There are projects like Miximus, which is an Eth tumbler with no operator. Participants deposit funds into a smart contract, then when they want to withdraw lat

There are projects like Miximus, which is an Eth tumbler with no operator. Participants deposit funds into a smart contract, then when they want to withdraw later, they use zero-knowledge proofs to show that they know one of the private keys without revealing which one. There's also Zcash, which applies similar logic to all shielded transactions.