Crypto mixer
Also called cryptocurrency tumbler, mixing service
A crypto mixer is a service or smart contract that pools crypto-assets from many users and pays them out to new addresses, breaking the visible link between sender and recipient on the blockchain. Mixers offer privacy, but they are also used to launder the proceeds of hacks, ransomware and sanctions evasion.
How it works
Users deposit funds into a shared pool and later withdraw the same value, minus a fee, to a fresh address, often after a delay or in different amounts. Custodial mixers are run by an operator who takes control of the funds; non-custodial mixers run as smart contracts with no operator holding the coins. Either way, blockchain analytics tools find it hard to match deposits to withdrawals.
For compliance teams, exposure to a mixer is a high-risk indicator. Know your transaction tools flag funds that come directly or indirectly from mixing services, and firms review them for source of funds and links to sanctioned actors. US authorities have designated mixers used by state-backed hackers, and from 10 July 2027 EU firms must not keep crypto-asset accounts that allow anonymisation or increased obfuscation of transactions.
The rules
OFAC designated Tornado Cash for laundering funds, including for North Korean hackers, and removed it after a federal appeals court ruled that its immutable smart contracts were not property that could be blocked.
US personsWould have required firms to report transactions involving international crypto mixing; FinCEN withdrew it in October 2026 without adopting a final rule.
US financial institutionsProhibits keeping crypto-asset accounts that allow anonymisation or increased obfuscation of transactions, including through anonymity-enhancing coins.
Credit institutions, financial institutions and crypto-asset service providersCommon questions
Is using a crypto mixer illegal?
Using a mixer is not in itself an offence in most countries. Laundering criminal proceeds through one is, and dealing with a sanctioned mixer breaches sanctions law. Several custodial mixer operators have been convicted of money laundering offences in the US.
Why was Tornado Cash removed from the SDN list?
In November 2024 the US Court of Appeals for the Fifth Circuit ruled that OFAC could not block Tornado Cash's immutable smart contracts because they are not property. OFAC removed Tornado Cash from the SDN List on 21 March 2025.
How do firms detect mixer exposure?
Blockchain analytics tools label known mixer addresses and trace funds back several hops. Firms set risk scores for direct and indirect exposure and review any deposit above their threshold before crediting it.
