Abstract:
Systems and methods for processing messages within a wireless communications system are disclosed. A server within the wireless communications system maintains a list of certificates contained in devices that use the server. The server synchronizes or updates the list of certificates based on information contained in message to and from the device. By providing a server with certificates associated with devices that use the server, and providing a system and method for synchronizing the certificates between the device and server, the server can implement powerful features that will improve the efficiency, speed and user satisfaction of the devices. The exemplary embodiments also enable advantageous bandwidth savings by preventing transmission of certificates unnecessarily.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is related to co-pending, commonly assigned, U.S. patent application Ser. No. 10/914,634 entitled “Server Verification of Secure Electronic Messages,” filed Aug. 10, 2004, the disclosure of which is incorporated herein by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to an electronic messaging system that is capable of processing encoded messages and information. In particular, the disclosure is directed to a system in which an electronic message server performs some functions typically performed by a mobile wireless communications device having secure electronic messaging capability. In order to perform such functions, the server is capable of storing and maintaining, for example, certificates, associated with the mobile wireless communications devices that use the server. Accordingly, the present disclosure is directed to systems and methods for ensuring that the information, such as certificates, associated with the devices that use the server and which are stored on the server is kept up to date. 
     2. Related Art 
     Exchanging cryptographically encoded secure electronic messages and data, such as, for example, e-mail messages, is well known. In many known electronic message exchange schemes, signatures, encryption or both are commonly used to ensure the integrity and confidentiality of information being exchanged between a sender and a recipient of the electronic messages. In an e-mail system, for example, the sender of an e-mail message may either sign the message, encrypt the message or both sign and encrypt the message. These actions may be performed using well-known standards, such as, for example, Secure Multipurpose Internet Mail Extensions (S/MIME), Pretty Good Privacy™ (PGP™), OpenPGP, and numerous other secure e-mail standards. 
     In general, secure e-mail messages are relatively large. For example, S/MIME can increase the size of an e-mail message by a factor of ten or more in some situations. This size augmentation, caused for example by appending certificates to the message, presents difficulties, especially in devices that have a limit on the size of a message that can be processed, such as, for example, a mobile wireless communications device. Such a device may also experience difficulty handling a message wherein only a portion of the message has been transferred to the device because of the above-mentioned size limitations. 
     To the extent processor intensive actions, such as, for example, verification of signatures, can be performed by a more powerful and faster device, such as, for example, a server, advantages with respect to device efficiency, speed and improved user satisfaction can be realized by a reduction of computational overhead of the device. However, in order to take advantage of the improved processor capability and speed of the server, it is necessary for the server to have the proper information available to perform the functions otherwise performed by the mobile device. For example, if the server maintains a list of certificates associated with devices using the server, the server will have the ability to verify signatures for the user. This is an especially powerful tool if the message is long. In addition, the server can effectively compress the certificate information that is sent in the S/MIME message. For example, if the server knows that a device already has a particular certificate on it, then when an S/MIME message to the device includes that certificate, the server can safely remove this certificate. This saves a great deal of bandwidth for each certificate that is removed. The bandwidth savings realized by removing redundant certificate information is especially useful because the certificate information limits the amount of bandwidth available for the message. However, to realize the efficiencies attendant with having device certificate information resident at the server, it is important to keep this certificate information up to date. To that end, what is needed is a system and method for synchronizing information, such as, for example, certificates, between the server and its associated devices. 
     BRIEF SUMMARY OF THE INVENTION 
     In view of the foregoing, we have now identified efficient and easy to implement systems and methods for synchronizing information, such as, for example, certificates between a server and the devices that use the server. By providing a server with certificates contained in devices that use the server, and providing a system and method for synchronizing the certificates between the devices and server, the server can implement powerful features that will improve the efficiency, speed and user satisfaction of the devices. 
