Paper 2004/102

The Exact Security of an Identity Based Signature and its Applications

Benoît Libert and Jean-Jacques Quisquater


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.

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Published elsewhere. Unknown where it was published
ID-based cryptographysignaturesprovable securityexact security
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libert @ dice ucl ac be
2004-05-24: last of 13 revisions
2004-05-07: received
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      author = {Benoît Libert and Jean-Jacques Quisquater},
      title = {The Exact Security of an Identity Based Signature and its Applications},
      howpublished = {Cryptology ePrint Archive, Paper 2004/102},
      year = {2004},
      note = {\url{}},
      url = {}
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