Design and analysis of efficient stream ciphers for constrained environments – RAPIDE

digital form raise many questions concerning the security that can be guaranteed in this context for the
information that has to be protected. This security lies at its root on the existence of ciphers that are
supposed to be secure, reliable (even perfect) and efficient, which is clearly not the case in many situations.
Hence the security of ciphers is a key-question that cannot be ignored when it comes to security in the
digital world.
A cipher aims at guaranteeing the confidentiality of a message, which means that transmitted information
can only be read by the legitimate recipient. Public key cryptography is undoubtedly the expected answer
to the problem of sharing a secret key over an insecure channel but it does not mean that secret key
techniques are becoming obsolete. On the contrary, they are the only ones adapted to the needs of high
bandwidths or constrained environments (in terms of power consumption, memory or number of gates)
that are encountered in many standard situations.
This project proposition concerns stream ciphers — named by opposition to block ciphers — and especially
stream ciphers with an internal state governed by a non-linear transition function. We will
particularly draw our attention to ciphers whose characteristics make them especially fit constrained environments.
These systems were not particularly studied up to now but could be good candidates to the
replacement of stream ciphers based on linear transition functions (LFSR based) whose security tends to
be less and less satisfying. The expected results of the project will be practical as well as theoretical and
will concerns both design and analysis of such stream ciphers.