Abstract:
A method of recording messages includes recording audio data in a first file structured in accordance with a file format that defines a first portion and a second portion. The audio data is recorded in the first portion of the first file. The method also includes encrypting the audio data stored in the first portion of the first file and generating a second file structured according to the file format. The second file includes decoy audio data in the first portion of the second file and the encrypted audio data in the second portion of the second file. The decoy audio data indicates a confidential status of the second file or serves as a red herring to distract from the encrypted audio data in the second portion of the second file.

Description:
TECHNICAL FIELD OF THE INVENTION 
     This invention relates in general to communication systems, and more particularly to communicating confidential messages. 
     BACKGROUND OF THE INVENTION 
     Modern telecommunication systems provide users with a variety of features that increase convenience and ease of use. One such feature, “unified messaging,” allows users to access voicemail messages using any of several different clients. As a result, a user can use email applications and web browsers to access audio files associated with voicemail recorded for that user. 
     This increased accessibility may however lead to security risks. Although a voicemail server may be able to monitor and regulate access to voicemail messages that are designated as confidential by the sending party, copies of such voicemail messages may be forwarded to other applications, including non-voicemail applications, that are not aware of or capable of enforcing confidentiality restrictions associated with these voicemails. As a result, unintended recipients may receive and access confidential messages diminishing the overall usefulness of the voicemail system. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, the disadvantages and problems associated with voicemail security have been substantially reduced or eliminated. In particular, a system and method for generating and playing confidential voicemail messages is provided. 
     In accordance with one embodiment of the present invention, a method of recording messages includes recording audio data in a first file structured in accordance with a file format that defines a first portion and a second portion. The audio data is recorded in the first portion of the first file. The method also includes encrypting the audio data stored in the first portion of the first file and generating a second file structured according to the file format. The second file includes decoy audio data in the first portion of the second file and the encrypted audio data in the second portion of the second file. 
     In accordance with another embodiment of the present invention, a method of recording messages includes accessing encrypted audio data stored in a first file structured in accordance with a file format that defines a first portion and a second portion. Decoy audio data is stored in the first portion of the first file and the encrypted audio data is stored in the second portion of the first file. The method also includes decrypting the encrypted audio data and generating a second file that includes the decrypted audio data. The second file is structured according to the file format. The decrypted audio data is stored in the first portion of the second file. 
     Technical advantages of certain embodiments of the present invention include providing an effective technique for structuring data in a voicemail message to maintain its confidentiality. Other technical advantages of certain embodiments of the present invention include providing an efficient encryption technique that can reduce the amount of time and resources needed to encrypt confidential messages and that also provides meaningful information to unauthorized recipients attempting to access information in the confidential message. 
     Other technical advantages of the present invention will be readily apparent to one skilled in the art from the following figures, descriptions, and claims. Moreover, while specific advantages have been enumerated above, various embodiments may include all, some, or none of the enumerated advantages. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present invention and its advantages, reference is now made to the following description, taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  illustrates a communication system according to a particular embodiment of the present invention; 
         FIG. 2  illustrates a voicemail server that may be utilized in particular embodiments of the communication system; 
         FIG. 3  illustrates an example operation of a particular embodiment of the voicemail server in encrypting voicemail messages; and 
         FIG. 4  illustrates an example operation of a particular embodiment of the voicemail server in decrypting encrypted voicemail messages. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  illustrates a communication system  10  according to a particular embodiment of the present invention. As shown, communication system  10  includes a plurality of local area networks (LANs)  80  coupled by a Public Switched Telephone Network (PSTN)  50 . Each LAN  80  additionally couples a plurality of communication devices  60 , a voicemail server  20 , a call manager  30 , and a gateway  40  to one another and to PSTN  50 . Voicemail server  20  provides voicemail service for users of communication devices  60  and may utilize particular encrypting techniques that provide enhanced security for voicemail messages  90  generated by voicemail servers  20 . 
     Communication devices  60  may each represent any suitable combination of hardware, software, and/or encoded logic to provide communication services to a user. For example, communication devices  60  may represent telephones, computers running telephony software, video monitors, cameras, or any other communication hardware, software, and/or encoded logic that supports the communication of voice, video, text or other suitable forms of data using communication system  10 . In the illustrated embodiment, communication devices  60   a ,  60   b ,  60   d , and  60   e  represent Internet Protocol (IP) telephones and communication devices  60   c  and  60   f  represent telephony-enabled personal computers (PCs). Additionally, communication device  60   i  represents a mobile phone coupling to communication system  10  through PSTN  50 . Although  FIG. 1  illustrates a particular number and configuration of communication devices  60 , communication system  10  contemplates any number and arrangement of such components to support communication of media. 
