Thread on developments exactly one month since Fidelity Bonds were added to JoinMarket
JoinMarket used to work by the user's wallet randomly choosing market makers out there to do a coinjoin with, but what if all those makers were actually controlled by the same person? That attacker could unmix all the coinjoins and spy on users, this is called a sybil attack
Fidelity bonds are a mechanism for resistance against such sybil attacks. Honest makers in JoinMarket are now incentivized to lock up bitcoins using the OP_CHECKLOCKTIMEVERIFY opcode. For a sybil attacker to be successful they have to lock up a huge amount of bitcoins
Currently 264 BTC are locked up, including this one maker who locked up 124 coins for one year. Several other makers have locked up tens of bitcoins each some for multiple years.
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