Method, Apparatus, and Program to Forward and Verify Multiple Digital Signatures in Electronic Mail

Abstract

A mechanism is provided for augmenting the mail header of a message with a list of digital signatures representing the chain of contributors to the message. The augmented header may also encode the actual contributions corresponding to each digital signature. The list is appended every time a message is forwarded. If a message has a portion with no corresponding digital signature or if one or more of the digital signatures is not trusted, the user may handle the message accordingly. Furthermore, a mail server or client may discard a message if the number of digital signatures exceeds a threshold to filter out unwanted messages, such as e-mail chain letters.

1 . A method for forwarding a message, comprising:
 receiving a message from a first user at a computer of a second user, wherein the message has attached thereto a first digital signature corresponding both to the first user and to a first contribution made by the first user;   attaching to the message a second digital signature corresponding both to the second user and to a second contribution made by the second user; and   forwarding the message to a third user.   
   
   
       2 . The method of  claim 1 , further comprising:
 identifying a contribution made by the second user; and   associating the contribution made by the second user with the second digital signature.   
   
   
       3 . The method of  claim 2 , wherein the contribution comprises a file attachment and the method further comprises associating a filename of the file attachment with the second digital signature. 
   
   
       4 . The method of  claim 1 , wherein the step of forwarding the message comprises forwarding the message as an attachment and the step of associating comprises associating the attachment with the first digital signature. 
   
   
       5 - 10 . (canceled) 
   
   
       11 . An apparatus for forwarding a message, comprising:
 receipt means for receiving a message from a first user at a computer of a second user, wherein the message has attached thereto a first digital signature corresponding to the first user and to a first contribution made by the first user;   attachment means for attaching to the message a second digital signature corresponding to the second user and to a second contribution made by the second user; and   forwarding means for forwarding the message to a third user.   
   
   
       12 . The apparatus of  claim 11 , further comprising:
 identification means for identifying a contribution made by the second user; and   association means for associating the contribution made by the second user with the second digital signature.   
   
   
       13 . The apparatus of  claim 12 , wherein the contribution comprises a file attachment and the association means comprises means for associating a filename of the file attachment with the second digital signature. 
   
   
       14 . The apparatus of  claim 11 , wherein the forwarding means comprises means for forwarding the message as an attachment and the association means comprises means for associating the attachment with the first digital signature. 
   
   
       15 - 20 . (canceled) 
   
   
       21 . An e-mail client, comprising:
 means for augmenting a header of an e-mail message with a list of digital signatures representing the chain of contributors in the e-mail message, wherein the list of digital signatures comprises a first digital signature corresponding both to the first user and to a first contribution made by the first user and a second digital signature corresponding to the second user and to a second contribution made by the second user; and   means for sending the e-mail message to an e-mail server.   
   
   
       22 . A computer program product, in a computer readable medium, for forwarding a message, comprising:
 instructions for receiving a message from a first user at a computer of a second user, wherein the message has attached thereto a first digital signature corresponding to the first user;   instructions for attaching to the message a second digital signature corresponding to the second user; and   instructions for forwarding the message to a third user.   
   
   
       23 - 24 . (canceled)