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Evaluating large degree isogenies and applications to pairing based cryptography
"... Abstract. We present a new method to evaluate large degree isogenies between elliptic curves over finite fields. Previous approaches all have exponential running time in the logarithm of the degree. If the endomorphism ring of the elliptic curve is ‘small ’ we can do much better, and we present an a ..."
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Abstract. We present a new method to evaluate large degree isogenies between elliptic curves over finite fields. Previous approaches all have exponential running time in the logarithm of the degree. If the endomorphism ring of the elliptic curve is ‘small ’ we can do much better, and we present an algorithm with a running time that is polynomial in the logarithm of the degree. We give several applications of our techniques to pairing based cryptography. 1
Efficient CMconstructions of elliptic curves over finite fields
 MATH. COMP.
, 2007
"... We present an algorithm that, on input of an integer N ≥ 1 together with its prime factorization, constructs a finite field F and an elliptic curve E over F for which E(F) hasorderN. Although it is unproved that this can be done for all N, a heuristic analysis shows that the algorithm has an expect ..."
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We present an algorithm that, on input of an integer N ≥ 1 together with its prime factorization, constructs a finite field F and an elliptic curve E over F for which E(F) hasorderN. Although it is unproved that this can be done for all N, a heuristic analysis shows that the algorithm has an expected run time that is polynomial in 2 ω(N) log N, whereω(N) isthe number of distinct prime factors of N. In the cryptographically relevant case where N is prime, an expected run time O((log N) 4+ε) can be achieved. We illustrate the efficiency of the algorithm by constructing elliptic curves with point groups of order N =10 2004 and N = nextprime(10 2004)=10 2004 +4863.
Generating Prime Order Elliptic Curves: Difficulties and Efficiency
 Considerations, in International Conference on Information Security and Cryptology – ICISC 2004, Lecture Notes in Computer Science
, 2005
"... Abstract. We consider the generation of prime order elliptic curves (ECs) over a prime field Fp using the Complex Multiplication (CM) method. A crucial step of this method is to compute the roots of a special type of class field polynomials with the most commonly used being the Hilbert and Weber one ..."
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Abstract. We consider the generation of prime order elliptic curves (ECs) over a prime field Fp using the Complex Multiplication (CM) method. A crucial step of this method is to compute the roots of a special type of class field polynomials with the most commonly used being the Hilbert and Weber ones, uniquely determined by the CM discriminant D. In attempting to construct prime order ECs using Weber polynomials two difficulties arise (in addition to the necessary transformations of the roots of such polynomials to those of their Hilbert counterparts). The first one is that the requirement of prime order necessitates that D ≡ 3 (mod 8), which gives Weber polynomials with degree three times larger than the degree of their corresponding Hilbert polynomials (a fact that could affect efficiency). The second difficulty is that these Weber polynomials do not have roots in Fp. In this paper we show how to overcome the above difficulties and provide efficient methods for generating ECs of prime order supported by a thorough experimental study. In particular,