- Fourth, mixing fees should be all-or-nothing, that is, for every chunk of money the mix should either retain all of it or none. This might sound strange, but it greatly improves anonymity against clever analysis of the blockchain. If every time a user mixes a chunk the mix takes a constant 2% cut (or a randomized 1–3% cut) as a fee, then a chunk passing through multiple mixes in a row will have its value decrease in a traceable way. We can avoid this with all-or-nothing fees.

There are two consequences of this. First, the chunks should be small enough (say 0.01 BTC at the current exchange rate) that most mix users will accept the variance associated with random transaction fees. Second, this will mean that to mix realistic volumes, users will necessarily have to automate their interactions with mixes.

How will users (or their client software) verify that mixes that aren’t taking more than their cut? In the paper, we provide a cryptographically secure way to do this. But that’s not strictly necessary — since these chunks are quite small and most users will have significant numbers of chunks that they’ll move through each mix, clients can statistically verify if the mix deviates from it’s posted policy on the transaction fee.