Abstract:
A challenge response scheme authenticates a requesting device by an authenticating device. The authenticating device generates and issues a challenge to the requesting device. The requesting device combines the challenge with a hash of a password provided by a user, and the combination is further hashed in order to generate a requesting encryption key used to encrypt the user supplied password. The encrypted user supplied password is sent to the authenticating device as a response to the issued challenge. The authenticating device generates an authenticating encryption key by generating the hash of a combination of the challenge and a stored hash of an authenticating device password. The authenticating encryption key is used to decrypt the response in order to retrieve the user-supplied password. If the user-supplied password hash matches the stored authenticating device password hash, the requesting device is authenticated and the authenticating device is in possession of the password.

Description:
REFERENCE TO PRIOR APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 10/996,369, filed Nov. 26, 2004, claiming priority from U.S. application Ser. No. 60/568,119, filed May 4, 2004. 
    
    
     BACKGROUND 
     1. Technical Field 
     The present invention relates generally to the field of communications, and in particular to a challenge response system and method. 
     2. Description of the Related Art 
     Mobile devices, such as personal digital assistants (PDAs), cellular phones, wireless communication devices and the like, are occasionally connected to a user&#39;s desktop system in order to synchronize information between the user&#39;s desktop system and their mobile device. Information such as a user&#39;s calendar, task list and phone book entries are examples of information that is routinely synchronized between the desktop system and the mobile device. 
     Such information is usually of a sensitive nature and should be secured. The user is thus provided with an option to specify a device password on the mobile device in order to secure the mobile device and prevent use of the device without knowledge of the device password. 
     When the mobile device is connected to the desktop system in order to synchronize information, the mobile device issues a challenge to the desktop system in order to determine if the desktop system is authorized to initiate a connection with the mobile device. The desktop system then provides a response to the mobile device. If the response provided by the desktop system matches the response expected by the mobile device, then the desktop system is allowed to connect to the mobile device and proceed to synchronize information. 
     Typically, the issued challenge is a request for the hash of the user password. A hash function, such as SHA-1, is a one-way function that takes an input or varying length and converts it into a unique output. The hash of the password provided by the user of the desktop system initiating a connection is sent to the device in response to the challenge by the mobile device. If the response matches the stored hash of the device password, the desktop system is allowed to connect to the mobile device and proceed to synchronize information. 
     The device password is typically not stored on the device. Only the hash of the device password is stored on the device. However, since the device password itself is not stored on the device, certain operations requiring use of the device password cannot be performed if only the hash of the device password is available on the mobile device. For instance, if the information on the mobile device is encrypted using the device password, then the device password must be supplied in order to decrypt the information prior to synchronizing with the desktop system. 
     SUMMARY 
     In accordance with the teachings provided herein, systems and methods are provided for a challenge response scheme within which a secret, such as a password, may be securely transferred between a requesting device and an authenticating device. As an example of a system and method, the authenticating device generates a challenge that is issued to the requesting device. The requesting device combines the challenge with a hash of a password provided by a user of the requesting device, and the combination of the hash of the password and the challenge is further hashed in order to generate a requesting encryption key that is used to encrypt the user supplied password. The encrypted user supplied password is sent to the authenticating device as the response to the issued challenge. The authenticating device generates an authenticating encryption key by generating the hash of a combination of the challenge and a stored hash of an authenticating device password. The authenticating encryption key is used to decrypt the response in order to retrieve the user supplied password. If a hash of the user supplied password matches the stored hash of the authenticating device password, then the requesting device has been authenticated and the authenticating device is in possession of the password. 
     According to an aspect of the invention there is provided a method for authentication of a requesting device by an authenticating device, the requesting device and the authenticating device each being operative to carry out a one-way hash operation and to carry out a key-based encryption operation, the authenticating device storing a hash of a defined password generated by applying the hash operation to the defined password, the authenticating device being further operative to carry out a key-based decryption operation for decrypting values obtained from the encryption operation, the method including the steps of: 
     the requesting device receiving a user password and carrying out the hash operation on the user password to obtain a hash of the user password, 
     the authenticating device determining and transmitting a challenge to the requesting device; 
     the requesting device receiving the challenge and defining a requesting encryption key by carrying out the hash operation on a combination of the challenge and the hash of the user password, 
     the requesting device carrying out the encryption operation using the requesting encryption key to encrypt the user password, 
     the requesting device transmitting a response including the encrypted user password to the authenticating device, 
     the authenticating device receiving the response and defining an authenticating encryption key by carrying out the hash operation on a combination of the challenge and the hash of the defined password; 
     the authenticating device using the authenticating encryption key in the decryption operation to decrypt the response to obtain a decrypted user password and carrying out the one-way hash operation on the decrypted user password; 
     the authenticating device comparing the hash of the decrypted user password with the hash of the defined password to authenticate the requesting device when the comparison indicates a match. 