     According to an exemplary embodiment of the present disclosure, a server within the wireless communications system has the ability to keep and maintain a list of certificates that are contained in devices that use the server. The server may keep this list up to date, i.e., synchronized, by building a list for each device, and maintaining the currency of the lists based on activity of the device, such as, for example, messages sent by the device that are processed by the server. For example, whenever the device sends an S/MIME message, the device may append a list of certificate thumbprints to the message together with an indication of what action is to be performed by the server with respect to the appended certificates so that the server can maintain the currency of the certificate lists. Initially, the thumbprints may be used to build the list of certificates residing on the server that are contained in the devices using the server. The actions that are to be performed may include, for example, adding the certificates to the list and/or removing the certificates from the list. The device may send the certificate thumbprints one at a time or in bulk in a single S/MIME message. When the server receives the message with the appended certificate information for processing, the server is able to strip out the certificate information field from the S/MIME message and then update the database. In this manner, the server database that includes the certificate information for devices using that server can be kept up to date or synchronized. 
     According to another exemplary embodiment of the disclosure, the server is operable to learn what certificates are on the devices using empirical techniques. For example, when an S/MIME message is sent to the device, the server may check the sender&#39;s certificate to determine if it is on the device. If the server believes that the certificate is on the device, it will automatically strip the certificate from the sender&#39;s message and put it in the server database list of certificates for the device. If the server does not know or otherwise does not believe that the certificate is on the receiving device, the server leaves the certificate data appended to the message. Upon receipt of the message, the device performs a check to determine what was done by the server with respect to the certificate information in the original message. If the server acted correctly, for example, stripped the certificate when it was on the device or left the certificate information with the message when it was not on the device, the device sends back an acknowledgement indicating to the server that the server took the correct action. If the server acted incorrectly, for example, by stripping the certificate when it was not on the device or included the certificate when it was on the device, the device provides an indication of this error to the server as well. In this interactive and iterative manner, the server ultimately learns the state of the device and its certificates. 
     The foregoing exemplary embodiments provide a solution to the problem of maintaining an up to date list of certificates that are in devices that use a particular server, thereby enabling the server to perform, for example, computationally intensive actions and thereby distributing the processing overhead of the mobile wireless communications devices to the server, thereby enabling the sharing of system resources to assist the device, for example, in verifying secured electronic messages. Moreover, the exemplary embodiments also enable advantageous bandwidth savings by preventing transmission of certificates unnecessarily. 
     The advantages attendant with the various embodiments of the invention described above are provided by the method and system of synchronizing certificates between a server and device disclosed and described herein with reference to the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other objects and advantages of exemplary embodiments of the present invention will be better understood and appreciated in conjunction with the following detailed description of exemplary embodiments taken together with the accompanying drawings, in which: 
         FIG. 1  is an overall system wide schematic view of an exemplary wireless e-mail communication system incorporating a mobile wireless communications device with the descriptive error messaging in accordance with an exemplary embodiment of the present invention; 
         FIG. 2  is a block diagram of a further exemplary communication system including multiple networks and multiple mobile communication devices; 
         FIG. 3  is an illustrative schematic block diagram of an exemplary mobile wireless communications device; 
         FIG. 4  is a block diagram depicting components used in handling messages; 
         FIG. 5  is an illustrative flow diagram of an exemplary operational scenario for maintaining and synchronizing certificates between the server and device according to an exemplary embodiment of the invention; and 
         FIG. 6  is an illustrative flow diagram of an alternative exemplary operational scenario according to another exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       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 at least one of 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  300 , 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  300  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  300  is the message server  400 , 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  400  to a mobile communication device  100 . Although the redirection program  45  is shown to reside on the same machine as the message server  400  for ease of presentation, there is no requirement that it must reside on the message server. The redirection program  45  and the message server  400  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  300 . 
     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  300  or a computer  35  within the system  300 . 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  400  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. 
     As depicted in  FIG. 3 , mobile communications device  100  includes a suitable RF antenna  102  for wireless communication to/from wireless network  20 . Conventional RF, demodulation/modulation and decoding/coding circuits  104  are provided. As those in the art will appreciate, such circuits may involve possibly many digital signal processors (DSPs), microprocessors, filters, analog and digital circuits and the like. However, since such circuitry is well known in the art, it is not further described herein. 
     The mobile communications device  100  will also typically include a main control CPU  106  that operates under the control of a stored program in program memory  108 , and which has access to data memory  110 . CPU  106  also communicates with a conventional keyboard  112  and display  114  (for example, a liquid crystal display or LCD) and audio transducer or speaker  116 . A portion of the data memory  310  is available for storing data required for decrypting encrypted messages, such as, for example, private keys, digital certificates, and the like. This portion  310  of the data memory  110  may also be use to store the certificates that are in devices that use the server. Suitable computer program executable code is stored in portions of the program memory  108  to constitute stored program logic for receiving and using new or added private keys and/or digital certificates or the like as described below (for example, via a wired serial I/O port or the wireless RF antenna  102 ). 
