Pseudorandom permutation

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In cryptography, a pseudorandom permutation, abbreviated PRP, is an idealized block cipher. It means the cipher that cannot be distinguished from a random permutation (that is, a permutation selected at random with uniform probability, from the family of all permutations on blocks of that size) with less computational effort than specified by the cipher's security parameters (this usually means the effort required should be about the same as a brute force search through the cipher's key space). If a distinguishing algorithm exists that achieves significant advantage with less effort than the security parameter specifies, the cipher is considered broken at least in a certificational sense, even if such a break doesn't immediately lead to a practical security failure.