     According to a further aspect of the invention there is provided the above method further including the step of the authenticating device using the decrypted user password to carry out operations on the authenticating device. 
     According to a further aspect of the invention there is provided the above method in which the authenticating device is a wireless handheld device and the requesting device is a desktop computer and in which the authentication of the requesting device is required to establish a connection between the wireless handheld device and the requesting device, the method further including the step of the requesting device sending a connection request to the authenticating device prior to the authenticating device determining a challenge and in which the step of authenticating the requesting device includes the step of refusing to establish a connection when the hash of the decrypted user password does not match the hash of the defined password. 
     According to a further aspect of the invention there is provided a computing device program product including code operative to perform the above methods. 
     According to a further aspect of the invention there is provided a system for an authentication device to authenticate a requesting device, including: 
     a challenge generator for generating a challenge, 
     a communications link for transmitting the challenge to the requesting device and receiving a response to the challenge from the requesting device, the response including a requesting password encrypted using a requesting encryption key, the requesting encryption key including a hash of a combination of the challenge and a hash of the requesting password; 
     a hash generator for generating an authenticating encryption key by hashing a combination of the challenge and a hash of a predetermined password; 
     a decryptor for decrypting the encrypted requesting password using the authenticating encryption key to obtain a decrypted response; and 
     a comparator for comparing a hash of the decrypted response with the hash of the predetermined password, whereby if the hash of the decrypted requesting password matches the hash of the predetermined password, the requesting device is authenticated. 
     According to a further aspect of the invention there is provided a method for securely transmitting information to a receiving device, the receiving device being provided with a hash of the information, a random number, and a receiving encryption key including a hash of the random number and the hash of the information, including the steps of: 
     receiving a random number from the receiving device; 
     encoding the information to produce a hash of the information; 
     combining the random number with the hash of the information; 
     hashing the combined random number and hash of the information to produce a transmitting encryption key; 
     encrypting the information using the transmitting encryption key; 
     transmitting the encrypted information to the receiving device for decryption by the receiving device using the receiving encryption key. 
     According to a further aspect of the invention there is provided a method for a requesting device to be authenticated by an authenticating device, the requesting device receiving a user password, the authenticating device being provided with a hash of a predetermined password, a random number, and a receiving encryption key including a hash of the random number and the hash of the predetermined password, including the steps of the requesting device: 
     receiving a random number from the authenticating device; 
     encoding the user password to produce a hash of the user password; 
     combining the random number with the hash of the user password; 
     hashing the combined random number and hash of the user password to produce a transmitting encryption key; 
     encrypting the user password using the transmitting encryption key; 
     transmitting the encrypted user password to the authenticating device for authentication by decryption by the authenticating device using the receiving encryption key. 
     According to a further aspect of the invention there is provided a method for authentication of a requesting device by an authenticating device, the requesting device and the authenticating device each being operative to carry out a one-way hash operation and to carry out a key-based encryption operation, the authenticating device storing a hash of a defined password generated by applying the hash operation to the defined password, the authenticating device being further operative to carry out a key-based decryption operation for decrypting values obtained from the encryption operation, the method including the steps of the authenticating device: 
     determining and transmitting a challenge to the requesting device; 
     receiving a response from the requesting device, the response including a requesting encryption key determined by carrying out the hash operation on a combination of the challenge and a hash of a received user password, the hash being defined by carrying out the hash operation on the received user password, 
     defining an authenticating encryption key by carrying out the hash operation on a combination of the challenge and the hash of the defined password; 
     using the authenticating encryption key in the decryption operation to decrypt the response to obtain a decrypted user password and carrying out the one-way hash operation on the decrypted user password; 
     comparing the hash of the decrypted user password with the hash of the defined password to authenticate the requesting device when the comparison indicates a match. 
     As will be appreciated, the invention is capable of other and different embodiments, and its several details are capable of modifications in various respects, all without departing from the spirit of the invention. Accordingly, the drawings and description of the preferred embodiments set forth below are to be regarded as illustrative in nature and not restrictive. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of a communication system for use with a requesting device and authenticating device. 
         FIG. 2  is a block diagram of a further communication system for use with multiple devices. 
         FIG. 3  is a schematic representation of a prior art challenge-response method. 
