I ran across their defining RFCs recently and noticed that each one
provides an explicit mathematical expression for the prime (since each
one is derived from the expansion of pi, with framing FFs and a
correction term to make it actually prime).
Those expressions can be re-evaluated trivially by spigot, so it seems
reasonable to add those spigot commands in comments. This also means
the comments contain citations for these primes in actual standards,
including both the hex digits and the mathematical expressions.
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!)
This clears up another large pile of clutter at the top level, and in
the process, allows me to rename source files to things that don't all
have that annoying 'ssh' prefix at the top.
sshblowf.h (as was) is 100% internal to that directory. And mpint_i.h
and ecc.h are specialist enough that it's reasonable to ask clients
outside the crypto directory to include them with a subdirectory path,
to hint that it's an unusual thing to be doing.
When preparing commit fca13a17b1, I redesigned the cmake test
function at the last minute, and apparently didn't quite get all the
call sites correctly rewritten. This one still omitted some of the
argument-type keywords, and had an obsolete parameter giving an
explicit name for a sub-library, which I later decided wasn't needed.
This applies to all of AES, SHA-1, SHA-256 and SHA-512. All those
source files previously contained multiple implementations of the
algorithm, enabled or disabled by ifdefs detecting whether they would
work on a given compiler. And in order to get advanced machine
instructions like AES-NI or NEON crypto into the output file when the
compile flags hadn't enabled them, we had to do nasty stuff with
compiler-specific pragmas or attributes.
Now we can do the detection at cmake time, and enable advanced
instructions in the more sensible way, by compile-time flags. So I've
broken up each of these modules into lots of sub-pieces: a file called
(e.g.) 'foo-common.c' containing common definitions across all
implementations (such as round constants), one called 'foo-select.c'
containing the top-level vtable(s), and a separate file for each
implementation exporting just the vtable(s) for that implementation.
One advantage of this is that it depends a lot less on compiler-
specific bodgery. My particular least favourite part of the previous
setup was the part where I had to _manually_ define some Arm ACLE
feature macros before including <arm_neon.h>, so that it would define
the intrinsics I wanted. Now I'm enabling interesting architecture
features in the normal way, on the compiler command line, there's no
need for that kind of trick: the right feature macros are already
defined and <arm_neon.h> does the right thing.
Another change in this reorganisation is that I've stopped assuming
there's just one hardware implementation per platform. Previously, the
accelerated vtables were called things like sha256_hw, and varied
between FOO-NI and NEON depending on platform; and the selection code
would simply ask 'is hw available? if so, use hw, else sw'. Now, each
HW acceleration strategy names its vtable its own way, and the
selection vtable has a whole list of possibilities to iterate over
looking for a supported one. So if someone feels like writing a second
accelerated implementation of something for a given platform - for
example, I've heard you can use plain NEON to speed up AES somewhat
even without the crypto extension - then it will now have somewhere to
drop in alongside the existing ones.
Similarly to 'utils', I've moved all the stuff in the crypto
build-time library into a source directory of its own, and while I'm
at it, split up the monolithic sshauxcrypt.c into its various
unrelated parts.
This is also an opportunity to remove the annoying 'ssh' prefix from
the front of the file names, and give several of them less cryptic
names.
