Patent Publication Number: US-9419950-B2

Title: Secure message forwarding system detecting user&#39;s preferences including security preferences

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. application Ser. No. 10/616,100, filed Jul. 8, 2003 (now U.S. Pat. No. 7,475,256), which is a continuation of U.S. application Ser. No. 09/595,416, filed Jun. 15, 2000 (now U.S. Pat. No. 6,732,101). The disclosures of the prior applications are considered part of and are incorporated by reference in the disclosure of this application. 
    
    
     FIELD OF THE INVENTION 
     The invention relates generally to computing systems and more particularly to a method and system for providing secure data transmissions between Internet users. 
     BACKGROUND OF THE INVENTION 
     The Internet is a global network of computers that uses a common communication protocol, the Transfer Control Protocol/Internet Protocol (TCP/IP), to transmit data from one location to another. Many application specific tasks, such as E-mail transmission and file transfer, are not directly supported by TCP/IP. Instead, support for these services is implemented by application specific protocols that in turn rely on TCP/IP for basic data transport services. One problem that is relatively unknown to individuals that make use of the Internet is the ease by which information can be obtained during transmission by unauthorized eavesdroppers. For example, most E-mail transmissions over the Internet are sent in cleartext. Cleartext is unencrypted data that can be intercepted anywhere along the path between a sender and the recipient. 
     Accordingly, sensitive business or personal information should not be transmitted in cleartext over the Internet. To do so is to risk its publication. To avoid this risk, sensitive data is often sent by courier services or other means at great cost. 
     Encryption mechanisms can be used to ensure the integrity of information sent over the Internet. Two common encryption techniques, symmetric key encryption and public key encryption, are described below. In a symmetric key encryption, a unique key is identified and used by the sender to encrypt and by the receiver to decrypt a message. In public key encryption, separate keys are used to encrypt and to decrypt. 
     Both symmetric key and public key encryption require a key exchange. That is, where symmetric key encryption is used, the sender must provide the recipient with the key so that the recipient can decrypt an associated message. In public key encryption, the key exchange includes the publication of a recipient&#39;s public key that in turn is used by the sender to encrypt a message. A corresponding private key is used by the recipient to subsequently decrypt the encrypted message. Publication can be by posting the public key, for example, to a central site, or by providing the public key directly to the sender. In each of these scenarios, the recipient&#39;s computer must include a decryption engine (software) that uses an appropriate key to decrypt the message. Because there are a variety of encryption algorithms being used on the Internet, a recipient needs to have many different types of decryption engines installed to be able to receive secure messages universally. If the intended recipient does not have a particular decryption engine, the sender cannot utilize that particular encryption technique to send the secure message. 
     Often a sender will desire to send the same information, for example, over the Internet, to plural recipients who have different decryption engines installed. This adds an additional level of difficulty to the transmission process, because the sender must select the appropriate encryption engine for each recipient. For those recipients who do not have any decryption engine installed, the message simply cannot be sent securely. 
     With the promulgation of the Internet, a globally available decryption engine has been installed in almost all new personal computers in the form of a web browser that supports the secure socket layer (SSL) protocol. What is desirable is a system that allows the recipient to use this universally available decryption engine to receive secure messages from any sender regardless of what encryption engine the sender uses. In addition, the system should allow a sender to use one encryption engine to deliver the message to any recipient regardless of what decryption engine the recipient uses. In case the sender and the recipient have compatible encryption and decryption engines, the message may be sent directly. In case the sender&#39;s encryption engine and the recipient&#39;s decryption engine are not compatible, the system will translate the message format to ensure universal interoperability between encryption and decryption engines 
     SUMMARY OF THE INVENTION 
     A system and method for providing secure E-mail services. The system includes a forwarding service operable to receive an E-mail message for delivery to a recipient, store the message at least temporarily in a storage means and check for recipient preferences for delivery of the E-mail message content. If no preference is specified and if Web-based delivery is specified, the system provides an E-mail notification to the recipient including a secure link to the message and responds to a page request from the recipient indicating the message including extracting the message from the storage means, formatting the message as a page and delivering the page to the recipient&#39;s web browser. If a preference for delivery other than Web-based is specified, the system delivers the message in accordance with the recipient&#39;s preference. 
     Implementations of the invention can include one or more of the following advantages. Messages can be encrypted using any available encryption means at the sender and sent to a forwarding service. The forwarding service can forward the message to each recipient according to the recipient&#39;s decryption capability and preference. 
     A system is provided for secure E-mail services. Secure E-mail messages can be composed or generated using the secure messaging system (using a particular encryption service), the result of which can be attached as a MIME or SMIME message to a conventional E-mail message for transfer to a recipient. In the event the recipient does not have the required decryption capabilities, the E-mail message can be forwarded to a forwarding service. The forwarding service provides an E-mail notification to the recipient of the message. A recipient is not required to have a special viewer or reader and can merely retrieve the message through a web browser by linking to the forwarding service via a secure link such as SSL. Alternatively, if the recipient has designated a preference for delivery, the message can be re-encrypted according to the recipient&#39;s preference and delivered to the recipient directly in accordance with the predefined delivery instructions. 
     These and other advantages of the present invention will become apparent from the following description and from the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1 a    is a schematic block diagram of a computing network for facilitating a secure data exchange. 
         FIG. 1 b    is a schematic block diagram of an operational perspective of the forwarding service of  FIG. 1   a.    
         FIG. 2 a    shows a generalized process for securely sending and receiving encrypted E-mail over a network. 
         FIGS. 2 b -2 e    show a flow diagram for a method of exchanging E-mail securely over a network between a sender and a recipient. 
         FIG. 2 f    is a flow diagram for creating a sending a message including creating a send authorization pass phrase (SAPP). 
         FIG. 2 g    is a flow diagram for creating an authorization pass phrase. 
         FIG. 2 h    is a flow diagram for receiving a message including specifying a receive authorization pass phrase (RAPP). 
         FIG. 3 a    shows a user interface presented by a wrapping application. 
         FIG. 3 b    shows a user interface presented by the wrapping application when the send button shown on  FIG. 3 a    is depressed. 
         FIG. 4 a    shows a user interface presented by the viewer application. 
         FIG. 4 b    shows a user interface presented by the web browser application for reviewing messages. 
         FIG. 4 c    shows a user interface presented by the web browser for sending messages. 
         FIG. 5  is a schematic block diagram of forwarding service for facilitating a secure data exchange between various types of senders and recipients. 
         FIG. 6  is a flow diagram for forwarding a message through the forwarding service of  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Most E-mail transmissions sent over the Internet are not secure. The contents of a transmission can be compromised by interlopers along the path traversed by the message when traveling from the sender to the recipient. Additionally, incoming and outgoing email messages are normally stored on servers that are accessible to computer department personnel or other Internet Service Providers. The present invention provides a communication system for securely and easily generating, sending and viewing E-mail transmissions or other messages sent to a recipient over a network. 
     A number of terms are used herein to describe network transmissions and related structures and processes. 
     “Authorization phrase” or “authorization pass phrase” refers to a password or pass phrase that may be supplied by a sender or a recipient to gain access to services provided by a forwarding service. The forwarding service is described in greater detail below. 
     “Client” refers to a computer program that, among other functions, requests services from a server and more generally as the computer that runs a client program or a browser. Here, a client program includes a communication program for sending electronic messages (such as E-mail) to other clients through a network, or for interpreting messages from other clients. 
     “Server” refers to a computer program that provides services to clients, and more generally refers to a computer that runs a server program. “Key server” refers to a computer that includes a server program for maintaining, validating and distributing public keys for use by clients in transmitting secure E-mail or other messages over a network. 
     “Exchange” refers to a communication between a client and a server over a network. The exchange occurs along a connection path between client and server and includes a request (generated by the client) and a response (from the specified server). Requests and responses can be generated by each of the client and server depending on the exchange. 
     “Secure transmission” or “secure E-mail transmission” refers to a secure communication between two endpoints over a network. Such a communication can be highly secure and include a wrapper, an encrypted message, a signature, and a time stamp certificate. Alternatively, the communication can have minimal security and include only a wrapper and a link to a message that is secured by using a transmission protocol (e.g., secure socket layer (SSL)) between devices. The wrapper can be received by a recipient&#39;s conventional E-mail service. The message (and other information e.g., signature and time stamp) can be recovered (and verified) by the recipient by invoking a secure message viewer at the recipient client computer or through a web browser. 
