Source: http://www.patentgenius.com/patent/8694769.html
Timestamp: 2019-01-16 13:50:04
Document Index: 641020337

Matched Legal Cases: ['Application No. 06101249', 'Application No. 2', 'Application No. 06101249', 'Application No. 06101249', 'Application No. 2', 'Application No. 2']

System and method for controlling data communications between a server and a client device - Patent # 8694769 - PatentGenius
8694769 System and method for controlling data communications between a server and a client device
Inventor: Bajar, et al.
U.S. Class: 713/150; 380/259; 380/270; 380/277; 380/278; 380/284; 709/237; 713/151; 713/152; 713/153; 713/165
Field Of Search: ;713/150; ;713/151; ;713/152; ;713/153; ;713/165; ;380/259; ;380/270; ;380/277; ;380/278; ;380/279; ;380/280; ;380/281; ;380/282; ;380/283; ;380/284; ;380/285; ;380/286; ;709/237
Foreign Patent Documents: 2575622; 1253797; 1816822; 2414145
Other References: European Communication Under Rule 51(4) EPC, Application No. 06101249.8, dated Sep. 21, 2007. cited by applicant.
Canadian First Office Action, Application No. 2,576,622, dated Feb. 8, 2010. cited by applicant.
European Search Report, Application No. 06101249.8, dated Jul. 11, 2006. cited by applicant.
United States Notice of Allowance, U.S. Appl. No. 11/346,255, dated Nov. 8, 2010. cited by applicant.
United States Office Action Response and Request for Continued Examination, U.S. Appl. No. 11/346,255, dated Oct. 4, 2010. cited by applicant.
United States Office Action, U.S. Appl. No. 11/346,255, dated Aug. 4, 2010. cited by applicant.
United States Office Action Response, U.S. Appl. No. 11/346,255, dated May 25, 2010. cited by applicant.
United States Office Action, U.S. Appl. No. 11/346,255, dated Feb. 26, 2010. cited by applicant.
United States Office Action Response and Request for Continued Examination, U.S. Appl. No. 11/346,255, dated Feb. 12, 2010. cited by applicant.
United States Office Action Response, U.S. Appl. No. 11/346,255, dated Jan. 18, 2010. cited by applicant.
United States Office Action, U.S. Appl. No. 11/346,255, dated Nov. 18, 2009. cited by applicant.
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United States Advisory Action Befoe the Filing of an Appeal Brief, U.S. Appl. No. 11/346,255, dated Jan. 29, 2010. cited by applicant.
European Deciision to Grant, Application No. 06101249.8, dated Feb. 28, 2008. cited by applicant.
United States Patent No. 7,904,709 entitled "System and Method for Controlling Data Communications Between a Server and a Client Device", issued Mar. 8, 2011. cited by applicant.
Co-pending U.S. Appl. No. 13/024,634 entitled, "System and Method for Controlling Data Communications Between a Server and a Client Device", filed Jun. 9, 2011. cited by applicant.
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Notice of Allowance, U.S. Appl. No. 13/024,634, dated Sep. 22, 2011. cited by applicant.
EP Response to European Search Report/Written Opinion for EP Patent No. 1,816,822,filed on Sep. 19, 2006. cited by applicant.
Canadian Notice of Allowance, Application No. 2,576,622, dated Jan. 5, 2012. cited by applicant.
1. A server comprising a processor and a memory, wherein the processor is configured to: encrypt data using a first key, wherein the encrypted data is decryptableusing a second key stored on a client device; transmit the encrypted data to the client device; receive stop data from the client device, wherein the stop data represents a command to the server, and wherein the stop data is pre-encoded using acryptographic operation; determine, based on the stop data, that the encrypted data was not decrypted using the second key by the client device; and cease transmitting data encrypted with the first key to the client device.
7. The server of claim 1, wherein the processor is configured to receive, from the client device, data other than the stop data, and wherein the stop data is encrypted using a same encryption key that is used to encrypt the data other than thestop data.
