Cryptanalysis and Design of Stream Ciphers

This thesis presents some novel results on the cryptanalysis and design of stream ciphers. The first part of the thesis introduces various stream ciphers design and cryptanalysis techniques. The second part of the thesis gives the cryptanalysis of seven stream ciphers. The properties of addition are exploited in the cryptanalysis of two stream ciphers: the differential-linear cryptanalysis against Phelix and the fast correlation attack on ABC v2. Resynchronization attacks are applied against several stream ciphers – DECIM, WG, LEX, Py and Pypy. Various cryptanalytic approaches (linear, differential and slide attacks) are used in these attacks. The third part of the thesis is on the design of stream ciphers. We demonstrate that strong and secure stream ciphers can be designed using nonlinear state updating function and nonlinear output function. The design of stream ciphers HC-256 and HC-128 are presented.