Paper 2021/979 Original: eprint.iacr.org/2021/979 ↗

Constant-Overhead Zero-Knowledge for RAM Programs

Abstract

We show a constant-overhead interactive zero-knowledge (ZK) proof system for RAM programs, that is, a ZK proof in which the communication complexity as well as the running times of the prover and verifier scale linearly in the size of the memory $N$ and the running time $T$ of the underlying RAM program. Besides yielding an asymptotic improvement of prior work, our implementation gives concrete performance improvements for RAM-based ZK proofs. In particular, our implementation supports ZK proofs of private read/write accesses to 64 MB of memory ($2^{24}$ 32-bit words) using only 34 bytes of communication per access, a more than $80\times$ improvement compared to the recent BubbleRAM protocol. We also design a lightweight RISC CPU that can efficiently emulate the MIPS-I instruction set, and for which our ZK proof communicates only $\approx$ 320 bytes per cycle, more than $10\times$ less than the BubbleRAM CPU. In a 100 Mbps network, we can perform zero-knowledge executions of our CPU (with 64 MB of main memory and 4 MB of program memory) at a clock rate of 6.6 kHz.