Abstract:
This specification describes technologies relating to imparting cryptographic information in network communications. In general, aspects of the subject matter described in this specification can be embodied in methods that include identifying a location in a pre-defined portion of a network communication to be sent in a client-server environment, wherein the pre-defined portion is reserved for random data, inserting cryptographic information into the pre-defined portion of the network communication at the location, and sending the network communication in the client-server environment to facilitate modifying interactions in the client-server environment based at least in part on a result of processing of the cryptographic information; and on a receiving side, receiving cryptographic information inserted into the pre-defined portion of the network communication in the client-server environment, identifying the location, processing the cryptographic information, and modifying interactions in the client-server environment based at least in part on a result of the processing.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of and claims the benefit of the priority of U.S. patent application Ser. No. 11/872,661, filed Oct. 15, 2007, and entitled “Imparting Cryptographic Information In Network Communications,” now issued as U.S. Pat. No. 7,961,878, which is hereby incorporated by reference. 
    
    
     BACKGROUND 
     The present disclosure relates to imparting cryptographic information in network communications. 
     A computer network is a collection of processing nodes coupled together with wired and/or wireless communication links. A computer network can be a single network or a collection of networks (e.g., an internetwork), and can use multiple networking protocols, including internetworking protocols (e.g., Internet Protocol (IP)). These protocols define the manner in which information is prepared for transmission through the network, and typically involve breaking data into segments generically known as packets (e.g., IP packets, ATM (Asynchronous Transfer Mode) cells) for transmission. These networking protocols are typically organized by a network architecture having multiple layers, where each layer provides communication services to the layer above it. The protocols can include shared-line protocols such as in Ethernet networks, connection-oriented switching protocols such as in ATM networks, and/or connectionless packet-switched protocols such as in IP. 
     Many computer networks use connectionless packet-switched protocols (e.g., IP). Packets are routed separately and can thus take different paths through the network. Various protocols have been built on top of connectionless packet-switched protocols, such as IP, to provide connection based communications over the underlying connectionless protocol. For example, Adobe Systems Incorporated has promulgated a communication protocol for the FLASH® Media Server in which a communication session is established through handshake communications between the server and the client. As part of this handshake, the Real Time Messaging Protocol (RTMP) included a random byte section in the communications for use in estimating the available bandwidth for the session between the client and the server. 
     SUMMARY 
     This specification describes technologies relating to imparting cryptographic information in network communications. In general, one aspect of the subject matter described in this specification can be embodied in a method that includes identifying a location in a pre-defined portion of a network communication to be sent in a client-server environment, wherein the pre-defined portion of the network communication is reserved for random data, inserting cryptographic information into the pre-defined portion of the network communication at the location, and sending the network communication in the client-server environment to facilitate modifying interactions in the client-server environment based at least in part on a result of processing of the cryptographic information. In addition, another aspect of the described subject matter can be embodied in a method that includes receiving cryptographic information inserted into a pre-defined portion of a network communication in a client-server environment, wherein the pre-defined portion of the network communication is reserved for random data, identifying a location of the cryptographic information in the pre-defined portion of the network communication, processing the cryptographic information, and modifying interactions in the client-server environment based at least in part on a result of the processing of the cryptographic information. Other embodiments of these aspects include corresponding systems, apparatus, and computer program products. 
     These and other embodiments can optionally include one or more of the following features. Identifying the location can include using at least part of the network communication to determine the location. The pre-defined portion can include the random data, and using at least part of the network communication to determine the location can include retrieving a portion of the random data, and determining an index into the pre-defined portion of the network communication based on the retrieved portion of the random data. Moreover, using at least part of the network communication to determine the location can include retrieving multiple different portions of the random data; and determining multiple different indices into the pre-defined portion of the network communication based on the different portions of the random data. 
     Processing the cryptographic information can include establishing a cryptographic key, and modifying interactions in the client-server environment can include initiating an encrypted session using the cryptographic key. In addition, processing the cryptographic information can include authenticating the network communication, and modifying interactions in the client-server environment can include turning on or off a feature of a program operating in the client-server environment. 
