feat(evidence-pack): Plan-09 MVP — casan pack / verify-pack + certified-run gate

evidence-pack.sh {pack|verify-pack} assembles a per-run proof pack from REAL on-disk logs (summaries only — no raw secret/PII copied; decision-log passes the data-exfil guard or the pack aborts). Produces the standard set: run-summary, h1..h7 reports, redteam-result, benign-fp-report, artifact-manifest, decision-log, plus a signed manifest head (evidence-pack.sig). Tamper-evident: verify-pack recomputes every file hash vs artifact-manifest.json (any change fails) and verifies the RSA signature over manifest-head.txt (a manifest re-forge fails without the off-repo key). Certified run: run-summary.certified is true ONLY when required gates pass (H4 exercised, H5 audit chain valid, H5 telemetry verified, no unresolved cost spike, benign-FP within budget) and none was silently skipped — missing evidence records an honest reason and does NOT certify. CLI mapping: `casan pack <id>` -> evidence-pack.sh pack; `casan verify-pack <id>` -> evidence-pack.sh verify-pack. phase3-evidence-pack-tests.sh covers it. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
2026-07-03 23:02:39 +09:00
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+#!/usr/bin/env python3
+"""CASAN Plan-09 — Evidence Pack verifier (MVP).
+
+Recomputes the hash of every file in a pack and compares it to the stored
+artifact-manifest.json. Any change to any packed file flips a hash and fails
+verification. (The bash wrapper additionally verifies the RSA signature over
+manifest-head.txt, which stops an attacker who rewrites the manifest too.)
+
+Argv: <pack_dir>
+Exit: 0 intact, 1 tamper detected / manifest missing.
+"""
+import hashlib
+import json
+import os
+import sys
+
+
+def main():
+    pack_dir = sys.argv[1]
+    manifest_path = os.path.join(pack_dir, "artifact-manifest.json")
+    if not os.path.isfile(manifest_path):
+        sys.stderr.write("EVIDENCE_PACK_NO_MANIFEST\n")
+        return 1
+    try:
+        manifest = json.load(open(manifest_path, encoding="utf-8"))
+    except ValueError:
+        sys.stderr.write("EVIDENCE_PACK_MANIFEST_CORRUPT\n")
+        return 1
+
+    stored = manifest.get("files", {})
+    mismatches = []
+
+    # Every file recorded in the manifest must still hash to the same value.
+    for fn, want in stored.items():
+        path = os.path.join(pack_dir, fn)
+        if not os.path.isfile(path):
+            mismatches.append(f"{fn}:missing")
+            continue
+        with open(path, "rb") as f:
+            got = hashlib.sha256(f.read()).hexdigest()
+        if got != want:
+            mismatches.append(f"{fn}:hash_changed")
+
+    # A new unmanifested file (except sig/head) is also tampering.
+    for fn in os.listdir(pack_dir):
+        if fn in ("artifact-manifest.json", "evidence-pack.sig", "manifest-head.txt"):
+            continue
+        if os.path.isfile(os.path.join(pack_dir, fn)) and fn not in stored:
+            mismatches.append(f"{fn}:unexpected_file")
+
+    # The stored manifest_head must match the recomputed head of `stored`.
+    canonical = json.dumps(stored, sort_keys=True, separators=(",", ":"))
+    head_now = hashlib.sha256(canonical.encode()).hexdigest()
+    if head_now != manifest.get("manifest_head"):
+        mismatches.append("manifest_head:mismatch")
+
+    if mismatches:
+        sys.stderr.write("EVIDENCE_PACK_TAMPERED " + " ".join(mismatches) + "\n")
+        return 1
+
+    cert = "unknown"
+    rs = os.path.join(pack_dir, "run-summary.json")
+    if os.path.isfile(rs):
+        try:
+            cert = str(json.load(open(rs, encoding="utf-8")).get("certified"))
+        except ValueError:
+            pass
+    print(f"EVIDENCE_PACK_INTACT files={len(stored)} certified={cert} head={head_now}")
+    return 0
+
+
+if __name__ == "__main__":
+    sys.exit(main())