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Here: http://safecurves.cr.yp.to/ , I read that the NIST P-256 elliptic-curve is not safe.

The article lists several aspects (off-curve point, side-channel, etc.) where implementing P256 can fail the security, how should we understand these?

I think this is valid for encrypting, but are these also valid for signing?

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    $\begingroup$ P256 is secure, it just lacks some nice-to-have features that make writing a fast and secure implementation easier. $\endgroup$ – CodesInChaos Oct 13 '17 at 7:11
  • $\begingroup$ Reading the article reminds me why we should not implement our own crypto but use libraries written by people who know what/how they are doing. $\endgroup$ – gusto2 Oct 13 '17 at 7:33
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    $\begingroup$ Claiming NIST curves as insecure but some obscure never–heard–of curves as secure is IMHO complete bullshit. $\endgroup$ – user27950 Oct 13 '17 at 15:02
  • $\begingroup$ As far as I know these attacks are for any use of the curve in crypto; i.e. it is not tied to any specific use case such as encryption / signing. $\endgroup$ – Maarten - reinstate Monica Jun 14 '18 at 11:47
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Quoting CodesInChaos:

P256 is secure, it just lacks some nice-to-have features that make writing a fast and secure implementation easier.

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