Inventor of Hashcash and the first person Satoshi Nakamoto contacted
On August 20, 2008, an email arrived in Adam Back’s inbox. The sender called himself Satoshi Nakamoto and asked about Hashcash citation format for an upcoming paper on a “new electronic cash system.” Eleven years earlier, in March 1997, Back had announced Hashcash on the cypherpunks mailing list. He answered the next day with the citation, then referred Satoshi to Wei Dai’s b-money. The same day, Satoshi replied:
Thanks, I wasn’t aware of the b-money page, but my ideas start from exactly that point.
This reply is one of the primary-source records of Satoshi’s independent arrival at Bitcoin’s design, examined in full in its own dedicated entry.
In April 2026, the NYT and journalist Carreyrou named Back as the strongest stylometric candidate for Satoshi in their analysis of forum and email corpora. Back denied it publicly. The hypothesis is weighed alongside other Satoshi-identity candidates in a dedicated identity analysis; in a reanalysis of van Dorst’s stylometric corpus, Back comes second behind Nick Szabo among the named candidates.
Adam Back (born 1970, United Kingdom) is a cryptographer and cypherpunk who earned a PhD in computer science from the University of Exeter. In 2014 he co-founded Blockstream, and he has been its CEO since October 2016.
On March 9, 1995, Back posted a five-line Perl program that implemented RSA encryption and decryption, small enough to carry as an e-mail signature, and Hal Finney soon posted an explanation of how it worked to the Cypherpunks list. Others sent ways to shorten it, and Back kept the list of versions. A U.S. Commerce Department statement obtained by law professor Peter Junger ruled that the program must not be exported from the US, and the three-line version went onto a T-shirt sold as a munition; by late August 1995 its seller reported over 500 shipped. That same month, Back and Piete Brooks organized the brute force of Hal Finney’s second SSL challenge, with a prize paid in DigiCash c$.
In March 1997, Back proposed Hashcash, a proof-of-work system originally designed to combat email spam and denial-of-service attacks. The system required senders to compute a partial hash collision — a computationally expensive operation — before sending an email, making mass spam economically impractical. Hashcash was not a digital currency or payment system — it was purely a computational cost mechanism.
Bitcoin later adopted its proof-of-work concept as the basis for mining and consensus, while Bitcoin’s monetary and payment design was Satoshi’s own — its closest conceptual antecedents being Wei Dai’s b-money (cited in the whitepaper) and, more loosely, Nick Szabo’s bit gold (not cited), neither directly inherited. The Bitcoin white paper cites Hashcash as one of its key references.
Back also worked at Zero-Knowledge Systems, the Montreal company whose Freedom network routed subscribers’ traffic through its own servers. In a 2013 BitcoinTalk post he described the work as “distributed trust privacy tech and anonymity designs,” and called Tor “a newer re-implementation of their freedom network.” The company switched Freedom off in 2001, one of the networks stopped at a single point before Satoshi named the pattern.
The August 2008 exchange runs across three days: Satoshi’s email to Back (Aug 20, citation request), Back’s reply with the Hashcash citation and the b-money referral (Aug 21), Satoshi’s same-day acknowledgment of not having seen b-money during the pre-disclosure period of his design and coding work (above), and Satoshi’s email to Wei Dai the next day asking for b-money’s publication date for the whitepaper citation.
The chain shows Bitcoin’s design was substantially complete before Back’s referral, examined further in the cypherpunk independent-arrival analysis.
Bitcoin Magazine later published Back’s correspondence with Satoshi — one of the few primary records of Bitcoin’s earliest conceptual phase. In February 2024, Back testified under oath in the COPA v Wright trial in London, recounting his exchanges with Satoshi and the timeline of Bitcoin’s creation. Five months after the original August 2008 exchange, Satoshi wrote to Back one last time, announcing the v0.1 release the day after it shipped.
In 2014, Back co-founded Blockstream, first as president and COO; he succeeded Austin Hill as CEO in October 2016. The company builds Bitcoin infrastructure — the Liquid Network sidechain, satellite broadcasting of the blockchain, and related protocol work. During the block-size war, this position made Back and his company the face of the “Blockstream controls Bitcoin” centralization charge, a charge tested against the documentary record on the linked page.
In November 2025, Back estimated Bitcoin faces no practical quantum-computing threat for 20 to 40 years, pointing to NIST-standardized post-quantum signatures Bitcoin could adopt well before that window closes.
Back’s contribution to Bitcoin was specifically the proof-of-work concept — the idea that computational cost can serve as a scarce, verifiable resource. Hashcash provided this mechanism; the currency design, peer-to-peer payment system, and monetary policy were separate innovations. His position as the first person Satoshi contacted places him at the very beginning of Bitcoin’s documented creation history.