     “Network” refers to a private or public network. Private networks include an intranet, that is, a network connecting one or more private servers such as a local area network (LAN). Alternatively, the network can be a public network, such as the Internet, in which data is passed over non-secure communication links. The network configuration can include a combination of public and private networks. For example, two or more LAN&#39;s can be coupled together with individual terminals using a public network such as the Internet. 
     “Internet” refers to all of the networks that use the TCP/IP suite, which cooperate to form a seamless network for their collective users. The invention has particular applicability to exchanges on the Internet between clients. However, other exchanges over other networks can also benefit from the secure transmission features disclosed herein. 
     “Encryption” refers to a process of encoding a document to hide its content from anyone except an intended recipient. “Decryption” refers to the reciprocal process of recovering the original document by a recipient. “Symmetric key encryption” refers to an encryption method in which the encipher key and the decipher key are the same. In one implementation, DES or Triple DES encryption is used for symmetric key encryption. “Public key encryption” refers to an encryption method in which the encipher key and decipher key are different. The encipher key can be made public to alleviate difficulty of a symmetric key exchange between the sender and recipient. The phrases “encrypted by the (recipient&#39;s) public key” and “decrypted using the (recipient&#39;s) private key” refer to steps implemented when using public key encryption. The phrases “encrypted by a session key” and “decrypted by a session key” refer to steps implemented when using symmetric key encryption. 
     “Signature” refers to a designator that is attached to a document that can be verified to authenticate the originator and the integrity of the document. “Signature phrase” is a password or pass phrase used to encrypt the private key to be stored on the user&#39;s computer. The signature phrase is used to derive a symmetric key which in turn is used to encrypt private key data. “Signing” or “signed” refer to a specific operation that is applied to a document, message or string to produce a verifiable form of a signature. “Signature verification” is the reciprocal process for validating the signature produced by the signing process. 
     A “Time Stamp Certificate,” as used herein, refers to a certificate signed by a central server (e.g., key server or key retrieval server) that is attached to a message. The time stamp certificate certifies the sender, the recipient, the time the message was sent, the message itself, the public key of the sender, and the public key of the recipient. Time stamp certificates are described in greater detail in co-pending application entitled “Secure Messaging System”, filed Jun. 28, 1999, and assigned Ser. No. 09/340,853, the contents of which are expressly incorporated herein by reference. 
     Referring now to  FIG. 1 , an interconnected computing system  100  for facilitating communication between two or more client computers (e.g., a “sender”  102  and one or more “recipients”  104 ) over network (Internet)  106  is shown. A key server  108  is also coupled to network  106  and can be accessed by the sender  102  and one or more recipients  104 . One or more key retrieval servers  180  are also coupled to network  106  and can be accessed by any of sender  102 , recipient  104  and key servers  108 . The key retrieval server  180  and key server  108  can be separate servers or can be combined. A trusted third party server  190  can be coupled to key server  108  through a direct connection  192  or a secure Internet connection through network  106 . Finally, a forwarding service  195  is coupled by a secure or non secure Internet connection through network  106  to sender  102  and one or more recipients  104 . 
     Sender  102  and recipient  104  each include an operating system  120  and one or more applications  122  executing on the client computers. Recipients  104  can be of two classes: fully configured recipients  104   a  and minimally configured recipients  104   b.    
     Minimally Configured Recipients 
     Minimally configured recipients  104   b  include a web browser application  123  that supports a secure communication protocol (e.g., SSL) for accessing the Internet and receiving and viewing minimally secure messages transmitted by the sender  102  and forwarded by forwarding service  195  to the minimally configured recipient  104   b . In addition, minimally configured recipients  104   b  include an E-mail application  126  for receiving notices from forwarding service  195  that a message is available to be reviewed. 
     Web browser application  123  can be an Internet browser program (referred to herein as a “browser”) such as NETSCAPE NAVIGATOR®. The customer can direct the browser to a web site associated with the forwarding service  195  and render or download a message from a server hosting the web site. The minimally configured recipient  104   b  can be implemented as a browser-based system in accordance with the standard protocols for communicating over the Word Wide Web, including SSL support. In such an implementation, a user of the minimally configured recipient computer  104   b  can execute browser application  123  to connect to and interact with the forwarding service  195 . Forwarding service  195  includes a web front end  191  that manages the communications with the client computer (such as recipient  104   b ). The user of the client computer can send or receive messages to/from forwarding service  195 . The details of the forwarding service are described in greater detail below. 
     E-mail application  126  can be any generic E-mail application, preferably an E-mail application that supports hyperlinks. 
     Fully Configured Recipients 
     Fully configured recipients  104   a  include decryption tools and viewers to support highly secure transmission of messages. Sender  102  and fully configured recipients  104   a  may include a HTTP post application  124 , an E-mail application  126 , a secure E-mail wrapping application (“wrapping application”)  128 , a viewer  130  and signature manager  132 , for sending and receiving highly secure transmissions over network  106 . 
     HTTP post application  124  can include an HTTP protocol. The HTTP protocol allows wrapping application  128  or viewer  130  to directly access key server  108  or key retrieval servers  180  via the network  106 . The HTTP protocol can also be used to transmit a secure message to forwarding service  195  if the sender does not have access to an SMTP server. A process for sending secure messages using HTTP posts is described in greater detail below. 
     E-mail application  126  can be any generic E-mail application that allows MIME attachments. Examples include CCMail, Netscape Messenger and Microsoft Outlook. 
     Wrapping application  128  can be invoked to wrap a secure E-mail and apply a signature that can be verified by a recipient. Wrapping application  128  includes a signing process  150  and encryption process  154 . Signing process  150  receives as an input a user signature phrase which is used to decrypt the user&#39;s private keys. The private keys are used to sign a message to produce a signed message. Encryption process  154  operates on the signed message to produce an encrypted message. The encryption process  154  generally requires the retrieval (or pre-retrieval) of a public key for each recipient of a secure message. Some recipients may be minimally configured recipients  104   b  and may not have a public key. Other recipients may prefer to receive their messages using an alternative secure messaging system than that chosen by the sender. To provide secure transmissions to these other recipients (e.g., minimally configured recipients  104   b  and other recipients without a locatable or valid public key), wrapping application  128  includes a forwarding application (forward process)  155  that can be used to forward secure messages to a recipient using forwarding service  195 . The processes of signing, encrypting and forwarding a message are described in greater detail below. 
     Viewer  130  can be called from E-mail application  126  and used to view a secure E-mail transmission. Viewer  130  includes a verification process  152  and decryption process  156 . Decryption process  156  decodes encrypted messages produced using encryption process  154 . After decryption, verification process  152  can be invoked to authenticate signatures produced using signing process  150 . In one implementation, wrapping application  128  and viewer  130  are bundled in a single application. 
     Signature manager  132  is a utility for managing encryption keys for a user. Prior to the use of wrapping application  128  or viewer  130 , each user (e.g., sender  102  or fully configured recipient  104   a ) must generate public and private keys. Signature manager  132  includes methods for generating public and private keys. Signature manager  132  submits the public key to key server  108  for publication. Key server  108  publishes the public keys in a key list which in turn can be distributed to key retrieval servers  180 . Signature manager  132  can be used to create new keys, change keys, delete keys or change signature phrases. Signature manager  132  includes key process  160  for creating and storing private and public keys for use in transmitting highly secure E-mail. Signature manager  132  stores a user&#39;s private key(s) in a key file  133 . Key file  133  may contain a plurality of keys stored for one or more E-mail addresses. The key file  133  may be transferred from a user&#39;s computer to another computer to allow a user to send and receive secure E-mail messages on a computer other than the computer used to create the private key. The private key can be encrypted using a symmetric key derived from the signature phrase. Only persons having the correct signature phrase can recover a user&#39;s private key. Signature manager  132  can also be bundled into another application. 
     Network  106  can be the Internet, an intranet or a combination of public and private networks. 
     Key server  108  can be a server computer executing one or more server programs. Key server  108  includes one or more server applications executing on the server computer and includes an operating system  200 , key exchange application  202 , HTTP post and forwarding proxy server application  204 , recovery application  206 , key list  208 , status list  209  and trusted third party (TTP) application  210 . In one implementation; key server  108  and key retrieval server  180  are the same server. 
