!!! Overview
[{$pagename}] is a [function] that is easy to compute in one direction, yet [difficult to compute|Computational Hardness Assumption] in the opposite direction (finding its inverse) without special information, called the "[trapdoor]". [{$pagename}] are widely used in [cryptography].

!! [RSA] Assumption
In this [example], having the inverse of e modulo φ(n), the Euler's totient function of n, is the trapdoor:

f(x)=x%%sup e %% mod (n)

If the [factorization] is known, 
* φ(n) can be computed, 
* so then the inverse d of e can be computed d = e−1 mod φ(n), 
* and then given y = f(x) we can find x = yd mod n = xed mod n = x mod n. 
Its hardness follows from RSA assumption.!! More Information
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