Paper 2017/238

Mixing Confidential Transactions: Comprehensive Transaction Privacy for Bitcoin

Tim Ruffing and Pedro Moreno-Sanchez

Abstract

The public nature of the blockchain has been shown to be a severe threat for the privacy of Bitcoin users. Even worse, since funds can be tracked and tainted, no two coins are equal, and fungibility, a fundamental property required in every currency, is at risk. With these threats in mind, several privacy-enhancing technologies have been proposed to improve transaction privacy in Bitcoin. However, they either require a deep redesign of the currency, breaking many currently deployed features, or they address only specific privacy issues and consequently provide only very limited guarantees when deployed separately. The goal of this work is to overcome this trade-off. Building on CoinJoin, we design ValueShuffle, the first coin mixing protocol compatible with Confidential Transactions, a proposed enhancement to the Bitcoin protocol to hide payment values in the blockchain. ValueShuffle ensures the anonymity of mixing participants as well as the confidentiality of their payment values even against other possibly malicious mixing participants. By combining CoinJoin with Confidential Transactions and additionally Stealth Addresses, ValueShuffle provides comprehensive privacy (payer anonymity, payee anonymity, and payment value privacy) without breaking with fundamental design principles or features of the current Bitcoin system. Assuming that Confidential Transactions will be integrated in the Bitcoin protocol, ValueShuffle makes it possible to mix funds of different value as well as to mix and spend funds in the same transaction, which overcomes the two main limitations of previous coin mixing protocols.

Metadata
Available format(s)
PDF
Category
Applications
Publication info
Preprint. MINOR revision.
Keywords
cryptocurrenciescoin mixinganonymity
Contact author(s)
tim ruffing @ mmci uni-saarland de
History
2017-03-11: received
Short URL
https://ia.cr/2017/238
License
Creative Commons Attribution
CC BY

BibTeX

@misc{cryptoeprint:2017/238,
      author = {Tim Ruffing and Pedro Moreno-Sanchez},
      title = {Mixing Confidential Transactions: Comprehensive Transaction Privacy for Bitcoin},
      howpublished = {Cryptology ePrint Archive, Paper 2017/238},
      year = {2017},
      note = {\url{https://eprint.iacr.org/2017/238}},
      url = {https://eprint.iacr.org/2017/238}
}
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