A birthday paradox for Markov chains, with an optimal bound for collision in the Pollard Rho algorithm for discrete logarithm

  • Authors:
  • Jeong Han Kim;Ravi Montenegro;Yuval Peres;Prasad Tetali

  • Affiliations:
  • Department of Mathematics, Yonsei University, Seoul, Korea;Department of Mathematical Sciences, University of Massachusetts at Lowell, Lowell, MA;Microsoft Research, Redmond and University of California, Berkeley, CA;School of Mathematics and School of Computer Science, Georgia Institute of Technology, Atlanta, GA

  • Venue:
  • ANTS-VIII'08 Proceedings of the 8th international conference on Algorithmic number theory
  • Year:
  • 2008

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Abstract

We show a Birthday Paradox for self-intersections of Markovchains with uniform stationary distribution. As an application, we analyzePollard's Rho algorithm for finding the discrete logarithm in a cyclicgroup G and find that, if the partition in the algorithm is given by arandom oracle, then with high probability a collision occurs in Θ(√|G|)steps. This is the first proof of the correct bound which does not assumethat every step of the algorithm produces an i.i.d. sample from G.