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Feistel Model

CS 465. Feistel Model. Last Updated: Aug 27, 2013. Feistel Cipher Structure. Described by Horst Feistel (IBM) in 1973 Many symmetric encryption algorithms use this structure DES, IDEA, Blowfish, RC6, MARS, Twofish Not AES Substitution-permutation network Block cipher

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Feistel Model

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  1. CS 465 Feistel Model Last Updated: Aug 27, 2013

  2. Feistel Cipher Structure • Described by Horst Feistel (IBM) in 1973 • Many symmetric encryption algorithms use this structure • DES, IDEA, Blowfish, RC6, MARS, Twofish • Not AES • Substitution-permutation network • Block cipher • Features – block size, key size, number of rounds, sub-key generation algorithm, round function • Decryption is essentially the same as encryption • Input: ciphertext • Use sub-keys in reverse order • Sources • Stallings NSE Fig 2.2 (next slide) • Wikipedie: Feistel Cipher

  3. Source: Network Security Essentials (Stallings)

  4. Source: Network Security Essentials (Stallings)

  5. The Feistel Network Round Function (F) • The Feistel network is guaranteed to be reversible if we can reconstruct its inputs, which are derived from the key • It doesn’t matter how complicated or simple F is or if it can be inverted

  6. Proof of Feistel Network • On the board • What is the disadvantage of a 1-round Feistel network?

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