     Key exchange application  202  operates to retrieve recipient and sender public keys, as well as public key status. The sender uses wrapping application  128  to retrieve the recipient&#39;s public key in order to encrypt a message so that only the recipient can read it. The recipient can use viewer  130  to retrieve the status of the correct public key of the sender so as to verify the integrity of the message and attached signature received from the sender. The exchanges between clients and key server  108  can themselves be secure as is described in greater detail below. Key exchange application  202  includes time stamp process  216 , (server) signing process  217 , key retrieval process  218  and status verification process  219 . 
     Time stamp process (“stamp” process)  216  is invoked when the sender retrieves the recipient&#39;s public key. In one implementation, a time stamp is signed by the server (producing a time stamp certificate) making the time stamp difficult to forge. The time stamp certificate can be included in the secure message sent by the sender to indicate irrefutably the time the message was sent to the recipient. 
     Server signing process  217  can be invoked by key server  108  to sign public keys stored in key list  208  with the private key of the server. In addition, server signing process can be used to sign messages transmitted back to a client including signing a time stamp to create a time stamp certificate. 
     Key retrieval process  218  is invoked when a sender retrieves public keys of a recipient from key list  208 . The public keys in key list  208  can be indexed by E-mail address and by a hash (or hashes) produced from an E-mail address. A second list, a status list  209 , is maintained by key server  108 . Status list  209  can be indexed by a key identifier (ID), which can be generated by taking a hash (or hashes) of an associated public key. Hash functions are described in greater detail in “Secure Messaging System.” Each entry in the status list includes a key ID, an associated E-mail address, a current status field and a valid time field. The current status field indicates the status of the public key, such as active, inactive, suspended, removed, hidden or deleted. The valid time field can indicate the date and time span over which the public key was (is) valid. Status list  209  can include all keys currently in key list  208  as well as all keys that have been deactivated, suspended, removed, hidden or deleted. 
     Server status verification process  219  is invoked by the recipient of a secure message to check the status of the message sender&#39;s public key. 
     HTTP post and forwarding proxy server application  204  provides an easy means of transmitting messages without requiring a sender to have access to a SMTP server or other communication server. The HTTP post application in the client application sends the secure message by an HTTP post method to a forwarding proxy. In one implementation, key server  108  includes an HTTP post and forwarding proxy server application  204  which is used to recover the secure message (still secured) from the HTTP post and forward or otherwise relay the message as an attachment to a conventional E-mail message. In one implementation, a plurality of dedicated forwarding proxy servers are provided, each separated from the key server, where the number is set based upon system requirements. 
     Recovery application  206  is invoked by a user (sender  102  or recipient  104 ) and supports the recovery of the private key of the user in the event the private key is lost or the signature phrase is forgotten. 
     Key list  208  is a repository for public keys. In one implementation, public keys are indexed by the owner&#39;s E-mail address and the hash of the E-mail address. A public key can be retrieved by submitting either the E-mail address or the hash of the E-mail address for the recipient (or the sender, depending upon the public key to be retrieved). A public key (PK) for the recipient is retrieved at the time a secure E-mail message is created. 
     Trusted third party application  210  facilitates the transfer of private keys of users to a trusted third party. Trusted third party application  210  is described in greater detail in “Secure Messaging System.” 
     Each of key retrieval servers  180  can be a server computer executing one or more server programs. Each key retrieval server  180  includes one or more server applications executing on the server computer. Key retrieval server  180  includes an operating system  120 , a key exchange application  202 , key list  208 , status list  209  and list update process  182 . In one implementation, key server  108  is a centralized server that maintains a master key list and status list that are published to each of the key retrieval servers  180 . As such, key exchange application  202  can be removed from the central server (key server) and distributed to one or more local key retrieval servers  180 . List update process  182  interfaces with key server  108  to maintain current key and status lists. Key retrieval server  180  can also include forwarding proxy services  184  for forwarding HTTP posts from a sender to a recipient. The process for forwarding such messages is described in greater detail “Secure Messaging System.” 
     Trusted third party server  190  can be a server computer executing one or more server programs. Trusted third party server  190  includes one or more server applications executing on a server computer and can include an escrow key list  194  and an escrow application  196 . Trusted third party server  190  receives encrypted private keys forwarded by key server  108  from users (sender and recipient  102  and  104 ). Escrow services are described in greater detail in “Secure Messaging System.” 
     Forwarding service  195  can be a server computer executing one or more server programs. Forwarding service  195  includes one or more server applications executing on the server computer and includes an encryption service  189 , a web front end  191 , a filter layer  193 , queue structure  197 , forwarding engine  198  and access list  199 . 
     Encryption service  189  can be invoked to encrypt a message in accordance with the preferences of a recipient. As will be described in greater detail below, a message received by the forwarding service  195  can be forwarded to a recipient in plural ways. First, if the recipient is a minimally configured recipient  104   b , then the forwarding service  195  can be enabled to send the recipient an E-mail message that includes instructions for how the message can be retrieved at the forwarding service  195  (viewed) using a secure web browser. If the recipient has decryption capabilities and has specified a delivery preference (e.g., using an alternative encryption/decryption technique), then the message can be delivered (e.g., encrypted) in accordance with the delivery preference. The delivery preference can include the specification of an encryption protocol. Encryption service  189  includes one or more tools for processing (e.g., encrypting) messages in accordance with each encryption protocol that is currently supported by the forwarding service  195 . The encrypted message can be attached to an E-mail addressed to the recipient and forwarded using forwarding engine  198  to the designated recipient. Recipient delivery preferences are described in greater detail below. 
     The web front end  191  receives messages forwarded from a sender  102 , the forwarding service processes the messages using filter layer  193  to produce a standard format message that can be stored in queue structure  197 . The web front end  191  also receives and processes message requests received from a recipient. The processing of requests from recipients is described in greater detail below. 
     The processing in filter layer  193  may include parsing, decryption and authentication services as well as other services. The filter layer  193  consists of several filter units each dedicated to process secure messages sent by a particular type of sending application. In one implementation, filter layer  193  includes a ZixMail unit, a PGP unit, a web-based compose form unit, and an X.509 S/MIME unit. Other filter units can be added to the filter layer  193  as required to support other messaging formats. Regardless which filter unit of the filter layer processes an inbound message, the resulting output of filter layer  193  is always in a standard format and can be rendered to the recipient in the same fashion. This solves the long-standing interoperability problem of different secure email programs. 
     Each filter unit in the filter layer supports a particular messaging format. A unit may support decryption, parsing, authentication and other services as appropriate for the message format. For example, a ZixMail unit may be configured to decrypt a received ZixMail message using a private key of the forwarding service  195 , authenticate the sender and message contents using an authentication routine, and parse the decrypted message to create a standard format message. 
     In one implementation, the standard format message data structure includes authentication data and message data (authentication block  502  and data block  504 , respectively). The authentication data can be provided from the sender or developed as a result of processing by the filter layer  193 . For example, the authentication data can be the result of the verification process for a digital signature. Alternatively, the authentication data may be the result of a sender provided authentication pass phrase. The standard format messages are securely stored in queue structure  197  until retrieval or other predefined criteria is encountered. Predefined criteria can include the passage of time or a removal notice from the sender. 
     Queue structure  197  includes a storage area for messages that may be retrieved using a web browser or other means by an intended recipient. In one implementation, the queue structure  197  includes a message area and an index area. Associated with each message (standard format message) is an index. The index can be used in a hyperlink that is forwarded to the intended recipient to identify the message. The generation of the hyperlink is described in greater detail below. In one implementation, filter layer  193 , as part of the message processing operations, generates a random number that can be used as an index. Alternatively, forwarding engine  198  can generate the index. 
     Forwarding engine  198  constructs an E-mail to be transmitted to an intended recipient. Each E-mail includes either a hyperlink that points to a message (stored in the queue structure  197 ) or another specified form of the message that is designated for direct delivery to the intended recipient (where the other specified form can be an encrypted message or a cleartext message). Forwarding engine  197  forwards the E-mail to the E-mail address associated with the recipient of the message. As described above, forwarding engine  198  can be used to forward a message encrypted by encryption engine  189  or other form of the message in accordance with the recipient&#39;s preferences. The encryption of messages in accordance with recipient preferences is described in greater detail below. While forwarding engine  198  is described herein as an email notification or email delivery engine, forwarding engine  198  can be configured to deliver either a message notification or the message itself via pager, fax, voice, or other communications medium. 
