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A CRT algorithm for constructing genus 2 curves over finite fields
, 2007
"... Abstract. — We present a new method for constructing genus 2 curves over a finite field Fn with a given number of points on its Jacobian. This method has important applications in cryptography, where groups of prime order are used as the basis for discretelog based cryptosystems. Our algorithm prov ..."
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Cited by 21 (8 self)
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Abstract. — We present a new method for constructing genus 2 curves over a finite field Fn with a given number of points on its Jacobian. This method has important applications in cryptography, where groups of prime order are used as the basis for discretelog based cryptosystems. Our algorithm provides an alternative to the traditional CM method for constructing genus 2 curves. For a quartic CM field K with primitive CM type, we compute the Igusa class polynomials modulo p for certain small primes p and then use the Chinese remainder theorem (CRT) and a bound on the denominators to construct the class polynomials. We also provide an algorithm for determining endomorphism rings of ordinary Jacobians of genus 2 curves over finite fields, generalizing the work of Kohel for elliptic curves. Résumé (Un algorithme fondé sur le théorème chinois pour construire des courbes de genre 2 sur des corps finis) Nous présentons une nouvelle méthode pour construire des courbes de genre 2 sur un corps fini Fn avec un nombre donné de points sur sa jacobienne. Cette méthode a des applications importantes en cryptographie, où des groupes d’ordre premier sont employés pour former des cryptosystèmes fondés sur le logarithme discret. Notre algorithme fournit une alternative à la méthode traditionnelle de multiplication complexe pour construire des courbes de genre 2. Pour un corps quartique K à multiplication complexe de type primitif, nous calculons les polynômes de classe d’Igusa modulo p pour certain petit premiers p et employons le théorème chinois et une borne sur les dénominateurs pour construire les polynômes de classe. Nous fournissons également un algorithme pour déterminer les anneaux d’endomorphismes des jacobiennes de courbes ordinaires de genre 2 sur des corps finis, généralisant le travail de Kohel pour les courbes elliptiques.
Constructing pairingfriendly genus 2 curves over prime fields with ordinary Jacobians
 IN: PROCEEDINGS OF PAIRING 2007, LNCS 4575
, 2007
"... We provide the first explicit construction of genus 2 curves over finite fields whose Jacobians are ordinary, have large primeorder subgroups, and have small embedding degree. Our algorithm is modeled on the CocksPinch method for constructing pairingfriendly elliptic curves [5], and works for a ..."
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Cited by 10 (2 self)
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We provide the first explicit construction of genus 2 curves over finite fields whose Jacobians are ordinary, have large primeorder subgroups, and have small embedding degree. Our algorithm is modeled on the CocksPinch method for constructing pairingfriendly elliptic curves [5], and works for arbitrary embedding degrees k and prime subgroup orders r. The resulting abelian surfaces are defined over prime fields Fq with q ≈ r 4. We also provide an algorithm for constructing genus 2 curves over prime fields Fq with ordinary Jacobians J having the property that J[r] ⊂ J(Fq) or J[r] ⊂ J(F q k) for any even k.
Computing endomorphism rings of jacobians of genus 2 curves
 In Symposium on Algebraic Geometry and its Applications, Tahiti
, 2006
"... Abstract. We present probabilistic algorithms which, given a genus 2 curve C defined over a finite field and a quartic CM field K, determine whether the endomorphism ring of the Jacobian J of C is the full ring of integers in K. In particular, we present algorithms for computing the field of definit ..."
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Cited by 10 (5 self)
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Abstract. We present probabilistic algorithms which, given a genus 2 curve C defined over a finite field and a quartic CM field K, determine whether the endomorphism ring of the Jacobian J of C is the full ring of integers in K. In particular, we present algorithms for computing the field of definition of, and the action of Frobenius on, the subgroups J[ℓ d] for prime powers ℓ d. We use these algorithms to create the first implementation of Eisenträger and Lauter’s algorithm for computing Igusa class polynomials via the Chinese Remainder Theorem [EL], and we demonstrate the algorithm for a few small examples. We observe that in practice the running time of the CRT algorithm is dominated not by the endomorphism ring computation but rather by the need to compute p 3 curves for many small primes p. 1.
