On Compression Functions over Small Groups with Applications to Cryptography

08/04/2022

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by   Koji Nuida, et al.

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In the area of cryptography, fully homomorphic encryption (FHE) enables any entity to perform arbitrary computation on encrypted data without decrypting the ciphertexts. An ongoing group-theoretic approach to construct FHE schemes uses a certain "compression" function F(x) implemented by group operators on a given finite group G (i.e., it is given by a sequence of elements of G and variable x), which satisfies that F(1) = 1 and F(σ) = F(σ^2) = σ where σ∈ G is some element of order three. The previous work gave an example of such F over G = S_5 by just a heuristic approach. In this paper, we systematically study the possibilities of such F. We construct a shortest possible F over smaller group G = A_5, and prove that no such F exists over other groups G of order up to 60 = |A_5|.