The plugboard provides a new layer of security for the enigma but why can we only swap at most 10 letters? I only found things like "10 was the most common." but why stop there? Isn't adding more going to provide more security?

At first, I thought it was not going to add more complexity at one point, because swapping two letters that have already been swapped by the rotors is not going to change anything. But after a rotor does a single turn, that wouldn't matter anymore.

  • $\begingroup$ No, it doesn't. It is just a fixed permutation on the view of the analyzer. $\endgroup$
    – kelalaka
    Commented Feb 15, 2021 at 11:07
  • 1
    $\begingroup$ That's explained in some detail there. Suggestion: make an answer out of this material. TLDR: it's a design compromise between security and ease of setup. Functionality in practice takes precedence over security, thus security that works must be convenient. $\endgroup$
    – fgrieu
    Commented Feb 15, 2021 at 12:34
  • $\begingroup$ Presumably they could only have a maximum of 13 $\endgroup$ Commented Feb 15, 2021 at 15:21
  • $\begingroup$ @user253751 What's your point? $\endgroup$ Commented Sep 12, 2022 at 19:03
  • $\begingroup$ @fgrieu The number of plugs which maximizes the possible layouts is 11 (which is shown in a table on the page you linked to). Surely you would agree that the difference in hassle between using 10 plugs and 11 is negligible. For that matter the difference between 10 and 13 is also all but meaningless. $\endgroup$ Commented Sep 12, 2022 at 19:10


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