Cryptology ePrint Archive: Report 2017/1168

Itsuku: a Memory-Hardened Proof-of-Work Scheme

Fabien Coelho and Arnaud Larroche and Baptiste Colin

Abstract: Proof-of-Work (PoW) schemes allow to limit access to resources or to share rewards for crypto-currency mining. The MTP-Argon2 PoW by Biryukov and Khovratovich is loosely based on the Argon2 memory-hard password hashing function. Several attacks have been published. We introduce a new transposed parallel implementation attack which achieves higher performance by circumventing apparent bandwidth requirements. We then present Itsuku, a new scheme that fixes known issues by changing MTP-Argon2 parameters and adds new operations to improve memory hardness. Our scheme is built on a simple security criterion: any implementation which requires half the memory or less should induce at least a times-64 computation cost for difficulty d <= 100. The Itsuku proof size is typically 1/16 th of the initial scheme, while providing better memory hardness. We also describe high-end hardware designs for MTP-Argon2 and Itsuku.

Category / Keywords: cryptographic protocols / hash functions

Date: received 29 Nov 2017, last revised 1 Dec 2017

Contact author: iacr org 20171129 at coelho net

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Version: 20171201:112100 (All versions of this report)

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