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I'm learning DES, but I have a question.

When the plain text input, it gets a permutation by a table. Table

But, I don't know why 01 -> 58 / 02 -> 50. Is there any special rule or principle of it? or was it just set by the creator of DES?

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  • $\begingroup$ That regularity comes from the initial implementation of DES in hardware: the plaintext was loaded sequentially as 8 octets, with at each of 8 loads each of the 8 bits of an octet entering an 8-bit shift register, 4 of which for L, 4 of which for R, with these 8 shift registers clocked simultaneously. A natural software implementations can mimic that (among other possibilities). $\endgroup$
    – kodlu
    May 26, 2021 at 2:52
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    $\begingroup$ possible duplicate see answer (partly quoted above) to crypto.stackexchange.com/questions/10542/… $\endgroup$
    – kodlu
    May 26, 2021 at 2:53

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