Patent Publication Number: US-2002007453-A1

Title: Secured electronic mail system and method

Description:
[0001] This application is based upon and claims benefit of Provisional Application Ser. No. 60/206,580, filed on May 23, 2000, to which a claim of priority is hereby made. 
    
    
     
       BACKGROUND OF THE INVENTION  
       [0002] 1. Field of the Invention  
       [0003] The present invention relates generally to a system and method for delivering secure electronic mail across a communication network, and more specifically to a system and method for encrypting, digitally signing, virus-checking, time/date stamping, preserving privacy, and authenticating electronic mail delivered across a communication network independent of the sender&#39;s and recipient&#39;s electronic mail platforms.  
       [0004] 2. Discussion of the Related Art  
       [0005] Electronic mail, or e-mail, has enjoyed vast popularity due to its simplicity, speed and cost effectiveness. In general, both commercial and private entities have made widespread use of e-mail as a communication tool to increase productivity and effectiveness. E-mail has become a fundamental communication tool, both for business and for personal use.  
       [0006] Perhaps because of the simplicity and speed of e-mail, users often fail to appreciate some of the drawbacks associated with sending information over an electronic network. For example, it is a simple matter to attach many different files of varying file types to an e-mail message for transmission to a number of recipients. If any of the transmitted files are infected with computer viruses, for example, it is possible for each recipient of the message to become infected with the virus.  
       [0007] Viruses spread rapidly if an infected message is forwarded to other recipients that become infected and then continue to propagate the virus by retransmitting or forwarding the infected message. This scenario illustrates how destructive viruses can be rapidly spread to a number of e-mail users. This danger in the widespread use of e-mail can actually be exacerbated by the design of some e-mail programs that provide a mechanism that permits a rogue e-mail to abuse access to an e-mail address list maintained within the e-mail platform. An e-mail message with destructive potential can access the e-mail address list maintained on a particular e-mail platform, and can cause itself to be sent to all addresses in the list. While virus checking software is available to ensure that the e-mail attachments are virus free, attachments in general are not affirmatively scanned as a matter of course.  
       [0008] Another drawback associated with e-mail communications is that they are relatively easy to intercept and view, which can compromise the security and confidentiality of e-mail messages. No tool is generally available to e-mail users to ensure that the e-mail message has not been intercepted. For example, sending an e-mail over a public network such as the Internet has been compared to sending a postcard through the postal mail, since the postcard content may be viewed at any time during its transmittal. In addition, it is possible to exploit a vulnerability in e-mail messages sent over a network that involves copying the e-mail message from one point to another. As the message is relayed between various points on the network, each relay point presents an opportunity for a copy of the e-mail message to be transmitted to a third party, or to the relaying system itself.  
       [0009] A partial solution to the difficulties discussed above involves using an encryption scheme to secure the content of the e-mail message. A typical encryption scheme is known as point to point encryption, which allows an e-mail sender to encrypt the e-mail message and send the encrypted message to one or more recipients, who can then unencrypt the message and view the contents. This type of point to point encryption typically relies upon a public key system in which the sender uses a public key to encrypt the e-mail message being sent, and the receiver can unencrypt the message using the recipient&#39;s private key paired with the sender&#39;s public key. One such well known public key system is typically referred to as pretty good privacy (PGP). Public key systems also offer the opportunity for digital signatures that can be used to verify document origin, in addition to providing tamper resistance for the transmitted document.  
       [0010] However, files secured by encryption offer no protection against viruses, for the simple reason that a file infected with a virus, once encrypted, will disguise the virus, which is also encrypted. In addition, available point to point encryption software is typically proprietary for each vendor. Accordingly, a sender and a receiver can only use point to point encryption if each uses the same encryption vendor&#39;s software. Unless the sender and receiver both subscribe to the same vendor encryption software, they cannot communicate securely. Moreover, even if an e-mail message is encrypted, an intercepting third party can still view the address and identity of both the sender and receiver, which remains unencrypted for transmission purposes.  
       [0011] In addition, it is possible that a sender or receiver using point to point encryption may have their system compromised, by having a portable computing device stolen, for example. A stolen device can provide an unauthorized third party with the private key of a user, permitting the third party to pose as a secure sender or receiver. Moreover, although an unlikely or rare occurrence, it is possible that a vendor may mistakenly distribute secure key pairs to third parties posing as a trusted content provider. Accordingly, the third party can pose as the content provider and fool persons accessing a web site, for example, into believing that the web site content is safe and from a trusted source.  
       [0012] Other schemes can potentially be used to fool a sender into believing an e-mail message is securely encrypted prior to transmission to the recipient, when in fact a third party is readily able to decode and read the message through a process known as spoofing. A spoofed e-mail message is one in which the sender is tricked into sending the encrypted message directly to a third party, who can then decode and read the message, and can then either (1) reencrypt the message to be read by the original intended recipient and forward the message, (2) modify the content of the message, reencrypt it and forward it to the original intended recipient, or (3) block the message altogether. Of course the interceptor can also forward the message to other parties for which the message was not intended to be received.  
       [0013] Another partial solution to the difficulty of securely transmitting e-mail is to use firewall based encryption and virus protection. According to this scenario, a firewall intercepts all incoming and outgoing e-mail messages and provides encryption-decryption service for each of the messages, in addition to scanning for viruses. However, the difficulties attendant with point to point encryption are also present with a security scheme involving a firewall. For example, the sender and recipient must use the same vendor public key encryption software. The correspondence activity between the sender and recipient can still be monitored with this scheme because the identity of the sender and receiver can be readily determined since they are not encrypted. In addition, since the encryption/decryption takes place at the firewall and typically not on the sender/recipient computer, the message must travel unencrypted between the sender/recipient computer and the firewall. In the course of this travel, the message is vulnerable to interception or inspection.  
       [0014] Another partial solution to the difficulty of securing e-mail communications is to provide a web based e-mail server. The sender of an e-mail using a web based e-mail server logs onto the server, typically using secure socket layer (SSL) communication link protection, and sends an e-mail message to one or more recipients. The e-mail message and any attachments are encrypted and can be checked for viruses. Each of the recipients of the e-mail message is then notified by regular unsecured e-mail messages. Each recipient upon receipt of the notification can log onto the web based e-mail server and read the message, which remains stored on the server itself.  
       [0015] The web based e-mail server scenario also has several drawbacks, including the fact that the sender and recipients all must learn a new interface to access the e-mail messages on the server. In addition, a web based e-mail server is typically less convenient to use, especially for a commercial entity that wishes to control and manage its own e-mail system, perhaps in conjunction with other associated activities such as calendaring, contact list maintenance and other types of group oriented electronic interchange. Furthermore, the web based e-mail server solution suffers from some of the same drawbacks as the other partial solutions described above, including vulnerability to third parties who can pose as recipients and obtain access to e-mail messages thought to be secure. In addition, when the sender uses the web based e-mail server to create a message to be sent to one or more recipients, the message arrives at the website in an unencrypted form. While the period of time between creation of the message and encryption is potentially short, the message is still vulnerable to interception and inspection. Websites are generally easy targets for persons or entities seeking to intercept messages or obtain information without authority, since websites are typically designed for easy access rather than for security. Security on a website is often more of an afterthought because the main intent and purpose of a website is to be open to the world.  
       [0016] Furthermore, since the web based e-mail server must notify all the recipients of a received e-mail, the e-mail communication is susceptible to activity tracking. For example, a third party wishing to know when the sender and recipients are communicating can monitor the notifications between the web based e-mail server and the recipients to obtain the identity of the parties communicating, and often the subject of the e-mail message.  
       [0017] Another partial solution to provide e-mail security involves a hybrid of the above described web based e-mail server. In this hybrid scenario, the sender logs on to a web server to obtain an encryption key. The sender then encrypts an e-mail message on their local terminal, and sends the e-mail message to the recipient, who must then access the web server to obtain the decryption key for the message. As with other partial solutions mentioned above, the hybrid solution also suffers from the drawback that a third party can potentially pose as the e-mail server and intercept communications for which the third party has the encryption/decryption keys. In addition, this hybrid method can not offer virus checking features. As with the standard web based e-mail server model discussed above, this hybrid solution is also susceptible to activity monitoring, because the actual e-mail itself, even though encrypted, is sent directly from sender to recipient. Moreover, the user of the hybrid system must become familiar with yet another application interface, which can lead to frustration and lack of productivity on the part of the user.  