     Web front end  191  processes requests from a recipient to display a web page that can include the message intended for the recipient. The communications between the web front end  191  and the recipient can be secured using the SSL protocol. The SSL protocol ensures privacy between a client (the recipient) and a server (the forwarding service) by using certificates to authenticate the server and optionally the client. Further, the SSL protocol supports encryption of data between the server and client. The SSL protocol is not tied to a particular application. Any application or protocol can be layered over SSL, such as the hyper text transfer protocol (HTTP) or file transfer protocol (FTP). The SSL takes care of encryption, security keys and authentication before the underlying application (e.g., the E-mail forwarding engine  198 ) sends or receives any data. In one implementation, in lieu of SSL, a secure communications channel can be created between the recipient and web front end  191  by use of a transmitted applet that contains encryption code and public keys for secured communications. The process of forwarding a message is described in greater detail below. 
     Forwarding engine  198  may also ensure that requests from the recipients are valid. Forwarding service  195  includes an access list  199  that includes a list of recipient identifiers (e.g., E-mail addresses) and authorization pass phrases (a receive authorization pass phrase or RAPP and a send authorization pass phrase or SAPP). Each entry in the access list  199  includes an identifier and a SAPP and/or RAPP. The creation of an authorization pass phrase (SAPP/RAPP) is described in greater detail below. In one implementation, the forwarding engine receives a page request from the web front end  191  that includes an authentication pass phrase from the recipient (a receive authorization pass phrase or RAPP). The RAPP can be verified prior to returning the web page including the message to the recipient. The creation of a RAPP is described in greater detail below. 
     The access list  199  may also include user preference data. The user preference data may specify an encryption/decryption protocol to be used by the forwarding service  195  when forwarding messages to the user. For example, when a message is received for an intended recipient, forwarding engine  198  may check the preference data associated with the intended recipient in the access list  199  to determine how to forward the message to the recipient. If recipient has no preference set or designates web delivery, then the forwarding engine  198  constructs an E-mail that includes a pointer to the message in the queue structure as described above. Alternatively, if an encryption/decryption protocol has been specified, the forwarding engine  198  can invoke the encryption service  189  to encrypt the message in accordance with the recipient&#39;s preference. Thereafter, the forwarding engine  198  can attach the encrypted message to an E-mail and forward the E-mail with attachments (if any) directly to the intended recipient. The processes invoked by the forwarding service  195  upon receipt of messages is described in greater detail below. 
     The operational structure of the forwarding service  195  is shown in  FIG. 1 b   . Operationally, forwarding service  195  includes plural layers including an origination layer  50 , a filter layer  193 , a standard message format layer  52 , an interoperability layer  54 , a notify and store layer  56  and delivery layer  58 . 
     Origination layer  50  includes a front end (e.g., web front end  191  or E-mail application) that is configured to receive messages of various forms that are to be processed by the forwarding service. A message can be of the form of an E-mail message (received at one or more E-mail addresses associated with the forwarding service  195 ), a web form, a voicemail message, a facsimile or other message with or without encryption. The origination layer  50  operates to collect messages for processing by the forwarding service  195 . 
     Filter layer  193  operates to decrypt, authenticate and parse messages in accordance with their designated format. As described above, the filter layer  193  includes plural filter units, one for each message type that specifies operations to be performed on a given message type prior to forwarding or storage in the queue structure  197 . In one implementation, the SAPP associated with the sender of the message can be checked in the filter layer to ensure that the sender is authorized to use the forwarding service prior to performing other layer operations. 
     Standard message format layer  52  operates to produce a standard format message for each received message processed by the filter layer  193 . The standard message format layer produces messages that include authentication data, message data and attachments (if any). 
     Interoperability layer  54  operates to decide how to forward a message to the recipient. In the interoperability layer  54 , a check is made (e.g., by the forwarding engine  198 ) to determine if the recipient has predefined preferences for delivery. The preferences can be stored in access list  199 . The preferences can specify the form of the message to be sent to the user along with forwarding instructions. For example, the recipient can have specified that all messages should be forwarded via fax. Alternatively, the recipient can specify that all messages should be encrypted according to a predefined protocol (supported by encryption service  189 ) and then forwarded directly to the recipient. Another preference can be the forwarding of messages using web delivery as described below. In one implementation, the interoperability layer (e.g., the forwarding engine  198 ) may check to see if the recipient has one or more public keys published (e.g., PGP keys, X.509 certificates, or other keys). If the user has such keys, the preference information can be evaluated to decide which encryption protocol to use in forwarding the message directly to the recipient. 
     In one implementation, the recipient may not directly specify a preference, yet the interoperability layer  54  may infer a preference. More specifically, the forwarding engine may check to see if the recipient has a public key published (e.g., PGP keys, X.509 certificates, or other keys). If the user has one or more of such keys, a preference can be inferred in accordance with a predefined hierarchical list of preferred secure messaging services. In each of these scenarios, where a recipient preference is determined that includes direct forwarding to the recipient of a form of the message, the processing continues in the delivery layer  58 , skipping the notify and store layer  56 . 
     The notify and store layer  56  is invoked when web (or other) delivery of the message is required. Web delivery can arise when a recipient has specifically requested web delivery in accordance with a delivery preference stored in access list  199 , or where no preference is defined. In the notify and store layer  56 , a standard format message is securely stored in the queue structure  197  including the associated index to the entry. Thereafter, or concurrently, the recipient is notified by E-mail, facsimile, pager or other means as specified in the preference data for the recipient or in accordance with a default specification. In one implementation, the default mechanism selected for notice is an E-mail message. The notifying message includes a link to the message stored in the queue structure  197 . In one implementation, the link is a hypertext (secure) link. 
     The delivery layer  58  operates to deliver the message to the recipient. Delivery can be direct or through a web browser. The delivery preferences can specify delivery by web page, email, cellular telephone, facsimile, pager or other communication means. For example, if the interoperability layer determines that the message is to be delivered in accordance with a particular encryption protocol, the delivery layer ensures that the protocol is applied and the encrypted message is attached to an E-mail wrapper and delivered directly to the recipient. The delivery layer also includes a web front end for interfacing with recipients to allow for the retrieval of messages stored in the queue structure  197 . 
     Operation 
     Referring now to  FIGS. 1 a  and 2 a   , an overview of a process for secure transmissions between a sender and a recipient over a network is shown. The process described below includes numerous process steps that can be performed at various locations of the computing system. The description provided indicates a possible configuration for the computing system, and should not be construed as limiting. In the example shown, prior to sending or receiving secure E-mail messages, an initial (initialization) process is required to be performed to generate public and private keys for the user (sender). The initialization process is described in greater detail in “Secure Messaging System.” The transmission process  6  begins with the user invoking wrapping application  128 , creating a secure E-mail message and designating one or more recipients ( 32 ). 
     Wrapping application  128  requests the public key for each recipient and a time stamp certificate ( 34 ) from key server  108 . Key server  108  obtains the sender&#39;s public key status from the status list  209  and each recipient&#39;s public key (if available) from the key list  208 , generates a time stamp certificate, and returns these data to wrapping application  128  ( 36 ) (As will be described in greater detail below, the data includes a list of recipient&#39;s for whom no key (PK) was located and may include the public key of the forwarding service.). 
     Wrapping application  128  performs a series of operations ( 38 ) to complete the secure E-mail message construction depending on the results returned from the key server. For all recipients having public keys the operations include: verifying the time stamp certificate and attaching it to the message (forming data), signing the data, encrypting the signed data with the recipient&#39;s public key, attaching the encrypted signed data to a wrapper and sending the wrapper to the recipient. For all recipients not having public keys available from the key server the operations can include: retrieving and verifying one time stamp certificate for sending to the forwarding server and attaching it to the message (forming data), signing the data, encrypting the signed data with a public key associated with the forwarding service, attaching the encrypted signed data to a wrapper and sending the wrapper to the forwarding service. In one implementation, when an identical message is to be sent to multiple recipients who do not have keys, only one copy of the message is sent to the forwarding service. Extra data fields are included in the message containing the email addresses of these multiple recipients. The forwarding service will deliver the message to these recipients according to the preference of each recipient. Such an implementation speeds up the process of sending to multiple recipients and reduces the forwarding server storage requirement. 
     While wrapping application  128  is described in some specificity, any generic wrapping application layer, including those in standard industry programs, such as Microsoft Outlook, could be used to create and send the composed (E-mail) message to forwarding service  195 . 
     Depending on whether the forwarding service is used or not, the process continues as follows. 
