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20
Solving the Pell Equation
, 2008
"... We illustrate recent developments in computational number theory by studying their implications for solving the Pell equation. We shall see that, if the solutions to the Pell equation are properly represented, the traditional continued fraction method for solving the equation can be significantly a ..."
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We illustrate recent developments in computational number theory by studying their implications for solving the Pell equation. We shall see that, if the solutions to the Pell equation are properly represented, the traditional continued fraction method for solving the equation can be significantly accelerated. The most promising method depends on the use of smooth numbers. As with many algorithms depending on smooth numbers, its run time can presently only conjecturally be established; giving a rigorous analysis is one of the many open problems surrounding the Pell equation.
Computing the endomorphism ring of an ordinary elliptic curve over a finite field
 Journal of Number Theory
"... Abstract. We present two algorithms to compute the endomorphism ring of an ordinary elliptic curve E defined over a finite field Fq. Under suitable heuristic assumptions, both have subexponential complexity. We bound the complexity of the first algorithm in terms of log q, while our bound for the se ..."
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Cited by 15 (7 self)
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Abstract. We present two algorithms to compute the endomorphism ring of an ordinary elliptic curve E defined over a finite field Fq. Under suitable heuristic assumptions, both have subexponential complexity. We bound the complexity of the first algorithm in terms of log q, while our bound for the second algorithm depends primarily on log DE, where DE is the discriminant of the order isomorphic to End(E). As a byproduct, our method yields a short certificate that may be used to verify that the endomorphism ring is as claimed. 1.
Order computations in generic groups
 PHD THESIS MIT, SUBMITTED JUNE 2007. RESOURCES
, 2007
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On values taken by the largest prime factor of shifted primes
 Journal of the Australian Mathematical Society
"... Let P denote the set of prime numbers, and let P(n) denote the largest prime factor of an integer n> 1. We show that, for every real number 32/17 < η < (4 + 3 √ 2)/4, there exists a constant c(η)> 1 such that for every integer a � = 0, the set � p ∈ P: p = P(q − a) for some prime q with p η < q < c( ..."
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Cited by 5 (2 self)
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Let P denote the set of prime numbers, and let P(n) denote the largest prime factor of an integer n> 1. We show that, for every real number 32/17 < η < (4 + 3 √ 2)/4, there exists a constant c(η)> 1 such that for every integer a � = 0, the set � p ∈ P: p = P(q − a) for some prime q with p η < q < c(η) p η � has relative asymptotic density one in the set of all prime numbers. Moreover, in the range 2 ≤ η < (4+3 √ 2)/4, one can take c(η) = 1+ε for any fixed ε> 0. In particular, our results imply that for every real number 0.486 ≤ ϑ ≤ 0.531, the relation P(q − a) ≍ q ϑ holds for infinitely many primes q. We use this result to derive a lower bound on the number of distinct prime divisors of the value of the Carmichael function taken on a product of shifted primes. Finally, we study iterates of the map q ↦ → P(q − a) for a> 0, and show that for infinitely many primes q, this map can be iterated at least (log log q) 1+o(1) times before it terminates. 1.
Smooth Orders and Cryptographic Applications
 Lecture Notes in Comptuer Science
, 2002
"... We obtain rigorous upper bounds on the number of primes x for which p1 is smooth or has a large smooth factor. Conjecturally these bounds are nearly tight. As a corollary, we show that for almost all primes p the multiplicative order of 2 modulo p is not smooth, and we prove a similar but weaker re ..."
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Cited by 5 (1 self)
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We obtain rigorous upper bounds on the number of primes x for which p1 is smooth or has a large smooth factor. Conjecturally these bounds are nearly tight. As a corollary, we show that for almost all primes p the multiplicative order of 2 modulo p is not smooth, and we prove a similar but weaker result for almost all odd numbers n. We also discuss some cryptographic applications.
Another generalization of Wiener’s attack on RSA
 Africacrypt 2008. LNCS
, 2008
"... Abstract. A wellknown attack on RSA with low secretexponent d was given by Wiener in 1990. Wiener showed that using the equation ed − (p − 1)(q − 1)k = 1 and continued fractions, one can efficiently recover the secretexponent d and factor N = pq from the public key (N, e) as long as d < 1 3 N 1 4 ..."
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Cited by 3 (3 self)
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Abstract. A wellknown attack on RSA with low secretexponent d was given by Wiener in 1990. Wiener showed that using the equation ed − (p − 1)(q − 1)k = 1 and continued fractions, one can efficiently recover the secretexponent d and factor N = pq from the public key (N, e) as long as d < 1 3 N 1 4. In this paper, we present a generalization of Wiener’s attack. We show that every public exponent e that satisfies eX − (p − u)(q − v)Y = 1 with 1 ≤ Y < X < 2 − 1 4 N 1 4, u  < N 1 [ 4, v = − qu p − u and all prime factors of p − u or q − v are less than 10 50 yields the factorization of N = pq. We show that the number of these exponents is at least N 1 2 −ε.
On the distribution of the Euler function of shifted smooth numbers’, Preprint, 2008, (available from http://arxiv.org/abs/0810.1093
"... We give asymptotic formulas for some average values of the Euler function on shifted smooth numbers. The result is based on various estimates on the distribution of smooth numbers in arithmetic progressions which are due to A. Granville and É. Fouvry & G. Tenenbaum. 1 ..."
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We give asymptotic formulas for some average values of the Euler function on shifted smooth numbers. The result is based on various estimates on the distribution of smooth numbers in arithmetic progressions which are due to A. Granville and É. Fouvry & G. Tenenbaum. 1
Smooth values of iterates of the Euler phifunction
 Canad. J. Math
"... Abstract. Let φ(n) be the Eulerphi function, define φ0(n) = n and φk+1(n) = φ(φk(n)) for all k ≥ 0. We will determine an asymptotic formula for the set of integers n less than x for which φk(n) is ysmooth, conditionally on a weak form of the ElliottHalberstam conjecture. Integers without large ..."
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Abstract. Let φ(n) be the Eulerphi function, define φ0(n) = n and φk+1(n) = φ(φk(n)) for all k ≥ 0. We will determine an asymptotic formula for the set of integers n less than x for which φk(n) is ysmooth, conditionally on a weak form of the ElliottHalberstam conjecture. Integers without large prime factors, usually called smooth numbers, play a central role in several topics of number theory. From multiplicative questions to analytic methods, they have various and wide applications, and understanding their behavior will have important consequences for number theoretic algorithms, which are an important tool in
On the Recognizability of SelfGenerating Sets
"... Let I be a finite set of integers and F be a finite set of maps of the form n ↦ → ki n+ℓi with integer coefficients. For an integer base k ≥ 2, we study the krecognizability of the minimal set X of integers containing I and satisfying ϕ(X) ⊆ X for all ϕ ∈ F. We answer an open problem of Garth and ..."
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Let I be a finite set of integers and F be a finite set of maps of the form n ↦ → ki n+ℓi with integer coefficients. For an integer base k ≥ 2, we study the krecognizability of the minimal set X of integers containing I and satisfying ϕ(X) ⊆ X for all ϕ ∈ F. We answer an open problem of Garth and Gouge by showing that X is krecognizable when the multiplicative constants ki are all powers of k and additive constants ℓi are chosen freely. Moreover, solving a conjecture of Allouche, Shallit and Skordev, we prove under some technical conditions that if two of the constants ki are multiplicatively independent, then X is not krecognizable for any k ≥ 2. 1