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Feistel Networks

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Modern Cryptography

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Abstract

Symmetric ciphers are commonly used for file encryption, storage encryption, and encrypting data in transit. The conceptual basis for symmetric ciphers is relatively easy to understand. The Feistel function (also called a Feistel network) is the foundation for many symmetric cryptographic algorithms. Feistel networks have existed since the 1970s. The term Feistel network defines a structure for creating symmetric ciphers. There are many cryptographic algorithms that utilize this structure. This makes Feistel functions an important structure to understand. We will first examine the general structure of the Feistel network and then explore numerous specific examples. Some algorithms will be covered in more detail than others, based on how widely those algorithms are used.

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Author information

Authors and Affiliations

  1. Georgetown University and Vanderbilt University, Plano, USA

    Chuck Easttom

Authors
  1. Chuck Easttom
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Test Your Knowledge

Test Your Knowledge

  1. 1.

    _____ has an 80-bit key and is an unbalanced cipher.

  2. 2.

    ____ is a Feistel cipher using variable length key sizes from 32 bits to 448 bits.

  3. 3.

    The following formulas describe what?

$$ {\displaystyle \begin{array}{l}{a}^{\prime }=a+b\kern0.62em \left(\operatorname{mod}\kern0.62em {2}^n\right)\\ {}{b}^{\prime }=a+2b\kern0.62em \left(\operatorname{mod}\kern0.62em {2}^n\right)\end{array}} $$

___________

  1. 4.

    Which of the following is a Russian cipher much like DES?

    1. (a)

      Blowfish

    2. (b)

      CAST

    3. (c)

      FEAL

    4. (d)

      GOST

  2. 5.

    What is the proper term for the algorithm used to derive sub keys (round keys) from the cipher key?

    1. (a)

      Key algorithm

    2. (b)

      Sub key generator

    3. (c)

      Key schedule

    4. (d)

      Round key generator

  3. 6.

    Which algorithm described in this chapter was an unbalanced Feistel cipher used with the clipper chip?

    ________

  4. 7.

    ________ used input whitening and output whitening as well as a pseudo-Hadamard transform.

  5. 8.

    _____ divides the input into the round function into four 32-bit words labeled A, B, C, and D and then uses three phases: the 16-round phase that is the core of the algorithm and the pre- and post-phases of forward and backward mixing.

  6. 9.

    With a 128-bit key, Camellia uses ___ rounds, but with the 192- or 256-bit key, it uses ___ rounds.

  7. 10.

    With ________, block of plain text is XOR’d with the previous cipher text block before being encrypted.

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Cite this chapter

Easttom, C. (2022). Feistel Networks. In: Modern Cryptography. Springer, Cham. https://doi.org/10.1007/978-3-031-12304-7_6

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  • DOI: https://doi.org/10.1007/978-3-031-12304-7_6

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  • Publisher Name: Springer, Cham

  • Print ISBN: 978-3-031-12303-0

  • Online ISBN: 978-3-031-12304-7

  • eBook Packages: Computer ScienceComputer Science (R0)

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