Coin mixer

A service or protocol designed to obscure the relationship between cryptocurrency inputs and outputs by combining activity from multiple users. Mixers take several forms: custodial services that receive deposits and make withdrawals; smart-contract-based protocols, sometimes using off-chain relayers; and CoinJoin systems, in which multiple users collaboratively construct a single transaction with outputs designed to make ownership harder to infer, typically without transferring custody to a mixer operator.

For custodial mixers, the link between deposits and withdrawals may be preserved in the operator's internal records, which can become available through cooperation or seizure. For smart-contract mixers and CoinJoin transactions, tracing instead relies on transaction structure, timing, amounts and other observable patterns. Links inferred across a mixer are generally probabilistic rather than conclusive. They may become more reliable when amounts are distinctive, few other users are active in the relevant time window, or users make operational mistakes. Examples include reusing addresses or funding a mixer withdrawal address with transaction fees from an address linked to the original deposit. Such evidence should be evaluated alongside other information (see Demixing).