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Mathematics of Computation

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Computing discrete logarithms in an interval


Authors: Steven D. Galbraith, John M. Pollard and Raminder S. Ruprai
Journal: Math. Comp. 82 (2013), 1181-1195
MSC (2010): Primary 11Y16, 68W20, 11T71
DOI: https://doi.org/10.1090/S0025-5718-2012-02641-X
Published electronically: August 17, 2012
MathSciNet review: 3008854
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Abstract: The discrete logarithm problem in an interval of size $ N$ in a group $ G$ is: Given $ g, h \in G$ and an integer $ N$ to find an integer $ 0 \le n \le N$, if it exists, such that $ h = g^n$. Previously the best low-storage algorithm to solve this problem was the van Oorschot and Wiener version of the Pollard kangaroo method. The heuristic average case running time of this method is $ (2 + o(1)) \sqrt {N}$ group operations.

We present two new low-storage algorithms for the discrete logarithm problem in an interval of size $ N$. The first algorithm is based on the Pollard kangaroo method, but uses 4 kangaroos instead of the usual two. We explain why this algorithm has heuristic average case expected running time of $ (1.715 + o(1)) \sqrt {N}$ group operations. The second algorithm is based on the Gaudry-Schost algorithm and the ideas of our first algorithm. We explain why this algorithm has heuristic average case expected running time of $ (1.661 + o(1)) \sqrt {N}$ group operations. We give experimental results that show that the methods do work close to that predicted by the theoretical analysis.


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Additional Information

Steven D. Galbraith
Affiliation: Mathematics Department, The University of Auckland, Private Bag 92019, Auckland 1142, New Zealand
Email: S.Galbraith@math.auckland.ac.nz

John M. Pollard
Affiliation: Tidmarsh Cottage, Manor Farm Lane, Tidmarsh, Reading, Berkshire RG8 8EX, United Kingdom
Email: jmptidcott@googlemail.com

Raminder S. Ruprai
Affiliation: Mathematics Department, Royal Holloway University of London, Egham, Surrey TW20 0EX, United Kingdom
Email: raminder@email.com

DOI: https://doi.org/10.1090/S0025-5718-2012-02641-X
Keywords: Discrete logarithm problem (DLP), random walks
Received by editor(s): December 1, 2010
Received by editor(s) in revised form: October 9, 2011
Published electronically: August 17, 2012
Additional Notes: This work was supported by EPSRC grant EP/D069904/1
Article copyright: © Copyright 2012 American Mathematical Society
The copyright for this article reverts to public domain 28 years after publication.

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