Post-Quantum Sanitizable Signatures from McEliece-Based Chameleon Hashing

2026-02-24

AI Summary

This work addresses the challenge of designing a post-quantum secure digital signature scheme that allows an authorized party to selectively modify designated portions of a signed message while preserving the integrity of the remaining content. We present the first code-based sanitizable signature scheme rooted in the McEliece cryptosystem, leveraging the trapdoor structure of Goppa codes and Patterson decoding to construct controlled collisions that enable a designated sanitizer to alter authorized message blocks without affecting the binding of other parts. By constraining the weight of the signing randomness, the scheme ensures statistical indistinguishability between original and sanitized signatures, achieving perfect transparency in the information-theoretic sense. The construction is proven existentially unforgeable and immutable in the random oracle model, offering a promising avenue for long-term secure applications in the post-quantum era.

Technology Category

• Machine Learning: Calibration & Uncertainty Quantification
• Multiagent Systems: Mechanism Design
• Constraint Satisfaction and Optimization: Satisfiability

Application Category

• Security and Privacy: Applications of cryptography
• Responsible Web: Measurement, analysis, and circumvention of Web censorship
• Economics, Online Markets and Human Computation: Economic aspects of blockchain and cryptocurrencies

Abstract

We introduce a novel post-quantum sanitizable signature scheme constructed upon a chameleon hash function derived from the McEliece cryptosystem. In this design, the designated sanitizer possesses the inherent trapdoor of a Goppa code, which facilitates controlled collision-finding via Patterson decoding. This mechanism enables authorized modification of specific message blocks while ensuring all other content remains immutably bound. We provide formal security definitions and rigorous proofs of existential unforgeability and immutability, grounded in the hardness of syndrome decoding in the random-oracle model, where a robust random oracle thwarts trivial linear hash collisions. A key innovation lies in our precise characterization of the transparency property: by imposing a specific weight constraint on the randomizers generated by the signer, we achieve perfect transparency, rendering sanitized signatures indistinguishable from freshly signed ones. This work establishes the first transparent, code-based, post-quantum sanitizable signature scheme, offering strong theoretical guarantees and a pathway for practical deployment in long-term secure applications.

Problem

• post-quantum
• sanitizable signatures
• chameleon hashing
• transparency
• code-based cryptography

Innovation

• post-quantum cryptography
• sanitizable signatures
• chameleon hashing
• McEliece cryptosystem
• transparency