The module's BIP 445 logic itself is unchanged and was independently
validated against the pinned spec commit bb5396f (BIP v0.10.0), both via
the checked-in test vectors and via differential testing against the
Python reference over 360 randomised configurations (n up to 128,
shuffled non-contiguous signer ids, mixed xonly/plain tweak chains,
variable-length messages, pubshares present and absent). Every change
below is structural: the differential harness produces byte-identical
pubnonces, aggnonces, partial signatures and final signatures before and
after.
Two classes of problem prevented the module from passing CI.
1. Constant-time violations (ctime_tests)
-----------------------------------------
The CI matrix enables FROST in rows that also run
"valgrind --error-exitcode=42 ./ctime_tests" -- WITH_VALGRIND and
CTIMETESTS both default to 'yes'. With the module enabled that job
reported 639 "conditional jump depends on uninitialised value" errors,
all originating from two sites:
- secp256k1_frost_derive_coefficient returned
!overflow && !secp256k1_scalar_is_zero(out)
where the short-circuiting && branches on `overflow`, which is
derived from the threshold secret key. The caller declassifies the
return value, but the branch has already happened inside the callee.
Replaced with a bitwise &, matching the existing idiom in
secp256k1_scalar_set_b32_seckey (src/scalar_impl.h).
- secp256k1_frost_sign_internal performs the self-verification
recommended by BIP 445, which runs the *variable-time*
secp256k1_ecmult over the partial signature s. nonce_pts and pk were
already declassified ahead of that call; s was not. Since s is the
public output of the function, declassifying it before the
self-verification is both correct and sufficient.
secp256k1_frost_deterministic_sign carried three more instances of the
same class, invisible until now because ctime_tests did not exercise
that path at all:
- the `if (!valid)` check on secp256k1_scalar_set_b32_seckey lacked the
declassify that the identical checks in secp256k1_frost_nonce_gen and
secp256k1_frost_sign_internal already have;
- secp256k1_frost_det_nonce_function used the same short-circuiting &&,
here over the secret nonces;
- the branch on that function's result was not declassified.
The && in det_nonce_function is rewritten via two int locals rather than
a bare bitwise &: clang's -Wbitwise-instead-of-logical fires when both
operands are `!f(...)` expressions, which would break the -Werror clang
builds.
ctime_tests now also covers secp256k1_frost_deterministic_sign, so that
path stays checked from here on.
None of these leak anything of value in practice -- they reveal only
negligible-probability events (a hash overflowing the curve order, a zero
nonce) or whether a secret share is a valid secret key -- but they
violate the project's declassification discipline and fail the ctime
test.
2. C90 conformance (-Werror -pedantic-errors)
---------------------------------------------
The project targets C90 (CMAKE_C_STANDARD 90, -std=c89 -pedantic) and CI
passes WERROR_CFLAGS='-Werror -pedantic-errors'. Compiling src/tests.c
with those flags produced 62 errors in three groups:
- 40x "ISO C forbids empty initializer braces before C2X" in the
generated vectors.h; empty {} initializers are C23-only. Fixed in
tools/test_vectors_frost_generate.py so it survives regeneration:
hexstr_to_intarray now emits "0" for an empty byte string (all six
of its call sites wrap the result in braces), and init_group's
`counted` helper emits "{ 0 }" for an empty group. In every affected
slot the paired count/length field is 0, so the padding element is
never read.
- 1x "comma at end of enumerator list" (C99+), also in the generator.
- 21x "initializer element is not computable at load time" across 11
lines of tests_impl.h. C90 requires constant expressions in
initializers for automatic aggregates, so
const secp256k1_frost_pubnonce *ptrs[2] = { &a, &b };
is invalid. Rewritten as a declaration plus assignments, the style
the musig tests already use, which is why the pre-existing tree was
green.
vectors.h is regenerated from the spec's JSON vectors. Its hex payload is
byte-identical (verified by hashing every 0xNN token) and the file still
reproduces exactly from tools/test_vectors_frost_generate.py.
Verification
------------
- gcc and clang, -std=c89 -pedantic-errors -Werror, with and without
-DVERIFY: clean (was 62 errors)
- ctime_tests under MemorySanitizer: 0 reports (was 639); exits 0 with
halt_on_error=1
- tests, noverify_tests and frost_example: pass
- vectors.h regenerates identically from the pinned spec vectors
- 240 signing + 120 deterministic-signing differential cases against
the BIP 445 Python reference: byte-identical to the pre-fix build
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
1605b02f cd49c57e 453949ab 57315a69 97de5120 c5da3bde 99ab4a10 d071aa56 1d146ac3 322d0a43 c7a7f732 ac561601 dfe042fe 3019186a 95e68158 10f546a2 c0a2aba0 ' into temp-merge-1811
c8206b1c b6c2a3cd e7f7083b be5e4f02 5c751833 540fec8a aa2a39c1 8d445730 f9a944ff 2d9137ce 4721e077 471e3a13 ebb35882 1a53f496 c7a52400 ' into temp-merge-1809
c8206b1c b6c2a3cd e7f7083b be5e4f02 5c751833 540fec8a aa2a39c1 8d445730 f9a944ff 2d9137ce 4721e077 471e3a13 ebb35882 1a53f496 c7a52400 ' into temp-merge-1809
libsecp256k1-zkp
A fork of libsecp256k1 with support for advanced and experimental features
Added features:
- Experimental module for ECDSA adaptor signatures.