AN ARITHMETIC INTERSECTION FORMULA FOR DENOMINATORS OF IGUSA CLASS POLYNOMIALS
"... Abstract. In this paper we prove an explicit formula for the arithmetic intersection number (CM(K).G1)ℓ on the Siegel moduli space of abelian surfaces, generalizing the work of BruinierYang and Yang. These intersection numbers allow one to compute the denominators of Igusa class polynomials, which ..."
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Cited by 5 (2 self)
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Abstract. In this paper we prove an explicit formula for the arithmetic intersection number (CM(K).G1)ℓ on the Siegel moduli space of abelian surfaces, generalizing the work of BruinierYang and Yang. These intersection numbers allow one to compute the denominators of Igusa class polynomials, which has important applications to the construction of genus 2 curves for use in cryptography. Bruinier and Yang conjectured a formula for intersection numbers on an arithmetic Hilbert modular surface, and as a consequence obtained a conjectural formula for the intersection number (CM(K).G1)ℓ under strong assumptions on the ramification of the primitive quartic CM field K. Yang later proved this conjecture assuming that OK is freely generated by one element over the ring of integers of the real quadratic subfield. In this paper, we prove a formula for (CM(K).G1)ℓ for more general primitive quartic CM fields, and we use a different method of proof than Yang. We prove a tight bound on this intersection number which holds for all primitive quartic CM fields. As a consequence, we obtain a formula for a multiple of the denominators of the Igusa class polynomials for an arbitrary primitive quartic CM field. Our proof entails studying the Embedding Problem posed by Goren and Lauter and counting solutions using our previous article that generalized work of GrossZagier and Dorman to arbitrary discriminants. 1.
Computing Igusa class polynomials via the Chinese remainder theorem
, 405
"... Abstract. We present a new method for computing the Igusa class polynomials of a primitive quartic CM field. For a primitive quartic CM field, K, we compute the Igusa class polynomials modulo p for certain small primes p and then use the Chinese remainder theorem and a conjectural bound on the denom ..."
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Cited by 3 (0 self)
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Abstract. We present a new method for computing the Igusa class polynomials of a primitive quartic CM field. For a primitive quartic CM field, K, we compute the Igusa class polynomials modulo p for certain small primes p and then use the Chinese remainder theorem and a conjectural bound on the denominators to construct the class polynomials. We also provide an extension to genus 2 of Kohel’s algorithm for determining endomorphism rings of elliptic curves. Our algorithm can be used to generate genus 2 curves over a finite field Fn with a given zeta function. 1.
Evil primes and superspecial moduli
 INTERNATIONAL MATHEMATICS RESEARCH NOTICES, VOLUME 2006, ARTICLE ID 53864
, 2005
"... For a quartic nonbiquadratic CM field K, we say that a rational prime p is evil for K if at least one of the principally polarized abelian varieties with CM by K reduces modulo a prime ideal pp to a product of supersingular elliptic curves with the product polarization. In [GL] we showed that fo ..."
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Cited by 3 (3 self)
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For a quartic nonbiquadratic CM field K, we say that a rational prime p is evil for K if at least one of the principally polarized abelian varieties with CM by K reduces modulo a prime ideal pp to a product of supersingular elliptic curves with the product polarization. In [GL] we showed that for fixed K such primes are bounded by a quantity related to the discriminant of K. In this paper, we show that evil primes are ubiquitous in the sense that, for any rational prime p, there are an infinite number of such CM fields K for which p is evil. (Assuming a standard conjecture, the result holds for a finite set of primes simultaneously.) The proof consists of two parts: (1) showing the surjectivity of the principally polarized abelian varieties with CM by K, for K satisfying some conditions, onto the superspecial points of the reduction modulo p of the Hilbert modular variety associated to the intermediate real quadratic field of K, and (2) showing the surjectivity of the superspecial points of the reduction modulo p of the Hilbert modular variety associated to a real quadratic field with large enough discriminant onto the superspecial points on the reduction modulo p of the Siegel moduli space parameterizing abelian surfaces with principal polarization.