Rigorous bounds on cryptanalytic time/memory tradeoffs

  • Authors:
  • Elad Barkan;Eli Biham;Adi Shamir

  • Affiliations:
  • Technion – Israel Institute of Technology, Computer Science Department, Haifa, Israel;Technion – Israel Institute of Technology, Computer Science Department, Haifa, Israel;Department of Computer Science and Applied Mathematics, The Weizmann Institute, Rehovot, Israel

  • Venue:
  • CRYPTO'06 Proceedings of the 26th annual international conference on Advances in Cryptology
  • Year:
  • 2006

Quantified Score

Hi-index 0.00

Visualization

Abstract

In this paper we formalize a general model of cryptanalytic time/memory tradeoffs for the inversion of a random function f:{0,1,..., N–1} ↦{0,1,..., N–1}. The model contains all the known tradeoff techniques as special cases. It is based on a new notion of stateful random graphs. The evolution of a path in the stateful random graph depends on a hidden state such as the color in the Rainbow scheme or the table number in the classical Hellman scheme. We prove an upper bound on the number of images y=f(x) for which f can be inverted, and derive from it a lower bound on the number of hidden states. These bounds hold for an overwhelming majority of the functions f, and their proofs are based on a rigorous combinatorial analysis. With some additional natural assumptions on the behavior of the online phase of the scheme, we prove a lower bound on its worst-case time complexity $T=\Omega(\frac{N^2}{M^2 \ln N})$, where M is the memory complexity. Finally, we describe new rainbow-based time/memory/data tradeoffs, and a new method for improving the time complexity of the online phase (by a small factor) by performing a deeper analysis during preprocessing.