While the private key to the ninth block is extremely likely to have been controlled by Satoshi, Wright's production of a message signed with that key would not in itself be conclusive proof that he and Satoshi are one and the same: Someone else could have used the private key at some time in the past to sign the message Wright claims to have signed.
Wright's refusal to sign a message chosen by someone else to demonstrate his possession of the key may be a sign that he cannot, as The Economist suggested.
The ninth block in the blockchain is important for its link to Finney, but the real Satoshi would also have possessed the private keys used to sign still earlier blocks in the bitcoin blockchain, including the all-important first.
Wright appeared to sign a message with the private key to the first block in a demonstration for The Economist but, the magazine warned, "Such demonstrations can be stage-managed; and information that allows us to go through the verification process independently was provided too late for us to do so fully." Nevertheless, the magazine said, Wright "seems to be in possession of the keys, at least for block 9."
Wright's claims and demonstration were enough to convince two stalwarts of the bitcoin community, Jon Matonis and Gavin Andresen, who communicated electronically with Satoshi in the early days of bitcoin without ever knowing his true identity.
Matonis, the founding director of the Bitcoin Foundation, corresponded with Satoshi in early 2010. He first ran into Wright at a conference on June 4, 2015, and that night told his wife he had "this weird feeling of having just met Satoshi," he wrote Monday morning in a blog post entitled, "How I met Satoshi."
At proof sessions in London last month, Matonis wrote, Wright signed and verified a message in his presence using the private keys from newly generated coins in the first and ninth bitcoin blocks.
"According to me, the proof is conclusive and I have no doubt that Craig Steven Wright is the person behind the Bitcoin technology, Nakamoto consensus, and the Satoshi Nakamoto name," Matonis wrote.
As for Andresen, who took over from Satoshi as lead developer of the bitcoin software, Wright's demonstrations were equally convincing: "I believe Craig Steven Wright is the person who invented Bitcoin," he wrote on his blog on Monday.
Andresen attended the same meetings in London as Matonis and the reporters from The Economist, the BBC and GQ.
"An initial email conversation convinced me that there was a very good chance he was the same person I’d communicated with in 2010 and early 2011. After spending time with him I am convinced beyond a reasonable doubt: Craig Wright is Satoshi," Andresen wrote.
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