I outline a protocol to allow mixing services in blockchain-based currencies such as Bitcoin to prove that they have paid every user of the service. This is done without revealing compromising information that would permit linking of users’ inputs and outputs in a way that normal mixing is not vulnerable to. I also show an extension of this protocol to allow users to specify multiple output addresses. This protocol relies on an efficient zero-knowledge set-membership proof (described in [1]) that drastically reduces the number of signatures that must be transmitted when multiple payments are being verified simultaneously.