This document provides details about the structure and design of the Data Encryption Standard (DES) cipher. It describes the operation of DES, including the use of substitution boxes (S-boxes) and permutation boxes (P-boxes) to provide confusion and diffusion in the cipher. It also discusses some weaknesses that have been found in DES, such as specific weak keys that allow plaintext to be recovered more easily. The document aims to explain the design principles and security properties of DES.