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docs: Correct proven-primes side channel risk.

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After reading Simon's wishlist write-up 'rsa-gen-side-channels'.
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Jacob Nevins 2022-01-12 01:15:55 +00:00
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@ -177,12 +177,14 @@ are prime, because it generates the output number together with a
proof of its primality. This takes more effort, but it eliminates that proof of its primality. This takes more effort, but it eliminates that
theoretical risk in the probabilistic method. theoretical risk in the probabilistic method.
There in one way in which PuTTYgen's proven-primes method is not There in one way in which PuTTYgen's \q{proven primes} method is not
strictly better than its probable-primes method. If you use PuTTYgen strictly better than its \q{probable primes} method. If you use
to generate RSA or DSA keys on a computer that is potentially PuTTYgen to generate an RSA key on a computer that is potentially
susceptible to timing- or cache-based \i{side-channel attacks}, such susceptible to timing- or cache-based \i{side-channel attacks}, such
as a shared computer, the \q{probable primes} method is designed to as a shared computer, the \q{probable primes} method is designed to
resist such attacks, whereas the \q{proven primes} methods are not. resist such attacks, whereas the \q{proven primes} methods are not.
(This is only a concern for RSA keys; for other key types, primes
are either not secret or not involved.)
You might choose to switch from probable to proven primes if you have You might choose to switch from probable to proven primes if you have
a local security standard that demands it, or if you don't trust the a local security standard that demands it, or if you don't trust the