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Polynomial-time quantum algorithms for Pell's equation and the principal ideal problem

Published:01 March 2007Publication History
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Abstract

We give polynomial-time quantum algorithms for three problems from computational algebraic number theory. The first is Pell's equation. Given a positive nonsquare integer d, Pell's equation is x2dy2 = 1 and the goal is to find its integer solutions. Factoring integers reduces to finding integer solutions of Pell's equation, but a reduction in the other direction is not known and appears more difficult. The second problem we solve is the principal ideal problem in real quadratic number fields. This problem, which is at least as hard as solving Pell's equation, is the one-way function underlying the Buchmann--Williams key exchange system, which is therefore broken by our quantum algorithm. Finally, assuming the generalized Riemann hypothesis, this algorithm can be used to compute the class group of a real quadratic number field.

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  1. Polynomial-time quantum algorithms for Pell's equation and the principal ideal problem

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          Harvey Cohn

          This is a comprehensive paper on how the (as yet unbuilt) quantum computers would be applied to widely known classical problems of number theory, such as Pell’s equation and class structure of a (real quadratic) field. It extends the scope of the basic work of Shor [1], originally applied to primality and factorization. Quantum algorithms are refined particularly for finding the order of a subgroup, and the role of the generalized Riemann hypothesis (GRH) is fully considered. Online Computing Reviews Service

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            cover image Journal of the ACM
            Journal of the ACM  Volume 54, Issue 1
            March 2007
            130 pages
            ISSN:0004-5411
            EISSN:1557-735X
            DOI:10.1145/1206035
            Issue’s Table of Contents

            Copyright © 2007 ACM

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            Publication History

            • Published: 1 March 2007
            Published in jacm Volume 54, Issue 1

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