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Security Fundamentals & Crypto · Advanced

Feistel Network

Block cipher structure that splits data into halves and applies repeated rounds of a round function and swapping.

Definition

Feistel networks allow the same structure to be used for encryption and decryption by reversing the round keys. DES, 3DES, Blowfish, and Twofish (a Feistel variant) use this design. AES instead uses a substitution-permutation network.

Example

DES runs 16 Feistel rounds on 32-bit halves of each 64-bit block.

Exam tip

AES is not a Feistel cipher; DES is.

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