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A verifier configured with WithTransparencyLog(N>1) or WithSignedCertificateTimestamps(N>1) expected defense-in-depth against the compromise of a single log instance. However, threshold counting treated verified entries per-entry rather than per-log. As a result, a single compromised transparency log could forge multiple entries with different indices, and a single compromised CT log could verify multiple times (either across multiple certificate chains or via multiple embedded SCTs), fully satisfying the multi-log threshold requirements and defeating the multi-log policy. This change ensures that a threshold of N can only be satisfied by N independent logs by enforcing that each distinct transparency log and CT log identity counts as at most one witness towards threshold and observer timestamp policies. Signed-off-by: Hayden <8418760+Hayden-IO@users.noreply.github.com>
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A verifier configured with WithTransparencyLog(N>1) or WithSignedCertificateTimestamps(N>1) expected defense-in-depth against the compromise of a single log instance. However, threshold counting treated verified entries per-entry rather than per-log.
As a result, a single compromised transparency log could forge multiple entries with different indices, and a single compromised CT log could verify multiple times (either across multiple certificate chains or via multiple embedded SCTs), fully satisfying the multi-log threshold requirements and defeating the multi-log policy.
This change ensures that a threshold of N can only be satisfied by N independent logs by enforcing that each distinct transparency log and CT log identity counts as at most one witness towards threshold and observer timestamp policies.
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