sigstore: reject duplicate-log SCTs (SPEC §5.2)#101
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Add an explicit anti-amplification guard: a leaf certificate whose embedded SCT list contains two or more SCTs sharing the same CT log ID is rejected, so a single (compromised or replayed) CT log cannot contribute more than one SCT toward the requirement. sigstore-python already rejects this case incidentally via its exactly-one-SCT rule, but reject_duplicate_sct_logs makes the rejection principled and on the same per-log-id basis as tinfoil-rs/-js/-go. It runs ahead of verify_dsse; single-SCT (real Fulcio) bundles are unaffected. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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Fix all with cubic | Re-trigger cubic
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Add an explicit guard: a leaf certificate whose embedded SCT list contains two or more SCTs sharing the same CT log ID is rejected, so a single CT log cannot contribute more than one SCT toward the requirement.
sigstore-python already rejects this case incidentally via its exactly-one-SCT rule, but reject_duplicate_sct_logs makes the rejection principled and on the same per-log-id basis as tinfoil-rs/-js/-go. It runs ahead of verify_dsse; single-SCT (real Fulcio) bundles are unaffected.
Summary by cubic
Enforces SPEC §5.2 by rejecting bundles whose signing certificate includes multiple SCTs from the same CT log. Adds a pre-verification guard so a single log cannot count more than once; real Fulcio single-SCT bundles are unaffected.
reject_duplicate_sct_logsto detect duplicate SCT log IDs and raiseVerificationError.tinfoil-rs/tinfoil-js/tinfoil-gobeyondsigstore-python’s generic exactly-one-SCT check.Written for commit f5e8289. Summary will update on new commits.