PGP and the Crypto Wars: Phil Zimmermann vs the US Government

In June 1991, a software engineer named Phil Zimmermann released a program called Pretty Good Privacy. It let ordinary people encrypt email and files with strong public key cryptography, and it spread quickly across the internet. The US government regarded this as a potential violation of export law. The ensuing dispute, known as the crypto wars, decided whether citizens would be allowed strong encryption at all.

Why Zimmermann wrote PGP

Zimmermann was a long-time peace and anti-nuclear activist with a strong interest in privacy. In 1991, the US Senate was considering a bill, Senate Bill 266, containing language that would have required communications systems to allow the government to obtain the plain text of voice and data communications. Zimmermann said that this spurred him to finish and release PGP earlier than planned.

PGP combined several existing ideas in a usable package: public key encryption using RSA for key exchange, a fast symmetric cipher for the content, digital signatures, and a system called the web of trust, in which users vouch for each other's keys instead of relying on a central authority.

Cryptography as a weapon

At the time, American law classified strong cryptographic software as a munition, in the same category as weapons, under the Arms Export Control Act. Exporting it without a licence was a crime. The rationale was that intelligence agencies, especially the National Security Agency, wanted to be able to read foreign communications.

PGP was uploaded to bulletin boards and to the early internet. Once on the internet, it could not be contained at national borders. Within months, copies were in use around the world. The government took the view that its spread abroad amounted to export, whoever had uploaded it.

The investigation

In 1993, the US Customs Service opened a criminal investigation into Zimmermann. For nearly three years, he lived under the possibility of prosecution. A legal defence fund was organised, and the case became a cause for the growing digital rights community, including the recently formed Electronic Frontier Foundation.

In 1995, Zimmermann's supporters had the full source code of PGP published as a printed book by MIT Press, relying on the idea that books are protected by the First Amendment and are easier to export than software. The book could be scanned and compiled abroad. In January 1996, the government announced that it had closed the investigation without bringing charges.

The Clipper chip

While the PGP case was proceeding, the government proposed another approach. In 1993 it announced the Clipper chip, a hardware encryption device for telephones that used a classified algorithm and included a built-in mechanism for authorised government agencies to obtain the keys, which was called key escrow. The proposal drew intense opposition from civil liberties groups, technology companies and security experts, who argued that a deliberate backdoor weakens the system for everyone. A researcher at Bell Labs, Matt Blaze, published a flaw in the scheme in 1994. The Clipper proposal faded away.

Courts and the end of the controls

In the late 1990s, the legal ground shifted. In the case of Daniel Bernstein, then a mathematics graduate student who wanted to publish an encryption algorithm, courts ruled that source code was a form of speech protected by the First Amendment, although the 1999 appeals ruling was later withdrawn for rehearing. At the same time, business pressure mounted, because American companies were at a disadvantage when selling products abroad that were limited to weak encryption. In 2000, the government substantially relaxed its export rules, and strong encryption became a standard part of mainstream software.

The legacy of PGP

• The OpenPGP standard, published as an internet standard, allows different programs to work together.
• GnuPG, a free implementation that reached version 1.0 in 1999, became widely used for signing software packages and encrypting email.
• The idea that a well-designed system should not contain a secret backdoor remains a central argument in security debates.

The same argument returns periodically. Governments say they need access to encrypted communications for investigations. Security experts reply that any mechanism that gives access to one party can be abused or stolen, and that there is no way to build a door that only the good people can use. The crypto wars of the 1990s are not over; they have only changed form.

How PGP actually worked

For readers who have not used it, the practical idea was simple. Each person generated a key pair. You published your public key, perhaps on a website or key server, and kept the private key secret. To send someone a private message, you encrypted it with their public key, and only their private key could open it. To prove a message came from you, you signed it with your private key and anyone could check it against your public key.

The weak point was usability. Managing keys, verifying fingerprints and understanding the web of trust was hard for non-specialists, and a famous 1999 paper by Alma Whitten and J. D. Tygar, "Why Johnny Can't Encrypt", studied exactly that problem. Many later tools succeeded by hiding the key management, which is why HTTPS, which works automatically, is now everywhere, while email encryption remains a niche.

The lesson for site owners today

Strong encryption is now available to every website owner, mostly for free, and there is little reason not to use it. HTTPS protects logins, forms and payments in transit. Encrypted email connections protect messages between servers. Encrypted backups protect your data if a storage device is lost.

1. Serve every page over HTTPS and redirect plain HTTP.
2. Use encrypted connections (SFTP or SSH) to manage your server, never plain FTP.
3. Turn on encryption in transit for email sending and receiving.
4. Encrypt any backup copies that you store off-site.

For mail on your own domain, see business email hosting.

Getting it set up

Every hosting plan includes free SSL, and it can be combined with Cloudflare. See the SSL page for details. For email, business email hosting lets you use your own domain with encrypted connections.