gpa-verify 1.1.0

Independent verifier for GetProofAnchor evidence bundles

gpa-verify

Independent verifier for GetProofAnchor evidence bundles.

Reads only the bundled ZIP — no network requests, no GetProofAnchor servers contacted at any point during verification. Same input → same verdict on every machine.

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Why does this exist?

A GetProofAnchor evidence bundle is a .zip containing a screenshot, HTML, HAR, video, TLS chain, eIDAS qualified timestamp, OpenTimestamps Bitcoin anchor, and an append-only hash chain. The bundle claims:

This URL existed in this exact form at this exact time.

For court use, the cryptographic part of that claim must be independently verifiable — a forensic expert appointed by a court should be able to confirm or deny it without relying on the GetProofAnchor service.

gpa-verify is the reference implementation of that verification protocol. It runs offline, contacts no external services at runtime, and produces a deterministic verdict.

Scope of verification

This tool verifies the cryptographic seals on an evidence bundle. A successful verdict establishes that the bundle is internally consistent, cryptographically intact since sealing, and bound to a qualified electronic timestamp from an EU-accredited Trust Service Provider.

It does not, on its own, establish that the screenshot or HTML faithfully represent what an ordinary visitor would have seen at the captured URL — that question depends on the trustworthiness of the capture process and is supported (but not proved) by the bundled video recording, HAR network log, and TLS evidence. A complete forensic opinion combines this cryptographic verification with the visual and network record, and any contextual evidence available to the examiner.

See the Threat model section below for a precise statement of what each layer catches and what is out of scope.

Install

pip install gpa-verify

Requires Python 3.9+. Two pure-Python wheels are installed automatically: asn1crypto (RFC3161 / CMS / X.509 parsing) and cryptography (RSA / ECDSA signature verification).

Note on Python command name: On Linux and macOS the command is python3 and pip3; on Windows it is python and pip.

Use

gpa-verify path/to/GetProofAnchor_Evidence_*.zip

GetProofAnchor Evidence Verifier
────────────────────────────────────────────────────────────────
  Proof ID:       aeb2b103-d7c5-441c-b540-c0df600a34cf
  Bundle format:  getproofanchor-evidence-2
  Generated at:   2026-05-07T08:30:25Z

  [PASS]  bundle_integrity
          31/31 files OK

  [PASS]  cross_references
          5/5 cross-checks OK

  [PASS]  chain_integrity
          1 entries, all linked

  [PASS]  eidas_signature
          valid RFC3161 token, signed by CN=SK TIMESTAMPING UNIT 2026R,
          gen_time=2026-05-07T08:30:24+00:00

  [PASS]  anchor_canonical_hash
          canonical SHA matches manifest (968f0c691384c87c...)

  [PASS]  ots_receipt
          valid OTS proof for anchor SHA 968f0c69..., bitcoin status=pending

  [PASS]  tls_evidence
          leaf cert SHA-256 matches tls.json (e7668f38708d0411...)

────────────────────────────────────────────────────────────────
  ✓ VERIFIED  (7 passed, 0 failed, 0 skipped)

JSON output for automation

gpa-verify --json bundle.zip > report.json

Exit codes

Code	Meaning
0	All checks passed
1	At least one check failed
2	Invalid arguments / cannot read ZIP

What it actually checks

Verification runs in seven layers, each tightening the forensic claim. All layers must pass for a VERIFIED verdict.

Layer 1 — Bundle integrity

Every file declared in manifest.json exists and its SHA-256 matches. Catches any byte-level tampering with the bundle.

Layer 2 — Cross-references

proof.json's SHA-256 claims for screenshot.png, page.html, content.txt, and capture/capture_meta.json agree with actual file contents. Sidecar *.sha256 files agree. Catches selective tamper that fixes one file but forgets another.

Layer 3 — Chain integrity

chain/proof_chain.jsonl entries form a valid hash chain: entry_hash == SHA256(prev_hash | event_type | proof_id | data_hash), recursively verified. chain/chain_head.json matches the last entry. Catches tampering with the append-only event log.

