#!/usr/bin/env python3 """Standalone verifier for the published Lean Transparency Log. Pure Python 3 standard library for hashing and structure; Ed25519 signature checking shells out to the `openssl` binary. Verifies, from the files in this repository alone: 1. every entry's leaf hash, 2. every historical Signed Tree Head against the recomputed prefix root (a split view or tampered entry fails here), 3. every STH Ed25519 signature, 4. a receipt as a FULL transparency receipt (--receipt FILE): its STH signature, key fingerprint, log id, tree-size agreement, that its leaf hash matches the named entry, that its STH is present in the published history, and its inclusion proof. FAIL-CLOSED: if signature checking is unavailable (no `openssl`, or the public key is missing), the run FAILS — signatures are load-bearing and a "couldn't check" is not a pass. Use --structural-only to explicitly ask for hashes/structure without signatures (it prints, and exits, as a reduced check, never as full verification). Usage: python3 verify.py --all python3 verify.py --receipt receipts/dalek-ed25519-verified.receipt.json python3 verify.py --all --structural-only # explicit reduced check """ import argparse import base64 import hashlib import json import shutil import subprocess import sys import tempfile from pathlib import Path HERE = Path(__file__).resolve().parent def leaf_hash(data: bytes) -> bytes: return hashlib.sha256(b"\x00" + data).digest() def node_hash(left: bytes, right: bytes) -> bytes: return hashlib.sha256(b"\x01" + left + right).digest() def merkle_root(leaves): if not leaves: return hashlib.sha256(b"").digest() if len(leaves) == 1: return leaf_hash(leaves[0]) split = 1 << ((len(leaves) - 1).bit_length() - 1) return node_hash(merkle_root(leaves[:split]), merkle_root(leaves[split:])) def verify_inclusion(leaf: bytes, index: int, size: int, proof, root: bytes) -> bool: if index >= size: return False fn, sn = index, size - 1 node = leaf_hash(leaf) for sibling in proof: if sn == 0: return False if fn % 2 == 1 or fn == sn: node = node_hash(sibling, node) if fn % 2 == 0: while fn % 2 == 0 and fn != 0: fn //= 2 sn //= 2 else: node = node_hash(node, sibling) fn //= 2 sn //= 2 return sn == 0 and node == root def canonical_json(document) -> bytes: return json.dumps(document, sort_keys=True, separators=(",", ":"), ensure_ascii=False).encode("utf-8") def load_leaves(): leaves, problems = [], [] for position, path in enumerate(sorted((HERE / "entries").glob("[0-9]*.json"))): record = json.loads(path.read_text()) data = canonical_json(record["leaf"]) if record.get("index") != position: problems.append(f"{path.name}: index {record.get('index')} at position {position}") if leaf_hash(data).hex() != record.get("leaf_hash"): problems.append(f"{path.name}: leaf_hash mismatch (tampered entry)") leaves.append(data) return leaves, problems def signatures_available() -> bool: return bool(shutil.which("openssl")) and (HERE / "provider.ed25519.pub").exists() def key_fingerprint() -> str: return hashlib.sha256((HERE / "provider.ed25519.pub").read_bytes()).hexdigest() def check_sth_signature(head) -> str: """VALID / INVALID / UNAVAILABLE. UNAVAILABLE is a FAILURE at the caller unless the run is explicitly --structural-only.""" openssl = shutil.which("openssl") key = HERE / "provider.ed25519.pub" if not openssl or not key.exists(): return "UNAVAILABLE" signatures = head.get("signatures") or {} ed = signatures.get("ed25519") or {} payload = canonical_json({k: v for k, v in head.items() if k != "signatures"}) with tempfile.TemporaryDirectory() as tmp: payload_path = Path(tmp) / "p" signature_path = Path(tmp) / "s" payload_path.write_bytes(payload) signature_path.write_bytes(base64.b64decode(ed.get("signature_base64", ""))) result = subprocess.run( [openssl, "pkeyutl", "-verify", "-pubin", "-inkey", str(key), "-rawin", "-in", str(payload_path), "-sigfile", str(signature_path)], capture_output=True, ) return "VALID" if result.returncode == 0 else "INVALID" def main() -> int: parser = argparse.ArgumentParser() parser.add_argument("--all", action="store_true") parser.add_argument("--receipt") parser.add_argument("--structural-only", action="store_true", help="skip Ed25519 signature checks explicitly; the run reports a " "REDUCED check and can never print full verification.") args = parser.parse_args() sigs_ok = signatures_available() if not args.structural_only and not sigs_ok: # Fail closed: a verifier that cannot check signatures must not # imply it did. Do not silently continue. print("FATAL: