Signed claims and public verification

FedGrade is built so that provenance can be checked with math rather than taken on trust. This article explains what is signed today, what is not yet, and how verification works.

What is signed today

Generated export files. When FedGrade generates an export file (for example a filled form package), it writes a provenance manifest alongside it: a SHA-256 hash of the exact file, what it was built from, and how. The manifest is signed with FedGrade's Ed25519 key. Change the file and the hash no longer matches.

Individual Brief claims are not signed yet. The signing machinery for single claims exists, but it only applies to library-wide (anonymous) briefs, and FedGrade does not produce those today. Briefs written for your workspace are never signed, because a signed artifact embeds the claim text and the verification endpoint is designed to be public. Until that changes, rely on the Brief's citations: each claim is validated against a verbatim excerpt of its source, a claim that fails the check is shown as failed rather than hidden, and citations link to the source record where one resolves. See Citation validation.

How verification works

An artifact is serialized to a deterministic canonical form (recursively sorted keys, no whitespace) and signed. Anyone holding the artifact can:

1. Fetch the public keys from /.well-known/fedgrade-keys.json (the JWKS).
2. Recompute the canonical form of the artifact.
3. Check the Ed25519 signature against the published key for the artifact's key id.
4. Optionally recompute the excerpt or file SHA-256 to confirm the cited content.

Retired public keys stay in the verification set, so artifacts signed under an old key keep verifying.

Where to verify

During private preview, the verifier page at /verify, the POST /api/verify endpoint and the key set at /.well-known/fedgrade-keys.json require you to be signed in. They are designed to open to the public — no account, CORS-open — when FedGrade launches publicly.

The verify_claim MCP tool exposes the underlying claim-support validator — the same check FedGrade's own Briefs must pass.

Honest limits

A valid signature proves an artifact was issued by FedGrade and has not been altered. It does not, by itself, prove the underlying source is correct — that is what the citation and the source link are for.