Encyclopedia of Cryptography and Security

2005 Edition
| Editors: Henk C. A. van Tilborg

Substitution–Permutation (SP) Network

  • Alex Biryukov
Reference work entry
DOI: https://doi.org/10.1007/0-387-23483-7_420

Shannon [1] suggested to use several mixing layers interleaving substitutions and permutations to build strong block ciphers. Such design is called a substitution–permutation sandwich or a substitution-permutation network (SPN). Although weak on its own, a line of substitutions followed by a permutation has good “mixing” properties: substitutions add to local confusion and permutation “glues” them together and spreads (diffuses) the local confusion to the more distant subblocks (see also substitutions and permutations). If one considers flipping a single bit at the input of such a network, it effects the m output bits of particular S-box which in turn are sent to different S-boxes by a permutation. Thus inputs/outputs of up to m S-boxes would be effected by the avalancheof change. These are again permuted into different S-boxes, covering almost all the S-boxes of the network. On the output of such network about half of the bits are effected by change and are flipped and about half of...

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  1. [1]
    Shannon, C.E. (1949). “Communication theory of secrecy system.” Bell System Technical Journal, 28, 656–715.MathSciNetGoogle Scholar

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© International Federation for Information Processing 2005

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  • Alex Biryukov

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