Steve writes:
Unfortunately, the CRLs available to the sender at the time of
transmission generally are not the ones needed by a recipient in
support of non-repudiation. What a receiver needs are the next set of
CRLs issued, ones issued after the message was sent, to prove that the
relevent certificates were not revoked at the time the message was
sent. The CRLs available to the originator would make a statement
about the revocation status of certificates prior to the sending of
the message. One could argue that for less stringent validation
situations (other than non-repudiation), the "older" CRLs would be
adequate, and that suggests that an option to send them in the header
as part of a regular message might be helpful.
This is an excellent point. Clearly the originator of a message cannot include
a CRL that hasn't been issued yet in his message, and in fact including a CRL
that is widely distributed in a message is pretty good way of coarsely
timestamping the message--it could not have originated prior to the date/time
of the CRL that is included.
I was just trying to come up with a reasonably standardized way of archiving
a message along with the entire certificate chain of the sender, together with
at least the current CRL, so that I can come back 40 years later and determine
whether that message was presumptively valid at the time it was sent.
Steve