Layer 4 — eIDAS signature

This is the cryptographic heart of the verification. The RFC3161 token in timestamp/eidas.tsr is verified for:

1. Status — token grant status is granted or granted_with_mods.
2. Imprint — the message digest the TSA signed equals SHA256(timestamp/eidas_payload.json). Binds the timestamp to this evidence bundle, not someone else's.
3. CMS signature — the SignedData blob is verified against the signer certificate's public key, with proper signed-attributes re-encoding ([0] → SET OF per RFC 5652).
4. timeStamping EKU — the signer certificate has the id-kp-timeStamping Extended Key Usage. Defends against substitution from a non-timestamping certificate.

Together these prove the token can ONLY have been issued by the named TSA, and ONLY for our exact payload.

Supported signature algorithms: RSA-PKCS1v15, ECDSA, RSA-PSS (across SHA-256, SHA-384, SHA-512 digests).

Layer 5 — Anchor canonical hash

manifest.anchor.payload_sha256 equals SHA-256 of the canonical JSON of anchor/anchor_payload.json (sorted keys, no whitespace, UTF-8). Catches anchor receipts pointing to a different chain than ours.

Layer 6 — OTS receipt structure

anchor/anchor_receipt.ots is a valid OpenTimestamps proof and its file-hash field equals the anchor canonical SHA. Catches substituted Bitcoin anchors. (Full Bitcoin block confirmation requires a Bitcoin node and is therefore out of scope; use the ots client for that.)

Layer 7 — TLS evidence

tls/leaf_cert.pem SHA-256 fingerprint matches the network/tls.json claim. Confirms the TLS leaf certificate stored in the bundle is the same one observed at capture time.

Threat model

gpa-verify defends against the following attacks:

Attack	Caught by
Modify any file (image, HTML, HAR, etc.)	Layer 1
Modify file + manifest SHA	Layer 2 (proof.json)
Modify chain entry	Layer 3
Forge eIDAS payload + update all SHAs	Layer 4 (imprint mismatch)
Substitute eIDAS token from non-TSA cert	Layer 4 (EKU check)
Substitute anchor for a different chain	Layer 5
Substitute OTS receipt	Layer 6
Substitute leaf TLS cert	Layer 7

It does not verify:

• Whether the OpenTimestamps receipt has been confirmed in a Bitcoin block. This requires an online Bitcoin node — use the ots client.
• Whether the TSA's certificate is currently listed on the EU Trusted List. The bundle includes a snapshot of the EU Trusted List as supporting context, but real-time validation against the live list is out of scope for an offline tool.
• Whether the captured page actually showed what the screenshot shows. This is a content question, not a cryptographic one. The bundled capture.webm video, HAR network log, and TLS evidence exist to support that forensic judgement, but interpreting them is the job of a qualified examiner.

API

from gpa_verify import verify_evidence_zip

with open("evidence.zip", "rb") as f:
    report = verify_evidence_zip(f.read())

if report.all_passed:
    print(f"VERIFIED  proof {report.proof_id}")
else:
    for c in report.checks:
        if not c.passed and not c.skipped:
            print(f"FAIL  {c.name}: {c.detail}")

Building from source

git clone https://github.com/Getproofanchor/gpa-verify.git
cd gpa-verify
pip install -e .[dev]
pytest

License

MIT — see LICENSE.

This tool is published as open source so any forensic expert, court-appointed examiner, or independent journalist can audit the verification logic line by line. The cryptographic algorithms used (RFC 3161, CMS / RFC 5652, X.509, SHA-256, RSA, ECDSA, OpenTimestamps) are open standards.

Standards & references

• eIDAS Regulation (EU) 910/2014, Article 41 — qualified electronic timestamps and their legal effect across EU Member States
• ETSI EN 319 422 — Time-stamping protocol and electronic time-stamp profiles
• ETSI EN 319 421 — Policy and security requirements for trust service providers issuing time-stamps
• ETSI EN 319 102-1 — Procedures for creation and validation of AdES digital signatures
• ISO/IEC 27037:2012 — Guidelines for identification, collection, acquisition and preservation of digital evidence
• RFC 3161 — Time-Stamp Protocol (TSP)
• RFC 5652 — Cryptographic Message Syntax (CMS)
• RFC 5280 — X.509 certificates
• OpenTimestamps — Bitcoin-anchored timestamps
• EU Trusted List — qualified TSPs