New efficient and secure protocols for verifiable signature sharing and other applications

Abstract

Verifiable Signature Sharing (V∑S) enables the recipient of a digital signature, who is not necessarily the original signer, to share such signature among n proxies so that a subset of them can later reconstruct it. The original RSA and Rabin V∑S protocols were subsequently broken and the original DSS V∑S lacks a formal proof of security. We present new protocols for RSA, Rabin and DSS V∑S. Our protocols are efficient and provably secure and can tolerate the malicious behavior of up to half of the proxies. Furthermore we believe that some of our techniques are of independent interest. Some of the by-products of our main result are: a new threshold cryptosystem, a new undeniable signature scheme and a way to create binding RSA cryptosystems.