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.

What is claimed is:  
     
         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 to the first user;    attaching to the message a second digital signature corresponding to 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 . A method for receiving a forwarded message, comprising: 
 receiving a message at a computer of a third user, wherein the message was sent from a first user to a second user and subsequently forwarded to the third user, and wherein the message has attached thereto a first digital signature corresponding to the first user and a second digital signature corresponding to the second user;    verifying the first digital signature and the second digital signature; and    opening the message if the first digital signature and the second digital signature are approved.    
     
     
         6 . The method of  claim 5 , wherein the step of verifying the first digital signature and the second digital signature comprises: 
 comparing the first digital signature and the second digital signature to a list of trusted digital signatures; and    approving the first digital signature and the second digital signature if they are in the list of trusted digital signatures.    
     
     
         7 . The method of  claim 6 , further comprising: 
 denying the first digital signature or the second digital signature if it is not in the list of trusted digital signatures;    prompting the third user to accept the denied digital signature; and    adding the denied digital signature to the list of trusted digital signatures if the user accepts the denied digital signature.    
     
     
         8 . The method of  claim 6 , further comprising deleting the message if the first digital signature or the second digital signature is not approved.  
     
     
         9 . The method of  claim 5 , further comprising: 
 attaching to the message a third digital signature corresponding to the third user; and    forwarding the message to a fourth user.    
     
     
         10 . A method for receiving a forwarded message, comprising: 
 receiving a message, wherein the message was forwarded by a plurality of users, and wherein the message has attached thereto digital signatures corresponding to each of the plurality of users;    determining the number of users in the plurality of users;    comparing the number to a threshold; and    discarding the message if the number exceeds the threshold.    
     
     
         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;    attachment means for attaching to the message a second digital signature corresponding to 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 . A apparatus for receiving a forwarded message, comprising: 
 receipt means for receiving a message at a computer of a third user, wherein the message was sent from a first user to a second user and subsequently forwarded to the third user, and wherein the message has attached thereto a first digital signature corresponding to the first user and a second digital signature corresponding to the second user;    verification means for verifying the first digital signature and the second digital signature; and    opening means for opening the message if the first digital signature and the second digital signature are approved.    
     
     
         16 . The apparatus of  claim 15 , wherein the verification means comprises: 
 comparison means for comparing the first digital signature and the second digital signature to a list of trusted digital signatures; and    approval means for approving the first digital signature and the second digital signature if they are in the list of trusted digital signatures.    
     
     
         17 . The apparatus of  claim 16 , further comprising: 
 means for denying the first digital signature or the second digital signature if it is not in the list of trusted digital signatures;    means for prompting the third user to accept the denied digital signature; and    means for adding the denied digital signature to the list of trusted digital signatures if the user accepts the denied digital signature.    
     
     
         18 . The apparatus of  claim 16 , further comprising means for deleting the message if the first digital signature or the second digital signature is not approved.  
     
     
         19 . The apparatus of  claim 15 , further comprising: 
 means for attaching to the message a third digital signature corresponding to the third user; and    means for forwarding the message to a fourth user.    
     
     
         20 . A apparatus for receiving a forwarded message, comprising: 
 receipt means for receiving a message, wherein the message was forwarded by a plurality of users, and wherein the message has attached thereto digital signatures corresponding to each of the plurality of users;    determination means for determining the number of users in the plurality of users;    comparison means for comparing the number to a threshold; and    discarding means for discarding the message if the number exceeds the threshold.    
     
     
         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; 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 . A computer program product, in a computer readable medium, for receiving a forwarded message, comprising: 
 instructions for receiving a message at a computer of a third user, wherein the message was sent from a first user to a second user and subsequently forwarded to the third user, and wherein the message has attached thereto a first digital signature corresponding to the first user and a second digital signature corresponding to the second user;    instructions for verifying the first digital signature and the second digital signature; and    instructions for opening the message if the first digital signature and the second digital signature are approved.    
     
     
         24 . A computer program product, in a computer readable medium, for receiving a forwarded message, comprising: 
 instructions for receiving a message, wherein the message was forwarded by a plurality of users, and wherein the message has attached thereto digital signature corresponding to each of the plurality of users;    instructions for determining the number of users in the plurality of users;    instructions for comparing the number to a threshold; and    instructions for discarding the message if the number exceeds the threshold.