Adding recipients to an encrypted message?

[Peter Gutmann]

Florian Weimer <Florian.Weimer at RUS.Uni-Stuttgart.DE> writes:
>Werner Koch <wk at gnupg.org> writes:
>>On Mon, 01 Oct 2001 21:33:49 -0400 (EDT), mbp2  said:
>>I can't think of a situation where you want to forward an encrypted
>>message to another recipient without reading the message first.
>Encrypted mailing lists could be implemented more efficiently if the main
>message part would not have to be encrypted over and over again. (Because of
>padding, the reused session key should not be a problem even with RSA, but I'm
>not sure about that.)

The S/MIME folks have looked at this problem in some detail over quite some
time, there are RFCs/RFC drafts available from the S/MIME WG home page
http://www.imc.org/ietf-smime/index.html.

(They also have a second home page at 
 http://www.ietf.org/html.charters/smime-charter.html which has a non-
 overlapping set of drafts, you may need to check there.  Try and ignore the
 fact that the page is shared with drafts on how to do X.400 with S/MIME).

Peter.