New definition of density on knapsack cryptosystems

  • Authors:
  • Noboru Kunihiro

  • Affiliations:
  • The University of Electro-Communications, Chofu-shi, Tokyo, Japan

  • Venue:
  • AFRICACRYPT'08 Proceedings of the Cryptology in Africa 1st international conference on Progress in cryptology
  • Year:
  • 2008

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Abstract

Many knapsack cryptosystems have been proposed but almost all the schemes are vulnerable to lattice attack because of its low density. To prevent the lattice attack, Chor and Rivest proposed a low weight knapsack scheme, which made the density higher than critical density. In Asiacrypt2005, Nguyen and Stern introduced pseudodensity and proved that if the pseudo-density is low enough (even if the usual density is not low enough), the knapsack scheme can be broken by a single call of SVP/CVP oracle. However, the usual density and the pseudodensity are not sufficient to measure the resistance to the lattice attack individually. In this paper, we first introduce a new notion of density D, which naturally unifies the previous two densities. Next, we derive conditions for our density so that a knapsack scheme is vulnerable to lattice attack. We obtain a critical bound of density which depends only on the ratio of the message length and its Hamming weight. Furthermore, we show that if D