     According to another aspect, a system can include a server computer programmed to establish both non-encrypted sessions and encrypted sessions over a network, with client computers, using a session startup handshake including a network communication including a pre-defined portion reserved for random data; a first of the client computers programmed to establish non-encrypted sessions with the server computer using the session startup handshake; and a second of the client computers programmed to establish encrypted sessions with the server computer using the session startup handshake including cryptographic information inserted into the pre-defined portion of the network communication; wherein the server computer and the second client computer are programmed to perform operations including: identifying a location of the cryptographic information in the pre-defined portion of the network communication, processing the cryptographic information, and modifying interactions between the server computer and the second client computer based at least in part on a result of the processing of the cryptographic information. 
     The client computers can include mobile devices (such as mobile phones, game machines, personal digital assistants, and laptop computers) and stationary devices (such as workstations, desktop computers, and super computers). The operations can include the various operations of the method(s) described. Processing the cryptographic information can include authenticating the network communication, and establishing a cryptographic key; and modifying interactions between the server computer and the second client computer can include turning on or off a feature of a program operating in the server computer or the second client computer, and initiating an encrypted session between the server computer and the second client computer using the cryptographic key. Moreover, the server computer and the second client computer can be programmed to perform the operations comprising: inserting a message authentication code and encryption key establishment information into the network communication. 
     Particular embodiments of the subject matter described in this specification can be implemented to realize one or more of the following advantages. Encrypted sessions can be established using a method that reduces the risk of reverse engineering and is also backward compatible with an existing non-encrypted session establishment protocol. Encryption credentials can be established using the method, which credentials can be used to start an encrypted session, or to verify various other pieces of information. The method can resist reverse engineering since the credentials can be, in essence, hidden in plain sight within data that has been used for bandwidth detection. Moreover, the data (with cryptographic information hidden therein) can still be used for other purposes, such as for bandwidth detection or for holding other information. 
     The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages of the invention will become apparent from the description, the drawings, and the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows an example client-server environment in which cryptographic information is imparted in network communications. 
         FIG. 2  shows an example process of imparting cryptographic information in network communications. 
         FIG. 3  shows an example network communication. 
         FIG. 4  shows another example client-server environment in which cryptographic information is imparted in network communications for use in playing media content. 
         FIG. 5  shows an example process of imparting cryptographic information in network communications for use in establishing encrypted sessions and enabling/disabling features in a media player/server system. 
     
    
    
     Like reference numbers and designations in the various drawings indicate like elements. 
     DETAILED DESCRIPTION 
       FIG. 1  shows an example client-server environment  100  in which cryptographic information is imparted in network communications. The client-server environment  100  can support both encrypted and non-encrypted sessions, both of which can include the use of a handshake  150 , which can include authentication and other communication protocols. Cryptographic information can be included in a previously existing section of the handshake  150  known to contain random bytes, allowing the cryptographic information to remain hidden in plain sight since the cryptographic information appears random itself (due to the nature of the cryptographic information). Re-using the random byte section in this way can handicap reverse engineering attempts and provide interoperability with previously written software. 
     The client-server environment  100  includes a server computer  110 . For example, the server computer  110  can be the FLASH® Media Server provided by Adobe Systems Incorporated of San Jose, Calif. The server computer  110  can use a network  120  (e.g., the Internet) to communicate with one or more first client computers  130  and one or more second client computers  140 . The handshakes  150   a  and  150   b  precede the sessions  135  and  145  and can include cryptographic information from the server  110  that the client(s)  130  may not know is there. 
