Which parameters and design choices determine the actual algorithm of a Feistel cipher?

  • Block size: Larger block sizes mean greater security but reduced encryption/decryption speed. A block size of 64 bits is a reasonable tradeoff and has been nearly universal in block cipher design.However, the new AES uses a 128-bit block size.
  • Key size:Larger key size means greater security but may decrease encryption/decryption speed.Key sizes of 64 bits or less are now widely considered to be inadequate, and 128 bits has ecome a common size.
  • Number of rounds: The essence of the Feistel cipher is that a single round offers inadequate security but that multiple rounds offer increasing security.A typical size is 16 rounds.
  • Subkey generation algorithm: Greater complexity in this algorithm should lead to greater difficulty of cryptanalysis.
  • Round function: Again, greater complexity generally means greater resistance to cryptanalysis.


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