     Forwarding Service for Minimally Configured Recipients and Others 
     Forwarding service  195  receives, at a minimum, each message to be forwarded to a recipient(s), processes the message including authentication of the sender, checking for recipient preferences or other public key data, securely stores the message in a queue (optional) and forwards an E-mail wrapper or other message to the recipient ( 41 ). If the recipient has designated an encryption/decryption delivery protocol preference, then the E-mail wrapper includes an encrypted form of the message (encrypted in accordance with the recipient&#39;s preferences) and can be opened immediately by the recipient ( 40   b ). 
     If the recipient is minimally configured or has designated a preference for web delivery, the E-mail wrapper includes a secure hyperlink that can be invoked by the user to link, using a web browser, to the web front end  191  of the forwarding service  195 . The link includes a pointer to the particular message stored in the forwarding service&#39;s queue structure  197 . In this scenario, the recipient (e.g. minimally configured recipient  104   b ) receives the E-mail wrapper, including hyperlink, through a conventional E-mail service ( 40   c ) or other means, such as pager, facsimile, or cell phone notification. The recipient can view the message by clicking on the hyperlink and invoking web browser application  123  which in turns performs a series of operations to process and display the secure E-mail message, including attached files if any. The process includes linking to the web front end  191  associated with the forwarding service  195  and can include providing a RAPP. The forwarding service  195  processes received page requests for messages, verifies the RAPP (as appropriate) and returns a web page that includes the message from the sender ( 43 ). In one implementation, the connection between a recipient and the web front end  191  conforms with the SSL protocol for secure communications between devices. The processes invoked by each of the recipients (e.g., minimally configured recipients  104   b ) and the forwarding service  195  is described in greater detail below. In one implementation, designated recipients may receive the message via synthesized voice delivery over standard or cellular telephone connections following proper authorization. 
     Fully Configured Recipients 
     All fully configured recipients can receive the wrapper, including encrypted and signed data, through a conventional E-mail service ( 40   a ). Each fully configured recipient invokes viewer  130  which in turns performs a series of operations to process and display the secure E-mail message, including attached files if any. The process includes decrypting the encrypted signed data, verifying the sender&#39;s signature, optionally verifying the time stamp certificate, verifying the authenticity of the server&#39;s public key and optionally retrieving the status of the sender&#39;s public key (using the key ID) ( 42 ). 
     Optionally, key server  108  looks-up the status of the sender&#39;s public key and returns the status information to the recipient&#39;s viewer  130  ( 44 ). Viewer  130  displays the decrypted message and time stamp along with the sender&#39;s public key (signature) status ( 46 ). In one implementation, the key status information returned from the key server can be signed and the key server signature can be verified. The individual processes executed by the sender and the recipient are described in greater detail below. 
     Secure Transmission 
       FIGS. 2 b -2 e    show user and program steps for secure transmissions between sender  102  and recipient  104  of  FIG. 1 a   . The process includes complementary send process  248  (including forwarding process  246  shown in  FIG. 2 c   ) and view processes  249  and  250  on  FIGS. 2 b , 2 d  and 2 e    respectively. Prior to transmission of any secure messages, each of sender  102  and fully configured recipients  104   a  must perform an initial process (the “initialization process”)  247 . The initialization process includes the generation of public and private keys and the designation of a signature phrase. The public keys for all users can be published at key server  108  for ready accessibility by other clients. The initialization process is only executed once, prior to sending or receiving secure E-mail messages. Once initialized, sender  102  can compose and send secure E-mail to any recipient  104  including highly secure transmissions to recipients having a public key stored in key server  108 . After initialization, a fully configured recipient  104   a  can receive and view secure E-mail from any sender having a public key stored in key server  108 . Similarly, a minimally configured recipient  104   b  can receive and view secure E-mail from any sender so enabled and verify the authenticity of any secure E-mail message received or digital signature affixed thereto. 
     Send Process 
     When a sender  102  desires to send a secure E-mail message to a recipient  104 , send process  248  is invoked by sender  102 . As noted above, prior to sending of messages (or receipt by a fully configured recipient  104   a ) each user (sender  102  and fully configured recipient  104   a ) must perform initialization routine  247 . As a reminder of this precondition,  FIG. 2 b    shows an initialization step in phantom. The initialization routine is described in greater detail in “Secure Messaging System.” 
     Referring to  FIGS. 1 a  and 2 b   , send process  248  begins when wrapper application  128  is invoked which in turn requires the user to designate one or more recipients ( 252 ). The body of the E-mail message is produced and any attachments are identified ( 254 ). In one implementation, the message, including any attachments, optionally can be compressed. A send message request is generated by sender  102  and transmitted to, key server  108  ( 258 ). The send message request includes the E-mail address (or hash of the E-mail address) of the recipient, the E-mail address (or hash of the E-mail address) of the sender, the public key ID of the sender, and the hash of the message to be sent. The request can itself be encoded, by first retrieving the public key for the server. The public key can then be used in encrypting the request message in order to secure the link between the sender and the recipient. When an identical message is to be broadcast to multiple recipients, the request can include the E-mail addresses (or hashes) of multiple recipients. Thereafter, the process waits for a response from key server  108  ( 259 ). 
     Assuming the recipient&#39;s E-mail address (or hash) is valid and locatable in the key server&#39;s key list and the key status is active, a time stamp certificate is received along with the public key(s) for the recipients that could be located ( 260 ). Thereafter the process continues in parallel along two paths. For each recipient who had a key that could be located, an encrypted message is created and sent directly to the recipient, unless the recipient has specifically indicated a preference to the contrary by setting a flag in the corresponding key status (stored in the key status list  209 ). When the key server sees such a preference flag, the key server can treat the public key as un-locatable. A fully configured recipient can turn on or off this preference flag using messages signed by the corresponding key and sent to the key server  108 . The process for recipients with locatable public keys is described starting at step  261 . For all recipients whose public key was determined to be invalid or otherwise un-locatable, a forwarding process is invoked starting at step  255 . The details of the forwarding process are described in greater detail below. 
     Sending Secure Messages Directly to a Recipient 
     Continuing along the path to step  261 , the time stamp certificate is verified. The time stamp certificate serves several purposes, including: 1) establish that the message was sent from the sender to the recipient; 2) certify the time the message was sent; 3) authenticate the recipient&#39;s and the sender&#39;s public keys; 4) certify the status of these keys at the time the message was sent; and 5) validate the integrity of the associated message. 
     For each recipient whose PK was returned, a message is constructed that includes the following steps. The time stamp certificate is attached to the message, forming data ( 262 ). The time stamp certificate produced and signed by key server  108  cannot be altered or attached to another message without detection. The inclusion of the key server certificate in the time stamp certificate ensures that the server&#39;s public key is authentic. Key server process  216  for retrieving a public key and for generating a time stamp certificate is described in greater detail in “Secure Messaging System.” 
     The data is signed using a signing process ( 264 ). The processes for signing data, verifying signed data and verifying the time stamp certificate is described in greater detail in “Secure Messaging System.” The signed data is encrypted by the recipient&#39;s public key (producing an encrypted message) ( 266 ). The process of encrypting data using public key encryption is described in greater detail in “Secure Messaging System.” A wrapper is produced that includes the recipient&#39;s E-mail address and an optional message body ( 268 ). The message body can include information from the key server  108  including: a message indicating that a secure E-mail message is attached, service updates or any other form of information including advertisements for services or products. The secure E-mail message is attached to the wrapper ( 272 ) and the wrapper and messenger are sent to the recipient ( 274 ). In one implementation, the wrapper is an SMTP wrapper. 
     Forwarding Process 
     Forwarding process  255  includes the creation of a message addressed to the forwarding service  195  that includes an indicator for all intended recipients whose public keys could not be located. The process includes creating a message (including header and body) that is addressed to the forwarding service ( 302 ). In one implementation, the forwarding service  105  supports plural sender types (e.g., ZixMail, X.509, PGP, HTTP post, web form, regular E-mail). The addressing of each message received by the secure forwarding service  195  can include an identifier for each sender type. For example, messages from a ZixMail client can be addressed to ZixMail@secure-forwarding-service.com. 
     After the message is addressed, the message header ( 304 ) and body ( 306 ) are populated. The message header or the message body includes extra fields to indicate the actual recipients of the secure message as designated by the sender. These extra fields, however, will not be displayed to the recipient when the message is rendered. The header can include other data including authorization data (e.g., a SAPP). Authorization data can be used to verify that the sender is authorized to use the forwarding service  195 . The use of authorization data is described in greater detail below. The body includes the message generated by the sender and can include the original sender message, attachments, and authentication data for authenticating the sender. 