- Experimental module for ECDSA sign-to-contract.
- Experimental modules for Confidential Assets (Pedersen commitments, range proofs, and surjection proofs).
- Experimental module for address whitelisting.
- Experimental module for Schnorr signature half-aggregation.
- Experimental module for FROST (BIP 445).
Experimental features are made available for testing and review by the community. The APIs of these features should not be considered stable.
Build steps
Obtaining and verifying
The git tag for each release (e.g. v0.6.0) is GPG-signed by one of the maintainers.
For a fully verified build of this project, it is recommended to obtain this repository
via git, obtain the GPG keys of the signing maintainer(s), and then verify the release
tag's signature using git.
This can be done with the following steps:
- Obtain the GPG keys listed in SECURITY.md.
- If possible, cross-reference these key IDs with another source controlled by its owner (e.g. social media, personal website). This is to mitigate the unlikely case that incorrect content is being presented by this repository.
- Clone the repository:
git clone https://github.com/bitcoin-core/secp256k1 - Check out the latest release tag, e.g.
git checkout v0.7.1 - Use git to verify the GPG signature:
% git tag -v v0.7.1 | grep -C 3 'Good signature' gpg: Signature made Mon 26 Jan 2026 07:42:46 PM UTC gpg: using RSA key 2840EAABF4BC9F0FFD716AFAFBAFCC46DE2D3FE2 gpg: Good signature from "Pieter Wuille <pieter@wuille.net>" [unknown] gpg: aka "Pieter Wuille <pieter.wuille@gmail.com>" [full] gpg: aka "[jpeg image of size 5996]" [undefined] gpg: WARNING: This key is not certified with a trusted signature! gpg: There is no indication that the signature belongs to the owner. Primary key fingerprint: 133E AC17 9436 F14A 5CF1 B794 860F EB80 4E66 9320 Subkey fingerprint: 2840 EAAB F4BC 9F0F FD71 6AFA FBAF CC46 DE2D 3FE2
Building with Autotools
$ ./autogen.sh # Generate a ./configure script
$ ./configure # Generate a build system
$ make # Run the actual build process
$ make check # Run the test suite
$ sudo make install # Install the library into the system (optional)
To compile optional modules (such as Schnorr signatures), you need to run ./configure with additional flags (such as --enable-module-schnorrsig). Run ./configure --help to see the full list of available flags. For experimental modules, you will also need --enable-experimental as well as a flag for each individual module, e.g. --enable-module-rangeproof.
Building with CMake
To maintain a pristine source tree, CMake encourages to perform an out-of-source build by using a separate dedicated build tree.
Building on POSIX systems
$ cmake -B build # Generate a build system in subdirectory "build"
$ cmake --build build # Run the actual build process
$ ctest --test-dir build # Run the test suite
$ sudo cmake --install build # Install the library into the system (optional)
To compile optional modules (such as Schnorr signatures), you need to run cmake with additional flags (such as -DSECP256K1_ENABLE_MODULE_SCHNORRSIG=ON). Run cmake -B build -LH or ccmake -B build to see the full list of available flags.
Cross compiling
To alleviate issues with cross compiling, preconfigured toolchain files are available in the cmake directory.
For example, to cross compile for Windows:
$ cmake -B build -DCMAKE_TOOLCHAIN_FILE=cmake/x86_64-w64-mingw32.toolchain.cmake
To cross compile for Android with NDK (using NDK's toolchain file, and assuming the ANDROID_NDK_ROOT environment variable has been set):
$ cmake -B build -DCMAKE_TOOLCHAIN_FILE="${ANDROID_NDK_ROOT}/build/cmake/android.toolchain.cmake" -DANDROID_ABI=arm64-v8a -DANDROID_PLATFORM=28
Building on Windows
The following example assumes Visual Studio 2022. Using clang-cl is recommended.
In "Developer Command Prompt for VS 2022":
>cmake -B build -T ClangCL
>cmake --build build --config RelWithDebInfo
Usage examples
Usage examples can be found in the examples directory. To compile them you need to configure with --enable-examples.
- ECDSA example
- Schnorr signatures example
- Deriving a shared secret (ECDH) example
- ElligatorSwift key exchange example
- MuSig2 Schnorr multi-signatures example
To compile the examples, make sure the corresponding modules are enabled.
Benchmark
If configured with --enable-benchmark (which is the default), binaries for benchmarking the libsecp256k1-zkp functions will be present in the root directory after the build.
To print the benchmark result to the command line:
$ ./bench_name
To create a CSV file for the benchmark result :
$ ./bench_name | sed '2d;s/ \{1,\}//g' > bench_name.csv
Reporting a vulnerability
See SECURITY.md
Contributing to libsecp256k1
See CONTRIBUTING.md