     Gateways  40  each comprise any suitable combination of hardware and/or software that performs translation functions to facilitate seamless communication between PSTN  50  and LANs  80 . These functions may include translation between transmission formats and between communication procedures. In addition, gateways  40  may also translate between audio and video CODECs and perform call setup and clearing on both the LAN side and the PSTN side. For example, gateway  40   a  may interface call manager  30   a  with PSTN  50 . As a result, when a call is placed by communication device  60   g  using PSTN  50 , gateway  40   a  translates the call format associated with PSTN  50  to a call format associated with call manager  30   a , such as, for example, SIP or another suitable packet-based communication protocol. Although  FIG. 1  illustrates a particular embodiment of communication system  10  that includes particular types of networks, specifically LANs  80  and PSTN  50 , coupling particular components of communication system  10 , communication system  10  may include any appropriate types and numbers of networks. 
     Call managers  30  each comprise any suitable combination of hardware and/or software operable to establish a connection between a calling component of communication system  10  and a called component, such as, for example, connecting a call between communication devices  60  or between a particular communication device  60  and voicemail server  20 . In a particular embodiment, call managers  30  comprise Voice Over Internet Protocol (VoIP) servers that perform the functions of signaling and session management within a packet telephony network. The signaling functionality of call managers  30  allows call information to be carried across network boundaries. The session management functionality of call managers  30  provides the ability to control the attributes of an end-to-end call across multiple networks in communication system  10 . In a particular embodiment, the VoIP protocol supported by call managers  30  comprises SIP, which is a standard for multimedia conferencing over internet protocol. In this embodiment, call managers  30  comprise SIP proxy servers that handle call processing, SIP requests, and SIP responses. Although the following description of call managers  30  is detailed with respect to SIP, it should be understood that call managers  30  may support other IP telephony protocols instead, such as the H.323 protocol. In particular embodiments, call managers  30  may also provide a number of telephony services for communication devices  60  and other devices located in LAN  80 , including, but not limited to, call forwarding, teleconferencing, network monitoring, and codec translation. 
     Voicemail servers  20  support voicemail services for users of communication devices  60 . More specifically, voicemail servers  20  may generate voicemail messages, receive voicemails messages generated by other voicemail servers  20 , store received or generated voicemail messages, and/or provide users access to stored voicemail messages. Voicemail servers  20  may include any appropriate combination of hardware and/or software suitable to provide the described messaging functionality. The contents of a particular embodiment of voicemail server  20  are described in greater detail below with respect to  FIG. 2 . Although the description below focuses on a particular embodiment of communication system  10  that supports messaging in the form of voicemail, the described messaging techniques may be utilized in a communication system that uses any form of messaging including, but not limited to, voice, video, and text. Additionally, voicemail servers  20  may be configured to operate with a variety of different types of communication devices  60 . In particular embodiments of communication system  10 , users may access a particular voicemail server  20  to generate or retrieve voicemail using telephones, personal computers (PCs), and/or any other appropriate types of communication devices  60 . For example, in particular embodiments, users may utilize a browser running on a PC to access their voicemail account and may then play recorded voicemails on the PC. 
     PSTN  50  supports communication between LANs  80 . Additionally, PSTN  50  may be configured to provide connections between one or more LANs  80  and communication devices  60  (such as communication devices  60   g - i ) that are located external to LANs  80  and that connect to communication system  10  through PSTN  50 . In particular embodiments, PSTN  50  may represent all or a portion of the public switched telephone network or any other appropriate circuit-switched network. Moreover, PSTN  50  may include routers, hubs, switches, gateways, call controllers, and/or any other suitable components in any suitable form or arrangement. 
     LANs  80  comprise any suitable communication links that support packet-based communications. LANs  80  couple one or more communications devices  60 , a call manager  30 , and a voicemail server  20  to one another and to PSTN  50 . LANs  80  may include bridges, switches, and/or any appropriate hardware and or software to support packet-based communication between the coupled components. Although  FIG. 1  illustrates a particular embodiment of communication system  10  that includes particular types of networks, specifically LANs  80  and PSTN  50 , coupling particular components of communication system  10 , communication system  10  may include any appropriate types and numbers of networks. 
     In operation, communication system  10  provides communication services for users of communication devices  60 . As part of providing these communication services, a particular voicemail server  20  generates recorded voicemail messages or receives recorded voicemail messages from other voicemail servers  20 . For example, a user (referred to here as “the caller”) may use communication device  60   b  to call another user (referred to here as “the called party”) associated with communication device  60   a . If the called party does not answer communication device  60 , call manager  30   a  may forward the call to voicemail server  20   a . The caller may then record a message for the called party as audio data, and voicemail server  20   a  may generate a voicemail message  90  that includes the recorded audio data. 