12. A server comprising a processor and a memory, wherein the processor is configured to: encrypt data using a first key, wherein the encrypted data is decryptable using a second key stored on a client device; transmit the encrypted data tothe client device; receive stop data from a device remote from both the server and the client device, wherein the stop data represents a command to the server, and wherein the stop data is pre-encoded using a cryptographic operation; determine, basedon the stop data, that the encrypted data was not decrypted using the second key by the client device; and cease transmitting data encrypted with the first key to the client device.
13. A method of controlling data communications between a server and a client device, the method comprising: encrypting data using a first key, wherein the encrypted data is decryptable using a second key stored on a client device; transmitting the encrypted data from the server to the client device; receiving stop data from the client device, wherein the stop data represents a command to the server, and wherein the stop data is pre-encoded using a cryptographic operation; basedon the stop data, determining, using a processor of the server, that the encrypted data was not decrypted using the second key by the client device; ceasing transmission of data encrypted with the first key to the client device.
Some devices, including some mobile devices for example, receive data that may be pushed to them by a server. For example, a system may comprise a central message server that receives messages, such as electronic mail ("e-mail") messages,addressed to a number of users. The system may, for example, further comprise support components for wireless communications such as a message management server, which processes messages that are received at the central message server and pushes themessages to mobile devices operated by the users. Generally, while messages may be stored on the central message server, the message management server may be used more specifically to control when, if, and how messages are to be sent to mobile devices. In this manner, messages may be forwarded to the users of mobile devices as they are received at the central message server, or in accordance with some other predefined schedule, or at some predefined interval, for example.
Where a server, such as the message management server, is adapted to push message data or other data to a mobile device, in some known implementations, the data is transmitted to the mobile device via a shared network infrastructure (e.g. thepublic Internet) and a wireless network. Such transmissions may be susceptible to interception and unauthorized access. In order to protect the confidentiality of these transmissions, data may be encrypted at the server prior to transmission, to besubsequently decrypted after the data is received at the mobile device. A key that is capable of decrypting encrypted data received from the server is usually stored on the mobile device. The key is typically downloaded to the mobile device during asynchronization process with a desktop computer, or when the mobile device is initially made ready for use, for example.
In the event that the key required to decrypt encrypted data received from the server is deleted, or becomes otherwise inaccessible, the received encrypted data cannot be decrypted until access to the key is restored. Furthermore, the server,unaware that the key has been deleted from the mobile device or has become otherwise inaccessible, may continue to push encrypted data to the mobile device. However, if, for example, the mobile device has been configured to discard data that it cannotdecrypt, some data transmitted by the server to the mobile device may be lost.
Embodiments of systems and methods described herein relate generally to data communication between a server and a client device (e.g. a mobile device), where the server is adapted to encrypt data using a first key, and to transmit encrypted datato the client device for decryption using a second key. In one example embodiment, the data is encrypted using a symmetric encryption technique, and accordingly, the first key for encrypting data and the second key for decrypting data may be the same.
More specifically, embodiments of systems and methods described herein relate generally to a technique where stop data, which when processed by the server, indicates to the server that there is at least some encrypted data that has been receivedby the client device from the server which could not be decrypted using the second key (e.g. as may be the case when the second key has been deleted from a key store on the client device). This stop data can be transmitted (e.g. by the client device) tothe server. Upon receiving the stop data, the server may, for example, withhold the transmission of data encrypted with the first key to the client device until the second key is restored on the client device. Alternatively, for example, the server mayretransmit certain data to the client device once the second key is restored on the client device or once a new set of keys for encoding and/or decoding data communications is provided to the server and client device.
In one broad aspect, there is provided a method of controlling data communications between a server and a client device, wherein the server is adapted to encrypt data using a first key and transmit encrypted data to the client device fordecryption using a second key, the method comprising the steps of: providing stop data which, when processed by the server, indicates to the server that encrypted data received by the client device from the server was not decrypted using the second key;receiving, at the client device, encrypted data from the server; attempting, at the client device, to decrypt encrypted data received at the receiving step using the second key; and if the encrypted data was not decrypted using the second key,transmitting the stop data to the server for processing.
