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

Presented by: 
R Montenegro [Massachusetts Lowell]
Date: 
Wednesday 26th March 2008 - 14:35 to 15:05
Venue: 
INI Seminar Room 1
Abstract: 

We show a Birthday Paradox for self-intersections of Markov chains with uniform stationary distribution. As an application, we analyze Pollard's Rho algorithm for finding the discrete logarithm in a cyclic group G and find that, if the partition in the algorithm is given by a random oracle, then with high probability a collision occurs in order |G|^0.5 steps. This is the first proof of the correct order bound which does not assume that every step of the algorithm produces an i.i.d. sample from G.

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University of Cambridge Research Councils UK
    Clay Mathematics Institute London Mathematical Society NM Rothschild and Sons