Feistel networks are one of the easiest ways to build pseudorandom permutations. Thanks to this property, many secret key algorithms (symmetric ciphers) have been designed as Feistel networks, and it is possible to design many others. The most famous of them is probably the Data Encryption Standard algorithm, a former U.S. National Institute of Standards and Technology standard block cipher, originally released in 1977. This book provides a comprehensive survey of different kinds of Feistel ciphers, including their definitions and mathematical/computational properties. Topics and features: Description of the best-known attacks against the Data Encryption Standard algorithm, including linear cryptanalysis, differential cryptanalysis, and Davies’ attack Generic attacks against balanced, unbalanced, and generalized Feistel networks Up-to-date security analysis of balanced Feistel networks Quantum cryptanalysis of Feistel networks The results consolidated in this volume provide an overview of this important cipher design to researchers and practitioners willing to understand the design and security analysis of Feistel ciphers.