signature checking unavailable (need the `openssl` binary and " "provider.ed25519.pub). Install openssl / fetch the key, or pass " "--structural-only to run an explicit hashes-and-structure check.") return 2 leaves, problems = load_leaves() print(f"entries: {len(leaves)}") failures = list(problems) for problem in problems: print("PROBLEM:", problem) history_path = HERE / "sth-history.jsonl" heads = [json.loads(line) for line in history_path.read_text().splitlines() if line.strip()] if history_path.exists() else [] if args.all or not args.receipt: # log-wide checks (GPT §4.3): history internally consistent AND the # published latest-sth.json is exactly the final history head. previous = -1 log_id = None for position, head in enumerate(heads): size = int(head["tree_size"]) if size > len(leaves): failures.append(f"STH #{position} claims size {size} > {len(leaves)} leaves") expected = merkle_root(leaves[:size]).hex() structural = "OK" if head["root_hash"] == expected and size >= previous else "MISMATCH" if structural != "OK": failures.append(f"STH #{position} prefix-root/monotonicity") if log_id is None: log_id = head.get("log_id") elif head.get("log_id") != log_id: failures.append(f"STH #{position} log_id changed mid-history") signature = check_sth_signature(head) if signature == "INVALID" or (signature == "UNAVAILABLE" and not args.structural_only): failures.append(f"STH #{position} signature {signature}") print(f"STH #{position} size={size} root={head['root_hash'][:16]}… prefix-root:{structural} signature:{signature}") previous = max(previous, size) latest_path = HERE / "latest-sth.json" if latest_path.exists() and heads: latest = json.loads(latest_path.read_text()) if canonical_json(latest) != canonical_json(heads[-1]): failures.append("latest-sth.json is not the final sth-history head") elif int(latest["tree_size"]) != len(leaves): failures.append(f"latest-sth tree_size {latest['tree_size']} != {len(leaves)} leaves") else: print(f"latest-sth: size {latest['tree_size']} == leaf count, and == final history head OK") if args.receipt: receipt = json.loads(Path(args.receipt).read_text()) sth = receipt["sth"] index = int(receipt["leaf_index"]) entry = json.loads((HERE / "entries" / f"{index:06d}.json").read_text()) leaf_bytes = canonical_json(entry["leaf"]) # (a) the receipt's STH must be signed by THIS log's key ... rsig = check_sth_signature(sth) if rsig == "INVALID" or (rsig == "UNAVAILABLE" and not args.structural_only): failures.append(f"receipt STH signature {rsig}") # (b) ... fingerprint the receipt names must be this key ... fp = (sth.get("signatures", {}).get("ed25519", {}) or {}).get("public_key_fingerprint_sha256") if sigs_ok and fp and fp != key_fingerprint(): failures.append("receipt STH signed by a different key than provider.ed25519.pub") # (c) ... its log_id must match the log ... meta_log_id = json.loads((HERE / "log-metadata.json").read_text()).get("log_id") if (HERE / "log-metadata.json").exists() else None if meta_log_id and sth.get("log_id") not in (None, meta_log_id): failures.append("receipt STH log_id does not match this log") # (d) ... the receipt's STH must actually appear in the published history ... if heads and canonical_json(sth) not in {canonical_json(h) for h in heads}: failures.append("receipt STH is not present in sth-history.jsonl") # (e) ... the receipt's leaf_hash must match the named entry ... if receipt.get("leaf_hash") and receipt["leaf_hash"] != leaf_hash(leaf_bytes).hex(): failures.append("receipt leaf_hash does not match the named entry") # (f) ... tree_size agreement ... if int(receipt.get("tree_size", -1)) != int(sth.get("tree_size", -2)): failures.append("receipt tree_size != its STH tree_size") # (g) ... and finally the inclusion proof itself. ok = verify_inclusion( leaf_bytes, index, int(receipt["tree_size"]), [bytes.fromhex(h) for h in receipt["inclusion_proof"]], bytes.fromhex(sth["root_hash"]), ) if not ok: failures.append("receipt inclusion proof") print(f"receipt leaf {index} of {receipt['tree_size']}: STH-sig:{rsig} bindings:" f"{'OK' if not any('receipt' in f for f in failures) else 'FAIL'} inclusion:{'VALID' if ok else 'INVALID'}") mode = "REDUCED (structural only, signatures NOT checked)" if args.structural_only else "full" if failures: print(f"RESULT: FAILED ({len(failures)} problems) [{mode}]") return 1 print(f"RESULT: OK [{mode}]" + ("" if not args.structural_only else " — signatures were NOT verified; this is not full verification")) return 0 if __name__ == "__main__": sys.exit(main())