       [0018] Accordingly, there is need for a secure system with a familiar user interface for transferring e-mail messages that also provides virus checking and a high level of privacy.  
       SUMMARY OF THE INVENTION  
       [0019] It is an object of the present invention to overcome the drawbacks of the prior art discussed above.  
       [0020] Briefly stated, there is provided according to the present invention a client-server system for sending and receiving secure e-mail transmissions that are date stamped, virus scanned and authenticated at a centralized server. The client application runs as an add-on or feature of the client e-mail system. The server acknowledges sent e-mail, and can provide a secure copy of the message and a return receipt to the sender. The sending and receiving parties are verified from a central database to aid in prevention of tampering. The e-mail message is given a digital signature for authentication upon being sent, and the server adds another digital signature, in addition to encrypting the message with a different key than that used by the sender before re-transmitting the secure message to the recipients. The sending and receiving parties of the e-mail message are not both exposed at the same time, thereby preventing activity monitoring. The recipients can receive, unencrypt, and read the secure e-mail message without fear of loss of privacy or infection by viruses. The digital signature provides a non-repudiation mechanism for verifying sending and receiving party intentions. The present invention satisfies a primary criteria for secure document transmission of confidentially, integrity, accountability, and ease of use.  
       [0021] According to an embodiment of the present invention, there is provided a sending station, a verification station and a receiving station. The sending station produces a hash code from a hashing operation on an electronic message, encrypts the message with a random encryption key and generates a digital signature from the hash code and a sender private key from a sender public/private key pair. The encrypted message, the random encryption key, the digital signature, the sender public key from the sender public/private key pair and a public key from the verification station are all transmitted in a package to the verification station. The verification station performs the reverse operations to obtain the original message, verifies the content with the hashing operation in comparison with the digital signature, time and date stamps the message and scans it for viruses. Once the message is verified, a new digital signature is generated as described above, and the message is encrypted with a new random encryption key and sent to the receiving station. The secure communication to the receiving station includes the digital signature, the encrypted message, the encrypted random encryption key, the receiving station public key (if available) and the verification station public key. A reverse process is undertaken at the receiving station to unpack and view the message.  
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0022]FIG. 1 is a diagram showing an overview according to the present invention;  
     [0023]FIG. 2 is a diagram of interconnectivity of components of the system according to the present invention;  
     [0024]FIG. 3 is a diagram of the end to end flow according to the present invention;  
     [0025]FIG. 4 is an example of mail center message flow according to the present invention;  
     [0026]FIG. 5 is a diagram showing load distribution and reciprocal backup according to the present invention;  
     [0027]FIG. 6 is a description of the sender message packaging according to the present invention;  
     [0028]FIG. 7 is a diagram showing an overview of the secure e-mail server according to the present invention;  
     [0029]FIG. 8 is a diagram showing unpacking and checking of the sender message at the server according to the present invention;  
     [0030]FIG. 9 is a diagram showing repackaging of the message at the server for transmission to the recipient(s) according to the present invention;  
     [0031]FIG. 10 is a diagram showing treatment of messages transmitted to recipients having various e-mail platforms according to the present invention;  
     [0032]FIG. 11 is a diagram showing treatment of a secure message received by a subscriber in a supported e-mail environment according to the present invention;  
     [0033]FIG. 12 is a diagram showing a secure message received by a subscriber using a generic e-mail environment;  
     [0034]FIG. 13 is a diagram showing a secure message received by a non-subscriber as a secure generic form e-mail message according to the present invention;  
     [0035]FIGS. 14A, B, and C show diagrams of support routines for obtaining public keys, verifying identities and status, respectively, according to the present invention;  
     [0036]FIG. 15 is a diagram of a menu table describing installation options according to the present invention; and  
     [0037]FIG. 16 is a diagram of sender options shown in a menu table according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     [0038] Referring now to FIG. 1, an overview of the system according to the present invention is shown. A sending computer  400  is connected to a communication network  130 , such as the Internet, over a communication link. A network node  132  handles packet switched communication between sending computer  400  and a central server  52 . Central server  52  is also connected to node  132  of communication network  130 . Node  132  is an abstract node, in the sense that it may be comprised of a number of nodes and interconnected computers comprising the communication network. Central server  52  is also connected to another node  134  of the communication network  130 . A receiving computer  405  is also in connection with node  134  of communication network  130 . The overview of FIG. 1 shows how e-mail messages can be sent by sending computer  400 , through central server  52  and received by receiving computer  405  through connections to node  132 ,  134  of communication network  130 .  
     [0039] The system according to the present invention shown in FIG. 1 permits secure e-mails to be sent from sending computer  400  and received in receiving computer  405 . Central server  52  provides secure authentication, virus checking, time and date stamping as well as flexibility with regard to the type of system used by the message sender and recipient. The system operates by encrypting an e-mail message at sending computer  400  and sending the encrypted message to central server  52  through communication network  130 . The encrypted e-mail message is unpacked, verified and virus checked, before being repackaged for transmission to receiving computer  405 . Once the e-mail message is repackaged in a secure format, it is transmitted through communication network  130  via node  134  to receiving computer  405 . The recipient is notified of the encrypted e-mail and, according to one embodiment of the present invention, is provided with instructions on opening and unencrypting the e-mail message, if necessary. The system operates with a number of different hardware and software platforms by which receiving computer  405  sends and receives e-mail messages.  
     [0040] Referring now to FIG. 2, central server  52  as illustrated in FIG. 1 is explained in greater detail. As shown in FIG. 2, central server  52  is comprised of a number of workstations and servers connected and operating through a local area network (LAN)  20 . LAN  20  has connected to it a file/database server  10  that provides network services such as printing, file sharing and access to an off-site backup and storage system  140 .  
     [0041] LAN  20  is connected through a hub  90  to external LAN  105 . External LANs  105  and  106  are connected to communications network  130  and provide load balancing, fire wall protection and routing for communication with communication network  130  and a node  25  comprising LAN  20 . LAN  105  includes a load balancer  40 , a fire wall  60  and a router  100 . Similarly, LAN  106  includes a load balancer  42 , a fire wall  62  and a router  102 . Load balancers  40  and  42  examine communication traffic from communication network  130  and determine how best to divide resources available to handle the communication traffic. Fire wall  60  protects LAN  20  from unauthorized access through communication network  130 . Fire walls  60  and  62  are designed to protect against unauthorized accesses such as can occur when communication network  130  is used to attack or infiltrate LAN  20 , for example, or when undesirable content is attempted to be transferred from communication network  130  to LAN  20 . Router  100  switches communication traffic between communication network  130  and LAN  20  under the direction and control of load balancer  40  and fire wall  60 .  
     [0042] It is preferable that LAN  20  operate at a 100 megabits per second or faster. LAN  20  is set up and maintained by an administration server  30  that has access to the equipment attached to LAN  20 . For example, administration server  30  can be operated to set up mail servers  50 , secure mail servers  80 , as well as load balancers  44  and  46 , and fire walls  64  and  66  that are attached to LAN  20 . Administration server  30  can be used to adjust settings in each of the network components, for example, specifying network addresses of communication network  130  that will not be accepted past fire walls  64  or  66 . Administration server  30  can also be used to configure LAN  20  to recognize Internet service provider connections  110  and  120  that are authorized to connect to LAN  20  through communication network  130 . For instance, a user that has been provided with authorized access to LAN  20  may wish to access LAN  20  through communication network  130  on a remote basis. Accordingly, administration server  30  can provide settings to enable the remote user to connect to LAN  20  from Internet service providers  110  and  120  via communication network  130 .  
