Permutation box (cryptography)

In cryptography, a P-box is a bit-trapping method used to swap or transpose bits through S-box inputs, waiting for broadcast while transposing. An example of a 64-bit P-Box that spreads the S-Box input to as many S-Box as possible.

In block ciphering, the S-Box and P-Box often mark the relationship between the message and hard-to-understand encryption (see Shannon's property of confusion). P-Boxes are typically classified as compression, expansion, and address, depending on whether the number of output bits is less than, greater than, or equal to the number of input bits. Only the P-Box address are invertible.

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