User Privacy in the Public Bitcoin Blockchain

Bitcoin is a peer-to-peer electronic cash system that maintains a public ledger with all transactions. The public availability of this information has implications for the privacy of the users. The public ledger consists of transactions that transfer funds from a set of inputs to a set of outputs. Both inputs and outputs are linked to Bitcoin addresses. In principle, the addresses are pseudonymous. In practice, it is sometimes possible to link Bitcoin addresses to real identities with the consequent privacy leaks. The possibilities of linking addresses to owners are multiplied when addresses are reused to receive funds multiple times. The reuse of addresses also multiplies the amount of private information that is leaked when an address is linked to a real identity. In this work we describe privacy-leaking effects of address reuse and gather statistics of address reuse in the Bitcoin network. We also describe collaborative (CoinJoin) transactions that prevent the privacy attacks that have been published in the literature. Then we analyze the Blockchain to find transactions that could potentially be CoinJoin transactions.