Paper 2025/602

Lattice-Based Sanitizable Signature Schemes: Chameleon Hash Functions and More

Abstract

Sanitizable Signature Schemes (SSS) enable a designated party, the sanitizer, to modify predefined parts of a signed message without invalidating the signature, making them useful for applications like pseudonymization and redaction. Since their introduction by Ateniese et al. (ESORICS'05), several classical SSS constructions have been proposed, but none have been instantiated from quantum-resistant assumptions. In this work, we develop the first quantum-secure sanitizable signature schemes based on lattice assumptions. Our primary focus is on SSS constructions that rely on chameleon hash functions (CHFs), a key component for enabling the controlled modification of messages. While lattice-based CHFs exist, they do not meet the required security guarantees for SSS, becoming insecure under adversarial access to an adapt oracle. To address this, we construct a novel lattice-based CHF that achieves collision resistance even in such settings, called full collision resistance. However, our CHF lacks the uniqueness property, a limitation we show to be inherent in lattice-based CHFs. As a result, our SSS constructions initially fall short of achieving the critical security property of accountability. To overcome this, we apply a transformation based on verifiable ring signatures (VRS), for which we present the first lattice-based instantiation. Additionally, we provide a comprehensive analysis of existing classical SSS constructions, explore their potential for post-quantum instantiations, and present new attacks on previously assumed secure SSS schemes. Our work closes the gap in constructing quantum-secure SSS and lays the groundwork for further research into advanced cryptographic primitives based on lattice assumptions.