Previous behaviour would not initialize r->y values in the case where infinity is passed in.
Furthermore, the previous behaviour wouldn't initialize anything in the case where all inputs were infinity.
This makes a difference with mingw builds on Wine, where the subsequent
fread() may abort early in the default text mode.
The Microsoft C docs say:
"In text mode, CTRL+Z is interpreted as an EOF character on input."
be0609fd54af95a15b76cea150e6907d581318dd Add unit tests for edge cases with delta=1/2 variant of divsteps (Pieter Wuille)
cd393ce2283e0e7234ea39a15c4931715f4dde1e Optimization: only do 59 hddivsteps per iteration instead of 62 (Pieter Wuille)
277b224b6aba942efbac4a6aae1054035a68d8dd Use modified divsteps with initial delta=1/2 for constant-time (Pieter Wuille)
376ca366db0469f39b93af0af762090986ea75f2 Fix typo in explanation (Pieter Wuille)
Pull request description:
This updates the divsteps-based modular inverse code to use the modified version which starts with delta=1/2. For variable time, the delta=1 variant is still used as it appears to be faster.
See https://github.com/sipa/safegcd-bounds/tree/master/coq and https://medium.com/blockstream/a-formal-proof-of-safegcd-bounds-695e1735a348 for a proof of correctness of this variant.
TODO:
* [x] Update unit tests to include edge cases specific to this variant
I'm still running the Coq proof verification for the 590 bound in non-native mode. It's unclear how long this will take.
ACKs for top commit:
gmaxwell:
ACK be0609fd54af95a15b76cea150e6907d581318dd
sanket1729:
crACK be0609fd54af95a15b76cea150e6907d581318dd
real-or-random:
ACK be0609fd54af95a15b76cea150e6907d581318dd careful code review and some testing
Tree-SHA512: 2f8f400ba3ac8dbd08622d564c3b3e5ff30768bd0eb559f2c4279c6c813e17cdde71b1c16f05742c5657b5238b4d592b48306f9f47d7dbdb57907e58dd99b47a
Before this commit, gen_context.c both included libsecp256k1-config.h
and basic-config.h: The former only to obtain ECMULT_GEN_PREC_BITS
and the latter to obtain a basic working configuration to be able to
use the library.
This was inelegant and confusing: It meant that basic-config.h needs
to #undef all the macros defined in libsecp256k1-config.h. Moreover,
it meant that basic-config.h cannot define ECMULT_GEN_PREC_BITS,
essentially making this file specific for use in gen_context.c.
After this commit, gen_context.c include only libsecp256k1-config.h.
basic-config.h is not necessary anymore for the modules used in
gen_context.c because 79f1f7a made the preprocessor detect all the
relevant config options.
On the way, we remove an unused #define in basic-config.h.
Instead of using eta=-delta, use zeta=-(delta+1/2) to represent
delta. This variant only needs at most 590 iterations for 256-bit
inputs rather than 724 (by convex hull bounds analysis).
This commit adds test coverage including Cirrus scripts, Valgrind
constant time tests for secret data, API tests, nonce function tests,
and test vectors from the spec.
This commit adds the ECDSA adaptor signature APIs:
- Encrypted Signing
Creates an adaptor signature, which includes a proof to verify the adaptor
signature.
- Encryption Verification
Verifies that the adaptor decryption key can be extracted from the adaptor
signature and the completed ECDSA signature.
- Signature Decryption
Derives an ECDSA signature from an adaptor signature and an adaptor decryption
key.
- Key Recovery
Extracts the adaptor decryption key from the complete signature and the adaptor
signature.
This commit adds proving and verification functions for discrete
logarithm equality.
From the spec (https://github.com/discreetlogcontracts/dlcspecs/pull/114):
"As part of the ECDSA adaptor signature a proof of discrete logarithm
equality must be provided. This is a proof that the discrete logarithm of
some X to the standard base G is the same as the discrete logarithm of
some Z to the base Y. This proof can be constructed by using equality
composition on two Sigma protocols proving knowledge of the discrete
logarithm between both pairs of points. In other words the prover proves
knowledge of a such that X = a * G and b such that Z = b * Y and that
a = b. We make the resulting Sigma protocol non-interactive by applying
the Fiat-Shamir transformation with SHA256 as the challenge hash."
This commit adds a nonce function that will be used by default
for ECDSA adaptor signatures.
This nonce function is similar to secp256k1_nonce_function_hardened
except it uses the compressed 33-byte encoding for the pubkey argument.
We need 33 bytes instead of 32 because, unlike with BIP-340, an ECDSA
X-coordinate alone is not sufficient to disambiguate the Y-coordinate.
The magnitude of the f and g variables generally goes down as the algorithm
progresses. Make use of this by keeping tracking how many limbs are used, and
when the number becomes small enough, make use of this to reduce the complexity
of arithmetic on them.
Refactored by: Pieter Wuille <pieter@wuille.net>
Both the field and scalar modulus can be written in signed{30,62} notation
with one or more zero limbs. Make use of this in the update_de function to
avoid a few wide multiplications when that is the case.
This doesn't appear to be a win in the 32-bit implementation, so only
do it for the 64-bit one.
Add a new run_inverse_tests that replaces all existing field/scalar inverse tests,
and tests a few identities for fixed inputs, small numbers (-999...999), random
inputs (structured and unstructured), as well as comparing with the output of
secp256k1_fe_inv_all_var.
This commit adds functions to verify and compare numbers in signed{30,62} notation,
and uses that to do more extensive bounds checking on various variables in the modinv
code.
This will fix the following compile error on macOS
In file included from src/num.h:17,
from src/num_impl.h:14,
from src/bench_whitelist.c:14:
src/num_gmp.h:10:10: fatal error: gmp.h: No such file or directory
This adds tests for the modinv{32,64}_impl.h directly (before the functions are used
inside the field/scalar code). It uses a naive implementation of modular multiplication
and gcds in order to verify the modular inverses themselves.
This adds a long comment explaining the algorithm and implementation choices by building
it up step by step in Python.
Comments in the code are also reworked/added, with references to the long explanation.
This was detected while running the tests with the `-Wconditional-uninitialized` flag
```
./autogen.sh
CC=clang CFLAGS="-Wconditional-uninitialized" ./configure
make check
```
The resulting warning is a false positive, but setting the value to -1
ensures that the CHECK below will fail if recid is never written to.
b6f649889ae78573f1959f04172a8e1fe15beab7 Add parens around ROUND_TO_ALIGN's parameter. This makes the macro robust against a hypothetical ROUND_TO_ALIGN(foo ? sizeA : size B) invocation. (Russell O'Connor)
Pull request description:
This makes the macro robust against a hypothetical `ROUND_TO_ALIGN(foo ? sizeA : size B)` invocation.
See also <https://wiki.sei.cmu.edu/confluence/display/c/PRE01-C.+Use+parentheses+within+macros+around+parameter+names>.
ACKs for top commit:
sipa:
ACK b6f649889ae78573f1959f04172a8e1fe15beab7. This is the way.
jonasnick:
utACK b6f649889ae78573f1959f04172a8e1fe15beab7
real-or-random:
utACK b6f649889ae78573f1959f04172a8e1fe15beab7
Tree-SHA512: 6a2685f959e8ae472259e5ea75fe12e8e6213f56f5aec7603a896c294e6a8833caae25c412607d9c9a3125370a7765a3e506127b101a1b87203f95e326f6c6c6