63 entries / 4 threads
On August 20, 2008 Satoshi emailed Adam Back a link to a draft titled "Electronic Cash Without a Trusted Third Party." Its title and abstract survive in two emails. The PDF does not.
Gwern lists where he looked for the draft Satoshi linked in August 2008: the file host, the Internet Archive, Google, BitcoinTalk, SVN. Dai, Back and Maxwell had no copy; Finney never replied.
A remailer gave up a name to a warrant, Napster's index fell to an injunction, e-gold pleaded guilty and the Liberty Dollar was raided. In November 2008 Satoshi named the pattern.
Until December 30, 1996, U.S. rules listed encryption software with weapons. Zimmermann was investigated, Karn sued over a floppy disk, Bernstein won in court, and Back put RSA on a T-shirt.
Adam Back proposes a pot of DigiCash c$ for whoever hits the key in Finney's second SSL challenge, donates c$ 50 himself, and asks the winner to cash it in on the ecash market.
Back lists the shrinking versions of his RSA-in-Perl program, smallest first, back to the five-line original of March 9, 1995, which Hal Finney explained on the Cypherpunks list soon after.
Back's page for his RSA program in Perl, small enough for an e-mail signature, which a U.S. Commerce Department statement ruled must not be exported, and which went onto T-shirts and tattoos.
On August 20, 2008 Satoshi called his C++ code nearly finished. Which precursors were in front of him by then? The earliest record for Hashcash, b-money, MicroMint, Bit Gold, DigiCash and RPOW.
Adam Back welcomes Sten Drescher's plan for a network of majordomos to carry a new Cypherpunks list and suggests mail exploders behind a central majordomo as a simpler design.
Adam Back proposes one main majordomo feeding many mail exploders, an architecture he credits John Gilmore with suggesting as the simpler alternative.
Jim Choate rejects a central majordomo: he envisions a fishnet of remailers where each node links to two others. "There should be no 'one main' anything on this project."
Adam Back reads RPOW as online ecash like Chaum's, without blinding and with hashcash to buy coins, and notes Finney turns remote attestation into a server users can audit.
Adam Back introduces himself on BitcoinTalk as the inventor of hashcash, the mining function, says he believes he got b-money added to Satoshi's paper in 2008, and that he owns not a single bitcoin.
Adam Back announces Hashcash: partial SHA-1 collisions as postage for remailers and spam control, costly to compute and instant to verify, and a stop-gap until digicash spreads.
How a 1992 Oakland meeting became the Cypherpunks mailing list: the name, the remailers, the Clipper fight, the 1997 split, and the Hashcash and b-money posts the Bitcoin whitepaper later cited.
Wei Dai called Bitcoin's fixed supply a failure in 2013. His own 1998 b-money design needed the same real-world value figure Satoshi said software has no way to know.
Doubters called it unscalable in 2008. A famed hacker failed to break the code. A judge, a dictionary, and a Nobel nominator weighed in. What others said about Satoshi, read as one record.
Weighing the 'Blockstream controls Bitcoin' charge against the documentary record: where it comes from, and how each link in the chain holds up.
Adam Back reposts the full text of Wei Dai's b-money proposal to the Cypherpunks list, with comments to follow — the message that opened the December 1998 b-money design discussion.
Hayek's 1976 case for competing currencies, the Extropians' imaginary 'Hayeks' currency of 1995, and Bitcoin, money no state issues: one line of thought, linked by ideas rather than proven influence.
Finding Satoshi (Tooley / Miele, April 2026) names Hal Finney and Len Sassaman as Bitcoin co-creators: Finney coded, Sassaman wrote the paper. Lopp and Back dispute it.
Bitcoin chose a hard 21M cap; b-money (1998) proposed elastic supply; fiat runs central-bank discretion. The cypherpunk debate, Wei Dai's 2013 regret, and 15 years of cryptocurrency variants.
Adam Back's reply to a question about whether Bitcoin faces near-term risk from quantum computing, pointing at NIST-standardized SLH-DSA and a 20–40 year horizon.
Adam Back's answer to a NYT investigation naming him as a leading stylometric match to Satoshi: "i'm not satoshi," followed by his account of his cypherpunk interest in ecash from about 1992.
Satoshi coded Bitcoin on Windows for 27 months, mainly with MinGW. In November 2009 he finished the Linux build Martti Malmi had started; by mid-2010 there were Windows, Linux and Mac releases.
The earliest known email from Satoshi Nakamoto: contacting Adam Back to verify the Hashcash citation and sharing a pre-release draft titled 'Electronic Cash Without a Trusted Third Party'.
Which Bitcoin assets are at risk from a cryptographically relevant quantum computer, and what the timeline and migration debate around post-quantum cryptography looks like.