     The session startup handshakes  150   a  and  150   b  can include one or more bytes that denote the version of the protocol (e.g., the RTMP protocol) and other information used to open a socket and establish a session. The handshakes  150   a  and  150   b  can also include other information, such as the current time as reported by the operating system (e.g., the number of milliseconds since the system was launched). The handshakes  150   a  and  150   b  include a block of bytes that contain random data, and the block of bytes can also include information useable for authenticating the network communications between server and client, and information for establishing an encrypted session. Such cryptographic information can be sent by the server computer  110  and the client computer(s)  140 , but the client computer(s)  130  need not know that such information is present or be able to send such information. 
     The first client computer  130  can be a computer programmed to establish non-encrypted sessions with the server computer  110  using the session startup handshake  150   a . For example, the first client computer  130  can include an older version of the FLASH® Player program, which starts a session with the server computer (e.g., the FLASH® Media Server). The server  110  can include cryptographic information in the block of random data in a network communication forming part of the handshake  150   a . However, if the first client computer  130  fails to recognize this cryptographic information, and thus doesn&#39;t send appropriate return cryptographic information, the session  135  that is established with the server  110  is a non-encrypted session. Note that other aspects of the interactions between the server  110  and the client  130  can also be affected by this failure on the part of the computer  130 , since the server  110  knows after the handshake  150   a  that the computer  130  is running a legacy program that is not aware of the new cryptographic information portion of the communication protocol. 
     In contrast, the second client computer  140  can be a computer programmed to establish encrypted sessions with the server computer  110  using the session startup handshake  150   b . For example, the second client computer  140  can include a newer version of the FLASH® Player program, which starts an encrypted session with the server computer (e.g., the FLASH® Media Server). The server  110  can include cryptographic information in the block of random data in a network communication forming part of the handshake  150   b . The second client computer  140  can recognize this cryptographic information and send appropriate return cryptographic information. This then allows the session  145  that is established with the server  110  to be an encrypted session. Note that other aspects of the interactions between the server  110  and the client  140  can also be affected by the handshake  150   b , since the server  110  knows after the handshake  150   b  that the computer  140  is running a newer program that is aware of the new cryptographic information portion of the communication protocol. Thus, the cryptographic information used to establish encrypted sessions with new client programs can be added to an existing communication protocol used to establish non-encrypted sessions with old client programs, without the old client programs being aware of the newly added cryptographic information. 
       FIG. 3  shows an example network communication  300 . The network communication  300  can be used, for example, as part of the handshakes  150   a  and  150   b  that precedes the sessions  135  and  145 . The network communication  300  includes a pre-defined portion  310  that includes random data. In addition, the pre-defined portion  310  includes embedded cryptographic information at a location  320 . In this way, the cryptographic information can be hidden in plain sight. Using this technique can reduce the likelihood that reverse engineering is able to discover the details of the communication protocol. 
     The location  320  of cryptographic information within the pre-defined portion  310  can vary with implementation or within a given implementation. For example, the cryptographic information can be located at a pre-determined byte location, or a pre-determined byte location can contain a value from which the location  320  of cryptographic information can be determined. In some implementations, using cryptographic information can include the use of an encryption key establishment protocol, such as a Diffie Hellman key exchange or other suitable technique for establishing one or more symmetric or asymmetric encryption keys. In some implementations, using cryptographic information can include the use an encrypted hash method of authenticating a transmission or content, such as a Hash Message Authentication Code (HMAC). 
     In addition, although the location  320  of cryptographic information is shown in  FIG. 3  as being entirely contained within the pre-defined portion  310 , it will be appreciated that either the beginning or end of the cryptographic information can be at the beginning or end of the pre-defined portion  310 , e.g., adjacent to either a header  330  or a payload  340 . The header  330  and the payload  340  can be, for example, part of the communication protocol that does not require encryption, such as to identify the version of the RTMP protocol being used. Such information can be used in handshake communications in both directions between the server computer  110  and the client computers  130  and  140 . 
