Kgothatso Ngako 3c962b00cc frost_enrollment: fix the example's stale n and failure-path hygiene
The last of the review findings, plus the comment and structure fixes it
listed.

The example's repair run used the pre-enrollment participant count.

  Two blocks earlier the example teaches that every participant must
  update its record of n from 3 to 4 after an enrollment, and the
  signing session duly uses N_PARTICIPANTS_AFTER. Then enroll() -- which
  hard-coded N_PARTICIPANTS -- ran the repair at n = 3. It worked only
  because the Lagrange math never involves n and every party in this
  single-process demo passed the same stale value.

  In a real post-enrollment repair it would not. n is bound into the
  parameters hash, so helpers feeding their updated n = 4 into
  shares_gen while the requester feeds n = 3 abort round 1.2 with no
  visible cause. enroll() now takes n_participants as a parameter, the
  repair passes N_PARTICIPANTS_AFTER, and both the function's contract
  comment and the repair call site say why. The repaired share is still
  byte-identical to the original, which is the point: n changes the
  hash, not the arithmetic.

The example leaked secrets on its failure paths.

  enroll() erased the delta and sigma buffers only on success; four
  early returns left them live. sign_and_verify() returned from three
  places without erasing already-generated secnonces. Both now route
  every exit through a cleanup block. This example is otherwise more
  careful about erasure than its siblings, so the asymmetry was exactly
  what a reader copying it would carry into production -- on the fault
  paths where hygiene matters most.

  The double-wipe of session_secrand is gone with it: shares_gen and
  nonce_gen both wipe the seed on every path, and doing it again read
  as uncertainty about the contract. The comment now states the
  contract instead. The fill_random failure path does erase, since
  nothing else has touched the buffer there.

The example's mismatch message asserted a cause it cannot know.

  It printed "Helper %u disagrees about the enrollment parameters" for
  what may equally be a corrupted share, per the previous commit's
  finding. It now says the helper "contributed a share this helper
  cannot use", with a comment noting that share_agg does not
  distinguish the two causes so neither can the message.

Comment and structure fixes, all noted in the review:

- The vector generator claimed case 4 was "the only case whose DERIVED
  public share has odd Y". It is not -- cases 1, 2 and 4 are odd and
  case 3 is even. The comment existed to justify a coverage choice and
  misinformed; both parity comments now describe the set accurately and
  say they document it rather than constrain it. Regenerating vectors.h
  still reproduces it byte for byte.
- The secp256k1_frost_sort_ids declaration in frost/session.h no longer
  duplicates the definition's doc comment, which was two copies to keep
  in sync. It says what the function is for and points at the
  definition for the contract.
- The t >= 2 rationale was stated in full in three places. The impl now
  states the conclusion and names frost_enrollment.md as the single
  place to edit if the policy moves.
- The ctime_tests comments read ambiguously ("the parameters hash is
  public, the delta values are not" against a header calling deltas
  secret), and computing direct_hash without asserting anything invited
  a "forgotten assertion" reading. Both are now explicit.
- The example moves next to frost_example in Makefile.am rather than
  after iceberg, matching the FROST-stack grouping used in
  configure.ac, ci.sh, ci.yml and README.
- frost_enrollment.md now distinguishes what is unstable (the C API)
  from what is frozen (the wire-visible encodings), which the two
  statements together previously left easy to conflate.

Not fixed, deliberately, and now recorded where the tree can see it: the
plan called for a CHANGELOG.md entry. That file states in its first two
lines that it is upstream libsecp256k1's changelog and not this fork's,
and none of frost, chilldkg, iceberg or prefractal has an entry. Adding
the first one is a decision about all five modules, not this one. The
README link is the fork's actual convention for announcing a module and
is in place.

Verification: autotools builds warning-free and `make check` is 12/12
including the example; ctime_tests is clean under valgrind; `make dist`
carries all nine frost_enrollment files; CMake with examples builds
warning-free and ctest is 542/542; the example source is clean under
gcc -std=c89 -pedantic -Wall -Wextra; regenerating vectors.h reproduces
it byte for byte.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
2026-09-04 10:27:17 +02:00
2026-09-04 02:56:23 +02:00
2013-05-09 15:24:32 +02:00

libsecp256k1-zkp

Dependencies: None

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 module for ChillDKG, distributed key generation for FROST (bip-frost-dkg draft).
  • Experimental module for Iceberg, a threshold scheme that lets a group of parties stand in for a single MuSig2 (BIP 327) participant.
  • Experimental module for Prefractal, a nested FROST+MuSig2 signer that lets a FROST group occupy one participant slot of an ordinary MuSig2 (BIP 327) session.
  • Experimental module for FROST enrollment, which grows a (t, n) FROST group into a (t, n+1) one, and repairs a lost share, without re-running key generation.

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:

  1. Obtain the GPG keys listed in SECURITY.md.
  2. 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.
  3. Clone the repository:
    git clone https://github.com/bitcoin-core/secp256k1
    
  4. Check out the latest release tag, e.g.
    git checkout v0.7.1
    
  5. 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.

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

Description
Experimental fork of libsecp256k1 with support for pedersen commitments and range proofs.
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