Cryptology ePrint Archive: Report 2001/048

Forward-Secure Signatures with Optimal Signing and Verifying

Gene Itkis and Leonid Reyzin

Abstract: Ordinary digital signatures have an inherent weakness: if the secret key is leaked, then all signatures, even the ones generated before the leak, are no longer trustworthy. Forward-secure digital signatures were recently proposed to address this weakness: they ensure that past signatures remain secure even if the current secret key is leaked.

We propose the first forward-secure signature scheme for which both signing and verifying are as efficient as for one of the most efficient ordinary signature schemes (Guillou-Quisquater): each requiring just two modular exponentiations with a short exponent. All previously proposed forward-secure signature schemes took significantly longer to sign and verify than ordinary signature schemes.

Our scheme requires only fractional increases to the sizes of keys and signatures, and no additional public storage. Like the underlying Guillou-Quisquater scheme, our scheme is provably secure in the random oracle model.

Category / Keywords: public-key cryptography /

Publication Info: to appear in Crypto-2001

Date: received 18 Jun 2001

Contact author: itkis at bu edu

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Version: 20010618:174719 (All versions of this report)

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