In another broad aspect, a data index (e.g. a packet identifier) that identifies encrypted data that could not be decrypted using the second key is transmitted with the stop data to the server. This may facilitate the retransmission of data tothe client device that might have been lost, for example.
Embodiments of the systems and methods described herein make reference to a client device. In some embodiments, the client device is a mobile device. A mobile device is a two-way communication device with advanced data communicationcapabilities having the capability to communicate with other computer systems. A mobile device may also include the capability for voice communications. Depending on the functionality provided by a mobile device, it may be referred to as a datamessaging device, a two-way pager, a cellular telephone with data messaging capabilities, a wireless Internet appliance, or a data communication device (with or without telephony capabilities). A mobile device communicates with other devices through anetwork of transceiver stations.
Referring first to FIG. 1, a block diagram of a mobile device in one example implementation is shown generally as 100. Mobile device 100 comprises a number of components, the controlling component being microprocessor 102. Microprocessor 102controls the overall operation of mobile device 100. Communication functions, including data and voice communications, are performed through communication subsystem 104. Communication subsystem 104 receives messages from and sends messages to awireless network 200. In this example implementation of mobile device 100, communication subsystem 104 is configured in accordance with the Global System for Mobile Communication (GSM) and General Packet Radio Services (GPRS) standards. The GSM/GPRSwireless network is used worldwide and it is expected that these standards will be superseded eventually by Enhanced Data GSM Environment (EDGE) and Universal Mobile Telecommunications Service (UMTS). New standards are still being defined, but it isbelieved that they will have similarities to the network behavior described herein, and it will also be understood by persons skilled in the art that the invention is intended to use any other suitable standards that are developed in the future. Thewireless link connecting communication subsystem 104 with network 200 represents one or more different Radio Frequency (RF) channels, operating according to defined protocols specified for GSM/GPRS communications. With newer network protocols, thesechannels are capable of supporting both circuit switched voice communications and packet switched data communications.
Short-range communications subsystem 122 provides for communication between mobile device 100 and different systems or devices, without the use of network 200. For example, subsystem 122 may include an infrared device and associated circuitsand components for short-range communication. Examples of short range communication would include standards developed by the Infrared Data Association (IrDA), Bluetooth, and the 802.11 family of standards developed by IEEE.
The particular design of communication subsystem 104 is dependent upon the network 200 in which mobile device 100 is intended to operate, thus it should be understood that the design illustrated in FIG. 2 serves only as one example. Signalsreceived by antenna 154 through network 200 are input to receiver 150, which may perform such common receiver functions as signal amplification, frequency down conversion, filtering, channel selection, and analog-to-digital (A/D) conversion. A/Dconversion of a received signal allows more complex communication functions such as demodulation and decoding to be performed in DSP 160. In a similar manner, signals to be transmitted are processed, including modulation and encoding, by DSP 160. TheseDSP-processed signals are input to transmitter 152 for digital-to-analog (DIA) conversion, frequency up conversion, filtering, amplification and transmission over network 200 via antenna 156. DSP 160 not only processes communication signals, but alsoprovides for receiver and transmitter control. For example, the gains applied to communication signals in receiver 150 and transmitter 152 may be adaptively controlled through automatic gain control algorithms implemented in DSP 160.
LAN 250 comprises a number of network components connected to each other by LAN connections 260. For instance, a user's desktop computing device ("desktop computer") 262a with an accompanying cradle 264 for the user's mobile device 100 issituated on LAN 250. Cradle 264 for mobile device 100 may be coupled to computer 262a by a serial or a Universal Serial Bus (USB) connection, for example. Other user computers 262b are also situated on LAN 250, and each may or may not be equipped withan accompanying cradle 264 for a mobile device. Cradle 264 facilitates the loading of information (e.g. PIM data, private symmetric encryption keys to facilitate secure communications between mobile device 100 and LAN 250) from user computer 262a tomobile device 100, and may be particularly useful for bulk information updates often performed in initializing mobile device 100 for use. The information downloaded to mobile device 100 may include certificates used in the exchange of messages. Theprocess of downloading information from a user's desktop computer 262a to the user's mobile device 100 may also be referred to as synchronization.