         FIG. 4  is a schematic representation of a challenge-response method for a requesting device and authenticating device. 
         FIG. 5  is a block diagram of a mobile communication device for use with the method illustrated in  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is an overview of an example communication system in which a wireless communication device may be used. One skilled in the art will appreciate that there may be hundreds of different topologies, but the system shown in  FIG. 1  helps demonstrate the operation of the encoded message processing systems and methods described in the present application. There may also be many message senders and recipients. The simple system shown in  FIG. 1  is for illustrative purposes only, and shows perhaps the most prevalent Internet e-mail environment where security is not generally used. 
       FIG. 1  shows an e-mail sender  10 , the Internet  20 , a message server system  40 , a wireless gateway  85 , wireless infrastructure  90 , a wireless network  105  and a mobile communication device  100 . 
     An e-mail sender system  10  may, for example, be connected to an ISP (Internet Service Provider) on which a user of the system  10  has an account, located within a company, possibly connected to a local area network (LAN), and connected to the Internet  20 , or connected to the Internet  20  through a large ASP (application service provider) such as AMERICA ONLINE® (AOL). Those skilled in the art will appreciate that the systems shown in  FIG. 1  may instead be connected to a wide area network (WAN) other than the Internet, although e-mail transfers are commonly accomplished through Internet-connected arrangements as shown in  FIG. 1 . 
     The message server  40  may be implemented, for example, on a network computer within the firewall of a corporation, a computer within an ISP or ASP system or the like, and acts as the main interface for e-mail exchange over the Internet  20 . Although other messaging systems might not require a message server system  40 , a mobile device  100  configured for receiving and possibly sending e-mail will normally be associated with an account on a message server. Perhaps the two most common message servers are MICROSOFT® EXCHANGE and LOTUS DOMINO®. These products are often used in conjunction with Internet mail routers that route and deliver mail. These intermediate components are not shown in  FIG. 1 , as they do not directly play a role in the secure message processing described below. Message servers such as server  40  typically extend beyond just e-mail sending and receiving; they also include dynamic database storage engines that have predefined database formats for data like calendars, to-do lists, task lists, e-mail and documentation. 
     The wireless gateway  85  and infrastructure  90  provide a link between the Internet  20  and wireless network  105 . The wireless infrastructure  90  determines the most likely network for locating a given user and tracks the user as they roam between countries or networks. A message is then delivered to the mobile device  100  via wireless transmission, typically at a radio frequency (RF), from a base station in the wireless network  105  to the mobile device  100 . The particular network  105  may be virtually any wireless network over which messages may be exchanged with a mobile communication device. 
     As shown in  FIG. 1 , a composed e-mail message  15  is sent by the e-mail sender  10 , located somewhere on the Internet  20 . This message  15  is normally fully in the clear and uses traditional Simple Mail Transfer Protocol (SMTP), RFC822 headers and Multipurpose Internet Mail Extension (MIME) body parts to define the format of the mail message. These techniques are all well known to those skilled in the art. The message  15  arrives at the message server  40  and is normally stored in a message store. Most known messaging systems support a so-called “pull” message access scheme, wherein the mobile device  100  must request that stored messages be forwarded by the message server to the mobile device  100 . Some systems provide for automatic routing of such messages which are addressed using a specific e-mail address associated with the mobile device  100 . In a preferred embodiment described in further detail below, messages addressed to a message server account associated with a host system such as a home computer or office computer which belongs to the user of a mobile device  100  are redirected from the message server  40  to the mobile device  100  as they are received. 
     Regardless of the specific mechanism controlling the forwarding of messages to the mobile device  100 , the message  15 , or possibly a translated or reformatted version thereof, is sent to the wireless gateway  85 . The wireless infrastructure  90  includes a series of connections to wireless network  105 . These connections could be Integrated Services Digital Network (ISDN), Frame Relay or T1 connections using the TCP/IP protocol used throughout the Internet. As used herein, the term “wireless network” is intended to include three different types of networks, those being (1) data-centric wireless networks, (2) voice-centric wireless networks and (3) dual-mode networks that can support both voice and data communications over the same physical base stations. Combined dual-mode networks include, but are not limited to, (1) Code Division Multiple Access (CDMA) networks, (2) the Groupe Special Mobile or the Global System for Mobile Communications (GSM) and the General Packet Radio Service (GPRS) networks, and (3) future third-generation (3G) networks like Enhanced Data-rates for Global Evolution (EDGE) and Universal Mobile Telecommunications Systems (UMTS). Some older examples of data-centric network include the Mobitex™ Radio Network and the DataTAC™ Radio Network. Examples of older voice-centric data networks include Personal Communication Systems (PCS) networks like GSM, and TDMA systems. 
