Fraud was prevented not by a kind of after-the-fact forgery analysis carried out by a bank authority but with an instantaneous check of the blockchain, the unforgeable public record of who possessed every single bitcoin. But that blockchain ledger system came at an enormous privacy cost: In Bitcoin, for good and for ill, everyone was a witness to every payment. Yes, identities behind those payments were obscured by pseudonymous addresses, long strings of between twenty-six and thirty-five characters. But to Meiklejohn, this seemed like an inherently dangerous sort of fig leaf to hide behind.
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