It will be understood by persons skilled in the art that user computers 262a, 262b will typically be also connected to other peripheral devices not explicitly shown in FIG. 4. Furthermore, only a subset of network components of LAN 250 areshown in FIG. 4 for ease of exposition, and it will be understood by persons skilled in the art that LAN 250 will comprise additional components not explicitly shown in FIG. 4, for this example configuration. More generally, LAN 250 may represent asmaller part of a larger network [not shown] of the organization, and may comprise different components and/or be arranged in different topologies than that shown in the example of FIG. 4.
For example, message management server 272 may: monitor the user's "mailbox" (e.g. the message store associated with the user's account on message server 268) for new e-mail messages; apply user-definable filters to new messages to determine ifand how the messages will be relayed to the user's mobile device 100; compress and encrypt new messages (e.g. using an encryption technique such as Data Encryption Standard (DES) or Triple DES) and push them to mobile device 100 via the shared networkinfrastructure 224 and wireless network 200; and receive messages composed on mobile device 100 (e.g. encrypted using Triple DES), decrypt and decompress the composed messages, reformat the composed messages if desired so that they will appear to haveoriginated from the user's computer 262a, and reroute the composed messages to message server 268 for delivery.
Certificates may be used in the processing of encoded messages, such as e-mail messages. An encoded message may be an encrypted message, or a digitally signed message, for example. While Simple Mail Transfer Protocol (SMTP), RFC822 headers,and Multipurpose Internet Mail Extensions (MIME) body parts may be used to define the format of a typical e-mail message not requiring encoding, Secure/MIME (S/MIME), a version of the MIME protocol, may be used in the communication of encoded messages(i.e. in secure messaging applications). S/MIME enables end-to-end authentication and confidentiality, and provides data integrity and privacy from the time an originator of a message sends a message until it is decoded and read by the messagerecipient. Other known standards and protocols may be employed to facilitate secure message communication, such as Pretty Good Privacy.TM. (PGP), variants of PGP such as OpenPGP, and others known in the art.
Secure messaging protocols such as S/MIME rely on public and private encryption keys to provide confidentiality and integrity, and on a Public Key Infrastructure (PKI) to communicate information that provides authentication and authorization. Data encrypted using a private key of a private key/public key pair can only be decrypted using the corresponding public key of the pair, and data encrypted using a public key of a private key/public key pair can only be decrypted using the correspondingprivate key of the pair. Private key information is never made public, whereas public key information is shared.
An encoded message may be encrypted, signed, or both encrypted and signed. The authenticity of public keys used in these operations is validated using certificates. A certificate is a digital document issued by a certificate authority (CA). Certificates are used to authenticate the association between users and their public keys, and essentially provides a level of trust in the authenticity of the users' public keys. Certificates contain information about the certificate holder, withcertificate contents typically formatted in accordance with an accepted standard (e.g. X.509). The certificates are typically digitally signed by the certificate authority.
User computers 262a, 262b can obtain certificates from a number of sources, for storage on computers 262a, 262b and/or mobile devices (e.g. mobile device 100). These certificate sources may be private (e.g. dedicated for use within anorganization) or public, may reside locally or remotely, and may be accessible from within an organization's private network or through the Internet, for example. In the example shown in FIG. 4, multiple PKI servers 280 associated with the organizationreside on LAN 250. PKI servers 280 include a CA server 282 for issuing certificates, a Lightweight Directory Access Protocol (LDAP) server 284 used to search for and download certificates (e.g. for individuals within the organization), and an OnlineCertificate Status Protocol (OCSP) server 286 used to verify the revocation status of certificates.
