“Crypto mixers” exist because of a peculiar feature of cryptocurrencies—most are fully traceable using their public blockchain ledgers. To provide more privacy to crypto account owners, a mixer will let people toss their crypto into a large pool, where it is “mixed” with other people’s crypto. At a later date, each crypto owner can choose to withdraw their money from the pool into a new, anonymous wallet, thus making the movement of the crypto harder to track.
Of course, the obfuscation doesn’t work well if the blockchain shows 1,231.7 BTC entering a mixer and 1,231.7 BTC being withdrawn to a new wallet. So mixers will take steps to disguise the transactions. Tornado Cash, which operated on the Ethereum blockchain, mandated that users could only deposit money into its pools in 0.1, 1, 10, and 100 ETH increments, making it far harder to spot specific amounts entering and leaving the mixer.
Tornado Cash also used a complex system of “relayers” to pay the Ethereum “gas fees” charged for transactions on the network; without doing this, it would be clear which old account was paying to “mix” money into which new account. The whole process relied on the use of irrevocable “smart contracts,” all of which sounds rather technically daunting, but Tornado put a nice user interface atop the details that made the service far easier to use than it might sound.
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