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From: mixmaster@remail.obscura.com (Mixmaster)
Newsgroups: comp.security.pgp.tech
Subject: (none)
Date: 27 Aug 1996 09:46:33 -0400
Organization: Paraspace Intelligence
Lines: 44
Sender: daemon@cs.yale.edu
Message-ID: <19960827094630.aaaa004Bw@babyblue.cs.yale.edu>
NNTP-Posting-Host: babyblue.cs.yale.edu

A little bird has told me that the Viacrypt 4.0
sign-only and encrypt-only keys work by having 
values of 2 and 3 in the algorithm byte in
the key format.

You can make normal PGP accept these keys as
dual use by changing the code near the following lines

[555] % cd ~crypt/pgp262ui/src
[556] % grep RSA_ALG *
crypto.c:       certificate[certificate_length++] = RSA_ALGORITHM_BYTE;
*crypto.c:       if (version_error(algorithm, RSA_ALGORITHM_BYTE))
*crypto.c:       if (version_error(algorithm, RSA_ALGORITHM_BYTE))
crypto.c:               alg = RSA_ALGORITHM_BYTE;
*crypto.c:               if (version_error(alg, RSA_ALGORITHM_BYTE))
keymgmt.c:      alg = RSA_ALGORITHM_BYTE;
*keymgmt.c:      if (version_error(alg, RSA_ALGORITHM_BYTE))
pgp.h:#define RSA_ALGORITHM_BYTE        1       /*      use RSA */
[557] %

and recompiling.

In the cases of the lines marked *

put the line

if(2==alg || 3==alg) alg=RSA_ALGORITHM_BYTE

immediately above the line

if (version_error(alg, RSA_ALGORITHM_BYTE))

The other lines don't need to change.

Alternatively, someone with a copy of the PGP documentation
appendix with message format could simply write a hex-edit
macro to toggle the 2s and 3s back to 1 in the keyring.

--
 _      ___         __ __            __
| | /| / (_)______ / // /__ ___ ____/ /
| |/ |/ / / __/ -_) _  / -_) _ `/ _  /
|__/|__/_/_/  \__/_//_/\__/\_,_/\_,_/