Embodiments of systems and methods are described herein that relate generally to data communications between a server (e.g. message management server 272 of FIG. 4) and a client device (e.g. mobile device 100 of FIG. 4). These datacommunications are typically encrypted to protect the confidentiality of data transmitted between the server and the client device.
In particular, before data is transmitted by the server to the client device, it may be encrypted with a first key accessible to the server. The first key is typically stored on the server. When the client device receives the encrypted datafrom the server, the client device decrypts the data with a second key accessible to the client device. The second key is typically stored on the client device, in a key store. The key may have been downloaded to the client device duringsynchronization (e.g. via cradle 264 of FIG. 4 coupled to a desktop computer 262a of FIG. 4) or at a time when the client device is initially made ready for use, for example. The first and second keys are related to each other, such that data encryptedwith the first key can only be decrypted with the second key.
Alternatively, a public key encryption technique may be employed, where the first and second keys may form a private key/public key pair associated with the client device. For example, data to be transmitted by the server to the client deviceis encrypted using the first key, which is a public key of the client device. The encrypted data can only be decrypted using the second key, which is a corresponding private key of the client device, expected to be known only to the client device. Aseparate private key/public key pair associated with the server may also exist, where the public key may be used to encrypt data to be transmitted by the client device to the server and where the corresponding private key may then be used to decrypt thatdata at the server, for example.
It will be understood that data communications between the server and the client device may be encrypted without specific regard to the nature of the type of data being communicated. For example, the data being communicated between the serverand the client device may comprise message data associated with a message (e.g. an e-mail message) that is addressed to a user of the client device, and that message may or may not itself be encrypted (or signed). The keys used to encrypt datacommunications between the server and client device are to be distinguished from the keys associated with particular individuals that might have been used to encode specific messages being transmitted as part of those data communications. It will beunderstood that depending on the particular system and the role of the server vis-a-vis that of the client device, data communicated between the server and the client device will not be limited to message data, but may also, or alternatively, compriseone or more other types of data.
When data encrypted with a first key is transmitted by the server to the client device, and subsequently received by the client device, the client device will first attempt to decrypt the data so that it can be further processed at the clientdevice. This typically requires the corresponding second key to be retrieved from a key store on the client device for use in decrypting the encrypted data.
Where the second key is initially stored on the client device, in certain situations, the second key may subsequently be deleted from the client device, or become otherwise inaccessible, thereby resulting in the client device being unable todecrypt the encrypted data. Such situations may arise when, for example, new applications are loaded onto the client device, the operating system or other applications on the client device are updated, the client device is re-initialized so that it maybe used by a different user, or in other situations where a secure "wipe" of the client device is performed.
When any of these situations arise and result in the deletion of the second key, the client device will be unable to decrypt the received data encrypted with the first key that it has received from the server as well as any additional dataencrypted with the first key subsequently received from the server, until the corresponding second key is restored on the client device. Depending on the configuration of the client device, encrypted data received from the server that cannot bedecrypted may be automatically deleted at the client device and permanently lost.
In other configurations, data received from the server that cannot be decrypted may instead be stored in a queue. However, if a new key is loaded onto the client device to replace the deleted second key, it will typically not be possible todecrypt the queued data with the new key, and that data may effectively also be lost.
Moreover, in any event, a server that is unaware that the second key has been deleted from the client device or has become otherwise inaccessible may continue to push encrypted data to the client device, despite the fact that the client devicecannot decrypt the data. This type of problem may be particularly prevalent in "push-based" environments.
Accordingly, in one broad aspect, at least one embodiment of the systems and methods described herein is directed to means for informing the server that certain encrypted data being transmitted to the client device might not be capable of beingdecrypted by the client device. The server may then, at its option, withhold the transmission of the certain data to the client device and/or retransmit certain data.
Referring to FIG. 5, a flowchart illustrating steps in a method of controlling data communications between a server and a client device in a number of example embodiments is shown generally as 300. Some of the features of method 300 have beendescribed earlier in this description.
In particular, it is generally desirable to ensure that when keys are provided to the client device via a data transfer from another device to the client device, that the transfer be performed in a secure manner so as to prevent the keys frombeing read or copied without authorization during the transfer.
