Subject: Davis paper revisited // separation of signed and encrypted messages into clearsigned messages

From: <[email-masked]>
Date: Thu, 21 Aug 2003 10:55:53 -0700

have been able to separate a signed and encrypted message into a freestanding
verifiable clearsigned message

have put up the example here:
http://www.angelfire.com/pr/pgpf/sclsf.html

(the keys and messages are in 3des, idea is not necessary )

would like to ask:

[1] is there any way to distinguish the composite reconstruction forgery
from a 'real' de novo clearsigned message ?

[2] is there a difference between GnuPG and PGP in the way a message
is clearsigned, as opposed to signed and encrypted,
that might distinguish the forged composite, from a real clearsigned
message?

while the Davis paper describes separating and re-encrypting,
it doesn't deal with separating into a freestanding clearsigned message.

tia,

vedaal

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From: Jon Callas <[email-masked]>
Date: Fri, 22 Aug 2003 18:16:56 -0700

I just want to make sure I understand this.

The problem is this:

Alice sends Bob an encrypted and signed message.

Bob decrypts the message, and then does byte-surgery to construct a
plaintext clearsigned message that the signature verifies, and anyone in the
world can read.

This is the "attack," right?

    Jon