       FIG. 2  is a block diagram of a further example communication system including multiple networks and multiple mobile communication devices. The system of  FIG. 2  is substantially similar to the  FIG. 1  system, but includes a host system  30 , a redirection program  45 , a mobile device cradle  65 , a wireless virtual private network (VPN) router  75 , an additional wireless network  110  and multiple mobile communication devices  100 . As described above in conjunction with  FIG. 1 ,  FIG. 2  represents an overview of a sample network topology. Although the encoded message processing systems and methods described herein may be applied to networks having many different topologies, the network of  FIG. 2  is useful in understanding an automatic e-mail redirection system mentioned briefly above. 
     The central host system  30  will typically be a corporate office or other LAN, but may instead be a home office computer or some other private system where mail messages are being exchanged. Within the host system  30  is the message server  40 , running on some computer within the firewall of the host system, that acts as the main interface for the host system to exchange e-mail with the Internet  20 . In the system of  FIG. 2 , the redirection program  45  enables redirection of data items from the server  40  to a mobile communication device  100 . Although the redirection program  45  is shown to reside on the same machine as the message server  40  for ease of presentation, there is no requirement that it must reside on the message server. The redirection program  45  and the message server  40  are designed to co-operate and interact to allow the pushing of information to mobile devices  100 . In this installation, the redirection program  45  takes confidential and non-confidential corporate information for a specific user and redirects it out through the corporate firewall to mobile devices  100 . A more detailed description of the redirection software  45  may be found in the commonly assigned U.S. Pat. No. 6,219,694 (“the &#39;694 Patent”), entitled “System and Method for Pushing Information From A Host System To A Mobile Data Communication Device Having A Shared Electronic Address”, and issued to the assignee of the instant application on Apr. 17, 2001, which is hereby incorporated into the present application by reference. This push technique may use a wireless friendly encoding, compression and encryption technique to deliver all information to a mobile device, thus effectively extending the security firewall to include each mobile device  100  associated with the host system  30 . 
     As shown in  FIG. 2 , there may be many alternative paths for getting information to the mobile device  100 . One method for loading information onto the mobile device  100  is through a port designated  50 , using a device cradle  65 . This method tends to be useful for bulk information updates often performed at initialization of a mobile device  100  with the host system  30  or a computer  35  within the system  30 . The other main method for data exchange is over-the-air using wireless networks to deliver the information. As shown in  FIG. 2 , this may be accomplished through a wireless VPN router  75  or through a traditional Internet connection  95  to a wireless gateway  85  and a wireless infrastructure  90 , as described above. The concept of a wireless VPN router  75  is new in the wireless industry and implies that a VPN connection could be established directly through a specific wireless network  110  to a mobile device  100 . The possibility of using a wireless VPN router  75  has only recently been available and could be used when the new Internet Protocol (IP) Version 6 (IPV6) arrives into IP-based wireless networks. This new protocol will provide enough IP addresses to dedicate an IP address to every mobile device  100  and thus make it possible to push information to a mobile device  100  at any time. A principal advantage of using this wireless VPN router  75  is that it could be an off-the-shelf VPN component, thus it would not require a separate wireless gateway  85  and wireless infrastructure  90  to be used. A VPN connection would preferably be a Transmission Control Protocol (TCP)/IP or User Datagram Protocol (UDP)/IP connection to deliver the messages directly to the mobile device  100 . If a wireless VPN  75  is not available then a link  95  to the Internet  20  is the most common connection mechanism available and has been described above. 
     In the automatic redirection system of  FIG. 2 , a composed e-mail message  15  leaving the e-mail sender  10  arrives at the message server  40  and is redirected by the redirection program  45  to the mobile device  100 . As this redirection takes place the message  15  is re-enveloped, as indicated at  80 , and a possibly proprietary compression and encryption algorithm can then be applied to the original message  15 . In this way, messages being read on the mobile device  100  are no less secure than if they were read on a desktop workstation such as  35  within the firewall. All messages exchanged between the redirection program  45  and the mobile device  100  preferably use this message repackaging technique. Another goal of this outer envelope is to maintain the addressing information of the original message except the sender&#39;s and the receiver&#39;s address. This allows reply messages to reach the appropriate destination, and also allows the “from” field to reflect the mobile user&#39;s desktop address. Using the user&#39;s e-mail address from the mobile device  100  allows the received message to appear as though the message originated from the user&#39;s desktop system  35  rather than the mobile device  100 . 