     In a particular embodiment of communication system  10 , voicemail server  20   a  records voicemail message  90  in a particular audio file format. As described in greater detail with respect to  FIGS. 2 and 3 , this file format may include a first portion and a second portion, with particular types of information stored in each portion. For example, in particular embodiments, voicemail message  90  may represent a Resource Interchange File Format (RIFF) file, such as a WAV file, that includes a first RIFF block and one or more additional RIFF blocks. The first RIFF block may include audio data associated with the message recorded by the caller and one or more additional RIFF blocks of the WAV file may include format information and other types of information for use by WAV-file players accessing voicemail message  90 . As used here, the labels “first” and “second” are intended to merely distinguish the two different portions of the voicemail message  90  and are not intended to describe the relative position of the two portions within voicemail message  90 . In addition, the structure of voicemail message  90  may include more than two portions without departing from the scope of this disclosure. 
     Any component of communication system  10  that supports the relevant audio file format may play voicemail messages  90  once a user has retrieved voicemail messages  90  from voicemail server  20   a , providing users significant flexibility in accessing and disseminating voicemail messages  90 . For example, a user may access his or her voicemail accounts through web browser on a personal computer (PC) and play voicemail message  90  using appropriate software, such as a WAV-file player, running on the PC. Users may also forward voicemail messages  90  to other parties, including parties external to LAN  80 , for example, as an email attachment. As noted above, this flexibility may make it difficult for voicemail server  20   a  to prevent unauthorized parties from playing voicemail message  90 . 
     To prevent such unauthorized access, particular embodiments of communication system  10  may implement certain safeguards to reduce or eliminate the ability of unauthorized users to access voicemail messages  90  that the caller indicates are to remain confidential. In particular, the caller may be prompted, before or after recording voicemail message  90 , to indicate whether voicemail message  90  is to remain confidential. If voicemail message  90  is not intended to remain confidential, voicemail server  20   a  may record voicemail message  90 , as described above, and subsequently make the message available to the called party based on appropriate policies of communication system  10 . For example, after voicemail message  90  has been recorded, the called party may be able to access a voicemail account of the called party and play the voicemail message. In particular embodiments of communication system  10 , the called party may additionally be able to forward the non-confidential voicemail message to other users of communication system  10  without limitation and those other users may also be able to play the message. 
     If, instead, the caller indicates that the voicemail message  90  is to remain confidential, voicemail server  20   a  may encrypt voicemail message  90  generating encrypted voicemail message  92 , as indicated by arrow  96  in  FIG. 1 . As part of generating encrypted voicemail message  92 , voicemail server may restructure information included in voicemail message  90  to prevent elements of communication system  10  other than voicemail server  20   a  from being able to access the recorded message. 
     More specifically, voicemail server  20   a , in particular embodiments, generates voicemail message  90  in accordance with a particular audio file format that includes at least a first portion and a second portion, such as a WAV file, as described above. As also noted above, audio data associated with the message recorded by the caller may be stored in the first portion of the voicemail message  90 . If voicemail server  20   a  determines that voicemail message  90  is to remain confidential, voicemail server  20   a  may, after generating voicemail message  90 , encrypt voicemail message  90  to generate an encrypted voicemail message  92 , also in the audio file format. The encrypted voicemail message  92  may however include the audio data in the second portion of encrypted voicemail message  92 , instead of the first portion as was the case with voicemail message  90 . Voicemail server  20   a  may also encrypt the recorded message stored in encrypted voicemail message  92 . As a result of the file structure of encrypted voicemail message  92  and the encryption of the recorded message, components that support the audio file format may not be capable of accessing confidential information stored in encrypted voicemail message  92 . Additionally, voicemail server  20   a  may include a decoy message in the first portion of encrypted voicemail message  92 . In particular embodiments, the decoy message may include audio information that is readable by components that are capable of reading files formatted according to the relevant audio file format and may explain to a party (referred to here as an “unauthorized recipient”) that is not included among the original recipients of the encrypted voicemail message  92  that encrypted voicemail message  92  is a confidential message. Alternatively, decoy message may be a default message that is readable by components that are capable of reading files formatted according to the relevant audio file format and that is designed to sound like the message in a typical voicemail message thereby preventing the unauthorized recipient from learning that encrypted voicemail message  92  includes confidential information The encryption techniques utilized in particular embodiments of communication system  10  are described in greater detail below with respect to  FIG. 3 . 