     The header  330  can include several pre-determined byte positions that can contain session information themselves or can identify byte locations of other information. For example, the FLASH® Player program can use a single byte to denote the version of the RTMP protocol. Such byte locations can depend, for example, on the version of the FLASH® Player program that a user has on a client device. Other specific byte positions can be used to identify the position of an HMAC and Diffie Hellman information. The payload  340  can include other information of the network communication  300 , such as parameters that can be used for establishing the session on the user&#39;s client device. For example, the payload  340  can include information about the session. In some implementations, the payload  340  can include checksum information that can be used to test the integrity of the payload  340  and/or the entire network communication  300 . 
       FIG. 2  shows an example process  200  of imparting cryptographic information in network communications. A pre-defined portion of a network communication, which includes random data, is received  210 . For example, the portion  310  can be received by the computer  140 . The location of cryptographic information in the pre-defined portion of the network communication can be identified  220 . For example, the computer  140  can use at least part of the network communication  300  to determine the location. This part of the network communication  300  can come from the portion  310 , from the header  330 , from the payload  340 , or combinations of these. In some implementations, one or more parts of the network communication  300  can be used as a coded integer from which an actual byte location can be calculated (e.g., using modulo calculations or other similar calculations). In some implementations, calculations can be based on pre-determined modulo divisors, or the byte lengths of certain blocks of the network communication can be used as the divisor in a modulo calculation. 
     The cryptographic information can be processed  230 . This can include establishing a cryptographic key, such as through Diffie Hellman key exchange. This can also include authenticating the network communication, such as through use of an HMAC. Interactions in the client-server environment can be modified  240  based at least in part on a result of processing the cryptographic information. Modifying the interactions can include turning on or off various features, such as editing, frame-based timelines, animation capabilities, shape primitives, development and/or language tools (e.g., JavaScript, ActionScript, etc.), sophisticated video tools, audio support, integration tools, conversion tools and rich drawing capabilities, to name a few examples. Modifying the interactions can include initiating an encrypted session using a cryptographic key. Note that the interactions in the client-server environment can also be based on identified capabilities of the client computer, since some features may be hardware dependent. 
       FIG. 4  shows another example client-server environment  400  in which cryptographic information is imparted in network communications for use in playing media content. The client-server environment  400  includes a client computer  402  and a media server  404 . The media server  404  can provide media content  406  to the client computer  402 . For example, media server  404  can include a FLASH® Media Server program. The media content  406  can include web applications, games and movies, and multimedia content for client computers (e.g., home personal computers, mobile phones, personal digital assistants, smart phones, or various embedded devices.) 
     The client computer  402  can include software, firmware and hardware. The hardware can include a computer readable medium  412 , a processor  414 , and one or more interface devices  416 . The computer readable medium  412  can include one or more hard drives, external drives, magnetic disks, optical disks, tape drives, memories devices, etc. The processor  414  can include one or more central processing units capable of interpreting computer program instructions and processing data, and each processing unit can include one or more processor cores. The interface devices  416  can include one or more display and audio devices (e.g., as computer screens, computer monitors, digital displays, liquid crystal displays (LCDs), light emitting diodes (LEDs), etc.) and audio-capable components (e.g., microphones, speakers, etc.). The interface devices  416  can support a graphical user interface (GUI) by which the user sees, hears and experiences the output of a media player application  408 . 
     The software/firmware can include the media player application  408  and an application execution environment  410 . For example, the media player application  408  can be a FLASH® Player program installed on a home computer or other electronic device. The media player application  408  can run in the application execution environment  410 , which can be an operating system (OS) for the computer  402 , or a cross-OS runtime environment installed on the computer  402 , such as the Adobe® Integrated Runtime (AIR™) environment available from Adobe System Incorporated of San Jose, Calif. 
