Iter 15. Lands ADR-120 §2.3 — the cryptographic foundation of invariant
I3 ("cross-site identity correlation is impossible"). rf_signature_hash
is now derived from a per-site secret and a daily epoch, so two nodes
observing the same physical person produce uncorrelated 256-bit digests.
Added (no_std-compatible):
- blake3 = "1.5", default-features = false (no_std, no SIMD by default)
- src/signature_hasher.rs:
* Constants SECONDS_PER_DAY (86_400), SITE_SALT_LEN (32), RF_SIGNATURE_LEN (32)
* SignatureHasher { site_salt: [u8; 32] } with new(salt) const ctor
* compute(day_epoch, &features) -> [u8; 32] (BLAKE3 keyed mode)
* compute_at(unix_secs, &features) -> [u8; 32] convenience
* day_epoch_from_unix_secs(unix_secs) -> u32 helper (floor(t / 86400))
- pub use SignatureHasher, RF_SIGNATURE_LEN, SITE_SALT_LEN from lib.rs
tests/signature_hasher.rs (8 named tests, all green):
deterministic_under_identical_inputs
different_site_salts_produce_different_hashes
different_day_epochs_rotate_the_hash
different_features_produce_different_hashes
output_length_is_32_bytes
day_epoch_from_unix_secs_matches_floor_division
(covers 0, 86_399, 86_400, and the 1.7e9 modern timestamp)
compute_at_matches_compute_with_derived_day
cross_site_hamming_distance_is_statistically_high
*** ADR-120 §2.7 AC2 acceptance test ***
Runs 100 trials with distinct (salt_a, salt_b) pairs observing
identical features, computes per-trial Hamming distance, asserts
mean >= 120 bits and min >= 80 bits. Empirically lands at ~128 bits
mean (the expected value for two independent 256-bit hashes), with
no trial below 80 bits — i.e., zero suspicious near-collisions.
ACs progressed:
- ADR-120 §2.7 AC2 — structurally enforced cross-site isolation, now
proven empirically by the Hamming-distance test. This is the
cryptographic half of invariant I3 in code, not just docs.
- ADR-118 invariant I3 — first runtime witness that two sites with
independent site_salts cannot correlate the same person's signature.
Test config:
- cargo test --no-default-features → 72 passed (64 + 8; signature_hasher is no_std)
- cargo test → 117 passed (109 + 8)
Out of scope (next iter target):
- Wire SignatureHasher into BfldEmitter: replace caller-supplied
rf_signature_hash with hasher.compute_at(ts, &features) so the
pipeline produces correct hashes end-to-end.
- IdentityFeatures canonical-bytes encoder so callers don't need to
hand-serialize per-feature representations.
Co-Authored-By: claude-flow <ruv@ruv.net>
0ca8a38cbc