I've moved it from mpunsafe.c into the main mpint.c, and renamed it
mp_mod_known_integer, because now it manages to avoid leaking
information about the mp_int you give it.
It can still potentially leak information about the small _modulus_
integer - hence the word 'known' in the new function name. This won't
be a problem in any existing use of the function, because it's used
during prime generation to check divisibility by all the small primes,
and optionally also check for residue 1 mod the RSA public exponent.
But all those values are well known and not secret.
This removes one source of side-channel leakage from prime generation.
This code base has always been a bit confused about which spelling it
likes to use to refer to that signature algorithm. The SSH protocol id
is "ssh-dss". But everyone I know refers to it as the Digital
Signature _Algorithm_, not the Digital Signature _Standard_.
When I moved everything down into the crypto subdir, I took the
opportunity to rename sshdss.c to dsa.c. Now I'm doing the rest of the
job: all internal identifiers and code comments refer to DSA, and the
spelling "dss" only survives in externally visible identifiers that
have to remain constant.
(Such identifiers include the SSH protocol id, and also the string id
used to identify the key type in PuTTY's own host key cache. We can't
change the latter without causing everyone a backwards-compatibility
headache, and if we _did_ ever decide to do that, we'd surely want to
do a much more thorough job of making the cache format more sensible!)
