Mixcoin Anonymity for Bitcoin with accountable mixes ( Full version ) PRE - PROCEEDINGS DRAFT version 0 . 163

We propose Mixcoin, a protocol to facilitate anonymous payments using the Bitcoin currency system. We build on the emergent phenomenon of currency mixes, adding an accountability mechanism to expose theft by mixes. Unlike other proposals to improve anonymity with Bitcoin our scheme can be deployed immediately with no changes to Bitcoin itself. We demonstrate that economic incentives of mixes and clients can be aligned to ensure that rational mixes will not steal from clients. We compare mixing for financial anonymity to the much-better studied problem mixing for anonymous communication, demonstrating important and subtle new attacks.