TumbleBit: An Untrusted Bitcoin-Compatible Anonymous Payment Hub

Abstract

This paper presents TumbleBit, a new unidirectional unlinkable payment hub that is fully compatible with today\u27s Bitcoin protocol. TumbleBit allows parties to make fast, anonymous, off-blockchain payments through an untrusted intermediary called the Tumbler. TumbleBit\u27s anonymity properties are similar to classic Chaumian eCash: no one, not even the Tumbler, can link a payment from its payer to its payee. Every payment made via TumbleBit is backed by bitcoins, and comes with a guarantee that Tumbler can neither violate anonymity, nor steal bitcoins, nor ``print money\u27\u27 by issuing payments to itself. We prove the security of TumbleBit using the real/ideal world paradigm and the random oracle model. Security follows from the standard RSA assumption and ECDSA unforgeability. We implement TumbleBit, mix payments from 800 users and show that TumbleBit\u27s off-blockchain payments can complete in seconds