     [0043] Load balancers  44  and  46  provide balancing services to LAN  20  for mail servers  50  and secure mail servers  80 , respectively. Through the use of load balancers  44  and  46 , each set of respective resources can be used with greater efficiency than if load balancers  44  and  46  were not present. For example, communication jobs directed to any of the various mail servers  50  can be distributed among various mail servers  50  according to the size of a job or resources available to particular mail servers  50 . Similarly, secure e-mail communication jobs can be distributed across the various secure mail servers  80  to improve the efficiency of communication handling and maximize utilization of available resources. When load balancers  40 ,  44  and  46  are configured to work in concert, for example, overall efficiency of node  25  can be improved.  
     [0044] Fire walls  64  and  66  provide an extra level of protection in addition to fire wall  60 , which is external to LAN  20 . For example, fire wall  64  adds protection to accesses made to mail servers  50  to prevent unauthorized or unwanted access or messages. Fire wall  66  provides a similar function for secure mail servers  80 .  
     [0045] It should be apparent that the configuration of node  25  is just one embodiment of a hardware configuration according to the present invention. Any number of node configurations are possible, provided a computer can be connected to a communication network such as communication network  130  to process electronic mail and provide security functions such as authentication, virus scanning and encryption or unencryption. In addition, access to node  25  can be provided on a wireless basis, such as is available with mobile phones and other wireless personal digital assistants (PDAs). Furthermore, the communication network exemplified by communication network  130  can be any type of communication network, including public, private, local, wide area and worldwide. The communication methods used by communication network  130  are not limited according to the present invention. That is, communication network  130  can take advantage of any technology for communication, including analog, digital, cable and wireless communication. It should be noted that backup, archival and storage functions provided by backup and storage system  140  can be any type of secure backup and archive storage system that can obtain and preserve data from LAN  20  through server  10  for retrieval at a later point in time. Backup and storage system  140  can be local, off site, network connected, or a manual media storage vault, for example.  
     [0046] Node  25  shown in FIG. 2 comprising LAN  20  and the attached components, can be replicated any number of times. For example, any number of nodes comprising a LAN  20  and attached components can be connected to each other directly, or through communication network  130 . Accordingly, various nodes can be distributed across a wide area or locally, and can function as a single network on an enterprise basis, for example.  
     [0047] Node  25  processes secure e-mail messages that are sent and received through LAN  20 , hub  90 , router  100  and communication network  130 . Secure e-mail messages are processed by secure mail servers  80  and provided to the appropriate party. For example, a sender or receiver may be located at node  25  and connected to LAN  20 . Such a sender or receiver would have direct access to the secure mail services provided by secure mail servers  80 . Alternatively, a secure e-mail user may be located remotely from node  25  and connected to node  25  through communication network  130 .  
     [0048] In the case where the secure e-mail user is directly connected to LAN  20 , the user workstation need not have secure e-mail software resident on their local PC. Instead, such a directly connected user can send and receive e-mails through LAN  20 , with the security, authentication and virus checking features being transparent to the user. An e-mail message sent by a user directly connected to LAN  20  is processed by secure mail server  80  to provide encryption, authentication and virus checking services. Secure mail server  80  processes the e-mail messages and packages the messages for transmission through communication network  130  to the intended recipients. The recipients of the packaged, secure e-mails can access the enclosed message in a number of flexible formats as discussed more fully below.  
     [0049] A user need not be directly connected to LAN  20  to send secure e-mail messages using secure mail server  80 . For example, if a user is located at a remote site, it is still possible for the user to connect to node  25  across communication network  130 . The remote user is typically given remote access authorization to remotely access node  25  and secure mail servers  80 . Secure mail servers  80  are again used to process and repackage the e-mail message to provide authentication, encryption and virus checking services. In this embodiment, however, the remotely located user has secure mail software resident on their (typically) portable personal computer. The resident secure mail software permits the e-mail messages sent by the remote user to be encrypted, digitally signed and packaged for transmission to node  25 . At node  25 , the e-mail message is unpacked, unencrypted, authenticated, virus checked and time and date stamped by secure mail servers  80 , prior to being retransmitted to the intended recipient(s). Once the secure e-mail message has been verified, it is repackaged with another digital signature, encrypted and ready to be retransmitted to the intended recipient(s).  
     [0050] Each transmission between node  25  and communication network  130  passes through fire walls  64  and  66 , and is routed according to balancing schemes determined by load balancers  44  and  46 . Node  25  further has an overall fire wall  60  attached through LAN  105  to router  100  to provide further protection for node  25  against unauthorized access through communication network  130 . Node  25  further is provided with load balancing services for all e-mail messages being sent and received through load balancer  40 .  
     [0051] Referring now to FIG. 3, a diagram of the flow of a typical secure e-mail message is shown. Sender computer  400  is used to composed an e-mail message, including any type of electronic file in the message body or as an attachment. The system according to the present invention supports a number of well known e-mail systems, any of which may be used to compose the e-mail message on sender computer  400 .  
     [0052] Once the sending user has completed the e-mail message to be sent, and selects a send function, software instructions stored in sending computer  400  execute to transform the complete e-mail message into a form according to the system of the present invention. When transformed into a form according to the system of the present invention, the sender private key is obtained to encrypt the message. The reformatted message is “hashed” according to an algorithm that provides a result that is highly unique with regard to the contents of the reformatted e-mail message. The resulting digital hash code is used in combination with the sender private key to produce a digital signature for the sender&#39;s message. The sender public key is then added to the reformatted message, and both are encrypted with a one time random symmetrical key. The one time random symmetrical key is then further encrypted with the secure mail system public key. The encrypted public key is packaged with the encrypted and reformatted message, the digital signature, the sender&#39;s encrypted public key and the secure mail system public key, all of which is sent as an attachment to secure mail server  80  through communication network  130 .  
     [0053] According to a preferred embodiment of the present invention, the sender&#39;s private key is not stored anywhere, but is rather generated whenever needed. An authentication password or pass phrase can be used as the seed for execution of an algorithm that generates a public/private key pair each time the password or pass phrase is entered into the system. Preferably, the public/private key pair only exists in volatile memory for a short period of time and is removed after being used for encrypting or decrypting a message.  
     [0054] Another alternative to generating a public/private key pair from a password or pass phrase is to provide a unique indicator of the sender or receiver identity through a device, and use the unique indicator to validate messages. For example, a device capable of providing a unique code is attached to a computer port and accessed each time a message is signed for transmission, or authenticated upon receipt. If the device is missing, or provides an improper code, the sender or receiver may not open the transmitted or received document, respectively.  
     [0055] Devices known as “smart cards,” which require possession of the device and entry of an identifying code to authenticate identity, can also be used to verify a message. The smart card produces a code that can be used as the seed for execution of an algorithm to generate the public/private key pair used in the encryption of a sent or received message. This result can also be achieved through the use of biometric confirmation devices, such as fingerprint readers, retinal scanners and hand-geometry readers, for example. A unique code generated by these types of identity confirmation devices can be used as the basis for generation of public/private key pairs to be used in authenticating messages, without ever having to store a private key.  
     [0056] Once the packaged e-mail is sent by the sending party, it is received by mail server  50  through communication network  130 , and is virus scanned to ensure that no viruses were attached to the e-mail during transmission. The scanned e-mail is then sent to secure mail server  80  for processing. The system load on available resources in node  25  of FIG. 3 is balanced as new messages are sent and received through mail server  50 .  
     [0057] Once a secure e-mail is received by secure mail server  80 , the message is time and date stamped. Time and date stamping provides the message with an indication of the time and date received by secure mail server  80 . Time and date functions with regard to stamping are assisted and processed by synchronization with, for example, atomic clocks providing synchronization signals through satellite communications.  
     [0058] After time and date stamping, the secure e-mail message is unpacked and verified for any changes during transmission or viruses in the message itself. Once verified, the message is given a new digital signature by secure mail server  80 , is repackaged and sent to the recipient(s). The reformatted message may at this point be stored along with the digital signature for a later verification, according to user options selected for the transmission of e-mail messages. In addition, accounting and transaction data is logged and recorded for use by file/database server  10  to keep track of customer or subscriber usage and generate information relating to accounting and billing.  
     [0059] Administration server  30  is used to manage the storage of messages in file/database  10  and also has access to accounting and billing information stored on file/database  10 . Administration server  30  generates accounting reports, billing statements and completes credit and debit transactions related to services used by subscribers and users. For example, the administration server  30  can be used to charge credit cards or accounts for services that are used, as well as transfer funds between vendors and customers, for instance.  