     As described above, even when a recipient&#39;s public key is unable to be located by the key server, a time stamp certificate is returned to the sender. Here the time stamp certificate serves several purposes, including: 1) establish that the message was sent by the sender via the forwarding service; 2) certify the time the message was sent; 3) authenticate the forwarding service&#39;s and the sender&#39;s public keys; 4) certify the status of these keys at the time the message was sent; and 5) validate the integrity of the associated message. In one implementation, the public key of the forwarding service is returned to the sender whenever any recipient&#39;s keys are unable to be located. The public key of the forwarding service is used to securely transmit the message to the forwarding service. Alternatively, the public key of the forwarding service can be separately requested, embedded in the sender&#39;s client application  102 , or otherwise discovered (as shown in phantom step  307  of  FIG. 2 c   ). 
     The time stamp certificate is verified ( 308 ) and then attached to the message, forming data ( 310 ). The time stamp certificate produced and signed by key server  108  cannot be altered or attached to another message without detection. The inclusion of the key server certificate in the time stamp certificate ensures that the server&#39;s public key is authentic. The key server process  216  for retrieving a public key and for generating a time stamp certificate is described in greater detail in “Secure Messaging System.” 
     The message is then signed using a signing process ( 312 ). The signed message (data) is encrypted by a public key associated with the forwarding service (producing an encrypted message) ( 314 ). The process of encrypting data using public key encryption is described in greater detail in “Secure Messaging System.” 
     A wrapper is produced that includes the forwarding service&#39;s address ( 316 ). The sender&#39;s message is attached to the wrapper ( 318 ) and the wrapper and message are forwarded to the forwarding service  195  ( 319 ). In one implementation, the message is forwarded to the forwarding service using a conventional E-mail service. In an alternative implementation, the message is HTTP posted to the forwarding server. 
     View by a Fully Configured Recipient 
     View process  249  ( FIG. 2 d   ) includes numerous steps. As noted above, prior to receipt of messages by a fully configured recipient (or transmission by a sender to a recipient) each user must perform an initialization routine  247 . As a reminder of this precondition,  FIG. 2 d    shows an initialization step ( 247 ) in phantom. View process  249  begins with the receipt of the wrapper and attached secure E-mail message ( 280 ). The wrapper is sent to the recipient using the recipient&#39;s E-mail address and arrives at the recipient&#39;s E-mail mailbox. The wrapper is opened using the recipient&#39;s conventional E-mail application (CCMail, Outlook and the like). The recipient invokes viewer  130  to unwrap the document. More specifically, the recipient opens the wrapper ( 282 ) and clicks or double clicks on the attached secure E-mail message to invoke viewer  130  ( 284 ). Viewer  130  decrypts the encrypted message included within the attached secure E-mail message in accordance with a decryption process ( 286 ). Viewer  130  verifies the sender&#39;s signature ( 287 ) and the time stamp certificate (TSC) ( 288 ) using verification processes described in detail in “Secure Messaging System.” 
     Viewer  130  optionally retrieves the status of the sender&#39;s public key (e.g., from key server  108  of  FIG. 1 ) ( 290 ). Thereafter, viewer  130  optionally verifies the server&#39;s public key that signed the returned status information using a verification procedure ( 292 ) and verifies that the public key of the sender was valid at the time indicated by the date stamp when the message was sent ( 294 ). Finally, the original contents of the E-mail message, the TSC and the signature status is displayed ( 296 ). Thereafter, the process ends. 
     View by a Minimally Configured Recipient 
     View process  251  for minimally configured recipients  104   b  ( FIG. 2 e   ) includes numerous steps. View process  251  begins with the receipt of the wrapper including hyperlink to the message ( 320 ). The wrapper is sent to the recipient using the recipient&#39;s E-mail address and arrives at the recipient&#39;s E-mail mailbox. Alternatively, the notification could be sent by cell phone, pager, facsimile or other notification method. The wrapper is opened using the recipient&#39;s conventional E-mail application (CCMail, Outlook and the like) and the hyperlink contained therein is invoked (clicked) which in turn launches the browser application to establish a SSL connection with the server associated with the forwarding service  195  ( 322 ). More specifically, the recipient clicks or double clicks on the hyperlink to invoke web browser  123  to retrieve a web page from the forwarding service that includes the message from the sender. Optionally, the forwarding server may require the recipient to provide an authorization pass phrase (i.e., a RAPP) to the server associated with the forwarding service  195  before sending the web page ( 324 ). If the authorization pass phrase is correct, the minimally configured recipient  104   b  receives via an encrypted communication, such as through the SSL link, the HTML content (a page, e.g., HTML, XML rendering instructions or the like) to be displayed in the browser ( 326 ). Thereafter, the minimally configured recipient can display the page ( 328 ). 
     The page can include authentication data (optional), message data and attachments, if any. The user can view the authentication data provided by the forwarding server. The forwarding server obtains the authentication data by conducting verification steps similar to the verification steps used by a fully configured recipient to validate the message. For example, the authentication data can include a certificate of authenticity generated/verified by the forwarding service as to the authenticity of the sender. The view process may conclude at this point, or the user may invoke one or more other actions including return reply, storage or printing of the message ( 330 ). Thereafter, the process ends. 
     The send and receive processes described above include numerous process steps. At least eight general processes are invoked by one or more of the clients, the sender, the forwarding service and the key server in the secure transmissions including: symmetric key encryption, hashing, HASH5000, public key encryption, public key decryption, a signature process, a signature verification process and a time stamp verification process. Each of these processes is described in greater detail in “Secure Messaging System.” While the process described above results in the rendering of a secure message to the recipient&#39;s browser, in an alternative implementation, approximately the same rendering can be delivered via fax or other means to the recipient. 
     Client Sender Process 
     The process  248  for sending a secure E-mail message is described above and shown in  FIG. 2   b.    
     The process for forwarding a secure message to a recipient is described above and shown in  FIG. 2   c.    
     In one implementation, similar to a minimally configured recipient, a minimally configured sender can send secure messages using a sending authorization pass phrase (SAPP). A minimally configured sender is not required to have a locatable public key, but may be required to create a SAPP. The SAPP can be a unique pass phrase. The process of sending a secure message via the forwarding service using a SAPP is shown in  FIG. 2 f    and begins after a sender completes a message. The client computer displays a dialog box in a client application executing on the sender&#39;s client computer that is being used to send the message ( 340 ). The client application can be an E-mail client application such as Outlook with a “plug-in” that provides a special button connected to a DLL or other extension to handle the SAPP authorization. Other E-mail applications or other applications can also be extended in a similar way to provide such functionality. The dialog can include one or more user send preferences and a data entry field for designating a SAPP. If operating in an interactive mode, such as using a Web browser, the sender may not require a plug-in but may need to establish a secure link (SSL) in order to transmit the message to the forwarding service. 
     The sender may select an “anonymous” preference. In this case, all communications between the forwarding server and the recipient, including the notification messages, will not reveal the identity of the sender to any outsider. Only the recipient can find out who the sender is when the message is viewed. 
     If the SAPP is provided, the forwarding server will check if the SAPP agrees with the stored SAPP data. In one implementation, the message sent using a SAPP can be authenticated by attaching a Message Authentication Code (MAC). For example, attaching HASH(SAPP+HASH(SAPP+Message)) to the message will provide such an authentication and will protect the integrity of the message. If the SAPP agrees and the MAC matches, the delivery is allowed. 
     If the sender/server connection is occurring in a non-interactive mode, and if a correct SAPP is not received (either the sender has forgotten their SAPP, or has not created a SAPP, or otherwise does not know the SAPP), the user is directed to create or re-create an authorization pass phrase. If the sender wants to create a SAPP ( 348 ), the process continues by allowing the user to create a SAPP ( 352 ). In one implementation, a link to a website where the user can create an authorization phrase is executed. The process for creating an authorization pass phrase, either SAPP or RAPP, is described in greater detail in  FIG. 2 g   . Once a SAPP is created, the process continues back at step ( 340 ). 
