Adam Back Adam Back (born July 1970) is a British cryptographer and crypto-hacker. He is the inventor of hashcash, the proof-of-work system used by several anti-spam systems. A similar system is used in bitcoin. He implemented credlib a library that implements the credential systems of Stefan Brands and David Chaum.
He is also known for pioneering the use of ultra-compact code with his 3-line RSA in Perl to protest the (now relaxed) United States cryptography export regulations.