History of PGP: from Zimmermann's 1991 release to OpenPGP

Updated November 2026

PGP (“Pretty Good Privacy”) was written by Phil Zimmermann and published free on the Internet in 1991. It brought strong public-key encryption to ordinary computer users, survived a US criminal investigation that was dropped in January 1996, passed through five companies, and became the open standard OpenPGP, which free programs such as GnuPG implement today.

Owners of the PGP product (dark) and milestones of the open standard and free software (light).

1991: a program for everyone

In his essay “Why I Wrote PGP”, Zimmermann points to Senate Bill 266, a 1991 anti-crime bill. A non-binding resolution in it said communications systems should let the government obtain the plain text of messages, which he read as a push for “trap doors” in encryption products. He writes that this “led me to publish PGP electronically for free that year”. The resolution was dropped after protests, but PGP was already spreading. The case the US Attorney’s office later closed concerned the posting of PGP to USENET in June 1991.

PGP combined existing ideas into one program: RSA public-key encryption to exchange a session key, a fast symmetric cipher for the message itself (IDEA in PGP 2.x), and digital signatures over a hash of the message (MD5 in PGP 2.x). RFC 1991 notes that versions after 1.0 were built “by an all-volunteer collaborative effort under the design guidance of Philip Zimmermann”. The PGP 2.x formats were written down in RFC 1991 in August 1996.

1993–1996: the export investigation

At the time, the US government treated strong encryption software as a munition under its export rules, the International Traffic in Arms Regulations (ITAR). Once PGP had spread outside the US, federal prosecutors opened a criminal investigation into Zimmermann over its export. Zimmermann and his lawyers describe it as a three-year investigation; one academic summary says a grand jury heard evidence for about 28 months.

Zimmermann was never charged. On 11 January 1996, assistant US Attorney William P. Keane in San Jose announced that the case was dropped, and the US Attorney for the Northern District of California, Michael J. Yamaguchi, said his office had declined prosecution. Zimmermann’s lead defense lawyer, Philip Dubois, announced the news on 12 January 1996. The government did not explain its decision. Zimmermann himself warned that nobody “should conclude that it is now legal to export cryptographic software.”

The wider “crypto wars” of the time included the Clipper chip proposal (April 1993) and the CALEA wiretapping law (1994). In his essay Zimmermann credits the spread of PGP, together with public pressure, for the relaxation of US export controls in 1999.

PGP as a product: five owners

1996: PGP Inc.: After the case was dropped, Zimmermann founded PGP Inc. to develop PGP commercially.
December 1997: Network Associates (NAI): Network Associates was formed in December 1997 by combining McAfee Associates and Network General, and in mid-December 1997 it bought Pretty Good Privacy, Inc., according to its annual report for 1997.
2002: PGP Corporation: NAI stopped developing and selling PGP in 2002 and sold the rights to a new company, PGP Corporation. Zimmermann served as an adviser there.
2010: Symantec: Symantec announced on 29 April 2010 that it would buy PGP Corporation and GuardianEdge for a combined price of more than $370 million, and announced on 7 June 2010 that the purchase was complete.
2019: Broadcom: On 4 November 2019 Symantec completed the sale of its Enterprise Security business to Broadcom for $10.7 billion. Broadcom still sells the commercial line as “PGP Encryption Desktop”, “PGP Encryption Server” and “PGP Command Line”; its support site lists version 11.5.2 HF6, released 1 October 2026.

Zimmermann was inducted into the Internet Hall of Fame in 2012.

From PGP to OpenPGP

Alongside the commercial product, the PGP format became an open standard named OpenPGP at the Internet Engineering Task Force (IETF), where work on it began in 1997. RFC 2440, published in November 1998, defined it and introduced the version 4 key format that most keys still use. RFC 4880 replaced it in November 2007, and RFC 9580 replaced that in July 2024. The details are in OpenPGP standards.

The open standard made independent free implementations possible. The best known is the GNU Privacy Guard (GnuPG). GnuPG’s project page says Werner Koch started it in 1997; its release notes list version 0.0.0 on 20 December 1997 as the first release and GnuPG 1.0.0 on 7 September 1999. On Windows it is distributed as part of Gpg4win. Its current stable series is 2.5 (2.5.24 as of November 2026). Other implementations include Sequoia, RNP and OpenPGP.js.

The keyservers

PGP’s web of trust needed a place to find keys, which led to the email and web keyservers of the 1990s, including the pgp.net network whose name this site carries. That story is told in Keyserver history.

About the old software in the archive

For history only. The download archive on this site keeps 1990s PGP software, such as the PGP 2.6.x releases for many platforms and the PGP 5.0 directory, exactly as it was on ftp.pgp.net. These programs are kept for research and for reading very old files. Do not use PGP 2.x or 5.x for real security today.

Why not:

PGP 2.x uses version 3 keys, MD5 and IDEA. RFC 9580 tells implementations to avoid MD5, IDEA and version 3 keys, and explains that v3 key IDs and fingerprints can be faked.
PGP 2.x encryption has no integrity protection; the Modification Detection Code was only standardized in RFC 4880.
None of this software has received security fixes for decades.
Modern GnuPG no longer accepts PGP 2 keys; its download page says only the legacy GnuPG 1.4 branch “still supports the unsafe PGP-2 keys”.

If you need to open an old PGP 2 file, use GnuPG 1.4 on an offline machine, then move the content to a modern key. For real work, start with Install GnuPG and Create a key.