A modified external-key cryptosystem for digital implementation

Over the past few years, new cryptographic algorithms, based on chaotic maps, have been proposed in order to give an alternative to classical methods. In this paper we propose some ideas to improve the performances of this kind of techniques based on the Lyapunov exponent for setting the parameter interval and on feedback mechanism which uses the most sensitive part of the value of the chaotic map, when a digital implementation is designed.