Verifiable signature sharing

Abstract

We introduce Verifiable Signature Sharing (VCS), a cryptographic primitive for protecting digital signatures. VCS enables the holder of a digitally signed document, who may or may not be the original signer, to share the signature among a set of proxies so that the honest proxies can later reconstruct it. We present efficient VCS schemes for exponentiation based signatures (e.g., RSA, Rabin) and discrete log based signatures (e.g., ElGamal, Schnorr, DSA) that can tolerate the malicious (Byzantine) failure of the sharer and a constant fraction of the proxies. We also describe our implementation of these schemes and evaluate their performance. Among the applications of VXS is the incorporation of digital cash into multiparty protocols, e.g., to enable cash escrow and secure distributed auctions.