     [0060] Once the verified e-mail message is digitally signed by secure mail server  80  and repackaged, it is re-sent to the recipient through communication network  130 . Examples of various types of recipients are shown in FIG. 3 as subscriber recipient  410 ,  420  and non-subscriber recipient  430 . Subscriber recipient  410  is an example of a recipient of a secure e-mail using a “supported” e-mail software package. For example, as mentioned above, a secure mail system according to the present invention supports several popular e-mail software and hardware platforms. This support feature potentially provides the sender and recipient with increased functionality for transferring e-mail messages.  
     [0061] For example, if sender computer  400  and subscriber recipient  410  both use the same, widely implemented software for calendaring of tasks and appointments, subscriber recipient  410  can immediately interpret a task or appointment sent by sender computer  400 , and the task or appointment can immediately be incorporated into a calendar for subscriber recipient  410 . According to this scenario, the reformatted e-mail message transformed from the sender&#39;s original message is readily interpreted in its original form and structure as provided by the sender when composing the original message. Subscriber recipient  410  is thus notified that a received e-mail is pending according to the format of the supported e-mail software. The e-mail, upon selection by the recipient, is decrypted with the recipient&#39;s private key and unpacked to become a normal message understood by the supported e-mail software used by subscriber recipient  410 , all of which is transparent to the user.  
     [0062] Subscriber recipient  420  is notified of pending e-mails in the same way as subscriber recipient  410 . However, subscriber recipient  420  employs a web based or other non-supported e-mail system. In this scenario, the received e-mail message is received as an attachment that is opened by the user. The attachment is decrypted with the recipient private key and opened as a reformatted form message providing the contents of the sender&#39;s message in generic form. A publicly available tool or interface can be used by subscriber recipient  420  to access and view the contents of the secure e-mail system, for example.  
     [0063] Non-subscriber recipient  430  is similarly notified of receipt of an e-mail, as with subscriber recipient  410  and  420 . However, the e-mail system used by non-subscriber recipient  430  is a format unknown to the secure mail system. Accordingly, when an attempt is made by the user at non-subscriber recipient  430  to open the secure e-mail, the user is prompted for an authorized password that has been conveyed by the sender separately through, for example, other communication means. Non-subscriber recipient  430  enters the password as requested, which is then used to generate a private key suitable for unencrypting the secure mail message. Once unencrypted, non-subscriber recipient  430  can access and view the contents of the secure e-mail message in a reformatted, generic form.  
     [0064] It should be noted that subscriber recipient  410 ,  420  and non-subscriber  430  all receive a secure, time and date stamped, digitally signed and authenticated, plus virus checked e-mail message. Subscribing users that can take advantage of supported e-mail interfaces can send and receive secured e-mail messages through a transparent overlay to their normal user interface. Subscribing users that employ web based or other non-supported e-mail systems receive simple generic form e-mail messages, containing all the content provided by the message sender, in a secured and easily accessed format. Non-subscriber users receive a simple executable attachment that can be viewed in a simple generic format, once accessed with a password or pass phrase.  
     [0065] Referring now to FIG. 4, a diagram of message flow through secure mail server  80  is illustrated. A secure mail message according to the present invention is sent through communication network  130  as a packet  900 . Packet  900  is received by mail server  50  from communication network  130  and is scanned for viruses before being transferred to secure mail server  80  through a load balancing process.  
     [0066] Once received at the processing secure mail server  80 , the secure mail message is unpackaged and the one time random symmetrical key is decrypted with a public key known to secure mail server  80 . The one time random symmetrical key is used to unencrypt the sender&#39;s public key and the generic reformatted message, together with the digital hash code representative of the generic reformatted message. The sender&#39;s public key is used together with the regenerated digital hash code to verify the digital signature and lack of tampering. The unencrypted e-mail is virus scanned and a date and time stamp is provided to further authenticate the message. The unencrypted message itself is not stored on any system susceptible to backup or archival methods, unless so designated by the user. Secure mail server  80  updates a log file, if the option is selected by the user, to record receipt and status of the secure e-mail message.  
     [0067] If the received e-mail message is properly authenticated and passes all other security checks, it is again digitally signed by secure mail server  80 . The digitally signed message is then encrypted with either a recipient&#39;s public key, if available, or a password generated public key, or encryption using a third party secure e-mail system. The reincrypted message is mailed from secure mail server  80  to the recipient through mail server  50  and communication network  130 . If the option is selected, the mail message can be stored with the encryption key, and a log can be updated regarding transmission of the e-mail message. At the same time, information related to accounting is accumulated and stored for use in tracking and billing account information for the e-mail message transaction.  
     [0068] The system according to the present invention permits the selection of various options for handling e-mail messages based on an assigned message status. For example, the sending user can select notification of receipt of the secure e-mail message, or notification if the message is determined to contain a virus. Alternately, the e-mail sender can select to send the e-mail message even after being apprised of its virus content. Options for transmission of secure e-mail are discussed in further detail below.  
     [0069] Referring now to FIG. 5, a diagram illustrating load balancing on various nodes is provided. Primary nodes  27  and  28  are coupled to communication network  130  and can send and receive electronic messages through the respective connections. Primary node  27  receives and processes all e-mail transmitted from communication network  130 . Primary node  27  acts as a distribution center for balancing and distributing the load of received e-mail for processing among the primary and secondary nodes. Primary node  27  is coupled through load balancer  47  to primary node  28  and secondary node  26 . If one of the primary nodes  28  or secondary nodes  26  become inoperable, load balancer  47  prevents distribution of e-mail to the inoperable node. If primary node  27  or load balancer  47  become inoperable, primary node  28  begins receiving all e-mail from communication network  130 , and distributes the e-mail to all other nodes in an even distribution or load balancing process. That is, primary node  28  takes over the role of primary node  27  in balancing the load of processed e-mail, and load balancer  48  takes over the role of load balancer  47  in distributing e-mail for processing among the various nodes. As with primary node  27 , if one of the nodes becomes inoperable, primary node  28  prevents e-mail messages from being sent to the inoperable node until the node again becomes operable.  
     [0070] This configuration of nodes handling e-mail loads in a balanced manner is also particularly useful for reciprocal backup. Each node, whether primary or secondary, is connected to two adjacent nodes. Accordingly, each node serves as a backup node for data stored at two other nodes, and is itself backed up by two other nodes to which it is coupled. If a node in this configuration becomes inoperable, its data files are still available at two other physical locations containing reciprocal backups of the inoperable node. The two nodes adjacent to the inoperable node have reciprocal backups coupled to them, so that backup information is still available even while the one node serving as a reciprocal backup is inoperable. With this distribution and load balancing configuration, a large volume of e-mail messages of widely varyings size and description can be handled efficiently by appropriate use of available resources through load balancing and reciprocal backup.  
     [0071] Referring now to FIG. 6, a diagram of the sender&#39;s e-mail message packaging and transmission is shown. The sending user first composes an e-mail message on sending computer  400 , using an e-mail application familiar to the sender. If the e-mail application used by the sender is supported by the secure mail system according to the present invention, the e-mail package for secure e-mail transmission is assembled automatically by selecting the secure mail option provided as an add-on to the supported e-mail software. If the sender is using an e-mail system that is not supported by the secure mail system according to the present invention, a secure mail package is again automatically assembled, however, the package must be manually inserted as an attachment to an e-mail in the system used by the sending user.  
     [0072] The assembled package includes the sender&#39;s e-mail as transformed by the system according to the present invention. The transformed message includes text messages and headers, attachments and optional recipient requests. The reformatted message is encrypted with a one time random symmetrical key to produce encrypted message form  902 . A public key  906  associated with the secure mail system according to the present invention is then used to encrypt the one time random key and a sender&#39;s public key to produce an encrypted one time random key  904  and an encrypted sender public key  908 . Encrypted sender public key  908  is the key used to verify the sender&#39;s digital signature once received at secure mail server  80 .  
