Cryptology ePrint Archive: Report 2004/102

The Exact Security of an Identity Based Signature and its Applications

Benoît Libert and Jean-Jacques Quisquater

Abstract: This paper first positively answers the previously open question of whether it was possible to obtain an optimal security reduction for an identity based signature (IBS) under a reasonable computational assumption. We revisit the Sakai-Ogishi-Kasahara IBS that was recently proven secure by Bellare, Namprempre and Neven through a general framework applying to a large family of schemes. We show that their modified SOK-IBS scheme can be viewed as a one-level instantiation of Gentry and Silverberg's alternative hierarchical IBS the exact security of which was never considered before. We also show that this signature is as secure as the one-more Diffie-Hellman problem. As an application, we propose a modification of Boyen's "Swiss Army Knife" identity based signature encryption (IBSE) that presents better security reductions and satisfies the same strong security requirements with a similar efficiency.

Category / Keywords: ID-based cryptography, signatures, provable security, exact security

Date: received 2 May 2004, last revised 24 May 2004

Contact author: libert at dice ucl ac be

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Version: 20040524:145134 (All versions of this report)

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