303a7caeae
Fourth of six commits. Twelve tests replacing the Phase 2 smoke test, plus
a vector generator and the frozen vectors it produces.
The regression vectors are the one part of this worth being precise
about, because they are easy to over-claim. FROST enrollment has no BIP
and no published vectors, and the reference proof of concept draws its
randomness from secrets.randbits, which is not seedable -- so there is
nothing to cross-validate against. tools/test_vectors_frost_enrollment_generate.py
therefore re-implements the math independently in stdlib-only Python,
including the group arithmetic written from the secp256k1 parameters
rather than borrowed, and freezes the output. What that buys: the two tag
strings, the params hash serialization, the share-splitting derivation
and the identifier conventions are now pinned, and changing any of them
is a loud vector-breaking change. What it does not buy is evidence of
protocol correctness. The generator header comment and the generated
file both say so, as does frost_enrollment.md.
The vectors passed on the first run against the C code, which is worth
recording: two independent implementations agree byte for byte on the
params hash, every delta, every sigma, the derived public share and the
final share, across four cases (2-of-3 minimal, 2-of-3 oversized at
u = 3 > t = 2, a 3-of-5 repair with a deliberately UNSORTED helper set,
and a 4-of-6 enrollment), covering both threshold-key Y parities.
The algebraic invariants are what actually carry correctness:
- Reconstruction (PoC test_generate_frost_share): after a 2-of-3 group
enrolls id 3, every pair {i, 3} reconstructs the original threshold
secret, and so does the untouched pair {0, 1}.
- Signing (PoC test_sign): a real BIP340 signature from {2, 3} verifying
against the unchanged threshold public key, with every partial
signature individually verified, plus the n -> n+1 bookkeeping --
secp256k1_frost_threshold_info_validate must accept the public share
table extended with pubshare_derive's output at n+1.
- Repair: byte-for-byte equality with the lost share, and the repaired
participant keeps its old public share.
- Oversized helper set: u = 3 and u = 2 over the same key material
produce the same share and the same derived public share.
- Randomized: COUNT iterations over 2 <= t <= u <= n <= 7, half
enrollment and half repair, with EVERY HELPER GIVEN THE IDENTIFIER SET
IN ITS OWN SHUFFLED ORDER. The params hash must come out identical
while the delta buffers stay aligned per helper -- which is the whole
point of canonicalizing ids inside the hash and nowhere else. Each
iteration then checks every t-subset containing the new participant.
The negative tests are organized around what each gate is actually for:
- Fault injection flips a bit in one sigma. secshare_gen fails and wipes
its output; the same call with expected_pubshare = NULL SUCCEEDS and
returns a wrong share. That second assertion is the point -- it is the
evidence that the parameter is load-bearing rather than decorative.
Tampered public shares are caught earlier, by
secp256k1_frost_threshold_info_validate, so the test exercises the
recommended flow and not just the module.
- Parameter mismatch, four angles: (a) one helper runs round 1.1 for a
different target and every other helper's share_agg aborts naming it
by identifier; (b) a caller that IGNORES that abort and finishes round
1.2 anyway still cannot produce a usable share, because the
public-share check catches the inconsistent sum -- defence in depth,
not a test of the test's own control flow; (c) the helpers agree with
each other on new_id = 3 while the target expects 4, which round 1.2
cannot see and round 2's own recomputation does; (d) two groups with
identical (t, n, ids, new_id) get different hashes, and a hash from one
fails share_agg in the other.
- Own-slot semantics: filling the caller's own slot of
received_params_hashes32 with garbage changes nothing, because it is
never read -- but the same garbage in a slot that IS read still aborts.
That pair is what makes "recomputation, not string comparison"
testable rather than merely asserted.
- Invalid parameters, including both deliberate divergences: t = 1
refused, enrollment refused at n = 128 while repair at n = 128 is
accepted, n_ids > 128 returning 0 with the output zeroed in a
production build.
Three bugs found while writing these, all in the tests, all worth
naming:
- pubshare_derive takes public shares ALIGNED WITH ids, and the test
helper was handing it the participant-indexed table. Those coincide
exactly when the helper set is 0..u-1, which every test until the
repair case used, so the first non-contiguous helper set {0, 2} was
what exposed it. There is now one helper that does the gather, with a
comment saying which confusion it exists to prevent.
- The fault-injection test compared against r.new_secshare without ever
running round 2, and the mismatch test compared against
r.params_hashes[0] one line before round 1.1 filled it. Both were
reads of uninitialized memory that happened to pass; valgrind found
both.
The randomized test loops COUNT times so -i scales it, following the
iceberg module (tests_impl.h:1322) rather than prefractal's run-once
convention -- a fuzzing loop that ignores the iteration count is not
much of one.
Verification: all twelve tests pass at the default iteration count, at
-i=200 and at -i=2000; ./tests, ./noverify_tests and ./exhaustive_tests
exit 0 with all five FROST-stack modules enabled; the module runs clean
under valgrind (0 errors from 0 contexts); ctime_tests is clean under
valgrind; regenerating vectors.h reproduces it byte for byte.
One note for anyone running these locally: ctime_tests must not be run
against a CPPFLAGS='-DVERIFY' build. secp256k1_scalar_verify branches on
scalar values, which ctime_tests deliberately marks secret, so every
scalar operation in the library reports a finding -- 75997 of them, none
in this module. The CI matrix already pairs -DVERIFY with
CTIMETESTS: 'no' (.github/workflows/ci.yml:119, :596) for this reason.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
6 lines
297 B
Makefile
6 lines
297 B
Makefile
include_HEADERS += include/secp256k1_frost_enrollment.h
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noinst_HEADERS += src/modules/frost_enrollment/main_impl.h
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noinst_HEADERS += src/modules/frost_enrollment/enrollment_impl.h
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noinst_HEADERS += src/modules/frost_enrollment/tests_impl.h
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noinst_HEADERS += src/modules/frost_enrollment/vectors.h
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