Abstract

To date, elliptic curves offer the most efficient cryptographic solution. Particularly efficient among elliptic curves, are those defined over binary composite finite fields, such as GF ((2 r ) n ). These curves were no longer considered secure when, in 1998, Gerhard Frey innovated a concept which paved the road for the GHS attack. The idea behind the GHS attack is to map the Discrete Logarithm Problem (DLP) over such a curve to an equivalent DLP over the jacobian of another curve, defined over the smaller field GF (2 r ). In this thesis, we study the theoretical structure of the GHS attack for elliptic curves defined over fields of arbitrary characteristics. We study the GHS attack using general quadratic extensions for elliptic curves defined over composite fields of even characteristic and we estimate the genus of resulting function field. We also implement the GHS attack and present some computational results. Keywords . GHS Attack, Elliptic Curve Cryptography, Function Fields