From: hughes@ah.com (Eric Hughes)
Date: Fri, 27 May 94 21:16:33 PDT
To: cypherpunks@toad.com
Subject: on detectability of PGP versions
Message-ID: <9405280422.AA25479@ah.com>
MIME-Version: 1.0
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The issue has arisen of whether displaying some particular version
number of PGP on the inside of messages or signatures implies that one
is using that version number.

How could it?  The format that one bit of public software makes can be
duplicated by another.  If there are two bodies of code which produce
the same output, an external observer can make no decision as to which
one was used if the only evidence were one of format.  If, however,
there were only one piece of code (say PGP 2.6), there would be a
statistically valid judgement that a 2.6 version number indicated a
2.6 use.

Let's say we want to avoid that.  I'd suggest that a future derivation
of the 2.3a code base or the as-yet-mythical 3.0 code base use the
version number in the PGP formats (both binary and ascii) as format
version numbers, and let the version numbers of PGP proper diverge.
To make it really convenient, the config file might have a
version_output flag which indicated what kind of message to generate.

There's no good functionality reason why such a PGP shouldn't write
post-Sept. 2.6 messages, 2.3 messages, 2.4 messages, even non-PKCS 2.2
messages.  Ditto for reading and verifying all those kinds of
messages.

Could anybody really tell the difference?

Eric