Replacing PGP 2.x with GnuPG

This article is based on an earlier PGP 2.x/GnuPG compatability guide written by Kyle Hasselbacher (). Mike Ashley () edited and expanded it. Michael Fischer v. Mollard () transformed the HTML source to DocBook SGML and also expanded it further. Some of the details described here came from the gnupg-devel and gnupg-user mailing lists. The workaround for both signing with and encrypting to an RSA key were taken from Gero Treuner's compatability script. Please direct questions, bug reports, or suggesstions to the maintainer, Mike Ashley.

This manual may be redistributed under the terms of the GNU General Public License.


This document describes how to communicate with people still using old versions of PGP 2.x GnuPG can be used as a nearly complete replacement for PGP 2.x. You may encrypt and decrypt PGP 2.x messages using imported old keys, but you cannot generate PGP 2.x keys. This document demonstrates how to extend the standard distribution of GnuPG to support PGP 2.x keys as well as what options must be used to ensure inter-operation with PGP 2.x users. It also warns of anomalies with the interoperation of PGP 2.x and GnuPG.

Note: Using the extension modules idea.c and rsa.c without licensing the patented algorithms they implement may be illegal. I do not recommend you use these modules. If you have PGP 2.x keys, I suggest you revoke them in favor of new keys and encourage correspondents who use PGP 2.x keys to do the same.