Paper 2021/832

Progressive And Efficient Verification For Digital Signatures

Cecilia Boschini, Dario Fiore, and Elena Pagnin

Abstract

Digital signatures are widely deployed to authenticate the source of incoming information, or to certify data integrity. Common signature verification procedures return a decision (accept/reject) only at the very end of the execution. If interrupted prematurely, however, the verification process cannot infer any meaningful information about the validity of the given signature. We notice that this limitation is due to the algorithm design solely, and it is not inherent to signature verification. In this work, we provide a formal framework to handle interruptions during signature verification. In addition, we propose a generic way to devise alternative verification procedures that progressively build confidence on the final decision. Our transformation builds on a simple but powerful intuition and applies to a wide range of existing schemes considered to be post-quantum secure including the NIST finalist Rainbow. While the primary motivation of progressive verification is to mitigate unexpected interruptions, we show that verifiers can leverage it in two innovative ways. First, progressive verification can be used to intentionally adjust the soundness of the verification process. Second, progressive verifications output by our transformation can be split into a computationally intensive offline set-up (run once) and an efficient online verification that is progressive.