Forward-Secure Signatures with Optimal Signing and Verifying

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 [GQ88]), 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 [GQ88] scheme, our scheme is provably secure in the random oracle model.