In 1991, he wrote the popular Pretty Good Privacy program, and made it available through public FTP for download, the first widely available program implementing public-key cryptography. Shortly thereafter, it became available overseas via the Internet, though Zimmermann has said he had no part in its distribution outside the United States. In 1995, he published a book "PGP Source Code and Internals", as a way to bypass limitation of exporting digital code. The book contains source code to a software package called PGP The very first version of PGP included an encryption algorithm, BassOmatic, developed by Zimmermann.
After a report from RSA Security, who were in a licensing dispute with regard to the use of the RSA algorithm in PGP, the United States Customs Service started a criminal investigation of Zimmermann, for allegedly violating the Arms Export Control Act. The United States Government had long regarded cryptographic software as a munition, and thus subject to arms trafficking export controls. At that time, PGP was considered to be impermissible for export from the United States. The maximum strength allowed for legal export has since been raised and now allows PGP to be exported. The investigation lasted three years, but was finally dropped without filing charges. After the government dropped its case without indictment in early 1996, Zimmermann founded PGP Inc. and released an updated version of PGP and some additional related products. That company was acquired by Network Associates in December 1997, and Zimmermann stayed on for three years as a Senior Fellow. NAI decided to drop the product line and in 2002, PGP was acquired from NAI by a new company called PGP Corporation. Zimmermann served as a special advisor and consultant to that firm until Symantec acquired PGP Corporation in 2010. Zimmermann is also a fellow at the Stanford Law School's Center for Internet and Society. He was a principal designer of the cryptographic key agreement protocol for the Wireless USB standard.
Silent Circle
Along with Mike Janke and Jon Callas, in 2012 he co-founded Silent Circle, a secure hardware and subscription based software security company.
In October 2013, Zimmermann, along with other key employees from Silent Circle, teamed up with Lavabit founder Ladar Levison to create the Dark Mail Alliance. The goal of the organization is to work on a new protocol to replace PGP that will encrypt email metadata, among other things that PGP is not capable of.
Zimmermann's Law
In 2013, an article on Zimmermann's Law quoted Phil Zimmermann as saying The natural flow of technology tends to move in the direction of making surveillance easier, and the ability of computers to track us doubles every eighteen months, in reference to Moore's law.
Awards and other recognition
Zimmermann has received numerous technical and humanitarian awards for his pioneering work in cryptography:
