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 - 14 . (canceled) 
   
   
       15 . An 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 and a second digital signature, the first digital signature corresponding to the first user and to a first contribution made by the first user, and the second digital signature corresponding to the second user and to a second contribution made by 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 at least one of the first digital signature if the first digital signature is not in the list of trusted digital signatures or the second digital signature if the second digital signature is not in the list of trusted digital signatures, wherein, by denying, a denied digital signature is formed;   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 . The apparatus of  claim 15  further 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 - 22 . (canceled) 
   
   
       23 . A recordable type medium containing a computer program product for receiving a forwarded message, the computer program product 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 and a second digital signature, the first digital signature corresponding to the first user and to a first contribution made by the first user, and the second digital signature corresponding to the second user and to a second contribution made by 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 . The computer program product of  claim 23 , wherein the computer program product further comprises:
 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.