Paper 2019/397

Feistel Structures for MPC, and More

Martin R. Albrecht and Lorenzo Grassi and Léo Perrin and Sebastian Ramacher and Christian Rechberger and Dragos Rotaru and Arnab Roy and Markus Schofnegger

Abstract

We study approaches to generalized Feistel constructions with low-degree round functions with a focus on x → x^3. Besides known constructions, we also provide a new balanced Feistel construction with improved diffusion properties. This then allows us to propose more efficient generalizations of the MiMC design (Asiacrypt’16), which we in turn evaluate in three application areas. Whereas MiMC was not competitive at all in a recently proposed new class of PQ-secure signature schemes, our new construction leads to about 30 times smaller signatures than MiMC. In MPC use cases, where MiMC outperforms all other competitors, we observe improvements in throughput by a factor of more than 7 and simultaneously a 16-fold reduction of preprocessing effort, albeit at the cost of a higher latency. Another use case where MiMC already outperforms other designs, in the area of SNARKs, sees modest improvements. Additionally, this use case benefits from the flexibility to use smaller fields.