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. It does NOT establish that the log itself is honest or complete, that the 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 a 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.