# Mimic function

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A '''mimic function''' changes a file <math>A</math> so it assumes the statistical properties of another file <math>B</math>. That is, if <math>p(t,A)</math> is the probability of some substring <math>t</math> occurring in <math>A</math>, then a mimic function <math>f</math>, recodes <math>A</math> so that <math>p(t,f(A))</math> approximates <math>p(t,B)</math> for all strings <math>t</math> of length less than some <math>n</math>. It is commonly considered to be one of the basic techniques for [hiding information](/source/Information_hiding), often called [steganography](/source/steganography). 

The simplest mimic functions use simple statistical models to pick the symbols in the output. If the statistical model says that item <math>x</math> occurs with [probability](/source/probability) <math>p(x,A)</math> and item <math>y</math> occurs with probability <math>p(y,A)</math>, then a random number is used to choose between outputting <math>x</math> or <math>y</math> with probability <math>p(x,A)</math> or <math>p(y,A)</math> respectively.

Even more sophisticated models use reversible [Turing machine](/source/Turing_machine)s.

==References==
* {{cite report | first = Peter | last = Wayner | author-link = Peter Wayner | title = Mimic Functions | publisher = Cornell University Department of Computer Science | id = TR 90-1176 | date = December 1990 | url = http://www.funet.fi/pub/crypt/old/mimic/mimic.text}}
* {{cite journal | first = Peter | last = Wayner | title = Mimic Functions | date = July 1992 | journal = Cryptologia | volume = 16 | number = 3 | pages = 193–214 | doi = 10.1080/0161-119291866883}}
* {{cite book | first = Peter | last = Wayner | title = Disappearing Cryptography | publisher = Morgan Kaufmann | isbn = 978-0123744791 | year = 2008 | edition = 3rd}}

Category:Steganography

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Adapted from the Wikipedia article [Mimic function](https://en.wikipedia.org/wiki/Mimic_function) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Mimic_function?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.