Editing Confusion and diffusion (section)

{{Short description|Properties of the operation of a secure cipher}}
{{More citations needed|date=April 2009}}

In [[cryptography]], '''confusion''' and '''diffusion''' are two properties of a secure [[cipher]] identified by [[Claude Elwood Shannon|Claude Shannon]] in his 1945 classified report ''A Mathematical Theory of Cryptography''.<ref>{{Cite book|title=Model Based Inference in the Life Sciences: A Primer on Evidence|date=2008-01-01|publisher=Springer New York|isbn=9780387740737|pages=51–82|language=en|doi=10.1007/978-0-387-74075-1_3|chapter = Information Theory and Entropy}}</ref>  These properties, when present, work together to thwart the application of [[statistics]], and other methods of [[cryptanalysis]].

Confusion in a [[symmetric cipher]] is obscuring the local correlation between the input ([[plaintext]]), and output ([[ciphertext]]) by varying the application of the [[Key (cryptography)|key]] to the data, while diffusion is hiding the plaintext statistics by spreading it over a larger area of ciphertext.{{sfn|Stamp|Low|2007|p=182}} Although ciphers can be confusion-only ([[substitution cipher]], [[one-time pad]]) or diffusion-only ([[transposition cipher]]), any "reasonable" [[block cipher]] uses both confusion and diffusion.{{sfn|Stamp|Low|2007|p=182}} These concepts are also important in the design of [[cryptographic hash function|cryptographic hash functions]], and [[pseudorandom number generator]]s, where decorrelation of the generated values is the main feature. Diffusion (and its [[avalanche effect]]) is also applicable to [[non-cryptographic hash function]]s.