     After generating and, if appropriate, encrypting voicemail message  90 , voicemail server  20   a  may then save the generated voicemail message  90  or encrypted voicemail message  92  in a voicemail account of the called party. Voicemail server  20   a  may save the message  90  or  92  in the relevant voicemail account by storing the message  90  or  92  in a portion of memory associated with the account, storing a pointer to the message  90  or  92  in a portion of memory associated with the account, attaching an identifier identifying the account to the message, or associating the message  90  or  92  with the account in any other appropriate manner. 
     The called party may subsequently access voicemail server  20   a  to listen to messages  90  or  92  saved in the called party&#39;s voicemail account. After any appropriate authentication of the identity of the called party, such as the receipt and verification of a Personal Identification Number (PIN), voicemail server  20   a  may play the recorded message  90  or  92  to the called party. If the message  90  or  92  represents an encrypted voicemail message  92 , voicemail server  20   a  may decrypt the encrypted voicemail message  92  to allow the called party to listen to the audio message encrypted in encrypted voicemail message  92 , as indicated by arrow  98  in  FIG. 1 . As part of decrypting encrypted voicemail message  92 , voicemail server  20   a  may access the recorded audio data stored in the second portion of encrypted voicemail message  92  and transmit this audio data to the called party to be played by a communication device  60  associated with the called party. If voicemail server  20  additionally encrypted the audio data stored in the second portion during encryption of encrypted voicemail message  92 , voicemail server  20   a  may also decrypt the audio data before transmitting the audio data to the relevant communication device  60 . The decryption techniques utilized in particular embodiments of communication system  10  are described in greater detail below with respect to  FIG. 4 . 
     If the called party attempts to forward an encrypted voicemail message  92 , using forwarding features of voicemail server  20   a  itself, to an unauthorized recipient, voicemail server  20   a  may determine encrypted voicemail message  92  is to remain confidential and prevent the called party from forwarding voicemail message  92  to the unauthorized recipient. Furthermore, as noted above, if the called party attempts to forward encrypted voicemail message  92  to the unauthorized recipient independent of voicemail server  20   a , for example, by forwarding encrypted voicemail message  92  as an email attachment, components of communication system  10  that support the audio file format of voicemail messages  90  may not be able to play the recorded message because the recorded message is stored in the second portion of encrypted voicemail message  92  and/or because the recorded message is encrypted. Such components may instead play the decoy message stored in the first portion of encrypted voicemail message  92 , which may, in particular embodiments, inform the unintended recipient that he or she is unable to access the recorded message because the recorded message is confidential. In particular embodiments, the decoy message may instead include a default message that sounds like a typical voicemail message when played by components of communication system  10  that support the audio file format of voicemail messages  90 . 
     As a result, particular embodiments of communication system  10  may reduce or eliminate the possibility that unauthorized recipients may access confidential messages without unnecessarily limiting access options for users of communication system  10 . As described below, particular embodiments of voicemail servers  20  may also utilize encryption techniques that result in faster encrypting and reduced computational complexity. Furthermore, particular voicemail servers  20  may generate encrypted voicemail messages  92  that provide an explanatory message indicating the voicemail is confidential when unauthorized recipients attempt to access the encrypted voicemail message  92  independent of voicemail servers  20 . As a result, particular embodiments of communication system  10  may provide a number of operational benefits. Various embodiments of communication system  10  may exhibit some, none, or all of these benefits. 
       FIG. 2  is a block diagram illustrating the contents of a particular embodiment of voicemail server  20 . As shown in  FIG. 2 , voicemail server  20  includes a processor  100 , a memory  110 , a network interface  120 , a key encryption module  130 , an audio encryption module  132 , a key lookup module  140 , a session key generation module  150 , a message recording module  160 , a message playback module  170 , a message forming module  180 , and a message extraction module  190 . Although  FIG. 2  illustrates particular components that are located within a particular embodiment of voicemail server  20 , any of key encryption module  130 , audio encryption module  132 , key lookup module  140 , session key generation module  150 , message recording module  160 , message playback module  170 , message forming module  180 , and message extraction module  190  may, in alternative embodiments, represent components external to voicemail server  20 . 
     Processor  100  may be a general purpose computer, dedicated microprocessor, or other processing device capable of communicating electronic information. Examples of processor  100  include application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), digital signal processors (DSPs) and any other suitable specific or general purpose processors. Memory  110  stores recorded messages  90  and  92  for users hosted by voicemail server  20 , public and private keys for users hosted by voicemail server  20 , code for processor  100 , and/or any other appropriate information, data, or instructions used by voicemail server  20 . Memory  110  may comprise any collection and arrangement of volatile or non-volatile, local or remote devices suitable for storing data such as, for example, random access memory (RAM) devices, read only memory (ROM) devices, magnetic storage devices, optical storage devices, or any other suitable data storage devices. 
