message (even though the day has not passed) by interacting with his app (e.g., by long pressing on the sent message as it appears to Bob and selecting an “expire now” (immediately expiring the message) or “expire faster” (expiring the message at a new time picked by Bob) option, as applicable).
At 1906, the message expiration time (“Expire Time”) is set as the Current Time (determined at 1904) with the TTL (e.g., 3600 seconds) added. Thus for example, when Alice opens message 1610 (e.g., at 1:26 pm), a Current Time is obtained from platform 102 (or another appropriate external time source), and a TTL of 3600 is added to the Current Time, resulting in an Expire Time of 2:26 pm.
At 1908, a determination is made as to whether the Current Time is greater than the Expire Time. If not (1910), Alice is able to view the message (1912), and after a period of time (e.g., one second elapsing), another check of the Current Time vs. the Expire Time is performed (1908). In various embodiments, the Current Time continues to be obtained from an external source (e.g., device 106 contacts platform 102 every second). In other embodiments, app 116 is responsible for maintaining the Current Time, at least a portion of the time, after performing an initial check with platform 102 of the Current Time upon message open. In some embodiments, if a Current Time cannot be obtained from an external source (e.g., platform 102 or another server) during the ongoing checking of portion 1908, the message will cease being available to Alice. So, for example, if Alice temporarily loses connectivity during the one hour window of time Bob has allowed her to read message 1610, Alice will be unable to read message 1610 during that portion of the hour. In some embodiments, the TTL countdown continues, irrespective of whether Alice is offline, meaning that Alice will not be given additional time to view the message to compensate for the period her device lacked connectivity. Eventually (e.g., after one hour has elapsed), the Current Time will exceed the Expire Time (1914), at which point the message is deleted (1916).
Although the foregoing embodiments have been described in some detail for purposes of clarity of understanding, the invention is not limited to the details provided. There are many alternative ways of implementing the invention. The disclosed embodiments are illustrative and not restrictive.