A unified framework for small secret exponent attack on RSA

  • Authors:
  • Noboru Kunihiro;Naoyuki Shinohara;Tetsuya Izu

  • Affiliations:
  • The University of Tokyo, Japan;NICT, Japan;Fujitsu Labs, Japan

  • Venue:
  • SAC'11 Proceedings of the 18th international conference on Selected Areas in Cryptography
  • Year:
  • 2011

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Abstract

We address a lattice based method on small secret exponent attack on RSA scheme. Boneh and Durfee reduced the attack into finding small roots of a bivariate modular equation: $x(N+1+y)+1 \equiv 0 (\bmod\; e)$ , where N is an RSA moduli and e is the RSA public key. Boneh and Durfee proposed a lattice based algorithm for solving the problem. When the secret exponent d is less than N0.292, their method breaks RSA scheme. Since the lattice used in the analysis is not full-rank, the analysis is not easy. Blömer and May gave an alternative algorithm. Although their bound d≤N0.290 is worse than Boneh---Durfee result, their method used a full rank lattice. However, the proof for their bound is still complicated. Herrmann and May gave an elementary proof for the Boneh---Durfee's bound: d≤N0.292. In this paper, we first give an elementary proof for achieving the bound of Blömer---May: d≤N0.290. Our proof employs unravelled linearization technique introduced by Herrmann and May and is rather simpler than Blömer---May's proof. Then, we provide a unified framework to construct a lattice that are used for solving the problem, which includes two previous method: Herrmann---May and Blömer---May methods as a special case. Furthermore, we prove that the bound of Boneh---Durfee: d≤N0.292 is still optimal in our unified framework.