     Network interface  120  comprises an interface operable to facilitate communication between the elements of voicemail server  20  and call manager  30 , communication devices  60 , and/or other components of communication system  10 . In a particular embodiment, network interface  120  supports VoIP communication using the Session Initiation Protocol (SIP) to establish communication sessions between voicemail server  20  and other elements of communication system  10 . Network interface  120  may include any appropriate combination of hardware and/or software suitable to provide this functionality. 
     Session key generation module  150  generates session keys  350  for use in encrypting the audio data of voicemail message  90 . Session key generation module  150  may use any appropriate algorithms for generating the session keys  350 . In particular embodiments, session key  350  generation module  150  generates, for each voicemail message  90  created by voicemail server  20 , a unique session key  350  for symmetric encryption and decryption of the audio data of voicemail messages  90 . Although, in  FIG. 2 , session keys  350  are shown, for purposes of illustration, as being stored in memory  110 , session key generation module  150  may, in particular embodiments, generate and use session keys  350  as needed during operation and may be configured to dispose of session keys  350  without saving them. 
     Audio encryption module  132  encrypts the audio data of voicemail messages  90  and decrypts the encrypted audio data of encrypted voicemail messages  92 . Audio encryption module  132  may utilize any appropriate encryption algorithms for encrypting and decrypting the audio data. In particular embodiments, audio encryption module  132  encrypts and decrypts audio data based on a symmetric encryption scheme using a session key  350  generated by session key generation module  150 . 
     Key encryption module  130  encrypts session keys  350  and decrypts encrypted session keys  370 . Key encryption module  130  may utilize any appropriate encryption algorithms for encrypting session keys  350  and decrypting encrypted session keys  370 . In particular embodiments, key encryption module  130  encrypts the session key based on an asymmetric encryption scheme using public and private keys obtained by key lookup module  140 . Although shown in  FIG. 2  as separate elements, key encryption module  130  and audio encryption module  132  may, in particular embodiments, represent a single component or module providing the functionality of both elements. 
     Key lookup module  140  identifies recipient public keys  340  for recipients during encryption of voicemail messages. Additionally, key lookup module  140  identifies recipient private keys  410  for recipients while decrypting voicemail messages. In particular embodiments, key lookup module  140  accesses a database that stores recipient private keys  340  and recipient public keys  410  for users hosted by voicemail server  20  and uses an identifier associated with the caller or called party, such as the phone number of a communication device  60  associated with the relevant party, a personal identification number (PIN) of the relevant party, or any other appropriate identifier, to identify the appropriate recipient private keys  340  and recipient public keys  410 . In particular embodiments, each user may be uniquely associated with a recipient private key  340  and a recipient public key  410  that are used to ensure that only that user can decrypt encrypted portions of encrypted voicemail message  92 . In alternative embodiments, each voicemail server  20  may be associated with a recipient private key  340  and a recipient public key  410  that is used for all users for which that voicemail server  20  hosts voicemail accounts. As a result, the recipient private key  340  and the recipient public key  410  may be shared by all users hosted by that voicemail server  20  and voicemail servers  20  may be responsible for enforcing the confidentiality policy with respect to individual users. Additionally, although shown as a single element in the illustrated embodiment, public key lookup and private key lookup may be performed by separate elements in alternative embodiments of voicemail server  20 . Moreover, as noted above, key lookup may be performed by components of communication system  10  external to voicemail server  20  such as a key server. 
     Message recording module  160  receives audio data from communication devices  60  and processes the audio data to generate voicemail messages  90 . Message recording module  160  may receive audio data from communication devices  60  in any appropriate form. In particular embodiments, message recording module  160  receives audio data stored in VoIP packets from communication devices  60 . 
     Message playback module  170  processes voicemail messages  90  and transmits audio data from voicemail messages  90  to communication devices  60 . Message playback module  170  may transmit the audio data to communication devices  60  in any appropriate form. In particular embodiments, message playback module  170  transmits audio data to communication devices  60  in the form of VoIP packets. 
     Key encryption module  130 , audio encryption module  132 , key lookup module  140 , session key generation module  150 , message recording module  160 , and message playback module  170  may each include any suitable combination of hardware and/or software to provide the described functionality. Furthermore, although  FIG. 2  illustrates an embodiment of voicemail server  20  that includes a separate key encryption module  130 , audio encryption module  132 , key lookup module  140 , session key generation module  150 , message recording module  160 , and message playback module  170 , any or all of these elements may include or represent common components. In particular embodiments, key encryption module  130 , audio encryption module  132 , key lookup module  140 , session key generation module  150 , message recording module  160 , and message playback module  170  all represent software processes running on processor  100 . 