     As depicted in  FIG. 1 , a secure wired synchronization connection  26  (for example, between serial I/O ports of the user&#39;s base unit  24  and the wireless device  100 ) is typically provided for normal data synchronization purposes (for example, to synchronize databases in the two devices with respect to such things as calendars, to-do lists, task lists, address books, etc.). Part of prior data synchronization processes has included a program logic such as Cert Sync for maintaining synchronization between cryptographic message certificates. If a secure over the air (OTA) synchronization connection  28  is available, it may also be used by Cert Sync to maintain synchronization of cryptographic message certificates. 
     As previously described, there is a communications link (for example, depicted in dotted lines at  30  in  FIG. 1 ) typically found between the device user&#39;s base unit  24  and a system message server  14 . Accordingly, there is an existing communication path that may be utilized for passing synchronization data from the user&#39;s base unit  24  via channel  30 , the server  14 , Internet  12 , wireless gateway  16  and wireless infrastructure  18  via the OTA synchronization connection  28 . 
     E-mail messages generated using the S/MIME and PGP techniques may include encrypted information, a digital signature on the message contents, or both. In signed S/MIME operations the sender takes a digest of a message and signs the digest using the sender&#39;s private key. A digest is essentially a checksum, CRC or other preferably non-reversible operation such as a hash of the message, which is then signed. The signed digest is appended to the outgoing message, possibly along with the certificate of the sender and possibly any required certificates or CRLs. The receiver of this signed message must also take a digest of the message, compare this digest with the digest appended to the message, retrieve the sender&#39;s public key, and verify the signature on the appended digest. If the message content has been changed, the digests will be different or the signature on the digest will not verify properly. If the message is not encrypted, this signature does not prevent anyone from seeing the contents of the message, but does ensure that the message has not been tampered with and is from the actual person as indicated on the “from” field of the message. 
     The receiver may also verify the certificate and CRL if they were appended to the message. A certificate chain is a certificate along with a number of other certificates required to verify that the original certificate is authentic. While verifying the signature on a signed message, the receiver of the message will also typically obtain a certificate chain for the signing certificate and verify that each certificate in the chain was signed by the next certificate in the chain, until a certificate is found that was signed by a root certificate from a trusted source, such as, for example, a large Public Key Server (PKS) associated with a Certificate Authority (CA), such as, for example, Verisign or Entrust, both prominent companies in the field of public key cryptography. Once such a root certificate is found, a signature can be verified and trusted, since both the sender and receiver trust the source of the root certificate. 
     In encrypted S/MIME message operations, a one-time session key is generated and used to encrypt the body of the message, typically with a symmetric cipher, such as, for example, Triple DES. The session key is then encrypted using the receiver&#39;s public key, typically with a public key encryption algorithm like RSA. If the message is addressed to more than one receiver, the same session key is encrypted using the public key of each receiver. The encrypted message body, as well as all encrypted session keys, is sent to every receiver. Each receiver must then locate its own session key, possibly based on a generated Recipient Info summary of the receivers that may be attached to the message, and decrypt the session key using its private key. Once the session key is decrypted, it is then used to decrypt the message body. The S/MIME Recipient Info attachment can also specify the particular encryption scheme that must be used to decrypt the message. This information is normally placed in the header of the S/MIME message. Those skilled in the art will appreciate that these operations relate to an illustrative example of S/MIME messaging and its associated encoding operations, namely encryption. It will also be understood that the instant disclosure is in no way limited thereto. 
       FIG. 4  illustrates a situation where messages are provided to a mobile device  410  by a server  408  contained within a wireless connector system  406 . With reference to  FIG. 4 , a message  404  from a sender  402  is provided to the wireless connector system  406 . The server  408  within the wireless connector system  406  analyzes the encoded message  404  with respect to any appended certificates. If the certificate list for the mobile device  410  is determined to require updating or synchronization (as will be described in detail herein), then the server  408  may notify the mobile device  410  of certificate list related information  414 . The server may process the message  412  before sending it to the mobile device such that the message  412  may be, for example, compressed by removing certificates that are contained in the destination mobile device  410 . Moreover, data item  412  may be further processed by the server  408  such that the message is decoded and verified using the updated certificate information maintained by the server  408  and the result of such processing sent to the mobile device  410 . 
