What is a coinjoin transaction?¶

A CoinJoin transaction is a collaborative cryptocurrency transaction in which several users combine inputs and outputs to make straightforward tracing more difficult.

Avoid the dangerous assumption¶

The dangerous assumption is that every input and output in the transaction belongs to one person or that CoinJoin use automatically proves criminal conduct.

Multiple participants contribute funds to one transaction.

The transaction then creates several outputs, often with repeated or similar amounts.

This structure reduces the reliability of simple assumptions about which input funded which output.

A CoinJoin can be organised by wallet software, a coordinator or another collaborative process.

The blockchain still records the transaction, inputs, outputs, fees and timing. What it does not provide is a reliable one-to-one map between each participant’s input and output.

What becomes less clear is the direct relationship between individual participants.

Preserve the transaction hash, network, all inputs and outputs, amounts, fees, timing and the analytical basis for identifying CoinJoin behaviour.

Do not assign every output to the controller of one known input.

Likewise, do not assume that one participant knew the identity or purpose of the others.

Use exchange records, seized-wallet data, later spending patterns, devices and communications to reconnect activity where possible.

Analytical tools may label a transaction as CoinJoin, but the method and confidence should be recorded.

When reporting, distinguish the observed collaborative structure from any conclusion about ownership, concealment or criminal intent.

Operational takeaway¶

Treat CoinJoin as a collaborative transaction that weakens direct input-to-output assumptions and use specialist analysis and corroborating evidence before attributing any output to a person.