Paper 2023/1621 Original: eprint.iacr.org/2023/1621 ↗

Withdrawable Signature: How to Call off a Signature

Abstract

Digital signatures are a cornerstone of security and trust in cryptography, providing authenticity, integrity, and non-repudiation. Despite their benefits, traditional digital signature schemes suffer from inherent immutability, offering no provision for a signer to retract a previously issued signature. This paper introduces the concept of a withdrawable signature scheme, which allows for the retraction of a signature without revealing the signer's private key or compromising the security of other signatures the signer created before. This property, defined as ``withdrawability'', is particularly relevant in decentralized systems, such as e-voting, blockchain-based smart contracts, and escrow services, where signers may wish to revoke or alter their commitment. The core idea of our construction of a withdrawable signature scheme is to ensure that the parties with a withdrawable signature are not convinced whether the signer signed a specific message. This ability to generate a signature while preventing validity from being verified is a fundamental requirement of our scheme, epitomizing the property of \textit{withdrawability}. After formally defining security notions for withdrawable signatures, we present two constructions of the scheme based on the pairing and the discrete logarithm. We provide security proof that both constructions are unforgeable under insider corruption and satisfy the criteria of withdrawability. We anticipate our new type of signature will significantly enhance flexibility and security in digital transactions and communications.