An Attempt to Cryptanalyze A Partially Known Cipher Algorithm

This paper presents an empirical crypt-analytical method to analyse a partially known cipher algorithm. During cipher evaluation, it is always a challenge to make any decision on the strength of a partially known cipher algorithm, and if the algorithm is suitable for deployment. The core concept will be presented first, followed by an example to illustrate the idea. The idea is to focus on one input bit at a time using a known keystream attack, assuming this bit is independent from the rest. By computing the statistics of related keystream bits and using the correlation method, one can derive this input bit with certain confidence. keywords Linear Feedback Shift Register, Correlation Coefficient, Stream Cipher.