Discouraging screen capture

Screen capture mitigation is disclosed. The presence of a first finger is detected in a first area of a display. In response to the detection, content id displayed. A determination is made that the position of the first finger has changed. A determination is made that the distance by which the first finger has changed position exceeds a tolerance. The content is ceased to be displayed in response to the determination that the tolerance has been exceed.

BACKGROUND OF THE INVENTION

Users of electronic devices increasingly desire to communicate privately and securely with one another. As one example, a sender of a message may desire that the message be read and immediately deleted after viewing by the recipient. Unfortunately, many devices natively support an ability to capture a screen shot of what is being viewed on the device. An unscrupulous recipient of a confidential message could use the screen shot feature to preserve a copy of message, against the wishes of the sender.

DETAILED DESCRIPTION

FIG. 1illustrates an embodiment of an environment in which the exchange of secure communications is facilitated by a security platform (e.g., security platform102). In the environment shown inFIG. 1, a “digital security bubble” (DSB), described in more detail below, encapsulates or is otherwise provided around a message. The DSB allows information such as encryption information, hardware binding information, message security controls, and decryption information—for multiple recipients—to securely travel with the message. Further, the DSB provides cross-platform support. For example, techniques described herein can be deployed on a variety of operating systems (e.g., Linux, iOS, and Windows), on a variety of smart phone platforms (e.g., iPhone, Android, Windows, Blackberry, etc.), and on a variety of device types (e.g., mobile smart phones, tablets, laptops, desktops, etc.). Using techniques described herein, only intended accounts on intended devices are able to decrypt the messages. Thus, for example, the security platform is unable to decrypt messages.

Users of client devices, such as client devices106-114communicate securely with one another using techniques described herein. As shown inFIG. 1, client devices include personal computers (110), laptop computers (108), tablets (106), and mobile telephony devices (112,114). Some client devices, e.g., tablet device106, make use of techniques described herein via a messaging application (also referred to as an “app”) obtained from a software distribution server106. Examples of software distribution servers (which can comprise a single server or multiple servers working in cooperation) include app stores (e.g., provided by Apple, Google, Blackberry, Microsoft, and Blackberry) and other webservers offering app downloads. Client devices can also make use of a web interface (e.g., provided by platform102) instead of or in addition to a dedicated messaging application. Other types of devices not depicted inFIG. 1can also be used in conjunction with the techniques describe herein, such as game consoles, video players (e.g., incorporating DVD, Blu-ray, Red Laser, Optical, and/or streaming technologies) and other network-connected appliances, as applicable.

Communications are exchanged via one or more networks (depicted collectively inFIG. 1as network cloud104). Such networks can include wired, wireless, cellular, and satellite networks. And, such networks can be closed/private networks, as well open networks (e.g., the Internet). Further, as used herein, “communications” and “messages” can take a variety of forms, including: text messages, documents, audiovisual files, SMSes, voice and video calls. Further, the content can pertain to electronic transactions such as credit card security, password protection, directories, and storage drive protection, video on demand security, online gaming, gambling, electronic distribution of music, videos, documents, online learning systems, databases, cloud storage and cloud environments, bank transactions, voting processes, military communications, security of medical records, communication between medically implanted devices and doctors, etc. As will be described in more detail below, the exchange of communications is facilitated by security platform102.

Suppose a user of client device106(hereinafter referred to as “Alice”) would like to send a secure message to her friend, Bob (a user of client device114) 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 server106). Bob similarly obtains an appropriate application suitable for his client device114(e.g., an Android-based smartphone) from an appropriate location (e.g., the Google Play store). In some embodiments, client devices make use of a web-based application (e.g., made available by platform102through interface118), instead of, or in addition to, a dedicated installed application.

Once Alice's tablet106has obtained a copy of the 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 inFIG. 1as app116(installed on device106). Examples of events that can occur during an installation/initialization/registration process (200) are illustrated inFIG. 2and will now be described.