     The random byte section that embeds the cryptographic information can be included in the network communications between the client computer  402  and the media server  404 . For example, the random byte section can be generated by a user&#39;s FLASH® Player program and by the FLASH® Media Server program. As noted above, cryptographic information (e.g., including Diffie Hellman key exchange and HMAC information) can be injected into the random byte section at pre-determined or program-determined locations. In some implementations, the locations can be determined by various algorithms, which can use pieces of the random data to index the locations of the cryptographic information. The receiving end of the communication, knowing the new protocol, can locate and remove the cryptographic information from the random byte section. If the cryptographic information can be verified, then the receiving side knows that the new protocol is being used. If the cryptographic information cannot be verified, one or more fallback positions can be checked before determining that the new protocol is not being used (because the expected cryptographic information cannot be found in the random byte section), and thus the communication is of a legacy type. Note that from the perspective of an external eavesdropper, the cryptographic information is seen as nothing more than the previously included random data, which can be used for bandwidth detection. 
       FIG. 5  shows an example process  500  of imparting cryptographic information in network communications for use in establishing encrypted sessions and enabling/disabling features in a media player/server system, such as the client-server environment  400 . The process  500  includes operations for authentication, determining encryption parameters, and turning on or off features associated with the network communication. For example, the network communication can involve a user employing a FLASH® Player program to play media available from the FLASH® Media Server program. In some implementations, features can be enabled or disabled based on version information that can be separate from the cryptographic information. For example, feature availability (e.g., audio or visual capabilities) may depend on the version of the FLASH® Player program installed on the user&#39;s client computer. 
     A first portion of the random data can be retrieved  502 . For example, in the network communication  300  sent by client computer, the server can look in a pre-determined byte position within the pre-defined portion  310 . A first index into the pre-defined portion can be determined  504  based on the retrieved first portion. For example, one or more bytes of the random data can be used as the dividend in a modulo operation, where the divisor is the length of the region of the pre-defined portion  310  set aside for a message authentication code (e.g., an HMAC), minus the length of the message authentication code. The first index can then be set equal to the remainder of this modulo operation plus a pre-defined offset (which may be zero). 
     Note that various combinations of the random data can be used to generate the dividend. For example, x bytes of the random data can be treated as a single binary number forming the dividend falling in the range of zero to 2 (8x) −1, or the same x bytes of the random data can be treated as x binary numbers that are added together to form the dividend falling in the range of zero to x(2 8 −1). Various other combinations of the random data are also possible. In addition, the first index can be determined from the first portion of the random data alone, or from the first portion in combination with other information retrieved from the network communication. For example, such other information can come from the header  330  or the payload  340 . 
     In any event, once the index is determined, this index corresponds to the starting position of the cryptographic information used for message authentication (e.g., the starting point of the HMAC) in the block of otherwise random data. The network communication is authenticated  506  using this cryptographic information. For example, the authentication can involve using the first index to access an HMAC in the network communication  300 . If the message authentication code is not confirmed  508 , then the process  500  can check  510  whether a fallback first portion is available. This occurs when the first index determined  504  fails to locate a message authentication code usable to authenticate  506  the network communication. 
     In this case, one or more fallback algorithms can be provided for retrieving  502  the first portion and determining  504  the first index. Each fallback algorithm can use a different technique for retrieving  502  the first portion and/or determining  504  the first index. determining  504  the first index. These fallback algorithms can provide additional security for the authentication process, allowing a server system to change the indexing technique when a currently used technique has been discovered, and the client computers can then automatically fall back to the new indexing technique. Once all available fallback algorithms have been tried, the process  500  ends without the network communication having been authenticated. 
     If the message authentication code is confirmed  508 , then a second portion of the random data is retrieved  512 . For example, in the network communication  300  sent by client computer, the server can look in another pre-determined byte position within the pre-defined portion  310 . A second index into the pre-defined portion can be determined  514  based on the retrieved second portion. For example, one or more bytes of the random data can be used as the dividend in another modulo operation, where the divisor is the length of the region of the pre-defined portion  310  set aside for encryption parameters (e.g., Diffie Hellman information), minus the length of the encryption parameters. The second index can then be set equal to the remainder of this modulo operation plus a pre-defined offset (which may be zero). 
