A mimic function changes a file ${\displaystyle A}$ so it assumes the statistical properties of another file ${\displaystyle B}$. That is, if ${\displaystyle p(t,A)}$ is the probability of some substring ${\displaystyle t}$ occurring in ${\displaystyle A}$, then a mimic function ${\displaystyle f}$, recodes ${\displaystyle A}$ so that ${\displaystyle p(t,f(A))}$ approximates ${\displaystyle p(t,B)}$ for all strings ${\displaystyle t}$ of length less than some ${\displaystyle n}$. It is commonly considered to be one of the basic techniques for hiding information, often called steganography.

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The simplest mimic functions use simple statistical models to pick the symbols in the output. If the statistical model says that item ${\displaystyle x}$ occurs with probability Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "http://localhost:6011/en.wikipedia.org/v1/":): {\displaystyle p(x,A)} and item ${\displaystyle y}$ occurs with probability Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "http://localhost:6011/en.wikipedia.org/v1/":): {\displaystyle p(y,A)} , then a random number is used to choose between outputting ${\displaystyle x}$ or ${\displaystyle y}$ with probability ${\displaystyle p(x,A)}$ or ${\displaystyle p(y,A)}$ respectively.

Even more sophisticated models use reversible Turing machines.

• Wayner, Peter (December 1990). Mimic Functions (Report). Cornell University Department of Computer Science. TR 90-1176.
• Wayner, Peter (July 1992). "Mimic Functions". Cryptologia. 16 (3): 193–214. doi:10.1080/0161-119291866883.
• Wayner, Peter (2008). Disappearing Cryptography (3rd ed.). Morgan Kaufmann. ISBN 978-0123744791.

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