     Message forming module  180  receives information output by key lookup module  140 , key encryption module  130 , and audio encryption module  132 , and/or additional information, such as decoy audio data  380 , expiration time  390 , and recipient identifiers  330 , and generates messages  90  and  92  from the appropriate elements of this information. In particular embodiments, as noted above, message forming module  180  creates messages  90  and  92  that include at least a first portion and a second portion. This process is described in greater detail below with respect to  FIG. 3 . 
     Message extraction module  190  extracts various elements of information from a particular message  90  or  92  when a user accesses voicemail server  20  to listen to that message  90  or  92 . Message extraction module  190  then provides these elements of information as inputs to key encryption module  130 , audio encryption module  132 , key lookup module  140 , and/or other components of voicemail server  20 . This process is described in greater detail below with respect to  FIG. 4 . 
       FIG. 3  illustrates example operation of a particular embodiment of voicemail server  20  in generating an encrypted voicemail message  92  for a caller using a communication device  60 . In particular,  FIG. 3  illustrates operation of an embodiment of voicemail server  20  that generates an encrypted voicemail message  92  that includes encrypted message audio data  360 , encrypted session keys  370 , recipient identifiers  330 , decoy audio data  380 , and an expiration time  390 . As one example, the described embodiment of voicemail server  20  may generate encrypted voicemail message  92  as a WAV file that includes decoy audio data  380  in a first RIFF block  300   a  and encrypted message audio data  360 , encrypted session keys  370 , and recipient identifiers  330  in a second RIFF block  300   b . As a result, particular embodiments of voicemail server  20  may generate encrypted voicemail message  92  in a form such that the conventional media player that is capable of playing WAV files will play decoy audio data  380 , when accessing encrypted voicemail message  92 , and will not be able to access encrypted message audio data  360 . 
     In this example, message recording module  160  receives data packet  310  representing, for example, VoIP packets. Message recording module  160  generates message audio data  320  based on incoming data packets  310 . As part of generating message audio data  320 , voicemail server  20  may buffer, order, and/or otherwise process data stored in incoming data packets  310 . After generating message audio data  320 , message recording module  160  transmits message audio data  320  to audio encryption module  132 . 
     Meanwhile, session key generation module  150  generates a session key  350 . As noted above, session key generation module  150  may generate a session key  350  in any appropriate manner. In a particular embodiment, session key generation module  150  generates a random, unique key for use with public key encryption algorithms such as RSA. After generating session key  350 , session key generation module  150  transmits session key  350  to audio encryption module  132  and to key encryption module  130 . 
     Once audio encryption module  132  has received message audio data  320  and session key  350 , audio encryption module  132  encrypts message audio data  320  using session key  350  to generate encrypted message audio data  360 . Audio encryption module  130  may encrypt message audio data  320  using any appropriate form of encryption. In particular embodiments, audio encryption module  132  encrypts message audio data  320  using a symmetric encryption algorithm such as 3DES. 
     Additionally, key lookup module  140  receives one or more recipient identifiers  330  from the caller. Recipient identifiers  330  may represent phone numbers associated with recipients or any other suitable form of identifier for recipients of the encoded voicemail message  92 . The caller may provide recipient identifiers  330  to key lookup module  140  in any appropriate manner. For example, in particular embodiments, the caller enters one or more phone numbers associated with the recipients using the keypad of communication device  60 , and communication device  60  transmits the phone numbers to key lookup module  140 . 
     Key lookup module  140  identifies a recipient public key  340  associated with each recipient identifier  330  received by key lookup module  140 . In particular embodiments of communication system  10 , each user of voicemail server  20  may be uniquely associated with a recipient public key  340 . In such embodiments, key lookup module  140  may access a key database that stores public keys for all users hosted by voicemail server  20 . Key lookup module  140  may use each recipient identifier  330  as an index to a record in the database that includes a recipient public key  340  associated with the same recipient as that recipient identifier  330 . Alternatively, all users supported by the relevant voicemail server  20  may be associated with a common public key  340 , and key lookup module  140  may access a designated location in a memory  110  to retrieve the public key  340  of that voicemail server  20 . 
     After identifying recipient public keys  340 , key lookup module  140  transmits recipient public keys  340  to key encryption module  130 . Once key encryption module  130  receives session key  350  and recipient public keys  340 , key encryption module  130  encrypts session key  350 , creating one or more encrypted session keys  370 . Key encryption module  132  may encrypt session key  350  using any appropriate form of encryption. In particular embodiments, key encryption module  132  utilizes a public key encryption algorithm such as RSA to encrypt session key  350  using the recipient public key  340  of each of the specified recipients for encrypted voicemail message  92 . Message forming module  180  may then create encrypted voicemail message  92  that includes encrypted message audio data  360  and one or more encrypted session keys  370 . 