     As with the message authentication code, various combinations of the random data can be used to generate the dividend. For example, x bytes of the random data can be treated as a single binary number forming the dividend falling in the range of zero to 2 8x −1, or the same x bytes of the random data can be treated as x binary numbers that are added together to form the dividend falling in the range of zero to x(2 8 −1). Various other combinations of the random data are also possible. In addition, the second index can be determined from the second portion of the random data alone, or from the second portion in combination with other information retrieved from the network communication. For example, such other information can come from the header  330  or the payload  340 . Moreover, it will be appreciated that the random data section needs to be larger than the total length of the message authentication code and the encryption parameters, e.g., larger than one hundred and sixty bytes when using a thirty two byte HMAC and one hundred and twenty eight bytes of Diffie Hellman information. 
     In any event, once the index is determined, this index corresponds to the starting position of the encryption parameters used for establishing a cryptographic key (e.g., the starting point of the Diffie Hellman information) in the block of otherwise random data. This cryptographic information in the network communication is confirmed  516 . This confirmation can involve using the second index to access and confirm encryption parameters in the network communication  300 . If the encryption parameters are not confirmed  518 , then the process  500  can check  520  whether a fallback second portion is available. This occurs when the second index determined  514  fails to locate encryption parameters usable to initiate encrypted communications in the client-server environment. 
     In this case, one or more fallback algorithms can be provided for retrieving  512  the second portion and determining  514  the second index. Each fallback algorithm can use a different technique for retrieving  512  the first portion and/or determining  514  the second index. Note that these algorithms can also be different than those used for the first index. These fallback algorithms can provide additional security for the encrypted session establishment process, allowing a server system to change the indexing technique when a currently used technique has been discovered, and the client computers can then automatically fall back to the new indexing technique. Once all available fallback algorithms have been tried, the process  500  ends without the encryption parameters having been confirmed. 
     If the encryption parameters are confirmed  518 , then a determination  522  can be made if an encrypted session is desired. For example, the encryption parameters can contain information that the session (e.g., session  145 ) is to be an encrypted session. If so, then the encrypted session is initiated  524 . Otherwise, an un-encrypted session can be initiated. Either session (e.g., encrypted or un-encrypted) can be between the client computer  402  (e.g., executing FLASH® Player program) and the media server  404  (e.g., FLASH® Media Server). 
     If it is determined  526  that one or more features are to be enabled or disabled, then one or more features of the media player, the media server or both, are turned on or off  528 . For example, a set of features can be turned on or off according to the version number of the client media player. This version number can be provided by the client media player (e.g., in non-encrypted and non-disguised form in the handshake  150 ), and the server can decide to trust the version number provided based on the fact that the client properly incorporated cryptographic information within the random byte section of a network communication (e.g., the client media player is not a legacy player that has been modified to improperly identify itself as a newer version). 
     Embodiments of the subject matter and the functional operations described in this specification can be implemented in digital electronic circuitry, or in computer software, firmware, or hardware, including the structures disclosed in this specification and their structural equivalents, or in combinations of one or more of them. Embodiments of the subject matter described in this specification can be implemented as one or more computer program products, i.e., one or more modules of computer program instructions encoded on a computer-readable medium for execution by, or to control the operation of, data processing apparatus. The computer-readable medium can be a machine-readable storage device, a machine-readable storage substrate, a memory device, a composition of matter effecting a machine-readable propagated signal, or a combination of one or more of them. The term “data processing apparatus” encompasses all apparatus, devices, and machines for processing data, including by way of example a programmable processor, a computer, or multiple processors or computers. The apparatus can include, in addition to hardware, code that creates an execution environment for the computer program in question, e.g., code that constitutes processor firmware, a protocol stack, a database management system, an operating system, or a combination of one or more of them. A propagated signal is an artificially generated signal, e.g., a machine-generated electrical, optical, or electromagnetic signal, that is generated to encode information for transmission to suitable receiver apparatus. 
