Paper 2024/295 Original: eprint.iacr.org/2024/295 ↗

An Efficient Hash Function for Imaginary Class Groups

Abstract

This paper presents a new efficient hash function for imaginary class groups. Many class group based protocols, such as verifiable delay functions, timed commitments and accumulators, rely on the existence of an efficient and secure hash function, but there are not many concrete constructions available in the literature, and existing constructions are too inefficient for practical use cases. Our novel approach, building on Wesolowski's initial scheme, achieves a 200 fold increase in computation speed, making it exceptionally practical for real-world applications. This optimisation is achieved at the cost of a smaller image of the hash function, but we show that the image is still sufficiently large for the hash function to be secure.