     With reference back to the port  50  and cradle  65  connectivity to the mobile device  100 , this connection path offers many advantages for enabling one-time data exchange of large items. For those skilled in the art of personal digital assistants (PDAs) and synchronization, the most common data exchanged over this link is Personal Information Management (PIM) data  55 . When exchanged for the first time this data tends to be large in quantity, bulky in nature and requires a large bandwidth to get loaded onto the mobile device  100  where it can be used on the road. This serial link may also be used for other purposes, including setting up a private security key  111  such as an S/MIME or PGP specific private key, the Certificate (Cert) of the user and their Certificate Revocation Lists (CRLs)  60 . The private key is preferably exchanged so that the desktop  35  and mobile device  100  share one personality and one method for accessing all mail. The Cert and CRLs are normally exchanged over such a link because they represent a large amount of the data that is required by the device for S/MIME, PGP and other public key security methods. 
       FIG. 3  shows a typical challenge response scheme used by an authenticating device, such as mobile device  10  to authenticate a requesting device, such as desktop system  35  that may be requesting a connection to the device  10 . When device  10  is connected to the desktop system  35 , for instance through a serial link such as a universal serial bus (USB) link, the user of the desktop system  35  is prompted to enter a password in order to authenticate the user to the device  10 . The desktop system  35  creates a one-way hash of the password provided by the user, and transmits the hash of the password to the device  10 . The device  10  then compares the hash of the password to a stored hash of the device password. If the two values match, then the user is authenticated and the desktop system  35  is allowed to form a connection with the device  10 . In this typical challenge response scheme, only the hash of the password is transmitted to the device  10 . If the password itself were sent over the communications link, an attacker would be able to intercept the transmission and gain knowledge of the password. 
       FIG. 4  illustrates a challenge response scheme in accordance with a preferred embodiment of the present invention. In the preferred embodiment, a requesting device, such as the desktop system  35 , is connected to an authenticating device, such as mobile device  10 , using a communications link, such as a universal serial bus (USB) link, through which the requesting device may send a connection request. The connection request may be in the form of a software request sent to the authenticating device, or the detection of a change in a hardware state of the communications link. The authenticating device detects that a connection is being requested, and proceeds to authenticate the requesting device in accordance with the challenge response scheme described below. It will be understood that the authenticating device may only initiate the challenge response scheme if the authenticating device has been secured by a device password (stored_password). In order to determine if a requesting device needs to be authenticated, the authenticating device may check for the presence of a hash of the device password H(stored_password) in a memory of the authenticating device. In other implementations, the authentication device may check for a flag indicating whether the device has been secured. 
     When the authenticating device detects a connection request, it generates a Challenge c to issue to the requesting device. The Challenge c may be a group of bits that have been randomly generated by the authenticating device. Alternatively, the numbers of bits used in the Challenge c may also be randomized. The authenticating device may use a hardware-based random number generator or a software-based random number generator to generate the random Challenge c. 
     The requesting device prompts the user of the requesting device for a password user_password. This password is hashed, using known hashing functions such as SHA-1, to create H(user_password) which is then combined with the Challenge c received from the authenticating device. In the preferred embodiment, the Challenge c and the hash of the password H(user_password) are concatenated together. It is understood that there are different ways in which to combine the two values. This combination of the Challenge c and the hash of the password H(user_password) is further hashed in order to generate a requesting encryption key k r =H(c∥H(user_password)) that is used in creating a response r to the challenge issued by the authenticating device. The response r is generated by encrypting the password user_password using known techniques such as AES or TripleDES. In some implementations, the response r may also be generated by applying the XOR function to the requesting encryption key k r  and the password user_password. The response r is then transmitted to the authenticating device. 
     The authenticating device determines an authenticating encryption key k a  by following a process similar to that followed by the requesting device. The authenticating device combines the stored hash of the device password H(stored_password) with the randomly generated Challenge c, and then generates a hash of the combination, in order to generate the authenticating encryption key k a =H(c∥H(stored_password)). The authenticating encryption key k a  is used to decrypt the response r received from the requesting device. A hash of the decrypted response H(decrypted_response) is then compared to the stored hash of the device password H(stored_password). If the two hashes match, then the decrypted response was the correct device password. Thus the authenticating device has authenticated the requesting device. The authenticating device is also in possession of the device password for use in operations that require the device password. If the two hashes do not match, then the user did not provide the correct password, and the authenticating device rejects the connection request from the requesting device, and thereby disallows the connection. 
