He began writing GNU Privacy Guard in 1997, inspired by attending a talk by Richard Stallman who made a call for someone to write a replacement for Phil Zimmermann's Pretty Good Privacy (PGP) which was subject to U.S. export restrictions.

[2] In 1999 Koch, via the German Unix User Group which he served on the board of,[2] received a grant of 318,000 marks (about US$170,000) from the German Federal Ministry of Economics and Technology to make GPG compatible with Microsoft Windows.

[4] Despite GnuPG's popularity, Koch has struggled to survive financially, earning about $25,000 per year since 2001[2] and thus considered abandoning the project and taking a better paying programming job.

[4] However, given Snowden's leaked documents showed the extent of NSA surveillance, Koch continued.

[2][5] Unrelated, in 2015 Koch was also awarded a one-time grant of $60,000 from the Linux Foundation's Core Infrastructure Initiative.