     Referring now to  FIG. 2 g   , a process for creating an authorization pass phrase begins by displaying a web page that requests a user to enter an E-mail address and an authorization pass phrase (either SAPP or RAPP or both) ( 360 ). Upon receipt of the E-mail address and authorization phrase ( 361 ), a confirming E-mail message is sent to the user ( 362 ). The E-mail prompts the user to send a confirmation message to the forwarding service. The forwarding service receives the confirmation ( 364 ) and “activates” user&#39;s E-mail address including storing the authorization pass phrase (RAPP/SAPP) in a respective location in the access list  199  in an entry associated with the user ( 366 ). Thereafter the respective send or receive process continues as described in association with  FIGS. 2 f  and 2 h   , respectively. 
     In one implementation, the SAPP and RAPP are not directly stored. Instead, a combination of a 128 bit “salt” and a HASH (passphrase+email address+salt) is stored on the forwarding server. Each user has a different salt. In this way, even if the database file that contains the SAPP and RAPP information is stolen, one is still required to mount a brute force (dictionary) attack to find each passphrase. 
       FIG. 3 a    shows a sample user interface presented by wrapper application  128  which can be manipulated to compose a secure E-mail message. Fields are included for entering a recipient&#39;s E-mail address  775 , a sender&#39;s E-mail address  776 , subject  777 , attachments field  779  and message body  780 . Buttons are included for attaching files  793 , saving a draft  794 , clearing a form  795 , printing a message  796 , looking-up an E-mail address  797  and editing an E-mail ID  798 . Activation of button  781  can provide access to a conventional address book that includes E-mail addresses (along with other recipient information). Subject  777  is a placeholder for a title to be displayed when an E-mail containing a secure E-mail message is displayed in a conventional E-mail application. Attachments field  779  is a field used to indicate documents that have been attached to the secure message. Files can be attached to a message using attachment button  790 . All attachments are first compressed and then encrypted along with the contents of the message body  780  forming the encrypted portion of the E-mail message transmitted to the recipient. Clicking the send button  792  will start the sending process, which includes prompting for signature phrase, retrieving recipient&#39;s public key and time stamp certificate, signing the message, encrypting the message, wrapping the encrypted message into a MIME message, and sending the message to the recipient using SMTP or HTTP relay. 
       FIG. 3 b    shows a user interface  791  presented by wrapping application  128  ( FIG. 1 ) when send button  792  is depressed. A field is included for entering a sender&#39;s signature phrase  799 . The user is prompted to enter a signature phrase. If the signature phrase is correct, then a public key for the recipient (or forwarding service) is retrieved along with a time stamp certificate. Upon receipt of the public key and time stamp certificate, the wrapping application encrypts and wraps the message and sends the message and time stamp certificate to the recipient. Alternatively, the message can be encrypted, wrapped and forwarded to forwarding service as described above. The sender may specify a SMTP server to use, or in the alternative, in one implementation, key server  108  may specify a SMTP server for the user. In one implementation, a HTTP to SMTP relay can be used to send the message. 
     Key Server Processes 
     Key server  108  ( FIG. 1 ) includes numerous processes in support of the transmission of secure E-mail messages. The operation of key server  108  is described in greater detail in “Secure Messaging System.” 
     Recipient Process 
     The process for viewing a secure E-mail message is described above and shown in  FIGS. 2 d  and 2 e   . The process can include verifying the sender&#39;s and the server&#39;s signatures, verifying the authenticity of the server&#39;s public key and retrieving the status of the sender&#39;s public key. Authentication data (e.g., the status of the sender&#39;s public key) is displayed along with the contents of the secure message by viewer  130  or web browser  123  ( FIG. 1 a   ). 
     The process for receiving a secure message by a minimally configured recipient is described above and shown in  FIG. 2 e   . Step  324  specifies when a RAPP is sent to the forwarding service. A user (recipient) that desires to make use of the forwarding service  195  may be required to create a RAPP. The RAPP can be a unique pass phrase. A process  324  for providing a pass phrase to the forwarding service  195  including creating a RAPP is shown in  FIG. 2 h    and begins after the forwarding service receives a message for web or other delivery to the recipient. The forwarding service determines if the recipient has a RAPP ( 370 ). If not, then the recipient is prompted to create a RAPP ( 372 ). In one implementation, the recipient is directed to a web site that includes instructions for creating an authorization pass phrase. The process for creating a RAPP is described above and shown in  FIG. 2 g   . If the recipient has a RAPP, then the user is prompted to provide the RAPP ( 374 ). The RAPP provided by the recipient is checked to determine if it matches the data on file (e.g., the RAPP or SAPP stored in the access list  199 ) ( 376 ). If no match is detected, the recipient may be prompted to try again ( 378 ). In one implementation, the user is limited to three incorrect attempts before he/she is prevented from retrieving the message. Assuming the RAPP is correct, the process for displaying and viewing the message is continued starting at step  326  of  FIG. 2 e   . In one implementation, a SAPP may be used in lieu of a RAPP to view a message. 
     A user interface presented by the viewer application is shown in  FIG. 4 a   . Fields, similar to the fields presented by the wrapping application user interface, display various portions of the secure E-mail contents after decryption. Buttons are included for opening a message  902 , replying to a message  904 , replying to all recipients  906 , forwarding a message  908 , clearing a message  910 , and printing a message  912 . In addition, a series of visual indicators  900  are provided to indicate the status of the signature verification process. In one implementation, one or more of the three visual indicators  900  are illuminated, as described below, in accordance with the information provided from key server  108  ( FIG. 1 a   ). The status information returned from key server  108  (or key retrieval server  180 ) of  FIG. 1 a    includes valid time and date(s)  914 . The time stamp recovered from the decrypted received package is compared to the status information. One or more indicators that look similar to a traffic light or other differentiating indicator are illuminated depending on the comparison results. Combinations can include:
         green only illuminated—valid signature detected;   yellow and green illuminated—signature is mathematically valid, public key of sender was valid at time sent, but now is out of date or otherwise invalid;   yellow only illuminated—signature is mathematically valid, but the connection to the key server is not functioning and the recipient computer cannot connect for confirmation from the key server; and   red only illuminated—all other conditions not listed above, including no key posted, no match of the public key with the E-mail address, tampering has occurred, message was signed after the key has been deactivated, etc.       

     A user interface presented by the web browser for viewing messages is shown in  FIG. 4 b   . Fields, similar to the fields presented by the viewer user interface, display various portions of the secure E-mail contents. Buttons can be included for replying to a message  904 , reply to all recipients  906 , forwarding a message  910  and deleting a message  912 . In addition, a series of visual indicators  900  can be provided to indicate authentication of the sender (e.g., the status of the signature verification process performed at the forwarding service  195 ). In one implementation, one or more of the three visual indicators  900  are illuminated, as described above, in accordance with the information originally provided from key server  108  ( FIG. 1 a   ) or other originating source. The status information can include valid time and date(s)  914  as well as authentication data. 
     Forwarding Proxy (HTTP Post) 
     Referring to  FIG. 1 a   , wrapping application  128  can send secure E-mail messages directly, or a conventional E-mail system can be used to forward the secure portions of the messages (as part of an attachment to a conventional E-mail message) directly to the recipient or through a forwarding service. While one implementation of the invention requires the client sender to have access to a SMTP server, an alternative implementation provides a method for easy transmission when no SMTP server is accessible. Wrapping application  128  can invoke HTTP post application  124  to send the secure message with an HTTP post. Transmission by HTTP post is described in greater detail in “Secure Messaging System.” 
     Alternative Implementations 
     The forwarding service  195  of  FIG. 1 a    can be used to forward messages from a plurality of different sender types. Referring to  FIG. 5 , an alternative implementation of a secure forwarding service  195  is shown. Messages from any number of types of senders  102  are addressed and transmitted to the forwarding service  195  using conventional or other transmission means. The conventional transmission means can include an E-mail, a web form or other form of post. Each message is processed by the forwarding service  195  and stored in the queue structure  197 . A user interface presented by the web browser for sending messages is shown in  FIG. 4 b   . Fields, similar to the fields presented by the wrapping application user interface  FIG. 3 a   ), allow the user to enter various portions of the message content, passphrase, attachments and other selections. 
     Forwarding service  195  processes each message including providing parsing, decryption, authentication and other services. Filter layer  193  processes each message to produce a standard format message that is stored in the queue structure  197 . The standard format includes a standardized authentication block  502  and a message block  504 . 
     The processing performed by filter layer  193  is uniquely determined by the type of message received. For example, filter layer  193  can include an application specific decryption and authentication routine for ZixMail messages. In this example, a decryption algorithm using a private key of the forwarding service extracts the original message and a sender signature. Thereafter, an authentication routine is used to verify the authenticity of the sender in accordance with the ZixMail secure messaging system described in “Secure Messaging System.” 