     [0073] Prior to an encryption of the reformatted message, a complex hash algorithm is used to generate a digital hash code from the reformatted message contents. The digital hash code can be used to verify the uniqueness of the reformatted message as an anti-tamper verification. The digital hash code is combined with the sender&#39;s private key (not shown) to produce a highly unique sender digital signature  910 . Sender digital signature  910  is used to authenticate the message and to verify that the message has not been tampered with.  
     [0074] Reformatted encrypted message  902 , encrypted one time random key  904 , secure mail system public key  906 , encrypted sender&#39;s public key  908  and sender digital signature  910  are all packaged together to form the assembly of the secure e-mail message that is transmitted to secure mail server  80 . Once the contents of the secure mail package are combined, the entire package is transmitted over communication network  130  to mail server  50  located within a secure mail server node, such as node  25  shown in FIG. 2.  
     [0075] Referring now to FIG. 7, a received secure e-mail package  900  is processed by secure mail server  80  to produce a recipient secure mail package  901 . The operation of secure mail server  80  is shown in FIG. 7 beginning with step S 700 , in which secure mail package  900  is received. Received secure mail package  900  is time and date stamped upon receipt by secure mail server  80  and the time and date stamp is stored in temporary files  701  in step S 702 . The message contents are unpacked and checked in a verification process in step S 704 . Checking the message ensures a valid, tamper-free transmission of the secure message.  
     [0076] Public key  906  is matched with an associated mail system private key that is retrieved for use in unencrypting the message. Encrypted one time random key  904  is then decrypted using the secure mail system private key, which in turn is used to unencrypt encrypted sender public key  908 . The message form is then decrypted using the one time random key, and the header information containing transmission information is saved.  
     [0077] Now that the message form is in unencrypted format, it is virus checked and operated on by a hashing algorithm to produce a digital hash code. The digital hash code is combined with the sender&#39;s unencrypted public key to verify digital signature  910  included in the message.  
     [0078] If the secure mail message passes all the verifications, as illustrated in decision step S 706 , the message is repackaged in step S 710 . If any of the verifications fail when the secure mail message is checked, decision step S 706  branches to step S 708  in which secure mail server  80  generates an error message for notification to the sender that there was a problem with the sent message.  
     [0079] The verified message is combined with the saved time and date stamp information saved in temporary files  701 , along with other indicia added by secure mail server  80  to produce a new, expanded, verified message form. The verified message form is operated on by a hashing algorithm to produce another digital hash code. The new digital hash code is then used with the secure mail server private key (obtained as the private key portion of the secure mail server public/private key pair matched with secure mail server public key  906 ) to produce a mail server digital signature unique to the new, expanded, verified message form. Another one time random key is generated and used to encrypt both the new, expanded, verified message form, and secure mail server public key  906 .  
     [0080] All the components of the message are repackaged and assembled for transmission in step S 710 , and can alternately be stored in secure mail server  80 , or an attached storage system, according to transmission options chosen by the sender. The message is retransmitted in step S 712 , while accounting and archive data is stored on file/database server  10  in step S 714 . While a particular archive and accounting database  12  is shown in FIG. 7, it should be apparent that any number of databases or storage locations can be used in accomplishing step S 714 . The processing of the secure mail message  900  completes in step S 716 , having sent secure mail package  901  in step S 712 .  
     [0081] When the message is repackaged in step S 710 , several repackaging options are available, depending on the recipient e-mail system. For example, if the recipient is a subscriber to the secure mail system, then the one time random key is encrypted with the recipient public key, as registered with the secure mail system according to the present invention. Once the one time random key is encrypted and packaged with the encrypted form, the encrypted secure mail system public key, the recipient public key and both digital signatures, the package is attached to an e-mail message and the original subject from secure mail package  900 , that is stored in temporary file  701 , is used to provide the subject field, and the e-mail is sent to the recipient, as in step S 712 .  
     [0082] If the recipient is not a secure mail system subscriber, the random symmetrical one time key is encrypted with a public key that is generated from a password, or pass phrase, packaged with the encrypted form, the encrypted secure mail system public key, the password, or pass phrase, generated public key and both digital signatures, and the package is sent as an attachment in an e-mail, in which again the original subject of secure mail package  900  is provided for the subject line in the retransmitted e-mail, in addition to the sender address. Again, the verified secure mail package  901  is sent in step S 712 .  
     [0083] Referring now to FIG. 8, a diagrammatic chart showing the process of unpacking and checking secure mail package  900  is shown. Secure mail package  900  is received at secure mail server  80 , at which point a system time and date is accessed for use with time and date verification stamping. Secure mail system public key  906  is extracted from secure mail package  900  and used in process S- 14 - 15  to look up a public/private key pair in a data base maintained in secure mail server  80 . In step S- 14 - 14  a return flag is initialized to show successful verification. If secure mail system public key  906  is not found in the public/private key pair data base, connector A is selected, leading to step S- 14 - 19 . In step S- 14 - 19  the return flag is set to indicate an error, caused by the lack of an entry for the transmitted secure mail system public key  906 .  
     [0084] If secure mail system public key  906  is found in the public/private key pair data base, a secure mail system private key is returned in step S- 14 - 16 . The secure mail system private key is used to decrypt encrypted one time random key  904  in step S- 14 - 1  to produce the unencrypted one time random key in step S- 14 - 2 .  
     [0085] The unencrypted one time random key is used to decrypt both the reformatted message in step S- 14 - 3  and encrypted sender&#39;s public key  908  in step S- 14 - 17 . The reformatted message decrypted with the one time random key results in the decrypted reformatted mail message in step S- 14 - 4 . The decrypted reformatted mail message is used to verify the sender&#39;s identity in step S- 14 - 20 , with an improper identity, or non-subscriber, being enunciated by an error code in the return flag as set in step S- 14 - 21 . If the sender&#39;s identity is verified as proper, and as a subscriber, in step S- 14 - 20 , then the decrypted reformatted mail message is virus scanned in step S- 14 - 5 . If a virus is found, the return flag is set to indicate an error in step S- 14 - 6 . Otherwise, if no virus is found, the process proceeds to return step S- 14 - 7 .  
     [0086] The decrypted reformatted mail message is also operated on by a hashing algorithm in step S- 14 - 8 , the result of which is compared to the digital hash code of the sender&#39;s original reformatted mail message, in step S- 14 - 9 . The digital hash code and sender&#39;s public key obtained after decryption with the one time random key in step S- 14 - 17  and S- 14 - 18  are combined to verify sender digital signature  910  provided with original secure mail package  900 , in step S- 14 - 10 . If a digital signature is verified properly, the verification and checking process has completed successfully and returns in step S- 14 - 7 . If the validation of the digital signature fails, the validation error flag is set in step S- 14 - 11 , and the return flag is set to indicate that an error has occurred.  
     [0087] According to the process of unpacking and checking the message, the only path that allows a return in step S- 14 - 7  without an error being set in the return flag is if the e-mail has been properly validated, and contains no virus after the virus scan. All other paths leading to the return in step S- 14 - 7  will return an error indicating a problem with secure mail package  900 .  
     [0088] Referring now to FIG. 9, a diagram showing the repackaging of the secure e-mail message according to the recipient e-mail system is shown. Repackaging of the secure message for transmission to the intended recipient begins with providing sender&#39;s digital signature  910 , the temporary time/date stamp file provided in step S- 14 - 13 , and the deencrypted reformatted mail message from step S- 14 - 4 , as shown in FIG. 8. These three items are combined together as shown in step S- 15 - 1  in FIG. 9 to produce an expanded reformatted mail message in step S- 15 - 2 . A hashing algorithm is applied to the expanded reformatted mail message in step S- 15 - 4 , to provide the digital hash code for the expanded reformatted mail message in step S- 15 - 5 . A secure mail system private key is obtained in step S- 14 - 16 , and combined with the digital hash code to produce a new secure mail system digital signature  911  in step S- 15 - 6 . An algorithm is executed in step S- 15 - 7  to generate a new random symmetrical one time key, shown in step S- 15 - 8 , that is used to encrypt the expanded reformatted mail message in step S- 15 - 3 . The random symmetrical one time key shown in step S- 15 - 8  is also used in step S- 15 - 17  to encrypt the secure mail system public key shown in step S- 15 - 15 . An encrypted secure mail system public key  907  results from the encryption of the secure mail system public key with the random symmetrical one time key.  
