[Resource Topic] 2022/1278: Fast Evaluation of S-boxes with Garbled Circuits

Welcome to the resource topic for 2022/1278

Title:
Fast Evaluation of S-boxes with Garbled Circuits

Authors: Erik Pohle, Aysajan Abidin, Bart Preneel

Abstract:

Garbling schemes, a formalization of Yao’s garbled circuit protocol, are useful cryptographic primitives both in privacy-preserving protocols and for secure two-party computation. In projective garbling schemes, n values are assigned to each wire in the circuit. Current state-of-the-art schemes project two values.
More concretely, we present a projective garbling scheme that assigns 2^n values to wires in a circuit comprising XOR and unary projection gates. A generalization of FreeXOR allows the XOR of wires with 2^n values to be very efficient. We then analyze the performance of our scheme by evaluating substitution-permutation ciphers. Using our proposal, we measure high-speed evaluation of the ciphers with a moderate increased cost in garbling and bandwidth. Theoretical analysis suggests that for evaluating the nine examined ciphers, one can expect a 4- to 70-fold increase in evaluation with at most a 4-fold increase in garbling cost and, at most, an 8-fold increase in communication cost when compared to state-of-the-art garbling schemes. In an offline/online setting, such as secure function evaluation as a service, the circuit garbling and communication to the evaluator can proceed before the input phase. Thus our scheme offers a fast online phase. Furthermore, we present efficient computation formulas for the S-boxes of TWINE and Midori64 in Boolean circuits. To our knowledge, our formulas give the smallest number of AND gates for the S-boxes of these two ciphers.

ePrint: https://eprint.iacr.org/2022/1278

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