Flags for constant-time masking rely
on the values being exactly 0 or 1 rather
than 0 or true. Add VERIFY_CHECKs to enforce
in VERIFY builds as a preventative
measure and add documentation where relevant.
Now that the `VERIFY_CHECK` compiles to empty in non-VERIFY mode, blocks
that only consist of these macros don't need surrounding `#ifdef VERIFY`
conditions anymore.
At some places intentional blank lines are inserted for grouping and
better readadbility.
- `secp256k1_scalar_set_int` in scalar_low uses input mod EXHAUSTIVE_TEST_ORDER
- directly store s in sig64 without reducing it mod the group order for testing
8e142ca410 Move `SECP256K1_INLINE` macro definition out from `include/secp256k1.h` (Hennadii Stepanov)
77445898a5 Remove `SECP256K1_INLINE` usage from examples (Hennadii Stepanov)
Pull request description:
From [IRC](https://gnusha.org/secp256k1/2023-01-31.log):
> 06:29 \< hebasto\> What are reasons to define the `SECP256K1_INLINE` macro in user's `include/secp256k1.h` header, while it is used internally only?
> 06:32 \< hebasto\> I mean, any other (or a new dedicated) header in `src` looks more appropriate, no?
> 06:35 \< sipa\> I think it may just predate any "utility" internal headers.
> 06:42 \< sipa\> I think it makes sense to move it to util.h
Pros:
- it is a step in direction to better organized headers (in context of #924, #1039)
Cons:
- code duplication for `SECP256K1_GNUC_PREREQ` macro
ACKs for top commit:
sipa:
utACK 8e142ca410
real-or-random:
utACK 8e142ca410
Tree-SHA512: 180e0ba7c2ef242b765f20698b67d06c492b7b70866c21db27c18d8b2e85c3e11f86c6cb99ffa88bbd23891ce3ee8a24bc528f2c91167ec2fddc167463f78eac
Apparently clang 15 is able to compile our cmov code into a branch,
at least for fe_cmov and fe_storage_cmov. This commit makes the
condition volatile in all cmov implementations (except ge but that
one only calls into the fe impls).
This is just a quick fix. We should still look into other methods,
e.g., asm and #457. We should also consider not caring about
constant-time in scalar_low_impl.h
We should also consider testing on very new compilers in nightly CI,
see https://github.com/bitcoin-core/secp256k1/pull/864#issuecomment-769211867
Apparently clang 15 is able to compile our cmov code into a branch,
at least for fe_cmov and fe_storage_cmov. This commit makes the
condition volatile in all cmov implementations (except ge but that
one only calls into the fe impls).
This is just a quick fix. We should still look into other methods,
e.g., asm and #457. We should also consider not caring about
constant-time in scalar_low_impl.h
We should also consider testing on very new compilers in nightly CI,
see https://github.com/bitcoin-core/secp256k1/pull/864#issuecomment-769211867
There were several places where the code was non-constant time
for invalid secret inputs. These are harmless under sane use
but get in the way of automatic const-time validation.
(Nonce overflow in signing is not addressed, nor is s==0 in
signing)
Thanks to elichai2 who noted that the literal '1' is a signed integer, and that shifting a signed 32-bit integer by 31 bits causes an overflow and yields undefined behaviour.
While 'scalar_low_impl''s 'secp256k1_scalar_cadd_bit' is only used for testing purposes and currently the 'bit' parameter is only 0 or 1, it is better to avoid undefined behaviour in case the used domain of 'secp256k1_scalar_cadd_bit' expands.
Identifiers starting with an underscore and followed immediately by a capital letter are reserved by the C++ standard.
The only header guards not fixed are those in the headers auto-generated from java.
If you compile without ./configure --enable-exhaustive-tests=no,
this will create a binary ./exhaustive_tests which will execute
every function possible on a group of small order obtained by
moving to a twist of our curve and locating a generator of small
order.
Currently defaults to order 13, though by changing some #ifdefs
you can get a couple other ones. (Currently 199, which will take
forever to run, and 14, which won't work because it's composite.)
TODO exhaustive tests for the various modules