     [0089] The repackaging operation differentiates the recipient e-mail systems to then provide further encryption functionality. In step S- 15 - 10 , each recipient listed in the sender&#39;s e-mail message is provided with a status according to their e-mail system. According to different statuses determined in decision S- 15 - 11 , the recipient can be a secure mail system subscriber, an unknown non-subscriber, or a subscriber to a third party e-mail software package. If the recipient is a secure mail system subscriber, the recipient&#39;s public key is retrieved from the secure mail system data base in step S  15 - 12 . If the recipient is not known as a subscriber to the secure mail system, a password or passphrase taken from the sender e-mail message is used as a seed to generate a public/private key pair in step S- 15 - 13 . This step permits the non-subscriber recipient to receive an e-mail message that can be opened by entry of the proper password or passphrase, obtained through separate communication channels from the sender. If the recipient subscribes to a third party e-mail software package, a third party form e-mail service message is generated in step S- 15 - 14  to provide the recipient with a seamless integration with the secure mail system. Once a public key is obtained in steps S- 15 - 13  or S- 15 - 12 , as shown in step S- 15 - 16 , the random symmetrical one time key is encrypted with the public key in step S- 15 - 9 , to produce an encrypted random symmetrical one time key  905 . If the recipient does not use a third party e-mail service, secure mail package  901  is prepared with encrypted expanded reformatted mail message  903 , encrypted random symmetrical one time key  905 , secure mail system digital signature  911 , recipient&#39;s public key  909  and encrypted secure mail system public key  907 . The entire package is then sent as an e-mail message to the recipient. If the recipient is a subscriber to a third party e-mail service, then the sender message is simply reformatted according to the third party e-mail service protocol, and sent to the third party e-mail service for processing, and subsequent delivery to the recipient.  
     [0090] Referring now to FIG. 10, secure mail system package  901  is encapsulated in an e-mail message according to whether the recipient is a secure mail system subscriber or not. Decision S- 10 - 1  determines whether the recipient is a secure mail system subscriber, and if so branches to step S- 10 - 2  to process secure mail system package  901  as a special form e-mail file shown in step S- 10 - 3 . The generated special form e-mail file from step S- 10 - 3  is provided as an attachment to a secure mail system message in step S- 10 - 4 , after which the e-mail message is ready to be sent in step S- 10 - 8 . If the recipient is not a subscriber to the secure mail system, secure mail system package  901  is encapsulated as a special executable file in step S- 10 - 5 . The special executable file shown in step S- 10 - 6  is attached to an e-mail message in step S- 10 - 7 , and is then ready for sending in step S- 10 - 8 .  
     [0091] If the recipient is identified as a user of a third party e-mail system, third party e-mail message format  913  is readied for transmission according to the third party software protocol in step S- 10 - 9 , and is then ready for sending in step S- 10 - 8 .  
     [0092] Referring now to FIG. 11, the process of transmission of secure mail system package  901  to a recipient using a supported mail platform is shown. Secure mail system package  901  is provided by secure mail server  80  to mail server  50  for transmission to subscriber recipient  410  over communication network  130 . The user at subscriber recipient  410  is notified of the secure mail message in their e-mail system inbox and selects the message to open the file. The secure mail system software resident on the computer of subscriber recipient  410  executes to unpack secure mail system package  901 . Encrypted random symmetric one time key  905  is decrypted with a private key assigned to subscriber recipient  410 . Once the random symmetric one time key is decrypted, it is used to decrypt encrypted expanded reformatted message  903 , in addition to decrypting encrypted secure mail system public key  907 . Once the expanded reformatted message is decrypted, a hashing algorithm is applied to the message to generate a digital hash code. The digital hash code and the secure mail system public key are combined to verify secure mail system digital signature  911 . If verification of secure mail system digital signature  911  fails, an error message is generated and processing terminates. Otherwise, the expanded reformatted message is transformed into a form suitable for use by the resident e-mail software used by subscriber recipient  410 . This completed transmission of the original sender e-mail message from sending computer  400  can be acknowledged with a return receipt that can be generated once the e-mail message is verified and used at subscriber recipient  410 . The return receipt can be in the form of an e-mail that is directed back to the sender through secure mail system server  80  in a process reverse to that described for the sender message.  
     [0093] Referring now to FIG. 12, a process for transmission of secure mail system package  901  to subscriber recipient  420  that uses a web based or unsupported e-mail system is shown. Secure mail system package  901  as assembled by secure mail system server  80  is transferred to mail server  50  for transmission to subscriber recipient  420  over communication network  130 . The user at subscriber recipient  420  is notified of the arrival of a new e-mail in their inbox, and can select the message for viewing. Upon selection, resident secure mail system software executes to retrieve and unpack the contents of secure mail system package  901 . A private key obtained from subscriber recipient  420  is used to decrypt encrypted random symmetrical one time key  905 . Once the random symmetrical one time key is unencrypted, encrypted expanded reformatted message  903  and encrypted secure mail system public key  907  can both be unencrypted using the random symmetrical one time key. The unencrypted expanded reformatted message has a hashing algorithm applied to produce a digital hash code. The secure mail system public key is combined with the digital hash code to verify secure mail system digital signature  911 . If secure mail system digital signature  911  cannot be verified, an error message is generated and processing of secure mail system package  901  ceases. Otherwise, secure mail system digital signature  911  is validated and the expanded reformatted message is displayed to the user of subscriber recipient  420 . Again, it is possible to send a return receipt to the message sender at sending computer  400 , communicating that the message was properly received and read, or that an error occurred in transmission from mail server  50  to subscriber recipient  420 . The return receipt message can be in the form of an e-mail transmitted to the sender at sending computer  400 , in a process reverse to that described for sending of the original e-mail message, i.e., via secure mail server  80 .  
     [0094] Referring now to FIG. 13, a diagram of the transmission of secure mail system package  901  to non-subscriber recipient  430  is shown. Secure mail system package  901  originates at secure mail server  80  on the second leg of the secure transmission path according to the present invention. Secure mail system package  901  is transferred to mail server  50 , for transmission to nonsubscriber recipient  430  over communication network  130 . The user of nonsubscriber recipient  430  is notified of receipt of an incoming e-mail message and can select the message for display. When the received message is displayed, it contains instructions describing operations needed to access and display the encapsulated secure mail message. The user activates the encapsulated executable file, which immediately prompts the user for a password, or a passphrase. The user enters a password or a passphrase, which is then used to generate a public/private key pair. The generated public key is compared with recipient public key  909  to verify the proper password or passphrase used to generate the public/private key pair. The password or passphrase is typically communicated to the recipient user through another familiar communication channel, such as face-to-face conversation, telephone, facsimile, and so forth. The user is permitted up to three attempts to enter the correct password or passphrase needed to generate the correct matching public key of the public/private key pair. Once the correct public key has been generated through entry of the correct password or passphrase, the associated private key is used to decrypt encrypted random symmetrical one time key  905 . Once the random symmetrical one time key is decrypted, it is used to unencrypt encrypted expanded reformatted message  903  and encrypted secure mail system public key  907 . The unencrypted expanded reformatted message is subjected to a hashing algorithm to produce a digital hash code for use in verification and authentication of the message. The digital hash code is combined with the unencrypted secure mail system public key to verify secure mail system digital signature  911 . If the verification fails, an error message is generated and the processing of secure e-mail system package  901  ceases. The error message can include, for instance, a message indicating that secure mail system package  901  was somehow corrupted in transmission between mail server  50  and non-subscriber recipient  430 . If the verification of secure mail system digital signature  911  succeeds, the unencrypted e-mail message is displayed in a generic format to the user. Once again, a return receipt can be provided to inform the sender that the e-mail message was successfully sent and received in proper form. Alternatively, a return receipt message can indicate if there were any problems in transmission of the e-mail message, including failed digital signature authentication, the existence of a virus in the message or an inappropriate secure mail system public key, for instance. The return receipt message can be in the form of a secure e-mail that is transmitted over a return route similar to the reverse of the original e-mail message path. Secure processing of the return receipt message would follow the same process as described for the originally sent message, but in reverse.  
