Final phase of the ChillDKG module: upstream test vectors, a
DKG->FROST integration test, boundary tests, full module
documentation and a runnable example.
Test vectors:
- tools/test_vectors_chilldkg_generate.py converts all 10 upstream
bip-frost-dkg JSON vector files into src/modules/chilldkg/vectors.h
(modeled on tools/test_vectors_frost_generate.py; takes the vectors
directory as an argument; upstream pinned to commit
a91896883f85b159415ecf298d5e844879af112d, recorded in the generated
header with the exact regeneration invocation; regeneration is
reproducible byte-for-byte).
- tests_impl.h vector runners execute 191 of 241 upstream cases
through the public API: hostpubkey_gen, params_hash,
participant_step1/step2/finalize/investigate,
coordinator_step1/finalize/investigate, recover. Happy paths are
byte-exact (pmsg1/cmsg1/pmsg2/cmsg2/dkg_output/recovery/cinv);
error cases assert both the fault enum and fault_index against
expectedError.participantId. The 50 skipped cases are
wrong-length/wrong-count inputs not expressible with the
fixed-size C API; each skip is documented in vectors.h.
Boundary/robustness tests: t=1, t=n, n=2, a full n=128/t=2 session
end-to-end with per-participant secshare*G == pubshare checks and a
recovery roundtrip, and a state1 memcpy roundtrip (step2 from a copied
state object).
DKG->FROST integration test (guarded by ENABLE_MODULE_FROST): a full
ChillDKG session (n=3, t=2) feeds (secshare, thresh_pk, pubshares)
directly into the frost module. ChillDKG's thresh_pk is already
TapTweak'ed, so frost_tweak_cache_init is called with no further
tweaks (frost's tweaked x-only key asserted equal to the x-only part
of the ChillDKG thresh_pk); signers 0 and 2 run nonce_gen, nonce_agg,
session_init with the shared x = id+1 convention, frost_sign,
partial_sig_verify and partial_sig_agg; the aggregate signature
verifies as a plain BIP-340 signature against the threshold key.
Example: examples/chilldkg.c runs a full 2-of-3 DKG session (host key
generation, params hash, participant/coordinator steps, finalize, and
a recovery roundtrip via participant_recover) with fixed-size buffers
and secret erasure. Wired into Makefile.am and
examples/CMakeLists.txt exactly like frost_example (runs as a TEST);
chilldkg_example binary added to .gitignore.
Docs: src/modules/chilldkg/chilldkg.md now documents the protocol
summary, message-flow table with exact byte sizes, blame taxonomy,
recovery workflow, security notes (host key reuse/retention, fresh
randomness per session, state secrecy, recovery-data sensitivity) and
the pinned reference commit; src/modules/frost/frost.md points at the
new module as the intended DKG.
Bug fix found by the vector runner (recover tcId 9): the internal
recover() passed a possibly-NULL fault_index from coordinator_recover
to certeq_verify, which dereferences it on failure; now uses a local.
Verified: make check 10/10 (3 test suites + 7 examples incl.
chilldkg_example, exit 0 when run); CMake ctest 428/428 with chilldkg
+ frost, and a no-frost build confirms the ENABLE_MODULE_FROST guard;
make distdir includes vectors.h, the example and the generator.
The module is feature-complete against bip-frost-dkg v0.3.0-dev at
a91896883f85b159415ecf298d5e844879af112d. The BIP is still a draft;
tagged hashes and wire formats may change upstream.
Add an empty, experimental `chilldkg` module as the foundation for a
ChillDKG implementation (distributed key generation for FROST) per the
bip-frost-dkg BIP draft (v0.3.0-dev):
https://github.com/BlockstreamResearch/bip-frost-dkg
The module lives in src/modules/chilldkg/ (separate from the frost
module, per the implementation plan in .idea/docs/
chilldkg-implementation-plan.md: FROST signing (BIP 445) and ChillDKG
are separate BIPs with separate reference repos, test vectors and
review cycles; the dependency between them is one-way bytes).
New files:
- include/secp256k1_chilldkg.h: public header skeleton with the same
"EXTREMELY DANGEROUS / work in progress" warning style as
secp256k1_frost.h, plus a note that the BIP is a draft and tagged
hashes/wire formats may change. No API yet (Phase 3+).
- src/modules/chilldkg/main_impl.h: implementation skeleton including
the public header.
- src/modules/chilldkg/tests_impl.h: trivial scaffolding unit test
(chilldkg_scaffolding_test) registered via the tests_chilldkg[]
CASE1 array used by this repo's unit-test framework.
- src/modules/chilldkg/Makefile.am.include: autotools file list,
mirroring the frost module's.
- src/modules/chilldkg/chilldkg.md: module doc stub (purpose, draft
status, dependency on the schnorrsig and ecdh modules).
Build wiring (mirrors the frost module exactly):
- configure.ac: --enable-module-chilldkg (default no, experimental
gate), dependency errors when schnorrsig or ecdh are explicitly
disabled, AM_CONDITIONAL(ENABLE_MODULE_CHILLDKG), summary line.
- Makefile.am: include src/modules/chilldkg/Makefile.am.include under
ENABLE_MODULE_CHILLDKG.
- src/secp256k1.c: guarded include of modules/chilldkg/main_impl.h
after the frost module.
- src/tests.c: guarded include of tests_impl.h and
MAKE_TEST_MODULE(chilldkg) registration.
