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Published March 2007 | public
Journal Article

Polynomial-Time Quantum Algorithms for Pell's Equation and the Principal Ideal Problem

Hallgren, Sean

Abstract

We give polynomial-time quantum algorithms for two problems from computational algebraic number theory. The first is Pell's equation. Given a positive non-square integer d, Pell's equation is x^2 − dy^2 = 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 is the principal ideal problem in real quadratic number fields. Solving this problem is at least as hard as solving Pell's equation, and is the basis of a cryptosystem which is broken by our algorithm.

Additional Information

© 2002 ACM, Inc. Supported in part by an NSF Mathematical Scienes Postdoctoral Fellowship, NSF through Caltech's Institute for Quantum Information, NSF under grant no. 0049092 (previously 9876172) and The Charles Lee Powell Foundation. Part of this work done while the author was at MSRI and U.C. Berkeley, with partial support from DARPA QUIST Agreement No. F30602-01-2-0524. Thanks to Hendrik Lenstra for many useful discussions and for suggesting these problems. Also thanks to Kirsten Eisenträger, Ashwin Nayak, Umesh Vazirani, and Ulrich Vollmer for useful discussions.

Additional details

Created:
August 19, 2023
Modified:
October 24, 2023