Cryptosystems based on continued fractions

In this paper, we propose three secret-key cryptosystems based on the theory of continued fractions for possible use in cryptographic applications. We present and analyze a sequence of rational numbers, whose randomness properties are demonstrated using well-know statistical packages. Accordingly, we propose a cryptosystem that acts on a group of characters at a time. Then, a binary keystream generator, generating keystreams with good randomness properties, is suggested for possible use in stream cipher applications. Finally, we propose a cryptosystem related to the well-known Baptista's cryptosystem that is based on a chaotic logistic map. However, our cryptosystem is based on the theory of continued fractions, and is shown to exhibit better properties and decrypts information much faster than Baptista's cryptosystem. Copyright (C) 2010 John Wiley & Sons, Ltd.