     In a further embodiment, the device password is concatenated with a random salt s, then hashed and stored in the memory of the authenticating device together with s. Therefore the authenticating device stores (s, H(s∥stored_password)). When the challenge c is transmitted to the requesting device, the salt s is likewise transmitted, and the requesting device then hashes a concatenation of s and user_password to generate an authenticating encrypting key k r =H(c∥H(s∥user_password)) using the process described above. Once the response r is transmitted to the authenticating device, the authenticating device determines an authenticating encryption key k a =H(c∥H(s∥stored_password)) by following a process similar to that described above. The authenticating encryption key k a  is used to decrypt the response r received from the requesting device. A hash of the decrypted response H(decrypted_response) is then compared to the stored hash of the salted device password H(s∥stored_password). If the two hashes match, then the decrypted response was the correct device password. 
     The systems and methods disclosed herein are presented only by way of example and are not meant to limit the scope of the invention. Other variations of the systems and methods described above will be apparent to those skilled in the art and as such are considered to be within the scope of the invention. For example, it should be understood that steps and the order of the steps in the processing described herein may be altered, modified and/or augmented and still achieve the desired outcome. 
     As another example, the systems and methods disclosed herein may be used with many different computers and devices, such as a wireless mobile communications device shown in  FIG. 5 . With reference to  FIG. 5 , the mobile device  100  is a dual-mode mobile device and includes a transceiver  311 , a microprocessor  338 , a display  322 , non-volatile memory  324 , random access memory (RAM)  326 , one or more auxiliary input/output (I/O) devices  328 , a serial port  330 , a keyboard  332 , a speaker  334 , a microphone  336 , a short-range wireless communications sub-system  340 , and other device sub-systems  342 . 
     The transceiver  311  includes a receiver  312 , a transmitter  314 , antennas  316  and  318 , one or more local oscillators  313 , and a digital signal processor (DSP)  320 . The antennas  316  and  318  may be antenna elements of a multiple-element antenna, and are preferably embedded antennas. However, the systems and methods described herein are in no way restricted to a particular type of antenna, or even to wireless communication devices. 
     The mobile device  100  is preferably a two-way communication device having voice and data communication capabilities. Thus, for example, the mobile device  100  may communicate over a voice network, such as any of the analog or digital cellular networks, and may also communicate over a data network. The voice and data networks are depicted in  FIG. 5  by the communication tower  319 . These voice and data networks may be separate communication networks using separate infrastructure, such as base stations, network controllers, etc., or they may be integrated into a single wireless network. 
     The transceiver  311  is used to communicate with the network  319 , and includes the receiver  312 , the transmitter  314 , the one or more local oscillators  313  and the DSP  320 . The DSP  320  is used to send and receive signals to and from the transceivers  316  and  318 , and also provides control information to the receiver  312  and the transmitter  314 . If the voice and data communications occur at a single frequency, or closely-spaced sets of frequencies, then a single local oscillator  313  may be used in conjunction with the receiver  312  and the transmitter  314 . Alternatively, if different frequencies are utilized for voice communications versus data communications for example, then a plurality of local oscillators  313  can be used to generate a plurality of frequencies corresponding to the voice and data networks  319 . Information, which includes both voice and data information, is communicated to and from the transceiver  311  via a link between the DSP  320  and the microprocessor  338 . 
     The detailed design of the transceiver  311 , such as frequency band, component selection, power level, etc., will be dependent upon the communication network  319  in which the mobile device  100  is intended to operate. For example, a mobile device  100  intended to operate in a North American market may include a transceiver  311  designed to operate with any of a variety of voice communication networks, such as the Mobitex or DataTAC mobile data communication networks, AMPS, TDMA, CDMA, PCS, etc., whereas a mobile device  100  intended for use in Europe may be configured to operate with the GPRS data communication network and the GSM voice communication network. Other types of data and voice networks, both separate and integrated, may also be utilized with a mobile device  100 . 
     Depending upon the type of network or networks  319 , the access requirements for the mobile device  100  may also vary. For example, in the Mobitex and DataTAC data networks, mobile devices are registered on the network using a unique identification number associated with each mobile device. In GPRS data networks, however, network access is associated with a subscriber or user of a mobile device. A GPRS device typically requires a subscriber identity module (“SIM”), which is required in order to operate a mobile device on a GPRS network. Local or non-network communication functions (if any) may be operable, without the SIM device, but a mobile device will be unable to carry out any functions involving communications over the data network  319 , other than any legally required operations, such as ‘911’ emergency calling. 