For example, where the client device is a mobile device, the keys provided to the client device at step 310 may be generated by the server or some other device in the system (e.g. host system 250), and then transmitted to a desktop device, fromwhich the keys can be downloaded to a mobile device via a cradle physically connected to the desktop device, or via some other form of private or secured connection.
The server is adapted to encrypt data using a first key of the keys provided at step 310, to be transmitted to the client device. After the encrypted data is transmitted by the server to the client device and subsequently received by the clientdevice, an attempt to decrypt the encrypted data at the client device will be made (e.g. see step 340 described below) using a second key of the keys provided at step 310.
If the data transmitted by the server to the client device is encrypted using a symmetric encryption technique, then the first and second keys may be a single key that is used both to encrypt and decrypt data. In that case, data transmitted bythe client device to the server may also be encrypted with the second key, for subsequent decryption by the server using the first key.
On the other hand, if the data transmitted by the server to the client device is encrypted using a public key encryption technique, then the first and second key may be a public and private key respectively, of a public/private key pairassociated with the client device. Keys of a separate public/private key pair associated with the server may also be provided at step 310, with the public key of that pair being made accessible to the client device and the private key of that pair beingmade accessible to the server.
Typically, stop data will be stored directly on the client device. However, in a variant embodiment, stop data may be stored on another device. In that embodiment, when required, the client device may retrieve stop data from the other devicefor transmission to the server, or may direct that stop data be transmitted by the other device to the server.
Stop data, when received by the server, will indicate to the server that at least some data encrypted with the first key has been received by the client device that could not be decrypted using the second key at the client device. Receipt ofthe stop data by the server may suggest to the server that any subsequent transmissions of data encrypted with the first key to the client device might also not be capable of being decrypted by the client device. The stop data may be considered torepresent a command or request to the server to cease transmitting data encrypted with the first key to the client device. While a server receiving the stop data will typically be configured to honor the request immediately, it may instead ignore therequest under certain conditions or perform some other predefined action(s), for example.
The stop data need not be in any particular form (e.g. it can be garbage data), so long as the server can recognize the data as stop data when the server receives it. Typically, however, particularly where the server is adapted to communicatedata to multiple client devices, the stop data will need to be encoded by the client device, include some identifier of the client device, or be otherwise associated with the client device in some manner, in order to identify the client device from whichthe stop data is being transmitted.
In one embodiment, stop data provided to the client device is stored in a non-volatile memory or storage component on the client device. For example, if the client device is a mobile device (e.g. mobile device 100), then the stop data may bestored in FLASH memory (e.g. FLASH memory 108) or in a ROM (not shown).
Data communications made between the server and the client device may be performed in accordance with a packet-based protocol. In this case, the stop data may be contained in a data packet ("stop packet") that is stored on the client device.
In a number of embodiments, stop data is encoded such that it can be subsequently decoded by the server. If the stop data is contained in a stop packet, only the stop data itself may be encoded, or the entire stop packet (which may includeother data) may be encoded, for example.
In some embodiments, stop data may be stored in an encrypted form on the client device. In one example embodiment, the key that is to be used to encrypt data transmitted by the client device to the server is also used to encrypt the stop data. In another embodiment, a separate key may be used to encrypt the stop data, with the corresponding key required to decrypt the stop data being provided to the server (e.g. at step 310). By encrypting the stop data to the server, the security of thesystem is enhanced as it minimizes the risk that an attacker will be able to construct bogus stop data or a bogus stop packet to successfully deny service to the client device.
In a variant embodiment, stop data is stored in a digitally signed form on the client device, such that when the server receives it, the server will be able to verify that the stop data actually originated from the client device, therebyenhancing security of the system.