     [0095] Referring now to FIG. 14, several support routines used by secure mail server  80  in unpacking and checking secure mail system package  900  are shown. The support routine shown in FIG. 14A is provided to verify any public key encapsulated in a sent secure e-mail, as indicated in step S- 800 . The secure mail system uses the secure mail system public key as a look up parameter to retrieve a matching secure mail system private key along with a version number in step S 802 . The look up is performed on subscriber data base S 804 , which holds public/private key pairs and accompanying version numbers. If a match for the public key look up was found in subscriber data base S 804 , as determined in step S 806 , the algorithm continues to step S 810  in which information related to the owner of the public key is saved for a later reference. If the public key is not found in subscriber data base S 804 , indicating a corrupted secure mail system public key, or a message that it is potentially compromised, decision step S 806  branches to return an error in step S 808 . The returned error from the routine is used to notify a sender or an operator that a sent e-mail message is potentially corrupted or compromised in some fashion.  
     [0096] Once a match for the public key is found in subscriber data base S 804 , and the algorithm branches at decision step S 806  to continue with step S 810 , the private key that forms the complementary pair of public/private keys is retrieved from subscriber data base S 804  along with an associated version number, and is used to set up algorithms to unpack and verify an incoming secure mail message, as illustrated, for instance, in FIG. 8. The successful matching of the secure mail system public key in subscriber data base S 804 , and subsequent retrieval of the paired private key results in a successful conclusion and return in the algorithm shown in step S 814 .  
     [0097] Referring now to FIG. 14B, an algorithm for use with verifying a sender&#39;s identity is shown. Beginning with step S 820 . Once the algorithm is entered through step S 820 , the sender&#39;s public key is applied in step S 822  to subscriber data base S 804  to retrieve the sender identity associated with the public key used as the look up tag. The subscriber information matching the sender&#39;s public key is retrieved from subscriber data base S 804  and compared with the sender information contained in the secure mail message in step S 826 . If the identity stored in subscriber data base S 804  matches that of the sender specified in the secure mail message, as determined in decision step S 828 , the algorithm concludes successfully in step S 832 . Otherwise, decision step S 828  branches to return an error in step S 830 . The returned error from step S 830  can be used to notify an operator that an error has occurred in matching a reported subscriber identity. Upon being alerted, an operator can take action to verify the subscriber information, notify a subscriber of the error, or take steps to determine whether the subscriber&#39;s ID was attempted to be used in an unauthorized fashion.  
     [0098] Referring now to FIG. 14C, an algorithm for verifying subscription status of a recipient is illustrated, beginning with step S 840 . Once the algorithm is entered through step S 840 , the recipient&#39;s identity is applied in step S 842  to subscriber data base S 804  to verify subscriber recipient information. If the application of the recipient&#39;s identity to subscriber data base S 804  results in a match, as illustrated in decision step S 846 , the recipient information is retrieved from subscriber data base S 804  and returned to the calling procedure in step S 850 . If the recipient is not found in subscriber data base S 804 , decision step S 846  branches to return an indication that the recipient is a non-subscriber and step S 848 . The results of the algorithm shown in FIG. 14C are used to determine the method by which the retransmitted secure mail package components will be encrypted, as illustrated in FIG. 9. For example, if the algorithm in FIG. 14C returns with an indication of a non-subscriber recipient in step S 848 , a public/private key pair is generated using a password or a passphrase provided by the sender, as illustrated in step S- 15 - 13  in FIG. 9. If the recipient is determined to be a subscriber as illustrated in step S 850 , the recipient&#39;s public key is retrieved from subscriber data base S 804  and used to encrypt the random symmetrical one time key, as illustrated in FIG. 9, steps S 15 - 12  and S- 15 - 9 .  
     [0099] Referring now to FIG. 15, a table of menu options illustrating installation options for the secure mail system according to the present invention is shown. Upon installation of the resident software for operation of the secure mail system according to the present invention, the user is presented with a number of options to properly set up the system according to their needs and desires. A first option selectable by the user is illustrated in menu table  600 , wherein the user can choose the e-mail platform preferred. The e-mail platforms listed in menu table  600  are supported by the secure mail system according to the present invention. For example, the secure mail system according to the present invention provides a transparent interface for the user for the widely used programs MS OUTLOOK, either stand alone or exchange server versions, LOTUS NOTES, either stand alone or LOTUS NOTES server version, NETSCAPE, either stand alone or NETSCAPE server version. A user that already has one of these supported e-mail platforms of MS OUTLOOK, LOTUS NOTES or NETSCAPE will continue to see the same application interface for their e-mail platform. In these instances where the e-mail platform is supported by the secure mail system according to the present invention, the user is presented with a simple add on function in an obtrusive but easily accessible portion of the user interface, for instance.  
     [0100] Alternatively, the user can select a web based e-mail platform, or other e-mail platforms that may not necessarily be supported. As described above, the secure mail system according to the present invention can be used with any type of e-mail system and hardware/software platform combinations with only minor variations in the way the user interacts with their preferred, potentially unsupported e-mail system.  
     [0101] A menu table  610  describes selections available for the user upon installation of the secure mail system software for storage of private keys. According to a preferred embodiment of the present invention as described above, it is not necessary to store the user&#39;s private key anywhere, but instead the public/private key pair for encyrption/decryption can be generated through a number of devices or mechanisms whenever needed to encrypt/decrypt a secure mail message. According to this embodiment, the user&#39;s private key is only stored in volatile memory, such as Random Access Memory (RAM), for example, whenever a public/private key pair needs to be generated to encrypt/decrypt a secure mail message. Therefore, according to this embodiment the private key enjoys heightened security by being securely regenerated whenever needed, and is never stored in a fixed media format.  
     [0102] According to options provided to the user on installation, the unstored private key can be generated according to various criteria, including such events as login or when the e-mail system is activated. Other options allow the user&#39;s password or pass phrase used to generate the private key to be “forgotten,” i.e., the user must reenter the password or pass phrase after a time-out, for example, or upon the occurrence of a secure event, such as receipt of a secure message.  
     [0103] In an alternate embodiment of the present invention, the private key can be generated or stored in encrypted form by secure mail server  80 , for instance. In this embodiment, the private key is generated, or the encrypted private key is retrieved from subscriber database S 804 , for example, and decrypted, and the private key applied to incoming and outgoing secure mail messages for verification and encryption/decryption. In this embodiment, as with the above discussed embodiment in which the user&#39;s private key is not stored anywhere, the user is protected from having their e-mail system potentially compromised by, for example, having their portable computer or wireless device stolen.  
     [0104] Because the system according to the present invention can be used on an individual or enterprise wide basis, for example, a number of billing options are provided for custom tailoring to the user&#39;s needs as shown in menu table  620 . As illustrated in menu table  620 , the user can select the installation option of entering a credit card number to be billed for secure mail transactions, in which one credit card account can be used for multiple users, or separate credit card accounts can be used for each individual user. In addition, a user can be identified by a customer account that is maintained by the secure mail system according to the present invention as illustrated in FIG. 3, for example. The billing for a customer account can be set up to have a single account for an entire enterprise, or single accounts for each individual user, or combinations thereof. It should be apparent that a number of versions of the secure mail system according to the present invention can be provided to accommodate a number of different billing schemes, such as monthly, on a transaction basis, or even billing on a no fee basis.  
     [0105] During installation, options can be selected for administration of the resident secure mail system, as illustrated in menu table  630 . During installation the system can be set up to permit anyone access on an administrative basis, access to a master administrator of the selected account, access to the administrative master and the particular user, or only the particular user. These features provided in menu table  630  allow optional administration schemes, such as over a network, or on a remote basis, in addition to local and automated administration. In a preferred embodiment, only an administrative master is permitted administrative access to the user set up.  
     [0106] During installation the resident secure mail system can be set up to have multiple user IDs as illustrated in menu table  640 . For example, a user ID related to access of various external systems, including such systems as listserves, can be set up on a specific basis. Alternately, user IDs related to specific tasks, for example, can be maintained for organizational purposes. Preferably, a single user ID is set up on installation of the resident&#39;s e-mail system.  
