Linear System Solution Attack on a Nonlinear Stream Cipher is a research study authored by Louay Flaieh Hasan and Malek Albezuirat. The study investigates cryptanalysis techniques for analyzing nonlinear stream cipher systems based on Linear Feedback Shift Registers (LFSRs), which represent a fundamental component in many modern cryptographic applications, including communication and secure data transmission systems. The research introduces a three-stage analytical approach for attacking the running key generator (RKG) by transforming the LFSR structure into a system of linear equations, evaluating the uniqueness of the obtained solution, and solving the system using classical mathematical techniques such as Gaussian elimination. The well-known Geffe generator was adopted as a case study to demonstrate the effectiveness of the proposed approach in recovering the initial states of the LFSRs. The findings highlight the importance of mathematical modeling and linear system analysis in evaluating the security level of nonlinear stream ciphers and provide insights into potential vulnerabilities associated with LFSR-based cryptographic designs. Keywords: Stream cipher, Cryptanalysis, Running key generator (RKG), Linear Feedback Shift Register (LFSR), Linear equation system, Feedback function, Combiner function, Geffe generator, Gaussian elimination, Cryptographic security.