Paper 2022/109

Perfectly-Secure Synchronous MPC with Asynchronous Fallback Guarantees

Ananya Appan
Anirudh Chandramouli
Ashish Choudhury

Secure multi-party computation (MPC) is a fundamental problem in secure distributed computing. An MPC protocol allows a set of $n$ mutually distrusting parties to carry out any joint computation of their private inputs, without disclosing any additional information about their inputs. MPC with information-theoretic security (also called unconditional security) provides the strongest security guarantees and remains secure even against computationally unbounded adversaries. Perfectly-secure MPC protocols is a class of information-theoretically secure MPC protocols, which provides all the security guarantees in an error-free fashion. The focus of this work is perfectly-secure MPC. Known protocols are designed assuming either a synchronous or an asynchronous communication network. It is well known that perfectly-secure synchronous MPC protocol is possible as long as adversary can corrupt any $t_s < n/3$ parties. On the other hand, perfectly-secure asynchronous MPC protocol can tolerate up to $t_a < n/4$ corrupt parties. A natural question is does there exist a single MPC protocol for the setting where the parties are not aware of the exact network type and which can tolerate up to $t_s < n/3$ corruptions in a synchronous network and up to $t_a < n/4$ corruptions in an asynchronous network. We design such a best-of-both-worlds perfectly-secure MPC protocol, provided $3t_s + t_a < n$ holds. For designing our protocol, we design two important building blocks, which are of independent interest. The first building block is a best-of-both-worlds Byzantine agreement (BA) protocol tolerating $t < n/3$ corruptions and which remains secure, both in a synchronous as well as asynchronous network. The second building block is a polynomial-based best-of-both-worlds verifiable secret-sharing (VSS) protocol, which can tolerate up to $t_s$ and $t_a$ corruptions in a synchronous and in an asynchronous network respectively.

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Cryptographic protocols
Publication info
Published elsewhere. ACM PODC 2022
Byzantine faults unconditional-security Byzantine agreement secret sharing privacy Multi Party Computation
Contact author(s)
ananya appan @ iiitb ac in
anirudh c @ iiitb ac in
ashish choudhury @ iiitb ac in
2022-08-09: last of 2 revisions
2022-01-31: received
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      author = {Ananya Appan and Anirudh Chandramouli and Ashish Choudhury},
      title = {Perfectly-Secure Synchronous MPC with Asynchronous Fallback Guarantees},
      howpublished = {Cryptology ePrint Archive, Paper 2022/109},
      year = {2022},
      doi = {10.1145/3519270.3538417},
      note = {\url{}},
      url = {}
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