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Adam Back (born July 1970) is a British cryptographer and crypto-hacker.

Adam Back
Adam Back

July 1970 (age 48)
London, England, UK
ResidenceSliema, Malta
Known forhashcash, Blockstream

He is the inventor of hashcash, the proof-of-work system used by several anti-spam systems. A similar system is used in bitcoin.[1] Hashcash has also been used in a number of other protocols such as combating blog spam,[2] and defending against user namespace pollution.[3]

He implemented credlib,[4] a library that implements the credential systems of Stefan Brands and David Chaum.

He was the first to formalize the Non-Interactive Forward-Secrecy[5] security property for email and to observe that any Identity Based Encryption scheme can be used to provide Non-Interactive Forward Secrecy.

He is also known for pioneering the use of ultra-compact code with his 3-line RSA in Perl[6] signature file and non-exportable T-shirts[7] to protest the (now relaxed) United States cryptography export regulations.

Today he is CEO of Blockstream, a company that seeks to further the development of bitcoin and blockchain technology.[8]

He has a computer science Ph.D. from University of Exeter.

See alsoEdit


  1. ^ "Bitcoin: A Peer-to-Peer Electronic Cash System" (PDF).
  2. ^ " - blog plugins".
  3. ^ "I2P's Threat Model".
  4. ^ "credlib - Credential Library".
  5. ^ "Non-Interactive Forward Secrecy".
  6. ^ "export-a-crypto-system sig".
  7. ^ "Munitions T-shirt".
  8. ^ "Blockstream".

External linksEdit