CoinJoin
A privacy technique that combines multiple users’ cryptocurrency payments into one transaction to make input-output links harder to trace.
CoinJoin is a transaction privacy method most commonly associated with Bitcoin. Instead of each person making a separate payment, several users create one shared transaction that includes inputs from all of them and outputs back to the intended recipients or to themselves. Because the transaction is built so that many outputs look similar, outside observers have a harder time telling which input belongs to which output. Importantly, CoinJoin is usually non-custodial: participants do not need to hand over their coins to a mixer, and each user signs only the part of the transaction that spends their own funds.
CoinJoin matters because public blockchains make transaction histories visible, which can expose spending patterns, balances, or relationships between addresses. Wallets and privacy tools may use CoinJoin to improve financial privacy and fungibility, similar to several people putting identical envelopes into a box and taking identical envelopes out. It does not guarantee perfect anonymity; poor wallet habits, uncommon amounts, timing, or later combining mixed coins can weaken the privacy gained. Some services may also scrutinize or reject coins with CoinJoin history, so users should understand the trade-offs before using it.
Other terms in Cryptography & Privacy
Crypto Mixer
A service or protocol that blends cryptocurrency from many users to make transaction trails harder to trace on a public blockchain.
Digital Signature
A digital signature is cryptographic proof that a message or transaction was approved by the holder of a specific private key.
Fully Homomorphic Encryption
A cryptographic method that lets data be processed while still encrypted, so only the key holder can reveal the final result.
Hash Function
A hash function turns any input into a fixed-length string of data that is easy to verify but extremely hard to reverse or predict.