     [0107] A user also provides upon installation a personal access code as shown in menu table  650 . The personal access code entered during installation according to menu table  650  can be used as the password or passphrase that generates a public/private key pair when sending a secure mail message to a non-subscriber recipient, as illustrated in step S- 15 - 13  in FIG. 9. Various options for personal access codes can be enabled, for instance to provide different levels of access to secure mail transmissions. For example a personal access code can be entered to permit the user to only read secure mail messages, or a personal access code can be entered to permit the user to only send secure mail messages, or a combination of both, as is preferred.  
     [0108] It should also be apparent that each of the installation options described in FIG. 15 can be set in an installation script that can run automatically upon installation of the resident secure mail system on a user&#39;s computer. For instance, if a user&#39;s computer is connected to a network, an automated installation script can reside on a central server of the network, and be used at each individual station in which a resident secure mail system is installed. It should also be apparent that each of the installation settings can be modified by a user, administrator, or automatically depending upon selected options. As a simple example, the user may be prompted to modify their personal access code over a set interval of time, such as every sixty days.  
     [0109] Referring now to FIG. 16, a set of options for a sender of a secure mail message is illustrated. The sender options are activated once the sender chooses to begin composing a secure mail message from their e-mail program. If the sender is using an unsupported e-mail platform, the sender&#39;s options are activated once the user selects the secure mail system for transmission of a message composed according to the user&#39;s e-mail platform. Option  700  permits the sender to select a password or a pass phrase that must be entered to open the e-mail message upon receipt by a recipient. Preferably, the user enters a password to further protect the message upon transmission. Option  702  permits the sender to select a return receipt notification once the transmitted message is received and opened by the intended recipient. The sender can select no return receipt, a return receipt only for the sender, or a return receipt for the sender and notification to the recipient. Preferably, a return receipt to the sender is provided.  
     [0110] Sender option  704  dictates the handling of a message that has been determined to contain a virus. The sender can select the option of stopping message altogether, or passing the message onto the recipient with an attached warning notifying the recipient of the detected virus. Preferably, the option for stopping the message is selected.  
     [0111] Sender option  706  illustrates a selection of storage criteria for the secure mail message once it has been verified and is ready for resending at central server  52  (FIG. 1). The user can select a variety of storage periods, including non-storage of the message. According to this option, messages that have been previously transmitted can be reverified, along with a time date stamp and other information related to their transmission, even after a number of years have passed. Option  708  describes the contents of the stored message that the sender wishes to have maintained. The sender can select to have the message alone stored, as is preferred, or the message and associated digital signature, or simply the digital signature alone. Accordingly, the sender can select appropriate storage needs depending on the application for which secure mail messages are transmitted.  
     [0112] The sending user can also select virus checking options as shown in option  710 . Preferably, standard virus checking is enable. Optionally, the user can select from among various virus checking programs according to their desires and needs. In addition, the user can select no virus checking to be done, in which case the original message sent by the user is not decrypted, but only the random symmetrical one time key packaged with the message as sent. The option of having no virus checking can potentially permit messages that are intended to be modified during transmission, or for the secure transmission of programs identified as viruses, to permit analysis thereof, for example.  
     [0113] According to the present invention a transmission between a sender and a receiver can be completed with confidentiality, virus protection, tamper proofing, authentication using digital signatures and time date authentication. All these features are available according to the present invention, while at the same time minimizing changes to the user&#39;s interface for sending e-mail messages. The time date stamp is driven by an atomic clock and is highly accurate. The secured message can be stored for extended periods of time and reverified at a point in the future if necessary. The system according to the present invention also operates on the transmitted e-mail message only in volatile memory, and is never stored in a more tangible or fixed medium, thus preventing operation such as an inadvertent backup, copy or saved version of a secure message. The system according to the present invention works with any e-mail system, and provides additional functionality for supported and widely used e-mail systems. If a recipient e-mail system is unsupported or unknown, the secure mail message is simply provided as a password or pass phrase accessible attachment that can be opened by the recipient having the appropriate password or pass phrase.  
     [0114] In addition, according to the present invention, the sender can receive a secure, digitally signed, time/date stamped copy of the message received by the recipient. Alternatively, the sender can receive a return receipt notification that is again secure, digitally signed and time date stamped, notifying the sender that the transmitted e-mail message was received. The system also prevents propagation of viruses while still using secure transmission methods, and notifying the sender that a virus was detected in the transmitted message.  
     [0115] The system according to the present invention provides advantages over prior systems and achieves a high level of security and reliability. For example, unlike fax transmissions, the time/date stamp on the secure mailed message according to the present invention is tamper proof and not susceptible to manipulation by a third party. The e-mail message can be scanned for viruses in its native format, rather than “hiding” a virus that can be potentially encrypted with a message sent using typical e-mail systems. For example, a typical firewall setup will not detect a virus embedded in an encrypted file, but rather pass the message directly to the recipient. The present invention, in contrast, can detect a virus in a transmitted message and prevent propagation of the message, while informing the sender of the message status.  
     [0116] The system according to the present invention further provides protection against activity monitoring by never including the end-to-end correspondence in the secure message transmission at the same time. Instead, only the sender is identified in a sent message that is received by the secure mail system, and only a recipient is identified in a message retransmitted from the secure mail system. Accordingly, if an eavesdropper wished to track activity between two parties, they would be unsuccessful in tracking communications between parties using the system according to the present invention. Each secure mail transmission is also digitally signed using a highly unique digital hash code to ensure the message has not been tampered with and to authenticate the transmitting and receiving parties. It should be apparent that the present invention is not limited to the embodiments described herein, but rather is applicable to a number of scenarios in which it is desired to have secure messages transmitted. For example, funds can be transferred in electronic form in a secure fashion with a high level of security and reliability. Senders and receivers of secure fund transmissions will instantly know whether any errors have occurred in the transmission of data, or whether a transmission has been tampered with in any way.  
     [0117] As another example, the popularity of third party hosted websites for use with resource intensive projects can benefit from the present invention by providing a high level of confidentiality, security and reliability to third party operators and customers. For example, it is known that parties to a litigation may share information required by law through a third party website that has the available resources to handle large volumes of documents and a variety of security access levels.  
     [0118] In the same vein, professionals in the medical, accounting and legal arts can benefit from secure and confidential exchange of documents that are required to be verified, or have the potential for future verification. For example, a medical file on a patient can be transmitted on a world wide basis, while being maintained private and free from tampering.  
     [0119] Other areas in which the present invention would be highly advantageous include law enforcement, journalism, financial services, and generally any type of operation in which a sender and recipient wish to have private secure communication.  
     [0120] It should be apparent that the present invention is not limited to communication systems involving computers, but can also include such applications as remote electronic entry, in which a user can request entry to a building or vehicle, for example, by sending a secure wireless transmission to an appropriate service that can automatically unlock the desired entrance. In a situation such as this, the sender can be verified, the authorization for entry can be authenticated and verified and any attempts at tampering or redirection can be identified and recorded. In addition, a log of individuals accessing secured areas can be maintained.  
     [0121] It should be further apparent that the present invention is not limited to applications involving security issues only, but is generally applicable to situations involving electronic commerce. These applications include commercial websites used for marketing raw materials, in which a supplier and customer must be verified prior to confirmation of a transaction taking place. Furthermore, electronic commerce examples in which the present invention is useful can include such items as ordering merchandise on line, to using a wiring device to select items from a vending machine.  
     [0122] It should also be apparent that the present invention is applicable where non-active systems are in use. For example, a user provided with a passive security card that is read by an active device can employ the system according to the present invention to authenticate the user, verify appropriate access, and other security related features. As another example, a user may take advantage of a hybrid device that contains passive and active elements, whereby a passive portion of a device can be read by a “recipient” device, and the active portion of the device can be modified by the recipient device to permit an exchange to validate secure authorization. Such systems can be employed, for example, with services available to the public, such as pay phones, vending machines, fuel purchases, and so forth.  
     [0123] The foregoing description of the preferred embodiments of the present invention has been provided for the purpose of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations are possible in view of the above teaching. It is thus intended that the scope of the invention not be limited to this detailed description, but rather to the claims appended hereto.