CoinJoin is a transaction-construction technique, not a special consensus rule or custodial mixer. Each participant checks the complete proposal and signs only their own inputs; the outcome depends on the coordination protocol, output structure, network metadata and later spending.
Chain analysis often assumes that the inputs of an ordinary transaction share one owner. CoinJoin deliberately makes that assumption false by placing inputs from different people in one transaction, so common input is not cryptographic proof of common ownership.
A coordinator or peer-to-peer protocol assembles an unsigned proposal. Before signing, each participant verifies their inputs, expected outputs, amounts and fee; without every required signature the transaction is invalid, and the coordinator alone cannot spend another participant's input.
Equal denominations can make input-to-output assignment harder. Unequal amounts, change, few participants or unique scripts shrink the effective anonymity set, so a wallet's displayed score is not a universal privacy measurement.
A coordinator may reject registrations, observe network metadata or face flooding, but should not gain signing control. Sybil participants can occupy much of a round and reduce ambiguity, so the exact protocol, fees and denial-of-service defenses matter.
Later consolidation, combining with a KYC withdrawal, address reuse or payment to a known counterparty can recreate links. UTXO separation, coin control and network privacy matter as much as the transaction shape itself.
Gregory Maxwell's original proposal, JoinMarket and coordinated wallet protocols use different incentives and communication models. PayJoin is a related two-party collaborative transaction, but it normally does not target a large equal-output anonymity set.
CoinJoin does not erase history or external records, guarantee legal or exchange acceptance, or automatically protect against a network observer. Verify the threat model, key control, full transaction proposal and post-round handling of outputs.
Gregory Maxwell — CoinJoin: Bitcoin privacy for the real world · JoinMarket client/server · JoinMarket — How it works · WabiSabi: Centrally Coordinated CoinJoins with Variable Amounts · Wasabi Wallet — CoinJoin documentation · BIP 78 — Payjoin
A common-input assumption becomes false
Alice and Bob each contribute one input to a collaborative transaction and receive separate outputs. An analyst who labels both inputs as one owner is now wrong, although later consolidation could reveal the relationship again.
For the clearest picture, read this entry together with Bitcoin, Bitcoin Privacy, Pseudonymity, Bitcoin wallet, UTXO, Transaction. The reverse links also lead from Change output, Bitcoin Privacy, Pseudonymity, KYC.
01Can a CoinJoin coordinator steal the inputs?+
In a properly non-custodial design, participants keep their keys and sign only a transaction containing the outputs they approved. A coordinator can disrupt or censor a round, but cannot create a valid spend without each required signature.
02Are CoinJoin outputs anonymous forever?+
No. Later address reuse, consolidation, identified payments, wallet fingerprints or network metadata can reduce or undo the ambiguity created by the collaborative transaction.