In some embodiments, process200is performed on a client device, such as Alice's client device106. The process begins at202when a public/private keypair for the application is generated, on client device106(e.g., using RSA, ECDH, or any other asymmetric encryption algorithms). As one example, the keypair can be generated using Eliptic Curve Algorithm with Diffie Helman Key Exchange (ECDH). Other cryptographic standards can also be used, such as RSA. At204, a “random server seed” is generated, and at206, a “random local seed” is generated. The seeds are used in conjunction with cryptographic key generation, and in some embodiments, the seeds are determined based on captured hardware information (described in more detail below).

At208, 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.

At210, Alice is asked, via an interface provided by app116, 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, app116can supply a cryptographic hash of “Alice” to platform102for checking. If platform102does not already have a record for that hash, the username “Alice” is available for Alice to use. If platform102already 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.

At212, 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, at214Alice's public key, deviceID, and appID are sent to platform102in a secure manner. As one example, in some embodiments app116is configured to communicate with platform102via TLS. At the conclusion of process200, Alice is ready to send and receive secure communications, described in Sections C and E below, respectively.

B. Security Platform

As mentioned above, security platform102is configured to facilitate the exchange of communications (e.g., among any/all of client devices106-114). Additional detail regarding various aspects of platform102will now be provided.

Security platform102includes one or more interface(s)118for communicating with client devices, such as client devices106-114. As one example, platform102provides an application programming interface (API) configured to communicate with apps installed on client devices, such as app116and app138. Platform102can 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 (OS). The web interface can allow users of client devices such as client devices108and110to 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.

Security platform also includes a database120. Included in database120is a record for each user of platform102. Each record has associated with it information such as the user's public key, deviceID(s), appID(s), and messages. As shown inFIG. 1, database120is relational and stores information in a variety of tables, including a table of hashed usernames (124), a table of public keys (126), a table of deviceIDs (128), a table of appIDs (130), and a table of messages (132). Other techniques can also be used to store the information used by platform102. For example, messages can be stored in a separate storage136instead of being stored within database120.

Finally, security platform102includes a processing engine134which performs a variety of tasks, including interacting with database120on behalf of interface(s)118. The embodiment of platform102depicted inFIG. 1comprises standard commercially available server hardware (e.g., having a multi-core processor(s), 8G+ of RAM, gigabit network interface adaptor(s), and hard drive(s)) running a typical server-class operating system (e.g., Linux). In various embodiments, platform102is implemented across a scalable infrastructure comprising multiple such servers, solid state drives, and/or other applicable high-performance hardware.

Whenever platform102is described as performing a task, either a single component or a subset of components or all components of platform102may cooperate to perform the task. Similarly, whenever a component of platform102is described as performing a task, a subcomponent may perform the task and/or the component may perform the task in conjunction with other components.

C. Sending DSB Secured Messages

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 platform102. And, Bob is also a user of platform102. Suppose Alice would like to send a message to Bob. She loads app116and 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 inFIG. 3. In particular,FIG. 3depicts interface300as rendered on an example tablet device106, connected to the Internet via an appropriate connection, such as: 3G, 4G or higher cellular connection, WiFi, Satellite, wireless or wired LANs, Bluetooth, etc. Tablet device106includes a touchscreen. An on-screen keyboard is provided for Alice in region306. Alice can enter the usernames of one or more recipients in region302. She can enter message text in region304. Alice can optionally add attachments by interacting with buttons shown in region308. Examples of attachments include, but are not limited to: documents, pictures, and audiovisual clips. By selecting button310, Alice can specify various message control options, such as: the lifetime/expiration of the message; on which device(s) it can be unencrypted/read; and sharing, saving, forwarding, recalling, and deleting options.

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 interface300. An example of the events that occur, in some embodiments, in conjunction with Alice sending a message is illustrated as process400inFIG. 4and will now be described.