- CMakeLists.txt: SECP256K1_ENABLE_MODULE_CHILLDKG option (OFF) +
summary line.
- src/CMakeLists.txt: dependency checks on
SECP256K1_ENABLE_MODULE_SCHNORRSIG and SECP256K1_ENABLE_MODULE_ECDH,
ENABLE_MODULE_CHILLDKG=1 compile definition, public header export.
Verified:
- ./autogen.sh && ./configure --enable-experimental
--enable-module-chilldkg --enable-module-schnorrsig
--enable-module-ecdh && make check: PASS 3/3 (tests, noverify_tests,
exhaustive_tests).
- configure fails with a clear error when schnorrsig or ecdh are
disabled, or when experimental is not enabled.
- CMake build with SECP256K1_ENABLE_MODULE_CHILLDKG=ON: ctest 345/345
passed; dependency errors fire correctly when schnorrsig/ecdh OFF.
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This change improves separation from CMake build directories, which
typically use the "build" prefix.
Additionally, corresponding `.gitignore` entries have been refactored.
Lightweight unit testing framework, providing a structured way to define,
execute, and report tests. It includes a central test registry, a flexible
command-line argument parser of the form "--key=value" / "-k=value" /
"-key=value" (facilitating future framework extensions), ability to run
tests in parallel and accumulated test time logging reports.
So far the supported command-line args are:
- "--jobs=<num>" or "-j=<num>" to specify the number of parallel workers.
- "--seed=<hex>" to specify the RNG seed (random if not set).
- "--iterations=<num>" or "-i=<num>" to specify the number of iterations.
Compatibility Note:
To stay compatible with previous versions, the framework also supports
the two original positional arguments: the iterations count and the
RNG seed (in that order).
Relocate the clock time getter to tests_common.h to
make it easily reusable across test programs. This
will be useful for the upcoming unit test framework.
Context - why not placing it inside testutil.h?:
The bench program links against the production-compiled library,
not its own compiled version. Therefore, `gettime_i64()` cannot
be moved to testutil.h, because testutil.h calls
`secp256k1_pubkey_save()`, which exists only in the internal
secp256k1.c and not in the public API.
This should hopefully be useful as orientation for users implementing
the key exchange part of BIP324. Conceptually the example is not very
different to the ECDH one, so a lot of code/comments are just copied
(e.g. context creation, secret key generation, shared secret comparison,
console output, cleanup with secret key clearing).
Widely available versions of GCC and Clang beat our field asm on -O2.
In particular, GCC 10.5.0, which is Bitcoin Core's current compiler
for official x86_64 builds, produces code that is > 20% faster for
fe_mul and > 10% faster for signature verification (see #726).
These are the alternatives to this PR:
We could replace our current asm with the fastest compiler output
that we can find. This is potentially faster, but it has multiple
drawbacks:
- It's more coding work because it needs detailed benchmarks (e.g.,
with many compiler/options).
- It's more review work because we need to deal with inline asm
(including clobbers etc.) and there's a lack of experts reviewers
in this area.
- It's not unlikely that we'll fall behind again in a few compiler
versions, and then we have to deal with this again, i.e., redo the
benchmarks. Given our history here, I doubt that we'll revolve
this timely.
We could change the default of the asm build option to off. But this
will also disable the scalar asm, which is still faster.
We could split the build option into two separate options for field
and scalar asm and only disable the field asm by default. But this
adds complexity to the build and to the test matrix.
My conclusion is that this PR gets the low-hanging fruit in terms of
performance. It simplifies our code significantly. It's clearly an
improvement, and it's very easy to review. Whether re-introducing
better asm (whether from a compiler or from CryptOpt) is worth the
hassle can be evaluated separately, and should not hold up this
improvement.
Solves #726.
It is a non-Libtool-specific way to explicitly specify the user's
intention to consume a static `libseck256k1`.
This change allows to get rid of MSVC linker warnings LNK4217 and
LNK4286. Also, it makes possible to merge the `SECP256K1_API` and
`SECP256K1_API_VAR` into one.
The scheme implemented is described below, and largely follows the paper
"SwiftEC: Shallue–van de Woestijne Indifferentiable Function To Elliptic Curves",
by Chavez-Saab, Rodriguez-Henriquez, and Tibouchi
(https://eprint.iacr.org/2022/759).
A new 64-byte public key format is introduced, with the property that *every*
64-byte array is an encoding for a non-infinite curve point. Each curve point
has roughly 2^256 distinct encodings. This permits disguising public keys as
uniformly random bytes.
The new API functions:
* secp256k1_ellswift_encode: convert a normal public key to an ellswift 64-byte
public key, using additional entropy to pick among the many possible
encodings.
* secp256k1_ellswift_decode: convert an ellswift 64-byte public key to a normal
public key.
* secp256k1_ellswift_create: a faster and safer equivalent to calling
secp256k1_ec_pubkey_create + secp256k1_ellswift_encode.
* secp256k1_ellswift_xdh: x-only ECDH directly on ellswift 64-byte public keys,
where the key encodings are fed to the hash function.
The scheme itself is documented in secp256k1_ellswift.h.
Adds a test using the Wycheproof vectors as outlined in #1106. The
vectors are taken from the Wycheproof repo. We use a python script
to convert the JSON-formatted vectors into C code.
Co-authored-by: Sean Andersen <6730974+andozw@users.noreply.github.com>