What Satoshi's design assumed about a fee-only future, and the documented debate over whether transaction fees alone can sustain proof-of-work security after the block subsidy ends around 2140.
Why Bitcoin's 2015-2017 fork wars were fights over what Bitcoin is, not OSS disputes: the authority vacuum after 2011, the money riding on rule choices, and three layers binding code to currency.
Wei Dai's b-money is whitepaper reference [1], his Crypto++ shipped inside Bitcoin v0.1, and he was the second person Satoshi contacted. The evidence for Wei Dai as Satoshi, weighed.
A reanalysis of van Dorst's stylometric corpus for the five most-cited candidates. Szabo led them, in the top 4.67% of 12,739 authors, but 594 unnamed authors came closer.
On February 22, 2021, Evan Hatch published Len Sassaman and Satoshi: a Cypherpunk history on Medium — the article that became the foundational case for the Sassaman = Satoshi Nakamoto hypothesis.
On December 1, 2013, blogger Skye Grey published Satoshi Nakamoto is (probably) Nick Szabo — the first public stylometric study naming Szabo as Satoshi, reported by TechCrunch on December 5.
On May 15, 2015, the New York Times published Nathaniel Popper's Decoding the Enigma of Satoshi Nakamoto — a Digital Gold excerpt naming Bit Gold designer Nick Szabo as Satoshi. Szabo denied it.
Adam Back announces Hashcash to the Cypherpunks list — a proof-of-work postage scheme against spam, pitched as a stopgap until digicash spread or a fallback if it failed.
Adam Back replies to Wei Dai on Cypherpunks, identifying seven monetary-design issues in b-money and proposing Hashcash as the minting mechanism — a substantive analysis ten years before Bitcoin.
Bitcoin v0.1 reuses one cypherpunk primitive (PoW from Hashcash), borrows general CS components (Merkle trees, linked timestamping, ECDSA), and synthesizes the rest (UTXO, mining, 21M cap, P2P).
On April 8, 2026, the New York Times published John Carreyrou's investigation naming Adam Back as the most likely Satoshi based on stylometric analysis. Back denied the identification.
Hashcash's inventor and the first person Satoshi contacted. In April 2026 the NYT named him the closest stylometric match among 620 cryptography-mailing-list writers. The evidence, weighed.
Satoshi has been hunted in public for years and left a large trail of material, yet remains unidentified. Why all that searching and all that material have not led to a name.
Twelve recurring Satoshi candidates, compared across four independent layers: profile match, stylometric attribution, direct correspondence and development environment.
Three primary-source clues to Satoshi's place among the cypherpunks: he had not heard of b-money, Wei Dai called him "not previously active," and what Satoshi did tracked Hughes's 1993 manifesto.
HBO documentary Money Electric (Cullen Hoback) named Peter Todd as a Satoshi candidate, citing a 2010 BitcoinTalk reply about RBF and Todd's later BIP 125. Todd called the claim ludicrous.
Before reading the draft, Adam Back points Satoshi to Rivest's MicroMint paper; a 2025 profile quotes him calling his failure to read the whitepaper carefully 'probably my biggest mistake.'
Satoshi thanks Adam Back for the b-money reference and reveals he was not previously aware of Wei Dai's proposal. Historically significant line: 'my ideas start from exactly that point.'
Satoshi's final email to Adam Back thanks Back for his reading suggestions and announces the software launch. The page also includes Hal Finney's project overview from the Cryptography mailing list.
Wei Dai replies to Adam Back on Cypherpunks, conceding b-money would be at most a niche mechanism and revealing his shift toward viewing the government monopoly of force as a net benefit.
Blockstream CEO Adam Back stated Bitcoin faces no quantum computing threat for ~20–40 years, pointing to NIST post-quantum signatures like SLH-DSA that Bitcoin can adopt before threats materialize.
Adam Back reflects on his August 2008 email exchange with Satoshi, his regret at not reading the whitepaper carefully, and his testimony in COPA v Wright, where the full email thread became public.
During Day 13 of COPA v Wright, Martti Malmi testified via video link and submitted 260 emails (140,000 words) exchanged with Satoshi between May 2009 and February 2011, published on GitHub.
Satoshi Nakamoto's earliest known email. He contacts Adam Back to verify the Hashcash paper citation and shares a pre-release draft titled 'Electronic Cash Without a Trusted Third Party' (ecash.pdf).
Adam Back confirms the Hashcash citation and suggests Satoshi look at Wei Dai's b-money proposal. This referral led Satoshi to contact Wei Dai and cite b-money in the Bitcoin whitepaper.
Hal Finney's RPOW system, a 2004 prototype for reusable proof-of-work tokens, gains posthumous recognition as one of Bitcoin's most important precursors.