Search

Supersingular elliptic curves have played an important role in the development of elliptic curve crytography. Scott Vanstone introduced the first author to elliptic curve cryptography, a subject that continues to be a rich source of interesting problems, results and applications. One important fact about supersingular elliptic curves is that the number of rational points is tightly constrained to a small number of possible values. In this paper we present some similar results for curves of higher genus. We also present an application to the problem of determining abelian varieties that occur as jacobians.

In the early 1980s Dan Hughes wrote two papers on semi-symmetric 3-designs, which are closely related to quasi-3 designs. In 1973 Peter Cameron asked whether the dual design of any quasi-3 design must also be quasi-3. In this article, we answer that question. We give some general constructions of quasi-3 designs which enable us to give the answer. The answer is no.

Using Hadamard matrices and mutually orthogonal Latin squares, we construct two new quasi-symmetric designs, with parameters 2 ? (66,30,29) and 2 ? (78,36,30). These are the first examples of quasi-symmetric designs with these parameters. The parameters belong to the families 2 ? (2u 2 ? u,u 2 ? u,u 2 ? u ? 1) and 2 ? (2u 2 + u,u 2,u 2 ? u), which are related to Hadamard parameters. The designs correspond to new codes meeting the Grey---Rankin bound.

We prove a conjecture of Brouwer, namely that a 2-(28,4,1) design has 2–rank at least 19, with equality occuring if and only if the design is the Ree unital. We give a similar characterization of the Hermitian unital.

Certain nonlinear binary codes contain more codewords than any comparable linear code presently known. These include the Kerdock and Preparata codes, which exist for all lengths 4^m ≥ 16. At length 16 they coincide to give the Nordstrom-Robinson code. This paper constructs a nonlinear (64, 2^37, 12) code as the binary image, under the Gray map, of an extended cyclic code defined over the integers modulo 4 using Galois rings. The Nordstrom-Robinson code is defined in this same way, and like the Nordstrom-Robinson code, the new code is better than any linear code that is presently known.