     A computer program (also known as a program, software, software application, script, or code) can be written in any form of programming language, including compiled or interpreted languages, and it can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. A computer program does not necessarily correspond to a file in a file system. A program can be stored in a portion of a file that holds other programs or data (e.g., one or more scripts stored in a markup language document), in a single file dedicated to the program in question, or in multiple coordinated files (e.g., files that store one or more modules, sub-programs, or portions of code). A computer program can be deployed to be executed on one computer or on multiple computers that are located at one site or distributed across multiple sites and interconnected by a communication network. 
     The processes and logic flows described in this specification can be performed by one or more programmable processors executing one or more computer programs to perform functions by operating on input data and generating output. The processes and logic flows can also be performed by, and apparatus can also be implemented as, special purpose logic circuitry, e.g., an FPGA (field programmable gate array) or an ASIC (application-specific integrated circuit). 
     Processors suitable for the execution of a computer program include, by way of example, both general and special purpose microprocessors, and any one or more processors of any kind of digital computer. Generally, a processor will receive instructions and data from a read-only memory or a random access memory or both. The essential elements of a computer are a processor for performing instructions and one or more memory devices for storing instructions and data. Generally, a computer will also include, or be operatively coupled to receive data from or transfer data to, or both, one or more mass storage devices for storing data, e.g., magnetic, magneto-optical disks, or optical disks. However, a computer need not have such devices. Moreover, a computer can be embedded in another device, e.g., a mobile telephone, a personal digital assistant (PDA), a mobile audio player, a Global Positioning System (GPS) receiver, to name just a few. Computer-readable media suitable for storing computer program instructions and data include all forms of non-volatile memory, media and memory devices, including by way of example semiconductor memory devices, e.g., EPROM, EEPROM, and flash memory devices; magnetic disks, e.g., internal hard disks or removable disks; magneto-optical disks; and CD-ROM and DVD-ROM disks. The processor and the memory can be supplemented by, or incorporated in, special purpose logic circuitry. 
     To provide for interaction with a user, embodiments of the subject matter described in this specification can be implemented on a computer having a display device, e.g., a CRT (cathode ray tube) or LCD (liquid crystal display) monitor, for displaying information to the user and a keyboard and a pointing device, e.g., a mouse or a trackball, by which the user can provide input to the computer. Other kinds of devices can be used to provide for interaction with a user as well; for example, feedback provided to the user can be any form of sensory feedback, e.g., visual feedback, auditory feedback, or tactile feedback; and input from the user can be received in any form, including acoustic, speech, or tactile input. 
     embodiments of the subject matter described in this specification can be implemented in a computing system that includes a back-end component, e.g., as a data server, or that includes a middleware component, e.g., an application server, or that includes a front-end component, e.g., a client computer having a graphical user interface or a Web browser through which a user can interact with an implementation of the subject matter described is this specification, or any combination of one or more such back-end, middleware, or front-end components. The components of the system can be interconnected by any form or medium of digital data communication, e.g., a communication network. Examples of communication networks include a local area network (“LAN”) and a wide area network (“WAN”), e.g., the Internet. 
     The computing system can include clients and servers. A client and server are generally remote from each other and typically interact through a communication network. The relationship of client and server arises by virtue of computer programs running on the respective computers and having a client-server relationship to each other. 
     While this specification contains many specifics, these should not be construed as limitations on the scope of the invention or of what may be claimed, but rather as descriptions of features specific to particular embodiments of the invention. Certain features that are described in this specification in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination. 
     Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In certain circumstances, multitasking and parallel processing may be advantageous. Moreover, the separation of various system components in the embodiments described above should not be understood as requiring such separation in all embodiments, and it should be understood that the described program components and systems can generally be integrated together in a single software product or packaged into multiple software products. 
     Thus, particular embodiments of the invention have been described. Other embodiments are within the scope of the following claims. For example, the actions recited in the claims can be performed in a different order and still achieve desirable results. The random data need not be truly random data, but rather can be pseudo random data. Moreover, the pre-defined portion of the network communication need only be reserved for random data, but need not actually include random data in all implementations.