Paper 2020/1568

Compact Certificates of Collective Knowledge

Silvio Micali and Leonid Reyzin and Georgios Vlachos and Riad S. Wahby and Nickolai Zeldovich

Abstract

We introduce compact certificate schemes, which allow any party to take a large number of signatures on a message $M$, by many signers of different weights, and compress them to a much shorter certificate. This certificate convinces the verifiers that signers with sufficient total weight signed $M$, even though the verifier will not see---let alone verify---all of the signatures. Thus, for example, a compact certificate can be used to prove that parties who jointly have a sufficient total account balance have attested to a given block in a blockchain. After defining compact certificates, we demonstrate an efficient compact certificate scheme. We then show how to implement such a scheme in a decentralized setting over an unreliable network and in the presence of adversarial parties who wish to disrupt certificate creation. Our evaluation shows that compact certificates are 50-280$\times$ smaller and 300-4000$\times$ cheaper to verify than a natural baseline approach.