Adam Back
Adam Back in 2025.
| Known for | Hashcash; co-founding Blockstream |
| Notable work(s) | Hashcash; Enabling Blockchain Innovations with Pegged Sidechains |
Adam Back is a British computer scientist, cryptographer and cypherpunk who invented Hashcash, a proof-of-work system announced in 1997 and later cited in the Bitcoin white paper, and co-founded the Bitcoin infrastructure company Blockstream.[1][2][3][4]
Background and Hashcash
Back received a Ph.D. in distributed systems and computer science from the University of Exeter. Before Blockstream, he worked in cryptography, electronic cash and privacy technology and held senior roles at Zero-Knowledge Systems, Microsoft, EMC and VMware; he also co-founded the cloud-infrastructure company Pi Corporation.[4]
Back first announced Hashcash on the cypherpunks mailing list in March 1997. It was designed to deter email spam and denial-of-service attacks by requiring a sender to calculate a proof-of-work stamp that was moderately costly to produce but inexpensive for a recipient to verify. Back described the system formally in his 2002 paper Hashcash - A Denial of Service Counter-Measure.[2][5]
Bitcoin adapted this computational asymmetry for a different purpose. The white paper describes a proof-of-work system similar to Hashcash for Bitcoin's distributed timestamp server: miners repeatedly hash block headers until one satisfies the network target, and the accumulated work helps establish transaction order, resist double-spending and secure the issuance of new coins.[3]
Correspondence with Satoshi Nakamoto
On 20 August 2008, Satoshi Nakamoto emailed Back a pre-release draft then titled Electronic Cash Without a Trusted Third Party and asked him to verify the citation to the Hashcash paper. Back confirmed the citation on 21 August and pointed Satoshi to Wei Dai's b-money proposal. Satoshi replied that he had not previously seen the b-money page and then contacted Dai to establish its publication date. The b-money citation became the first reference in the published Bitcoin white paper, while Hashcash appeared as the sixth.[6][7]
Back later suggested that Satoshi also examine MicroMint, another micropayment proposal. Their next documented contact was on 10 January 2009, when Satoshi informed Back that the Bitcoin software had been released.[6]
The correspondence was made public when Back gave evidence in the 2024 Crypto Open Patent Alliance case concerning Craig Wright's claim to be Satoshi. The High Court judgment described Back's evidence as careful, considered and truthful, and found that the emails contradicted Wright's account of Bitcoin's development.[7]
Blockstream and sidechains
In October 2014, Back was one of nine authors of Enabling Blockchain Innovations with Pegged Sidechains. The paper proposed two-way pegs that would allow bitcoins and other ledger assets to move between separate blockchains, enabling experimentation while attempting to isolate failures from the Bitcoin main chain.[8]
In 2014, Back was one of Blockstream's 11 co-founders. The company initially focused on sidechains and other protocol-level extensions to Bitcoin and announced a US$21 million seed round in November 2014.[9] Back served as president and chief operating officer before Blockstream appointed him CEO on 3 October 2016.[4]
In a 2014 statement, Back said Blockstream would support decentralisation, end-to-end security, user control and permissionless innovation, and described sidechains as the company's most pressing technical work.[10] During the 2017 scaling dispute, he publicly opposed the SegWit2x hard-fork proposal.[11][12]
Satoshi identity speculation
In April 2026, The New York Times published an investigation claiming that Back was the person behind the Satoshi Nakamoto pseudonym. Back denied being Satoshi and said the similarities cited by the investigation were coincidences among people with similar experience and interests.[1]
See also
References
- ↑ 1.0 1.1 Down, Aisha (8 April 2026). "British computer scientist denies he is bitcoin developer Satoshi Nakamoto". The Guardian. https://www.theguardian.com/technology/2026/apr/08/british-computer-scientist-adam-back-denies-he-is-bitcoin-developer-satoshi-nakamoto. Retrieved 4 July 2026.
- ↑ 2.0 2.1 "Hashcash papers". Hashcash.org. http://www.hashcash.org/papers/. Retrieved 17 July 2026.
- ↑ 3.0 3.1 Nakamoto, Satoshi (31 October 2008). "Bitcoin: A Peer-to-Peer Electronic Cash System". https://bitcoin.org/bitcoin.pdf. Retrieved 4 July 2026.
- ↑ 4.0 4.1 4.2 "Blockstream Appoints Hashcash Inventor Dr. Adam Back as CEO". Blockstream. 3 October 2016. https://blockstream.com/press-releases/2016-10-03-blockstream-appoints-hashcash-inventor-dr-adam-back-as-ceo/. Retrieved 4 July 2026.
- ↑ Back, Adam (1 August 2002). "Hashcash - A Denial of Service Counter-Measure". http://www.hashcash.org/papers/hashcash.pdf. Retrieved 17 July 2026.
- ↑ 6.0 6.1 Back, Adam (17 July 2023). "First Witness Statement of Dr Adam Back". High Court of Justice. https://bitcoindefense.org/assets/documents/First-Witness-Statement-of-Dr-Adam-Back.pdf. Retrieved 17 July 2026.
- ↑ 7.0 7.1 Mellor, James (20 May 2024). "Crypto Open Patent Alliance v Craig Steven Wright: Approved Judgment". High Court of Justice of England and Wales. https://www.judiciary.uk/wp-content/uploads/2024/05/COPA-v-Wright-Judgment.pdf. Retrieved 17 July 2026.
- ↑ Back, Adam et al. (22 October 2014). "Enabling Blockchain Innovations with Pegged Sidechains". Blockstream. https://blockstream.com/sidechains.pdf. Retrieved 17 July 2026.
- ↑ "Blockstream closes $21M seed round". Blockstream. 17 November 2014. https://blog.blockstream.com/en-blockstream-closes-21m-seed-round/. Retrieved 17 July 2026.
- ↑ Back, Adam (17 November 2014). "Blockstream: A Champion of Bitcoin's Core Values". Blockstream. https://blog.blockstream.com/en-blockstream-a-champion-of-bitcoins-core-values/. Retrieved 17 July 2026.
- ↑ Adam Back on X, 28 September 2017.
- ↑ “It is time to call off NYA/segwit2x”, Reddit, 27 September 2017.