The implementation calls the secp256k1_modinvNN_jacobi_var code, falling back
to computing a square root in the (extremely rare) case it failed converge.
This introduces variants of the divsteps-based GCD algorithm used for
modular inverses to compute Jacobi symbols. Changes compared to
the normal vartime divsteps:
* Only positive matrices are used, guaranteeing that f and g remain
positive.
* An additional jac variable is updated to track sign changes during
matrix computation.
* There is (so far) no proof that this algorithm terminates within
reasonable amount of time for every input, but experimentally it
appears to almost always need less than 900 iterations. To account
for that, only a bounded number of iterations is performed (1500),
after which failure is returned. In VERIFY mode a lower iteration
count is used to make sure that callers exercise their fallback.
* The algorithm converges to f=g=gcd(f0,g0) rather than g=0. To keep
this test simple, the end condition is f=1, which won't be reached
if started with non-coprime or g=0 inputs. Because of that we only
support coprime non-zero inputs.
d21647520532957a78027be1ab606b814a2ec720 test secp256k1_i128_to_i64 (Russell O'Connor)
4bc429019dc4bff6af0f9824ad6ab6745f09f8ba Add a secp256k1_i128_to_u64 function. (Russell O'Connor)
Pull request description:
I wanted to experiment with what would be required to split up `secp256k1_i128_to_i64` between those cases when a signed 64 bit value is being demoted, versus an unsigned 64 bit value is being extracted from the lower bits, and this is the result.
I'm not sure this is a useful PR, so feel free to close it. However, since it is already written, I figured it is worth at least discussing.
ACKs for top commit:
sipa:
utACK d21647520532957a78027be1ab606b814a2ec720
real-or-random:
ACK d21647520532957a78027be1ab606b814a2ec720
Tree-SHA512: 41dbb1d33b3078bee8e71a838cfad6f1859c0bba602ae061259add8e9e8ea5aa482daa41de79dbd7433ddbef4a0bc52757f3c45d63acc9c0eb05aa3ca891b922
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>
The vector has been taken from https://www.di-mgt.com.au/sha_testvectors.html.
It can be independently verified using the following Python code.
```
h = hashlib.sha256()
for i in range(1_000_000):
h.update(b'a')
print(h.hexdigest())
```
070e772211b3fcd297577b90b56bbf7a5cfbd0a3 Faster fixed-input ecmult tests (Pieter Wuille)
Pull request description:
Given how much #920 slowed down the tests with low iteration count, replace it with 3 different similar test:
* count >= 1: a test with 1024 multiplies that tests any pattern of 6 bits in windows not more than 20 bits wide
* count >= 3: a test with 2048 multiplies that tests any pattern of 8 consecutive bits
* count >= 35: the old test (which effectively tests all 2-bit patterns)
ACKs for top commit:
robot-dreams:
ACK 070e772211b3fcd297577b90b56bbf7a5cfbd0a3, the addition of the `CONDITIONAL_TEST` macro is nice.
real-or-random:
ACK 070e772211b3fcd297577b90b56bbf7a5cfbd0a3
Tree-SHA512: b4ccca42c71fcd1baa7143f73d1c3ac9d012c296485164a03341dbeee02e4ba9f7c7ad6b441923a5fe0286c97eff60815033adb4e1d30b3ef08bcb79590327ff
3d7cbafb5fd7f152fc47dc907af5df03150accc0 tests: Fix test whose result is implementation-defined (Tim Ruffing)
Pull request description:
A compiler may add struct padding and fe_cmov is not guaranteed to
preserve it.
On the way, we restore the name of the function. It was mistakenly
renamed in 6173839c90553385171d560be8a17cbe167e3bef using
"search and replace".
ACKs for top commit:
robot-dreams:
ACK 3d7cbafb5fd7f152fc47dc907af5df03150accc0
sipa:
utACK 3d7cbafb5fd7f152fc47dc907af5df03150accc0
Tree-SHA512: f8bb643d4915e9ce9c4fe45b48a2878f6cf1f29e654be1c150cdf65c6959cf65f8491928cf098da5a01f1d488ba475914905ca96b232abed499eb6ed65e53fb8
A compiler may add struct padding and fe_cmov is not guaranteed to
preserve it.
On the way, we improve the identity check such that it covers the
VERIFY struct members.