FIG. 4illustrates an example of a process for sending a DSB-secured message. In some embodiments, process400is performed on a client device, such as Alice's client device106. The process begins at402when the public key, deviceID, and appID of a recipient are obtained from platform102. As will be explained in more detail below, the recipient's public key, deviceID and appID are used in the encryption of the symmetric key used to encrypt data, and in the DSB encapsulation of the message for the hardware/appID binding of the message. As one example, app116can request the information from platform102via an API (e.g., interface118). In some embodiments, the information is retrieved when Alice enters the recipient's name into region302. In other embodiments, the information is retrieved when Alice clicks send button314, or at any other appropriate time (e.g., while she is composing a message). In the example shown inFIG. 3, Alice is only sending a message to Bob. If she also desires to send the message to other recipients, she can enter their names in region302as well, and their respective public keys, deviceIDs, and appIDs will also be retrieved at402.

At404, a random symmetric encryption key is generated (e.g., by app116on device106). As one example, the symmetric key is an AES 256 bit key. At406, 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., her public key, deviceID(s), and appID(s) are included in the DSB as well. Finally, at408, the symmetric key is encrypted with the public key of each recipient. A DSB encapsulation is then generated, and contains the aforementioned components. 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 device114and112, 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 platform102(e.g., by being encrypted with a symmetric key shared by the app and platform102, 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 platform102. Upon receipt of the DSB, processing engine134opens the DSB and determines the recipients of the message. Specifically, the processing engine134performs a match against the deviceIDs (in a cryptographic hash and camouflaged representation) included in the DSB and the deviceIDs stored in database120as well as the username (in a cryptographic hash and camouflaged representation) in the DSB and the ones stored in the database120. 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 engine134also creates an entry for the received DSB in message table132and notifies the recipient(s) that a new message is available. In various embodiments, other actions are also performed by platform102with respect to the DSB. As one example, platform102can be configured to remove the DSB as soon as the recipient successfully downloads it. As another example, platform102can 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, platform102can 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).

FIG. 5illustrates an example of a digital security bubble (DSB). DSB500is an example of output that can be generated by app116as a result of executing process400. In the example shown, DSB500includes a message and optional attachments (502), and one or more message controls (504) encrypted with a key Ek1,1(encrypted portion506). In some embodiments, key Ek1,1is generated by app116at portion404of process400. Additional detail regarding portion506is shown inFIG. 7, where SSK inFIG. 7is Ek1,1ofFIG. 5and represents the sender's symmetric shared key used to encrypt the message and attachments.

DSB500also includes, for each message recipient1-n, the key Ek1,1encrypted by each of the recipient's respective public keys (as shown in region508). Further, DSB500includes a combination of each recipient's respective deviceID, hashed username, and appID (collectively denoted HWk1-n) in region510. These constituent parts are also referred to herein as “parameters.” Additional detail regarding the parameters is shown in FIG.9—namely, a plurality of parameters (such as hashed username, deviceID, and appID) are encrypted using SK2, which is a symmetric key generated by the client and shared with platform102.

In some embodiments (e.g., as is shown inFIG. 5), a spreading function is used to spread the encrypted symmetric keys inside the DSB (as shown in region512), by spreading the bits of the encrypted key in a spreading function generated pattern, with the default function being a sequential block or data. The spreading function also contains the cryptographic hashed representation of the recipient usernames that are used by the server to identify the recipients of the message and to set the message waiting flag for each of them. Finally, the DSB is itself encrypted using key Ek1,2(encrypted portion514), which is a symmetric key shared between app116and platform102. Additional detail regarding portions514and508are shown inFIG. 8, where SK1inFIG. 8is Ek1,2inFIG. 5and represents the symmetric encryption key shared by the app and platform102, and where User1Pubkey inFIG. 8is Ek2,1inFIG. 5and represents the recipient's public key (e.g., generated at202).

