The Infrastructure of a Global Field of Arbitrary Unit Rank

In this paper, we show a general way to interpret the infrastructure of a global field of arbitrary unit rank. This interpretation generalizes the prior concepts of the giant step operation and f-representations, and makes it possible to relate the infrastructure to the (Arakelov) divisor class group of the global field. In the case of global function fields, we present results that establish that effective implementation of the presented methods is indeed possible, and we show how Shanks' baby-step giant-step method can be generalized to this situation.Comment: Revised version. Accepted for publication in Math. Com

Explicit infrastructure for real quadratic function fields and real hyperelliptic curves

In 1989, Koblitz first proposed the Jacobian of a an imaginary hyperelliptic curve for use in public-key cryptographic protocols. This concept is a generalization of elliptic curve cryptography. It can be used with the same assumed key-per-bit strength for small genus. More recently, real hyperelliptic curves of small genus have been introduced as another source for cryptographic protocols. The arithmetic is more involved than its imaginary counterparts and it is based on the so-called infrastructure of the set of reduced principal ideals in the ring of regular functions of the curve. This infrastructure is an interesting phenomenon. The main purpose of this article is to explain the infrastructure in explicit terms and thus extend Shanks\u27 infrastructure ideas in real quadratic number fields to the case of real quadratic congruence function fields and their curves. Hereby, we first present an elementary introduction to the continued fraction expansion of real quadratic irrationalities and then generalize important results for reduced ideals

Key-Exchange in Real Quadratic Congruence Function Fields

We show how the theory of real quadratic congruence function fields can be used to produce a secure key distribution protocol. The technique is similar to that advocated by Diffie and Hellman in 1976, but instead of making use of a group for its underlying structure, makes use of a structure which is "almost" a group. The method is an extension of the recent ideas of Scheidler, Buchmann and Williams, but, because it is implemented in these function fields, several of the difficulties with their protocol can be eliminated. A detailed description of the protocol is provided, together with a discussion of the algorithms needed to effect it. 1 Introduction Conventional or one-key cryptosystems are still the secure communication schemes of choice for many installations. This is because they are both fast and sufficiently secure for most applications. The real difficulty in employing such cryptosystems is the problem of securely transmitting the key between communicants. In 1976, Diffie and..

Key-exchange in real quadratic congruence function fields

We show how the theory of real quadratic congruence function fields can be used to produce a secure key distribution protocol. The technique is similar to that advocated by Diffie and Hellman in 1976, but instead of making use of a group for its underlying structure, makes use of a structure which is “almost ” a group. The method is an extension of the recent ideas of Scheidler, Buchmann and Williams, but, because it is implemented in these function fields, several of the difficulties with their protocol can be eliminated. A detailed description of the protocol is provided, together with a discussion of the algorithms needed to effect it.