SELF-SYNCHRONIZING STREAM CIPHERS AND DYNAMICAL SYSTEMS: STATE OF THE ART AND OPEN ISSUES
Gilles Millérioux, P. Guillot · International Journal of Bifurcation and Chaos · 2010
Dynamical systems play a central role in the design of symmetric cryptosystems. Their use has been widely investigated both in "chaos-based" private communications and in stream ciphers over finite fields. In the former case, they take the form of automata named Moore or Mealy machines. The main charateristic of stream ciphers lies in that they require synchronization of complex sequences generated by the dynamical systems involved both at the transmitter and the receiver ends. In this paper, we focus on a special class of symmetric ciphers, namely the Self-Synchronizing Stream Ciphers. Indeed, such ciphers have not been seriously explored so far although they show interesting properties of synchronization which could make them very appealing in practice. We review and compare different design approaches which have been proposed in the open literature, and fully-specified algorithms are detailed for illustration purposes. Open issues related to the validation and the implementation of Self-Synchronizing Stream Ciphers are developed. We highlight the reason why some concepts borrowed from control theory appear to be useful to this end.