Cryptology ePrint Archive: Report 2020/1244

Taming the many EdDSAs

Konstantinos Chalkias and François Garillot and Valeria Nikolaenko

Abstract: This paper analyses security of concrete instantiations of EdDSA by identifying exploitable inconsistencies between standardization recommendations and Ed25519 implementations. We mainly focus on current ambiguity regarding signature verification equations, binding and malleability guarantees, and incompatibilities between randomized batch and single verification. We give a formulation of Ed25519 signature scheme that achieves the highest level of security, explaining how each step of the algorithm links with the formal security properties. We develop optimizations to allow for more efficient secure implementations. Finally, we designed a set of edge-case test-vectors and run them by some of the most popular Ed25519 libraries. The results allowed to understand the security level of those implementations and showed that most libraries do not comply with the latest standardization recommendations. The methodology allows to test compatibility of different Ed25519 implementations which is of practical importance for consensus-driven applications.

Category / Keywords: public-key cryptography / EdDSA, ed25519, malleability, blockchain, cofactor

Original Publication (with minor differences): Security Standardisation Research Conference (SSR 2020)

Date: received 8 Oct 2020, last revised 21 Oct 2020

Contact author: valerini at fb com,kostascrypto@fb com,fga@fb com

Available format(s): PDF | BibTeX Citation

Note: Submitted to SSR conference on Aug 31, 2020.Accepted to SSR conference on Oct 1, 2020.

Version: 20201021:182553 (All versions of this report)

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