Trusted Everywhere, Impact Everywhere

One of the private keys behind eight eMudhra intermediate CA certificates was the integer 4. Several other keys in the same set were nearly as easy to recover. Keys capable of supporting trusted TLS issuance made it through key generation, certification, auditing, and root program review before an outside researcher noticed, and the previous article examined how that happened. This article asks why a failure at an Indian CA became an incident response problem for relying parties around the world that had never chosen to use eMudhra. The answer lies in how the WebPKI allocates trust. A CA admitted without constraints to a browser or operating system root store can certify names far beyond the customers, country, language, or regulatory regime it actually serves. Root stores differ, some CAs carry name constraints, and some applications maintain their own trust stores, so not every client trusts every CA. Wherever that authority is accepted, though, the relying party inherits the…