Adam Back — inventor of Hashcash (1997), the proof-of-work system cited in the Bitcoin whitepaper — has reflected on his earliest interaction with Satoshi Nakamoto:
On the August 2008 email exchange:
In August 2008, Satoshi contacted Back to verify the citation for his Hashcash paper. Back confirmed the citation and suggested Satoshi look at Wei Dai’s b-money proposal.
“I suggested looking into b-money, but it seemed he wasn’t aware of it at that point.”
Satoshi replied: “Thanks, I wasn’t aware of the b-money page, but my ideas start from exactly that point.”
On his biggest regret:
“I initially failed to read the Bitcoin whitepaper carefully. That was probably my biggest mistake.”
Back opened the attached whitepaper, gave it a cursory glance, typed back a brief response suggesting Wei Dai’s b-money, and closed his laptop. He didn’t begin actively using or promoting Bitcoin until around 2013.
On his early doubts about Bitcoin (CoinShares interview):
“I had questions about its sustainability: it was in 2009, there was no exchange, no value. Earlier systems had failed due to centralisation or unverifiable issuance, but Bitcoin’s decentralised model promised a better path.”
“From those experiences, it became clear that decentralisation was essential to succeed where others failed.”
COPA trial testimony (February 21, 2024):
During the COPA v. Craig Wright trial, Back testified in person at the London High Court and submitted the complete five-email chain between himself and Satoshi as evidence. The emails — dating from August 20, 2008 onward — were made public for the first time.
[Back later founded Blockstream in 2014, one of the most prominent Bitcoin infrastructure companies. Despite his regret at not engaging earlier, his Hashcash invention remains a fundamental building block of Bitcoin’s proof-of-work consensus mechanism.]