Applied Stream Ciphers in Mobile Communications

The reprinted Ph.D. research was done from 2001 to 2006 at EPFL, Switzerland. The author studying at LASEC under supervision of Prof. Serge Vaudenay, was in the early twenties then. With more than ten years of pioneering research in advance of cryptography and security, the author discovered that the main subject - noisy sparse Walsh-Hadamard Transform (WHT) is of greatest importance in cryptography. Independently, this emerging topic attracted much interdisciplinary research efforts and interests in signal processing, communications, during this time period. Loosely speaking, noisy sparse WHT refers to the case that the number of large Walsh coefficients is much smaller than the dimension while there exists a large number of small nonzero Walsh coefficients. Most recently, the author has the special opportunity of debating the topic's future directions with the world's top scientists in the fields. Though everyone agrees that the problem is so invaluable that it is suitable for submission to the nature journal, the debate is ongoing and is unlikely to end sooner. It is the author's main wish that the reprint of the thesis would encourage and stimulate further studies in academia.