In embodiments where stop data is stored in an encoded (e.g. encrypted or signed) form on the client device, preferably the encoding is performed prior to storage such that the stop data is stored pre-encoded in a "ready-to-transmit" form, andwill not require further processing. This is because the key that is needed to encode the stop data (which in one embodiment is the same key that is used to encrypt data transmitted by the client device to the server) may subsequently become lost orotherwise inaccessible, making it impossible to encrypt the stop data at a later time. Typically, both the keys (at step 310) and the encoded stop data (at step 320) will be provided during the same provisioning process when the client device isinitialized (or re-initialized) for use. If the provisioning is performed securely, then the stop data will also be secure, as an attacker would not have access to the key used to encode the stop data in order to construct bogus stop data or a bogusstop packet.
In one embodiment, a key identifier is associated and stored with the stop data. The key identifier identifies the specific stop data stored on the client device that is to be transmitted to the server when the client device encountersencrypted data received from the server that it cannot decrypt with the second key (e.g. because the key has been deleted). For example, the key identifier may identify the second key, which has been deleted or become otherwise inaccessible.
At step 350, if the attempt to decrypt the encrypted data made at step 340 is successful, normal processing of the decrypted data will continue at step 360. After the data is further processed on the client device, data may be transmitted bythe client device to the server. In the meantime, additional data may also be received by the client device from the server (e.g. method 300 may be repeated from step 330).
However, if the attempt to decrypt the encrypted data made at step 340 is not successful, which may be the case when the second key is deleted or has become otherwise inaccessible on the client device for example, then at step 370, the stop datathat was provided to the client device at step 320 is located. As noted earlier, a key identifier identifying the second key may be used to locate the appropriate stop data that is to be transmitted to the server. As noted with reference to step 320,the stop data will typically be stored on the client device (e.g. in FLASH memory 108 of mobile device 100 or ROM).
In one embodiment, a data index, such as a packet identifier for example, is also transmitted to the server at step 380. The data index identifies encrypted data received by the client device that could not be decrypted. For example, the dataindex may indicate the first packet in an indexed series of packets that have been received by the client device that could not be decrypted.
Use of a data index enables the server to identify the data that could not be decrypted (the server may also assume that any subsequent encrypted data transmissions might also not be decrypted), so that when either the original second key isrestored on the client device or a new second key is provided to the client device (e.g. when the client device is reprovisioned with new keys), potentially lost data can be retransmitted. Accordingly, recovery of any data transmitted to the clientdevice between the time the second key was determined to be deleted or became otherwise inaccessible and the time the second key is restored or a new second key is provided to the client device is facilitated.
Stop data transmitted at step 380, when processed by the server, indicates to the server that at least some of the data encrypted with the first key has been received by the client device that could not be decrypted using the correspondingsecond key. Accordingly, as shown at step 390, the server, after receiving the stop data, may be adapted to stop sending data encrypted with the first key, until, for example, the second key is restored on the client device.
It will be understood that different sets of keys may be used to encrypt different types of data (e.g. associated with different services) that is transmitted by the server, and different stop data or packets may be associated with the differentdata types.
Accordingly, for example, at step 390, the server may stop transmitting data associated with one particular service to the client device upon receiving particular stop data, while the same server may continue to transmit data associated with adifferent service for which stop data has not been received from the client device.
In one embodiment, the server may be further adapted to ignore repeat instances of the same stop data being received at the server. This may provide enhanced security as it minimizes the risk that an attacker can intercept and retransmit thesame stop data to disrupt future transmissions between the server and the client device.
In one embodiment, the server may be further adapted to invalidate the first key once stop data associated with the corresponding second key is received. More specifically, after a second key is determined to have been deleted or otherwiseinaccessible on the client device, and the associated stop data is transmitted to the server (step 380), method 300 may be repeated from step 310, wherein new first and second keys to replace the previously provided keys are provided to the server andthe client device for use in encoding data communications between them. New stop data may also be provided to the client device at step 320, particularly if the stop data is to be encoded with one of the new keys.
The new keys may be used to encode and decode data that is retransmitted by the server to the client device (step not shown) that may have been lost. In one embodiment, as described above, the data to be retransmitted may be determined based ona data index transmitted with the stop data previously received by the server from the client device.
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