Title: Enhancing user and transaction privacy in bitcoin with unlinkable coin mixing scheme

Authors: Albert Kofi Kwansah Ansah; Daniel Adu-Gyamfi

Addresses: School of Computer Science and Engineering, University of Electronic Science and Technology of China, No. 2006, Xiyuan, Chengdu, 611731, China; Department of Computer Science and Engineering, University of Mines and Technology, TK 237, Tarkwa, Ghana ' Department of Computer Science and Informatics, University of Energy and Natural Resources, Sunyani, Ghana

Abstract: The concept of coin mixing is significant in blockchain and achieves anonymity and has merited application in bitcoin. Albeit, several coin mixing schemes have been proposed, we point out that they either hoard input transactions and address mapping or not fully satisfy all requirements of practical anonymity. This paper proposes a coin mixing scheme (mixing countersignature scheme, ring signature, and coin mixing approach) that allows users to transact business untraceably and unlinkably without having to trust a third party to ensure coins are safe. Our proposed novel countersignature scheme simulation results prove the countersignature scheme's correctness with an average running time of 4 μs using PBC type A.80. The scheme's security and privacy are met with standard ring signature, ECDSA unforgeability and our countersignature. We demonstrated the efficiency of the mixing scheme using bitcoin's core regtest mode to set up a private bitcoin network. The mix takes 80, 160, 320, 640, 800 secs to service 500, 1,000, 2,000, 4,000, 5,000 users respectively. It was observed that the number of users scales linearly with average running time.

Keywords: bitcoin; blockchain; user privacy; transaction privacy; coin mixing; bilinear pairing; elliptic curve digital signature algorithm; ECDSA; ring signature; countersignature; anonymity.

DOI: 10.1504/IJCSE.2020.113183

International Journal of Computational Science and Engineering, 2020 Vol.23 No.4, pp.381 - 395

Received: 05 Apr 2020
Accepted: 20 Jul 2020

Published online: 10 Feb 2021 *

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