     Alternatively, other decryption algorithms or authentication routines can be invoked in the filter layer  193 . The particular processes invoked depend on the format of the message received. At a minimum, parsing services are provided to extract sender and recipient information from the received message. The received message is parsed to extract the address for the intended recipient that is in turn used to generate an E-mail message or other message form for transmission to the recipient. The E-mail message can include an encrypted message (encrypted in accordance with recipient preferences), a link to a message stored in queue structure  197  or a phone number to call. Sender information is extracted to verify the sender is authorized to use the forwarding services. In one implementation, the message includes an authorization pass phrase (SAPP) that is linked to the sender&#39;s E-mail address. The filter layer performs a lookup in the access list  199  on the sender&#39;s E-mail address to verify the sender is an authorized user. 
     One or more different types of senders  102  may provide messages to be forwarded to one or more recipients  104 . Sender  102  may be a ZixMail sender  102   a  that forwards secure ZixMail messages in accordance with the description provided above. Sender  102  may be another secure messaging sender (e.g., a S/MIME sender having an X.509 certificate  102   b , a Pretty Good Privacy (PGP) sender  102   c ). As used herein, a “secure messaging sender” is a client computer (or other device) that includes one or more client applications that provides secure messaging services. The application can provide encryption, decryption and key services or support a communication protocol that includes some form of security using either encryption or certificate services. Examples of client applications that include secure messaging services include Microsoft&#39;s Outlook application. Other applications may provide secure messaging services using one or more certificates generated by, for example, EnTrust, Inc., or VeriSign, Inc. 
     Each sender  102  desiring to use the forwarding service  195  addresses and subsequently sends the intended message to the forwarding service  195 . Each intended message is addressed to forwarding service  195  using a unique address. In one implementation, messages are addressed according to sender type. For example, messages from a ZixMail client are addressed to the forwarding service  195  using the address ZixMail@secure-forwarding-service.com. The unique addressing can be used to invoke particular processing operations in the filter layer  193  for each message. 
     Each sender may utilize a unique format for a message. The format may be proprietary or non-proprietary. In order to support such diverse formats, the forwarding service  195  includes a filter unit (in filter layer  193 ) for processing each message type. 
     In general, the processes required to be executed by the sender (client application) include creating a message to be transferred to a recipient (using the forwarding service  195 ), addressing the message to the forwarding service, including a recipient address and authorization data in the message and sending the message to the forwarding service  195 . 
     The forwarding service  195  invokes the particular filter unit associated with the message type to parse, decrypt and authenticate the received message. No matter the form, each message generally includes header information and message data. The header information includes, at a minimum, sender information and a recipient address. In one implementation, the sender information includes the sender&#39;s address and a sender identifier (SAPP) that can be used to verify the sender is authorized to use the forwarding service  195 . In addition, the header may include other information or service designators for one or more services to be invoked by the filter layer  193 . For example, the header may include authorization data for the sender (SAPP), a request for a return receipt, a request for anonymous forwarding of the message (anonymizing the “from” field in the message sent to recipient) and other information. The message also can include a message body and attachments. 
     Alternatively, the sender can be a conventional E-mail user  102   d  or a web-form user  102   e  (where a message is constructed as part of a form presented on a web page and subsequently submitted to the forwarding service  195  as response data). That is, the message need not be sent by a secure messaging sender, and can be provided through conventional means directly to the forwarding service  195 . While the security level of these communications may be lower than that provided using a secure messaging sender, the forwarding service  195  can still provide an extra measure of security (i.e., using the SSL protocol) for these “non secure messages”. In addition, the sender can be required to have an authorization pass phrase (SAPP) set up with the forwarding service  195  as described in further detail above. Examples of other senders  102  can include an HTTP Post application  102   f , a facsimile device  102   g , a messaging device (e.g., a cellular telephone or pager)  102   h , or other digital or analog device (PDA or the like). One or more of these devices may be coupled via a gateway to the network  106  (e.g., Internet). 
     No matter the sender type, the message generated by the sender  102  must be properly addressed (to the forwarding service and include any type indicator for invoking any special processing in the filter layer  193 ), must include a recipient designator (either in the header, message body or in the address) and include appropriate identifying data that can be used to verify the sender is an authorized user of the forwarding services. 
     Referring to  FIG. 6 , a process implemented by the forwarding service includes receiving a message from a sender ( 602 ). The message is processed by the filter layer ( 604 ). The processing includes decrypting the message in accordance with a decryption algorithm specified for the message type (optional), parsing the message to extract sender and recipient information, checking to determine if the sender is an authorized user of the forwarding service, authenticating the sender and any other specified services. Thereafter, a check is made to determine recipient delivery preferences ( 605 ). If the user has preferences, a check is made to determine if the preference specifies web delivery ( 606 ). 
     If the preferences are not for web delivery, then a message is constructed ( 630 ) and forwarded to the recipient in accordance with recipient preferences ( 632 ). The process of constructing a message can include the encrypting of the message using a specified encryption algorithm (e.g., invoking encryption service  189 ) or the sending of the message in clear text. Thereafter the process ends. 
     If no preferences are located or web delivery is specified, then the process continues at step  607  where a standard encrypted format message is constructed and populated with the authentication data and the message including any attachments. A unique random number is generated ( 608 ) and the standard format message is stored in the queue structure  197  using the random number as part of an index ( 610 ). The forwarding engine  198  generates an E-mail message that includes a hypertext link (e.g., https://secure-forwarding.com//readmessage?index=a202fa8048d61ad50824ab5bcd705cf) that points to the message stored in the queue structure. 
     When a recipient invokes the link, a page request is transmitted to and received at the secure forwarding service  195  that includes the index information. An authorization pass phrase may be required of the recipient ( 612 ) before sending the actual message contents. In one implementation, the first time that a recipient uses the secure forwarding service  195 , the recipient can be requested to establish an authorization pass phrase (RAPP). Subsequent retrievals of messages by the same recipient (i.e., the same E-mail address) can be made by providing the authorization pass phrase (RAPP). In one implementation, the SAPP may be used in lieu of a RAPP. When the page request is received by the web front end of forwarding service  195 , a check is made to determine if the authorization pass phrase received is correct (as appropriate) ( 614 ). An authorization pass phrase/preference data pairing indexed by E-mail address (E-mail, RAPP, SAPP, and preference data) can be stored in access list  199  and checked to ensure that the recipient is the authorized to retrieve the message. Assuming that the authorization pass phrase (RAPP) is correct, forwarding service  195  retrieves the standard format message from the secure queue structure  197  using the index information provided in the page request ( 616 ). Thereafter, the page is decrypted, returned to the recipient and then loaded for display by the recipient computer&#39;s web browser ( 618 ). 
     The common filtering (using filter layer  193 ) and storage format (standard message format) allows for alternate branding of the services provided by the secure forwarding service. For example, Brand X company can advertise secure forwarding services using its own company brand name. The brand name can be used as the message type identifier when forwarding messages to the secure forwarding service. The brand can be a pointer to a particular message type including a secure message format. In this way, all client messages can be delivered under the client brand using the central services of the forwarding service. 
     The architecture for forwarding services includes a generic forwarding mechanism that can be configured to support new or changing messaging services. Only the front end filtering operations are required to be added/updated when adding a new message type, the remaining architecture and processes are unaffected by a new (updated) content provider. The standard message format, which may also be branded, is used for delivery of all messages via browsers to recipients. 
     In one implementation, each time a message is retrieved from the forwarding service a receipt can be generated that can be returned to or picked up by the sender. That is, the sender can specify a return receipt be generated by the forwarding service  195  and stored for future pick up or immediate delivery to the sender. Forwarding engine  198  can be configured to forward return receipts to the sender. The receipt can be used to indicate that the message was retrieved by the recipient. 
     In one implementation, messages can be forwarded with carbon copies (cc) sent to the sender and blind carbon copies (bcc) sent to the other designated parties. The process for sending a message to each recipient (a cc or a bcc recipient) is the same as described above 
     While this invention has been described in terms of several preferred implementations, it is contemplated that alterations, modifications and permutations thereof will become apparent to those skilled in the art upon a reading of the specification and study of the drawings. 
     Furthermore, certain terminology has been used for the purposes of descriptive clarity, and should not be construed to limit the invention. It is therefore intended that the following appended claims include all such alterations, modifications and permutations as fall within the true spirit and scope of the present invention.