Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!asuvax!ncar!zaphod.mps.ohio-state.edu!usc!apple!agate!ucbvax!VAX1.UMKC.EDU!PH461A04
From: PH461A04@VAX1.UMKC.EDU (Guerra de Bureau)
Newsgroups: comp.protocols.tcp-ip
Subject: Certified Mail Systems...
Message-ID: <B47A485D5BFF012862@vax1.umkc.edu>
Date: 24 Feb 91 23:30:00 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 29



Regarding a protocol for SMTP certified mail, can anyone suggest
why the following procedure would not work??
	1) Local mail system encrypts mail with time-varying key
	2) Local system forwards mail to remote system
	3) Remote system delivers (encrypted) mail to designated user
	4) Designated user requests key from remote system
	5) Remote system requests key from local system
	6) Local system indicates to message originator that message
	   has been received and key requested.
	7) Local forwards key to remote
	8) If remote system does note recieve key withing (x) units,
	   repeats request for (y) tries before informing recipient key
	   unavailable
	9) Remote delievers key to remote user/unencrypts original message

The only failure that I see is if a) the remote system requests the
key from the local system; b) the local system acknowledges the request,
and c) the anknowlegment(key) never gets back to the remote, and finally
d) the remote is not able to re-request the key within the designated
time frame.  Given the increasing network reliability and the decreasing
network transfer time and a sufficient number of retries/length of
time before discard this system would seem fairly secure.

Any problems??

Jonathan E. Oberg
ph461a04@vax1.umkc.edu


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