     After any required network registration or activation procedures have been completed, the mobile device  100  may the send and receive communication signals, including both voice and data signals, over the networks  319 . Signals received by the antenna  316  from the communication network  319  are routed to the receiver  312 , which provides for signal amplification, frequency down conversion, filtering, channel selection, etc., and may also provide analog to digital conversion. Analog to digital conversion of the received signal allows more complex communication functions, such as digital demodulation and decoding to be performed using the DSP  320 . In a similar manner, signals to be transmitted to the network  319  are processed, including modulation and encoding, for example, by the DSP  320  and are then provided to the transmitter  314  for digital to analog conversion, frequency up conversion, filtering, amplification and transmission to the communication network  319  via the antenna  318 . 
     In addition to processing the communication signals, the DSP  320  also provides for transceiver control. For example, the gain levels applied to communication signals in the receiver  312  and the transmitter  314  may be adaptively controlled through automatic gain control algorithms implemented in the DSP  320 . Other transceiver control algorithms could also be implemented in the DSP  320  in order to provide more sophisticated control of the transceiver  311 . 
     The microprocessor  338  preferably manages and controls the overall operation of the mobile device  100 . Many types of microprocessors or microcontrollers could be used here, or, alternatively, a single DSP  320  could be used to carry out the functions of the microprocessor  338 . Low-level communication functions, including at least data and voice communications, are performed through the DSP  320  in the transceiver  311 . Other, high-level communication applications, such as a voice communication application  324 A, and a data communication application  324 B may be stored in the non-volatile memory  324  for execution by the microprocessor  338 . For example, the voice communication module  324 A may provide a high-level user interface operable to transmit and receive voice calls between the mobile device  100  and a plurality of other voice or dual-mode devices via the network  319 . Similarly, the data communication module  324 B may provide a high-level user interface operable for sending and receiving data, such as e-mail messages, files, organizer information, short text messages, etc., between the mobile device  100  and a plurality of other data devices via the networks  319 . The microprocessor  338  also interacts with other device subsystems, such as the display  322 , the RAM  326 , the auxiliary input/output (I/O) subsystems  328 , the serial port  330 , the keyboard  332 , the speaker  334 , the microphone  336 , the short-range communications subsystem  340  and any other device subsystems generally designated as  342 . 
     Some of the subsystems shown in  FIG. 5  perform communication-related functions, whereas other subsystems may provide “resident” or on-device functions. Notably, some subsystems, such as the keyboard  332  and the display  322  may be used for both communication-related functions, such as entering a text message for transmission over a data communication network, and device-resident functions such as a calculator or task list or other PDA type functions. 
     Operating system software used by the microprocessor  338  is preferably stored in a persistent store such as non-volatile memory  324 . The non-volatile memory  324  may be implemented, for example, as a Flash memory component, or as battery backed-up RAM. In addition to the operating system, which controls low-level functions of the mobile device  310 , the non-volatile memory  324  includes a plurality of software modules  324 A- 324 N that can be executed by the microprocessor  338  (and/or the DSP  320 ), including a voice communication module  324 A, a data communication module  324 B, and a plurality of other operational modules  324 N for carrying out a plurality of other functions. These modules are executed by the microprocessor  338  and provide a high-level interface between a user and the mobile device  100 . This interface typically includes a graphical component provided through the display  322 , and an input/output component provided through the auxiliary I/O  328 , keyboard  332 , speaker  334 , and microphone  336 . The operating system, specific device applications or modules, or parts thereof, may be temporarily loaded into a volatile store, such as RAM  326  for faster operation. Moreover, received communication signals may also be temporarily stored to RAM  326 , before permanently writing them to a file system located in a persistent store such as the Flash memory  324 . 
     An exemplary application module  324 N that may be loaded onto the mobile device  100  is a personal information manager (PIM) application providing PDA functionality, such as calendar events, appointments, and task items. This module  324 N may also interact with the voice communication module  324 A for managing phone calls, voice mails, etc., and may also interact with the data communication module for managing e-mail communications and other data transmissions. Alternatively, all of the functionality of the voice communication module  324 A and the data communication module  324 B may be integrated into the PIM module. 
     The non-volatile memory  324  preferably also provides a file system to facilitate storage of PIM data items on the device. The PIM application preferably includes the ability to send and receive data items, either by itself, or in conjunction with the voice and data communication modules  324 A,  324 B, via the wireless networks  319 . The PIM data items are preferably seamlessly integrated, synchronized and updated, via the wireless networks  319 , with a corresponding set of data items stored or associated with a host computer system, thereby creating a mirrored system for data items associated with a particular user. 
