[exim-dev] [Bug 1895] Default groups for DH possibly backdoo…

https://bugs.exim.org/show_bug.cgi?id=1895

--- Comment #11 from Jeremy Harris <jgh146exb@???> ---
The commit of https://bugs.exim.org/show_bug.cgi?id=1895#c5 includes, for the
RFC 7919 params, text "The group size is: q = (p-1)/2".

This matches a comment in
https://security.stackexchange.com/questions/94390/whats-the-purpose-of-dh-parameters
:-
"Finding the prime p means finding a value for p for which p=2q+1 holds, with q
being a prime. p is then called a safe prime."

Is this the q we're talking about?

If so, assuming the p for a parameter has been chosen as a "safe prime",
q is entirely dependent on p - which we have from the PEM representation.
Why do we care about loading q?

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