     As an exemplary operational scenario, if the message is signed, and the server  408  knows the certificates that are contained in the mobile device  410 , the server  408  in this situation may perform message verification and provide an indication to the mobile device  410  that verification has already been done by the server. The user receiving this message will then be aware that verification of the message has already been accomplished. In another operational example, the server may strip the message of certificate information known to be contained in the mobile device, thereby reducing the size of the message and providing significant bandwidth savings. Once again, an indication that certificate information has been stripped from the message may be provided to the mobile device. 
     According to an exemplary embodiment of the present invention, as illustrated in  FIG. 5 , the server is operable to synchronize certificates between the device and server. In particular, according to this example, the mobile device sends an S/MIME message to the server that includes at least one certificate thumbprint, together with an indication of an action to be taken by the server with respect to the appended certificate thumbprint. Of course, it will be understood that the S/MIME messages may be used to send one certificate thumbprint at a time, may send a thumbprint of all certificates on the device at once, or may send any intermediate number of certificate thumbprints, at the discretion of the user. For convenience, the description may refer to certificate thumbprints in the singular or plural, but it will be understood that any number may be processed. In addition to the certificate thumbprints, the S/MIME message includes an “action” or instruction for the server with respect to the appended certificate thumbprint. These actions are, for example, “add” or “remove.” 
     Upon receipt of the S/MIME message from the device, the server determines which action is to be taken  503  based upon the action information contained in the received S/MIME message. If the action is to add a certificate to the list for a particular device, the server operates to update the certificate list associated with the device with the certificate or certificates appended to the message  505 . Upon updating the certificate list, the server may, optionally, notify the device that the certificate list at the server has been updated  509 . On the other hand, if the action is to remove a certificate from the list for a particular device, the server operates to update the certificate list associated with the device by removing or deleting the certificate or certificates appended to the message  507  from the certificate list associated with the device. Once again, upon updating the certificate list, the server may, optionally, notify the device that the certificate list at the server has been updated in accordance with the S/MIME message  509 . 
     Another example is illustrated in  FIG. 6 . According to this operational example, the server may be operable to learn what certificates are on the mobile device by employing an empirical testing scheme. For example, when an S/MIME message is sent to the device  601 , and is processed by the server  603 , the server checks the sender&#39;s certificate  605 . The server then determines whether it believes that the certificate appended to the sender&#39;s message is contained in the destination device  607 . This may be done, for example, by comparing the certificate in the message with current list of certificate thumbprints for the destination device. Upon making a determination in step  607 , the server then takes a particular action which, based on the determination made in step  607 , will aid in synchronizing the certificates between the server and the device. For example, if the server determines that the certificate appended to the sender&#39;s message is in the destination device  607 , the server operates to strip the certificate  609  from the sender&#39;s message, and to update the certificate list for the device  611  in the server memory. The server then sends a notification to the device of the action that has been taken  615 . Alternatively, if, in step  607 , the server determines that the certificate appended to the sender&#39;s message is not contained in the destination device, the server leaves the certificate appended to the message  613 , and notifies the device of what action was performed by the server  615 . 
     The device, upon receipt of the notification provided in step  615  then determines if the action taken by the server was correct  617 . For example, if the server stripped a certificate from the sender&#39;s message, and the certificate was, indeed, present on the destination device, or that the server properly determined that the certificate appended to the sender&#39;s message was not present on the destination device and therefore did not strip the certificate, the device would send an acknowledgement to the server that the correct action had been taken  619 . On the other hand, if the server improperly stripped the certificate from the sender&#39;s message, or left the certificate appended to the sender&#39;s message, when the device contained the certificate, the device would send the appropriate notification to the server  621 , and remedial steps  623  could optionally be taken to correctly synchronize the certificates between the server and the device. 
     While the foregoing has been described in conjunction with specific exemplary embodiments, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, the exemplary embodiments set forth herein are intended to be illustrative, not limiting. Various changes may be made without departing from the true spirit and full scope of the invention as defined in the appended claims.