     Message forming module  180  may also include expiration time  390  and decoy audio data  380  in encrypted voicemail message  92 . More specifically, particular embodiments of communication system  10  may support expiration of encrypted voicemail message  92 . In such embodiments, expiration time  390  may indicate a date and/or time at which encrypted voicemail message  92  is to expire. As described in greater detail below with respect to  FIG. 4 , voicemail server  20  may be configured so that voicemail server  20  will not decrypt encrypted voicemail message  92  after expiration date to ensure that encrypted voicemail message  92  can not be played by recipients after the date and/or time indicated by expiration time  390 . 
     Decoy audio data  380  includes audio data formatted in a manner that is readable by one or more elements of communication system  10  when accessed by these elements without decrypting encrypted voicemail message  92 . Because of the encryption of message audio data  320 , recipients of encrypted voicemail message  92  will be unable to access the confidential message recorded in encrypted message audio data  360  without decrypting encrypted voicemail message  92 . However, recipients attempting to access encrypted voicemail message  92  without decrypting encrypted voicemail message  92  may be notified of the confidential status of encrypted voicemail message  92  as a result of information stored in decoy audio data  380 . This may provide a useful explanation to unauthorized recipients who might otherwise think encrypted voicemail message  92  is corrupted or that the media player has malfunctioned as a result of the its inability to properly read encrypted message audio data  360 . In particular embodiments, instead of providing an indication of the confidential status of encrypted voicemail message  92 , decoy audio data may comprise audio information designed to sound like a typical voicemail message. This may, as a result, conceal from unauthorized recipients the fact that confidential information is included in encrypted voicemail message  92 , thereby reducing the likelihood that unintended recipients may attempt to find alternative techniques for accessing the confidential information stored in encrypted voicemail message  92 . 
     For example, encrypted voicemail message  92  may represent a WAV file with decoy audio data  380  stored in first portion  300   a , comprising the data block of the WAV file, and encrypted audio data stored in second portion  300   b , comprising the format block of the WAV file. Under such circumstances, media players that access encrypted voicemail message  92 , such as the PC of an unauthorized recipient who has received encrypted voicemail message  92  by email, may play decoy audio data  380 . When played, decoy audio data  380  may provide an audio message such as “This voice message is confidential and can only be played by accessing the voice mail server by phone. If you received this message in error notify the sender and destroy it immediately.” 
     After generating encrypted voicemail message  92 , message forming module  180  may store encrypted voicemail message  92  in voicemail accounts of local recipients, as described above with respect to  FIG. 1 . Voicemail server  20  may also transmit encrypted voicemail message  92  to other voicemail servers  20  that host voicemail accounts for recipients not hosted by the voicemail server  20  that generated encrypted voicemail message  92 . 
     As a result, voicemail server  20  may generate encrypted voicemail messages  92  that are not accessible by unauthorized recipients. Voicemail server  20  may also provide a meaningful indication to recipients improperly accessing encrypted voicemail message  92  as to why they are unable to access encrypted voicemail message  92 . Thus, particular embodiments of voicemail server  20  may offer a number of operational benefits. Various embodiments of communication system  10  may exhibit some, none, or all of these benefits. 
       FIG. 4  illustrates operation of a particular embodiment of voicemail server  20  in decrypting the audio data of encrypted voicemail message  92 . In particular,  FIG. 4  illustrates operation of voicemail server  20  as voicemail server  20  decrypts the example encrypted voicemail message  92  generated in  FIG. 3 . As noted above, the example encrypted voicemail message  92  includes encrypted message audio data  360 , encrypted session keys  370 , recipient identifiers  330 , decoy audio data  380 , and expiration time  390 . 
     In operation, voicemail server  20  may generate encrypted voicemail message  92  or may receive encrypted voicemail message  92  from another voicemail server  20  and may store encrypted voicemail message  92  in a voicemail account of one or more recipients designated by encrypted voicemail message  92 . For example, when voicemail server  20  receives encrypted voicemail message  92 , voicemail server  20  may determine one or more recipients of encrypted voicemail message  92  based on one or more recipient identifiers  330  stored in encrypted voicemail message  92  and store encrypted voicemail message  92  in the voicemail accounts of those recipients. When a recipient of encrypted voicemail message  92  subsequently accesses his or her voicemail account and/or requests playback of encrypted voicemail message  92 , voicemail server  20  may decrypt encrypted voicemail message  92 . 
