Malicious Security in Collaborative zk-SNARKs: More than Meets the Eye
摘要
Collaborative zk-SNARKs (Ozdemir and Boneh, USENIX’22) are a multiparty variant of zk-SNARKs where multiple, mutually distrustful provers, each holding a private input, jointly compute a zk-SNARK using their combined inputs. A sequence of works has proposed efficient constructions of collaborative zk-SNARKs using a common template that involves designing secure multiparty computation (MPC) protocols to emulate a zk-SNARK prover without making non-black-box use of cryptography. To achieve security against malicious adversaries, these works adopt compilers from the MPC literature that transform semi-honest MPC into malicious-secure MPC. In this work, we revisit this design template. To the best of our knowledge, this is the first example of non-trivial computations where semi-honest MPC protocols achieve malicious security. The observations underlying our positive results are general and may have applications beyond collaborative zkSNARKs.