Paper 2023/784

History-Free Sequential Aggregation of Hash-and-Sign Signatures

Abstract

A sequential aggregate signature (SAS) scheme allows multiple users to sequentially combine their respective signatures in order to reduce communication costs. Historically, early proposals required the use of trapdoor permutation (e.g., RSA). In recent years, a number of attempts have been made to extend SAS schemes to post-quantum assumptions. Many post-quantum signatures have been proposed in the hash-and-sign paradigm, which requires the use of trapdoor functions and appears to be an ideal candidate for sequential aggregation attempts. However, the hardness in achieving post-quantum one-way permutations makes it difficult to obtain similarly general constructions. Direct attempts at generalizing permutation-based schemes have been proposed, but they either lack formal security or require additional properties on the trapdoor function, which are typically not available for multivariate or code-based functions. In this paper, we propose a (partial-signature) history-free SAS within the probabilistic hash-and-sign with retry paradigm, generalizing existing techniques to generic trapdoor functions. We prove the security of our scheme in the random oracle model and we instantiate our construction with three post-quantum schemes, comparing their compression capabilities. Finally, we discuss how direct extensions of permutation-based SAS schemes are not possible without additional properties, showing the lack of security of two existing multivariate schemes.