This change eases the use of alternate build systems by moving
the variables in `src/libsecp256k1-config.h` to compiler macros
for each invocation, preventing duplication of these variables
for each build system.
Co-authored-by: Ali Sherief <ali@notatether.com>
Instead of supporting configuration of the field and scalar size independently,
both are now controlled by the availability of a 64x64->128 bit multiplication
(currently only through __int128). This is autodetected from the C code through
__SIZEOF_INT128__, but can be overridden using configure's
--with-test-override-wide-multiply, or by defining
USE_FORCE_WIDEMUL_{INT64,INT128} manually.
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)
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
This has the effect of making `secp256k1_scalar_mul_shift_var` constant
time in both input scalars. Keep the _var name because it is NOT constant
time in the shift amount.
As used in `secp256k1_scalar_split_lambda_var`, the shift is always
the constant 272, so this function becomes constant time, and it
loses the `_var` suffix.
Designed with clear separation of the wNAF conversion, precomputation
and exponentiation (since the precomp at least we will probably want
to separate in the API for users who reuse points a lot.
Future work:
- actually separate precomp in the API
- do multiexp rather than single exponentiation