     Context objects representing at least partially decoded data items, as well as fully decoded data items, are preferably stored on the mobile device  100  in a volatile and non-persistent store such as the RAM  326 . Such information may instead be stored in the non-volatile memory  324 , for example, when storage intervals are relatively short, such that the information is removed from memory soon after it is stored. However, storage of this information in the RAM  326  or another volatile and non-persistent store is preferred, in order to ensure that the information is erased from memory when the mobile device  100  loses power. This prevents an unauthorized party from obtaining any stored decoded or partially decoded information by removing a memory chip from the mobile device  100 , for example. 
     The mobile device  100  may be manually synchronized with a host system by placing the device  100  in an interface cradle, which couples the serial port  330  of the mobile device  100  to the serial port of a computer system or device. The serial port  330  may also be used to enable a user to set preferences through an external device or software application, or to download other application modules  324 N for installation. This wired download path may be used to load an encryption key onto the device, which is a more secure method than exchanging encryption information via the wireless network  319 . Interfaces for other wired download paths may be provided in the mobile device  100 , in addition to or instead of the serial port  330 . For example, a USB port would provide an interface to a similarly equipped personal computer. 
     Additional application modules  324 N may be loaded onto the mobile device  100  through the networks  319 , through an auxiliary I/O subsystem  328 , through the serial port  330 , through the short-range communications subsystem  340 , or through any other suitable subsystem  342 , and installed by a user in the non-volatile memory  324  or RAM  326 . Such flexibility in application installation increases the functionality of the mobile device  100  and may provide enhanced on-device functions, communication-related functions, or both. For example, secure communication applications may enable electronic commerce functions and other such financial transactions to be performed using the mobile device  100 . 
     When the mobile device  100  is operating in a data communication mode, a received signal, such as a text message or a web page download, is processed by the transceiver module  311  and provided to the microprocessor  338 , which preferably further processes the received signal in multiple stages as described above, for eventual output to the display  322 , or, alternatively, to an auxiliary I/O device  328 . A user of mobile device  100  may also compose data items, such as e-mail messages, using the keyboard  332 , which is preferably a complete alphanumeric keyboard laid out in the QWERTY style, although other styles of complete alphanumeric keyboards such as the known DVORAK style may also be used. User input to the mobile device  100  is further enhanced with a plurality of auxiliary I/O devices  328 , which may include a thumbwheel input device, a touchpad, a variety of switches, a rocker input switch, etc. The composed data items input by the user may then be transmitted over the communication networks  319  via the transceiver module  311 . 
     When the mobile device  100  is operating in a voice communication mode, the overall operation of the mobile device is substantially similar to the data mode, except that received signals are preferably be output to the speaker  334  and voice signals for transmission are generated by a microphone  336 . Alternative voice or audio I/O subsystems, such as a voice message recording subsystem, may also be implemented on the mobile device  100 . Although voice or audio signal output is preferably accomplished primarily through the speaker  334 , the display  322  may also be used to provide an indication of the identity of a calling party, the duration of a voice call, or other voice call related information. For example, the microprocessor  338 , in conjunction with the voice communication module and the operating system software, may detect the caller identification information of an incoming voice call and display it on the display  322 . 
     A short-range communications subsystem  340  is also included in the mobile device  100 . The subsystem  340  may include an infrared device and associated circuits and components, or a short-range RF communication module such as a BLUETOOTH® module or an 802.11 module, for example, to provide for communication with similarly-enabled systems and devices. Those skilled in the art will appreciate that “BLUETOOTH®” and “802.11” refer to sets of specifications, available from the Institute of Electrical and Electronics Engineers, relating to wireless personal area networks and wireless local area networks, respectively. 
     The systems&#39; and methods&#39; data may be stored in one or more data stores. The data stores can be of many different types of storage devices and programming constructs, such as RAM, ROM, Flash memory, programming data structures, programming variables, etc. It is noted that data structures describe formats for use in organizing and storing data in databases, programs, memory, or other computer-readable media for use by a computer program. 
     The systems and methods may be provided on many different types of computer-readable media including computer storage mechanisms (e.g., CD-ROM, diskette, RAM, flash memory, computer&#39;s hard drive, etc.) that contain instructions for use in execution by a processor to perform the methods&#39; operations and implement the systems described herein. 
     The computer components, software modules, functions and data structures described herein may be connected directly or indirectly to each other in order to allow the flow of data needed for their operations. It is also noted that a module or processor includes but is not limited to a unit of code that performs a software operation, and can be implemented for example as a subroutine unit of code, or as a software function unit of code, or as an object (as in an object-oriented paradigm), or as an applet, or in a computer script language, or as another type of computer code.