Fiat-Shamir Bulletproofs are Non-Malleable (in the Algebraic Group Model)

Fiat-Shamir Bulletproofs are Non-Malleable (in the Algebraic Group Model)
Chaya Ganesh, Claudio Orlandi, Mahak Pancholi, Akira Takahashi, Daniel Tschudi
In: Dunkelman, O. and Dziembowski, S. (eds.) Advances in Cryptology - EUROCRYPT 2022 - 41st Annual International Conference on the Theory and Applications of Cryptographic Techniques, Trondheim, Norway, May 30 - June 3, 2022, Proceedings, Part II, pp. 397–426, Springer, 2022.

Abstract. Bulletproofs (Bünz et al. IEEE S&P 2018) are a celebrated ZK proof system that allows for short and efficient proofs, and have been implemented and deployed in several real-world systems. In practice, they are most often implemented in their non-interactive version obtained using the Fiat-Shamir transform, despite the lack of a formal proof of security for this setting. Prior to this work, there was no evidence that malleability attacks were not possible against Fiat-Shamir Bulletproofs. Malleability attacks can lead to very severe vulnerabilities, as they allow an adversary to forge proofs re-using or modifying parts of the proofs provided by the honest parties. In this paper, we show for the first time that Bulletproofs (or any other similar multi-round proof system satisfying some form of weak unique response property) achieve simulation-extractability in the algebraic group model. This implies that Fiat-Shamir Bulletproofs are non-malleable.

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