Adam Back

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Adam Back
Adam Back

July 1970 (age 49)
London, England, UK
Known forhashcash, Blockstream

Adam Back (born July 1970) is a British businessman and cryptographer.


Back was born in London, England, United Kingdom, and he now resides in Sliema, Malta.

He has a computer science Ph.D. from University of Exeter in South West England.

Cryptography software[edit]

In 1997[1], Back invented Hashcash, the proof-of-work system used by several[who?] anti-spam systems.[citation needed] A similar system is used in Bitcoin.[2] Hashcash has also been used in a number of other protocols such as combating blog spam,[3] and defending against user namespace pollution.[4]

He also implemented credlib,[5] a library that implements the credential systems of Stefan Brands and David Chaum.

He was the first to formalize the "Non-Interactive Forward-Secrecy"[6] 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[7] signature file and non-exportable T-shirts[8] to protest cryptography export regulations.

Business career[edit]

Adam is currently the CEO of Blockstream, a technology company that seeks to further the development of bitcoin and blockchain technology.[9] Blockstream provides funding for the development of Bitcoin Core, the predominant Bitcoin network client software.

See also[edit]


  1. ^ Back, Adam. "Hashcash - A Denial of Service Counter-Measure" (PDF). Retrieved 29 May 2019.
  2. ^ "Bitcoin: A Peer-to-Peer Electronic Cash System" (PDF).
  3. ^ " - blog plugins".
  4. ^ "I2P's Threat Model".
  5. ^ "credlib - Credential Library".
  6. ^ "Non-Interactive Forward Secrecy".
  7. ^ "export-a-crypto-system sig".
  8. ^ "Munitions T-shirt".
  9. ^ "Blockstream".

External links[edit]