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I've heard in some lecture that the weak keys in DES implies the existence of $2^{32}$ fixed points in the algorithm, i.e. that $DES_k(x)=x$ for $2^{32}$ such $x$'s.

I couldn't find anything about that issue, can you give some reference or explain it here?

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You want an explanation of why DES has weak keys or of what the issue is with having weak keys? I'm assuming the former (as the latter should be obvious), but your question is a little unclear. – mikeazo Dec 19 '14 at 19:04
@mikeazo: The DES weak keys have been discussed in this question, but I think what Bush is asking about the existence of fixed points for those weak keys, as discussed e.g. here and here. – Ilmari Karonen Dec 19 '14 at 22:47
@IlmariKaronen those links are exactly what I've been looking for :) I've only read the beginning though. You can write it as answer. – Bush Dec 21 '14 at 1:16

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