From the course: Symmetric Cryptography Essential Training

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S-Box and P-Box

S-Box and P-Box

From the course: Symmetric Cryptography Essential Training

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S-Box and P-Box

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- [Instructor] We're taking the first big step into the structure of modern block ciphers. Now we'll talk about S-boxes and P-boxes. Substitution boxes and permutation boxes are key components of modern block ciphers. S-boxes are non-linear transformations of a few input bits that provide confusion and P-boxes simply shuffle the input bits around to provide diffusion as we've talked about before. So, the purpose of the S-box, as I said, is to provide confusion. This is a property I mentioned earlier that prevents the output from being easily converted back into the input. The table listed here has 16 possible input values, zero through 15, and these can be represented with four input bits. As far as I can tell, the four-bit output values here do not represent any sequence of arithmetic steps that operated on the input. I generated these randomly from random.org. Modern block ciphers will actually use several different S-boxes to further increase the difficulty of analyzing the cipher,…

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