Lands the M1 mitigation cryptographic primitive that ticket #000018
§5.2 + §9.2 specified, scoped per ticket #000035 §3.1-§3.3. Pure
stdlib (hashlib + hmac); no third-party dependency.
arborist/v7/__init__.py
=======================
First module landed under the v7 namespace. v7 plastic-training is
currently paper-stage (per #000037 §17.2); this is where its
deterministic primitives accumulate ahead of an active deployment
target so the building blocks are unit-tested + KAT-pinned the
moment v7 needs them.
arborist/v7/anchor_prg.py
=========================
Implements ``phi_prg(hard_hash_32, dim_h, *, seed) -> list[float]``
per #000035 §3.1. Construction is SP 800-108 KDF in counter mode
over HMAC-SHA-512:
Output(SEED, C(M), n_bytes) :=
i = 0
out = b""
while len(out) < n_bytes:
out += HMAC-SHA-512(SEED, C(M) || i.to_bytes(4, 'big'))
i += 1
return out[:n_bytes]
Float conversion: f(u32) := 2 * (u32 / 2**32) - 1
↑ uniform on [-1, 1)
Security argument from #000035 §2.1: HMAC-SHA-512 is a PRF under
the standard SHA-512 + HMAC assumption; distinguishing advantage
from random bounded by SHA-512 collision-resistance (~2^256), which
structurally matches the substrate's SHA-256 hard-hash family. The
seed is published, not secret — secrecy is not the security
property; the property is computational indistinguishability of the
output from random, which holds even when the seed is public.
Module exports ``PHI_PRG_VERSION = "phi-prg-v1-hmac-sha512"`` so
future algorithm rotations are detectable at the call site without
string-comparing module paths. Per #000035 risk §6.1, a
``phi_prg_version`` field in the v7 manifest will let future
deployments swap to a successor PRF without breaking historical
replay; this version string is the runtime-side mirror.
Hard-hash input length checked exactly at 32 bytes — silently
padding shorter input would break the PRF security argument.
``dim_h`` validated as positive int.
tests/test_anchor_prg.py
========================
20 tests covering #000035 §3.2 acceptance criteria + the strict
range invariant + the input-validation surface:
- Determinism: same (seed, hard_hash, dim_h) → identical floats.
- Range: every output in [-1, 1) with strict upper bound. Three
edge cases pinned: u32=0 → -1.0, u32=2^31 → 0.0,
u32=2^32-1 → just below 1.0.
- Chi² loose-uniformity: 4096-sample bin-test (df=15) with a
generous threshold (60); catches catastrophic PRG bugs (counter
cycling, mis-keyed HMAC) without claiming cryptographic-grade
evidence.
- Boundary: dim_h=1 + dim_h=16384 both produce sensible output.
- Avalanche, seed-bit: flip top bit of seed[0]; require 35-65% of
output bits flipped (PRF avalanche property).
- Avalanche, hash-bit: same surface for the hard-hash input.
- Validation rejects: short hashes, long hashes, non-bytes hashes,
zero / negative / non-int dim_h.
- Module export shape: PHI_PRG_VERSION + PLACEHOLDER_SEED.
- KAT regression: pinned vectors verified against
``bench/fixtures/phi-prg/known-answer-tests.jsonl``.
bench/fixtures/phi-prg/known-answer-tests.jsonl
================================================
10 KAT vectors generated against the placeholder seed + custom
seed/hash combinations; covers smoke (placeholder seed × small
dim_h), block boundaries (HMAC-SHA-512 blocks are 64 bytes, so
dim_h=16 is exactly one block, dim_h=17 is two blocks with
truncation), seed/hash one-bit-flip variants, and a 4096-element
stress sample.
Each row pins the SHA-256 of the raw byte stream (not the float
list) — that's the durable contract; switching from list[float] to
array.array('f', ...) or numpy arrays at the float layer would not
invalidate the fixture. Algorithm changes MUST bump
PHI_PRG_VERSION and create a new fixture file under
bench/fixtures/phi-prg/; old runs replay against old data per the
v7 spec replay discipline.
#000035 status flip
===================
docs/tickets/ticket-000035-prg-choice-phi-prg.md §7 updated from
"open · awaiting go/no-go" to "in progress · Phase 1 landed
2026-05-10". §7 now carries Phase 1 close-out details + Phase 2
gating criteria (active v7 deployment target + spec maintainer
review of §3.4 amendment text). The §3.4 v7 §9.10 amendment text
stays as the draft awaiting Phase 2 landing.
docs/TICKETS.md index row was already updated by fox in commit
ed470dc; my edit was idempotent.
Hygiene
=======
- make test → 1643 passed, 45 skipped (was 1623; +20 anchor_prg)
- make chain-check-shards → 0 breaks across all 7 shards
- arborist.v7 namespace picked up automatically by the existing
pyproject.toml [tool.setuptools.packages.find] include="arborist*"
glob; no setup change required.
- fox's in-flight #000037 ticket modifications + a parallel
#000031 ticket update left untouched.
russell@unturf.com
06c95a03ab