This report provides a comprehensive analysis of the Data Encryption Standard (DES) and the Advanced Encryption Standard (AES), two widely used symmetric-key encryption algorithms. It delves into the history, structure, and working principles of both algorithms, highlighting their strengths and weaknesses. The report also examines the security vulnerabilities of DES and the advancements made by AES in addressing these vulnerabilities. Finally, it concludes with a comparison of the two algorithms and their suitability for modern cryptographic applications.