On 24/02/2021 19:53, Jim Jackson wrote:
ISTR it being printed on tee-shirts too.

Are you confusing with DeCSS ... from wipipedia ...

"In protest against legislation that prohibits publication of copy
protection circumvention code in countries that implement the WIPO
Copyright Treaty (such as the United States' Digital Millennium
Copyright Act), some have devised clever ways of distributing
descriptions of the DeCSS algorithm, such as through steganography,
through various Internet protocols, on T-shirts and in dramatic
readings, as MIDI files, as a haiku poem (DeCSS haiku),[8][9] and even
as a so-called illegal prime number.[10]"

I've had to check, as I was working from memory. I was sort of right.
The tee-shirts were about RSA encryption, which was one of the methods
used by PGP.