FIGS. 6-9illustrate additional examples of the construction of an embodiment of a DSB.FIG. 6illustrates an example of a DSB600. DSB600encapsulates three subcomponents—part700(the encrypted message, attachments, and controls), part800(the symmetric key encrypted with each recipient's public key), and part900(encrypted message parameters). As with DSB500, a symmetric key (shared by app116and platform102) is used to secure the DSB. In addition, the transmission of the DSB to the server is encapsulated with TLS for an additional security layer.FIG. 7illustrates part700of DSB600. In particular, part700includes the message controls (702), message (704), and attachments (706). Part700is encrypted using a shared symmetric key SSK (e.g., Ek1,1).FIG. 8illustrates part800of DSB600. In particular, part800includes the shared symmetric key, encrypted to each of the recipients' respective public keys. Further, the collection of encrypted keys (802-806) is encrypted using symmetric key SK1.FIG. 9illustrates part900of DSB600. In particular, part900includes encrypted message parameters. Part900is encrypted using symmetric key SK2.

E. Receiving DSB Secured Messages

As mentioned above, Bob is also a user of platform102. When Bob loads his copy of the messaging app on his smartphone (i.e., app138on device114), the app communicates with platform102(e.g., via interface118) to determine whether Bob has any new messages. Since Alice has sent a message to Bob since he last used app138, a flag is set in database120, indicating to app138that one or messages are available for download.

FIG. 10illustrates an example of a process for accessing a message included inside a digital security bubble. In some embodiments, process1000is performed on a client device, such as Bob's client device114. The process begins at1002when a DSB is received. As one example, a DSB is received at1002when app138contacts platform102, determines a flag associated with Bob's account has been set, and downloads the DSB from platform102. In such circumstances, upon receipt of the DSB, client114is configured to decrypt the DSB using Bob's private key (e.g., generated by Bob at202in process200).

At1004(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 device114) 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 at202) which can in turn be used to decrypt Alice's message.

F. Discouraging Screen Capture

As explained above, in addition to text messages (e.g., shown in region304ofFIG. 3), users can compose messages that include a variety of multi-media attachments (e.g., by interacting with region308ofFIG. 3). Returning to the example ofFIG. 3, suppose Alice attached a picture of her dog, Fido, to the message prior to sending to Bob. As explained above, and as illustrated inFIGS. 5 and 7, attachments to her message (i.e., the dog photograph) will also be encrypted, and can only be decrypted by intended recipients.

Some devices, such as tablet device106and phone114provide native support for users of those devices to capture their screens. As one example, a user of an iOS device can capture what is being displayed on the device by holding down the menu button and, while the button is being held, also pressing the power/lock button. Alice may wish for Bob to be able to view her dog photograph for a limited time, and then have it no longer available to him. Unfortunately, if Bob uses the built-in screen capture feature of his phone while viewing Alice's picture, he'll be able to save a copy for later viewing.

In some embodiments, messaging app138is configured to help mitigate screen capture attempts by users. An example of the process is shown inFIG. 12. In some embodiments, process1200is performed on a client device, such as Bob's client device114. The process begins at1202when x,y coordinates of one or more fingers are detected in an appropriate region. As one example, portion1104of interface1100includes a message to Bob, asking him to place his finger on icon1104in order to view Alice's dog picture. When Bob does so, the x,y coordinates of his finger will be detected (at1202).

The x,y coordinates are checked every time they change (for example, when the finger touching the icon moves). If the move is more than a few pixels (e.g., more than 10 pixels), this can be indicative of a user attempting to manipulate the device and take a screen shot while also holding down icon1104. The attachment preview will accordingly end (at1204) if the change in finger position is too great, minimizing the possibility of a receiver taking unauthorized screen shots of attachments received in a secure message. Once an attachment preview has ended in this manner, in some embodiments, the user can view the attachment again (so long as it has not expired) by placing and holding a finger steady in region1104.

In some embodiments, the number of pixels by which a finger may move without being considered an attempted screen capture is adjustable by the sender. For example, a sender can allow for more pixels (less sensitive) or fewer pixels (more sensitive) depending on the desired sensitivity. The number of pixels can also be determined by the application (e.g., based on the native resolution of the device, or other characteristics of the device, etc.).

In some embodiments, multiple screen areas or screen figures are required to be touched. This forces the user to hold more than one finger to tap and hold an area or areas, making it even more difficult to attempt to take a screen shot with the device.