     As part of decrypting encrypted voicemail message  92 , message extraction module  190  extracts expiration time  390 , encrypted message audio data  360 , encrypted session keys  370 , and recipient identifier  330  as shown. Additionally, key lookup module  140  may identify a recipient private key  410  associated with the recipient. Key lookup module  140  may determine the appropriate recipient private key  410  in any suitable manner. For example, in particular embodiments, each user of communication system  10  is associated with a unique private key, and key lookup module  140  identifies the appropriate recipient private key  410  based on a recipient identifier  330  associated with the relevant recipient. For example, the recipient may transmit the recipient identifier  330  to voicemail server  20  while accessing his or her account, key lookup module  140  may identify the recipient identifier  330  based on the telephone number of the recipient, or lookup module  140  may determine the recipient identifier  330  in any other appropriate manner. 
     In alternative embodiments, voicemail server  20  may itself be assigned a private key and each user supported by voicemail server  20  may be associated with this common private key. In such embodiments, the public/private key encoding may be used to ensure that encrypted voicemail message  92  is only decrypted by components that enforce confidentiality policies. Then, once an appropriate device decrypts encrypted voicemail message  92 , that device may be responsible for enforcing the confidentiality policy. As a result, such embodiments may reduce the time and computational complexity required to encrypt the relevant portions of encrypted voicemail message  92  as the process may not have to be repeated for multiple users hosted by the same voicemail server  20 . Additionally, such embodiments may dramatically reduce the number of private/public key pairs that are generated and maintained. 
     After identifying the appropriate recipient private key  410 , key lookup module  140  transmits recipient private key  410  to key encryption module  130 . Using the identified recipient private key  410 , key encryption module  130  then decrypts a particular session key  350  stored in encrypted voicemail message  92 . For example, in particular embodiments, voicemail server  20  matches the recipient identifier associated with the recipient retrieving encrypted voicemail message  92  to one of the recipient identifiers  330  stored in encrypted voicemail message  92 . Voicemail server  20  then identifies an encrypted session key  370  associated with the matched recipient identifier  330  and decrypts that encrypted session key  370 . 
     After key encryption module  130  decrypts session key  350 , audio encryption module  132  decrypts encrypted audio data using session key  350  to restore message audio data  320 . Audio encryption module  132  may then transmit message audio data  320  to message playback module  170 . Message playback module  170  generates data packets  310  based on message audio data  320  and transmits audio data packets  310  to the communication device  60  through which the recipient is accessing voicemail server  20 . Message playback module  170  may transmit any appropriate form of audio data packets  310  to the recipient. In particular embodiments, message playback module  170  transmits VoIP packets to the recipient. 
     Additionally, particular embodiments of voicemail server  20  may support expiration of voicemail messages. In such embodiments, voicemail server  20  may use expiration time  390  stored in encrypted voicemail message  92  to determine whether encrypted voicemail message  92  has expired. If voicemail server  20  determines that encrypted voicemail message  92  has expired, voicemail server  20  may deny recipient&#39;s request to play encrypted voicemail message  92 , play decoy audio data  380  to the recipient, and/or take any other appropriate action depending on the configuration of voicemail server  20 . 
     Furthermore, as noted above, if a recipient attempts to access encrypted voicemail message  92  without the use of voicemail server  20 , but using an element of communication system  10  that supports the audio file format, such as a conventional media player  510  capable of playing WAV files, the recipient will hear the message recorded in decoy audio data  380  because decoy audio data  380  is stored in the first portion where components that support the audio file format expect to find audio data. As a result, the recipient may be able to determine why he or she is unable to listen to the message. Consequently, voicemail server  20  may generate encrypted voicemail message  92  that can provide meaningful information even when accessed independently of voicemail server  20 . 
     Thus, voicemail server  20  provides an effective technique for communicating confidential messages within a voicemail system. Additionally, particular embodiments of voicemail server  20  may be configured to generate encrypted voicemail message  92  that can be recognized by and provide meaningful information to components and/or users of communication system  10  that are not authorized to access the confidential message. Additionally, particular embodiments of voicemail server  20  utilize encryption techniques that limit the time and computational resources required to encrypt and decrypt encrypted voicemail messages  92 . As a result, particular embodiments of voicemail server  20  may provide multiple operational benefits. Various embodiments of communication system  10  may exhibit some, none, or all of these benefits. 
     Although the present invention has been described with several embodiments, a myriad of changes, variations, alterations, transformations, and modifications may be suggested to one skilled in the art, and it is intended that the present invention encompass such changes, variations, alterations, transformations, and modifications as fall within the scope of the appended claims.