OpenChainGraph Suite · ART-424 · Transparency & Anchoring
Witness Cosignature Verifier
Verifies a C2SP tlog-checkpoint + witness-cosignature note (SPEC.md §20.2) entirely offline: parses the signed note, checks its origin and root against your batch anchor's declared hash, and verifies each pinned witness's cosignature — Ed25519 cosignature/v1 or ML-DSA-44 — against a k-of-n threshold. A cosignature line with no matching valid signature, or fewer than k valid witnesses, FAILS the verdict.
This tool states only that ≥k of your pinned witness keys signed the note's root (cosignature mode) or that a proof correctly bridges two checkpoints (consistency mode). It does NOT establish that the log itself is honest or complete, that pinned keys belong to the parties they claim to be, or that any specific artifact leaf is included in the tree (see SPEC.md §20.1 for leaf inclusion).
🔒 All inputs are processed locally in your browser. No data is transmitted. This tool consumes checkpoint note text you already have (e.g. from a c2sp.org/tlog-proof bundle) — it performs zero network fetches and never operates, mirrors, or serves a log.
Batch Anchor + Checkpoint Note
The sha256:-prefixed (or bare hex) root your §20/§20.1 anchor binding declares.
If set, the note's origin line must match exactly.
The C2SP tlog-checkpoint signed note: origin, size, base64 root, a blank line, then one — <name> <base64> cosignature line per witness.
Each entry: {"name","algorithm":"ed25519"|"ml-dsa-44","public_key_b64"}. Pin these out-of-band — this tool does not establish key ownership.
Two Checkpoints + Consistency Proof
Verifies the log did NOT rewrite history between an older checkpoint you observed and a newer one — a proper RFC 6962 consistency proof. This is complementary to witness-cosignature verification above (which checks a single checkpoint's signatures), not a replacement for it: pin/verify each checkpoint's own authenticity separately.
If set, both checkpoints' origin lines must match this exactly (as well as each other).
The earlier signed checkpoint: origin, size, base64 root (cosignature lines, if any, are ignored in this mode).
The later signed checkpoint from the same log.
The RFC 6962 §2.1.2 consistency-proof node list, e.g. from a c2sp.org/tlog-proof bundle's consistency endpoint.