letsencrypt / letsencrypt/boulder
CA: Add lint/check that SCTs validate before issuing final cert
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- Dominant language
- Go
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Description
This idea came out of remediation for https://bugzilla.mozilla.org/show_bug.cgi?id=1838667
Recently we've seen two reasons that the SCTs included in a final cert might not actually validate:
- A GTS incident where they used the SCTs from the wrong precert
- Our incident where the SCT signatures were calculated over different bytes (because the precert didn't match the final cert)
However, we have no lint that checks this. The certificate-transparency-go library checks that the SCTs returned by CT logs actually validate over the precert contents, but we don't have a check that they also validate over the final cert contents.
We should add a lint-like check which confirms this. It will need the CT log public keys in order to successfully validate the SCT signatures. https://github.com/zmap/zlint/issues/728 may handle this for us, in which case this bug should track updating and enabling that lint.
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start by reviewing certificate-transparency-go's SCT validation behavior and the requirements for obtaining CT log public keys. Check whether zlint issue #728 provides the needed lint, then determine how it could be updated and enabled for Boulder. Done means a lint confirms that SCTs in a final certificate validate against that certificate's contents.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- go
- Domain
- cryptography, security
- Issue type
- Feature
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 38/100