Researcher shows a Google C2PA chain with a trivial leaf key
Original title: C2PA's eMudhra Moment
David Buchanan says media tools often lack revocation and that a known C2PA issuance flaw breaks its trust model.
David Buchanan compares the eMudhra CA compromise response with C2PA, which he says is still immature and often lacks revocation support. He publishes a signed CMS message chaining to Google's C2PA root on the official trust list, using a leaf whose private key is the digit 4. He says he can have Google's intermediate sign any leaf he chooses by an undisclosed, already public method, and that this breaks the C2PA trust model even though it is not a compromised intermediate.
Unconfirmed: The issuance method is undisclosed; Buchanan says the flaws are already public and the demo is a leaf, not a compromised intermediate.
- The demo leaf private key is the single digit 4.
- The signature chains to Google C2PA Root CA G3.
- Buchanan says the issues are publicly known and not bounty-eligible.
- He says he will not describe the issuance method.
- He contrasts this with browsers that quickly picked up eMudhra revocations.
Impact: Forged C2PA signatures accepted under Google's trust chain
| Product | Affected |
|---|---|
| Google C2PA certificates | — |
From the original article
2 min read at da.vidbuchanan.co.ukThe eMudhra incident has shown how the modern Web PKI ecosystem reacts to a CA compromise. All things considered, I think it went smoothly—all the web browsers I use picked up the revocations swiftly. But it has also been a clusterfuck, with eMudhra trying to downplay their responsibilities and refusing to elaborate on how exactly the failure occurred.
By da.vidbuchanan.co.uk by retr0id · da.vidbuchanan.co.uk
A short excerpt; the article and its images belong to the publisher. Summary, key facts and assessment above are AI-written from the article and can be wrong.