The embedded Sigstore trusted root has one Rekor log; the live one has two — verification breaks when cosign moves to Rekor v2 #259

Time-sensitive, and it will present as "signatures suddenly stop verifying" rather than as an obvious staleness bug.

The gap

The trusted_root.json embedded in wsc — including on main — is 4,537 bytes and contains one transparency log: rekor.sigstore.dev.

The live Sigstore trusted root contains two: rekor.sigstore.dev and log2025-1.rekor.sigstore.dev, the latter added 2025-09-23 as part of the Rekor v2 / tiled-log migration.

Why it works today and won't tomorrow

RekorKeyring::from_embedded_trust_root() is what the non-bundle verification path uses (signer.rs:629; CertificatePool::from_embedded_trust_root at format.rs:437). Entries written to the v1 log verify, because their logID matches the embedded key.

Checked against a real artifact: varve's v0.28.0 release bundle carries logID c0d23d6a…, which matches the embedded key. So it verifies now.

The moment the cosign version in use starts writing to a log2025-* shard, verify_set fails with "No public key found for log ID", and every newly-created signature becomes unverifiable by wsc's embedded path. Old signatures keep working, which makes it look like a regression in the signing side rather than a stale root.

What survives and what doesn't

• Bundle path survives — an AirGappedVerifier uses RekorKeyring::from_pem_logs(&self.trust_bundle.transparency_logs), so a bundle built from a current trusted root carries both keys. This is a genuine argument for the bundle design.
• Embedded path does not. It is pinned to whatever was vendored at build time.

Asks

1. Refresh the embedded trusted root to include the log2025-* log key. Immediate, mechanical.
2. Make the staleness visible — a build-time or runtime warning when the embedded root is older than some threshold, or when a logID is unknown, saying "this log is not in the embedded trusted root, which was vendored on " rather than a bare "no public key found". The current message sends the reader to look at the signature, not the root.
3. Consider making RekorKeyring::from_trusted_root public (rekor_verifier.rs:421) so a consumer can supply a current root without adopting the whole bundle machinery. That is the smallest possible escape hatch for anyone who hits this before a release lands.

Also note trusted_root_to_bundle (tuf.rs:176-199) converts only certificateAuthorities and tlogs — it drops ctlogs (2 present) and timestampAuthorities (1 present) from the real trusted root, so SCT verification is not possible offline from a converted bundle. Separate concern, same function.

Found while evaluating wsc for varve (varve DD-026). Related: sigil#257 (0.11.0 unpublished), sigil#137 (inclusion proofs).