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March 29, 2018

These Three Companies Are Doing the Internet a Solid By Running Certificate Transparency Logs

When we use the Internet, we rely on the security of the certificate authority system to ensure we are talking with the right people. Unfortunately, the certificate authority system is a bit of a mess. One of the ways we're trying to clean up the mess is Certificate Transparency, an effort to put all SSL certificates issued by public certificate authorities in public, verifiable, append-only logs. Domain owners can monitor the logs for unauthorized certificates, and web browsers can monitor for compliance with the rules and take action against non-compliant certificate authorities. After ramping up for the last four years, Certificate Transparency is about to enter prime time: Google Chrome is requiring that all certificates issued on or after April 30, 2018 be logged.

But who is supposed to run these Certificate Transparency logs? Servers, electricity, bandwidth, and system administrators cost money. Although Google is spearheading Certificate Transparency and operates nine logs that are recognized by Chrome, Certificate Transparency is supposed to benefit everyone and it would be unhealthy for the Internet if Google ran all the logs. For this reason, Chrome requires that certificates be included in at least one log operated by an organization besides Google.

So far, three organizations have stepped up and are operating Certificate Transparency logs that are recognized by Chrome and are open to certificates from any public certificate authority:

DigiCert was the first non-Google organization to set up a log, and they now operate several logs recognized by Chrome. Their DigiCert 2 log accepts certificates from all public certificate authorities. They are also applying for recognition of their Nessie and Yeti log sets, which accept certificates from all public certificate authorities and are each split into five shards based on the expiration year of the certificate. (They also operate DigiCert 1, which only accepts certificates from some certificate authorities, and have three logs acquired from Symantec which they are shutting down later this year.)

DigiCert is notable because they've written their own Certificate Transparency log implementation instead of using an open source one. This is helpful because it adds diversity to the ecosystem, which ensures that a bug in one implementation won't take out all logs.

Comodo Certification Authority (which is thankfully no longer owned by the blowhard who thinks he invented 90 day certificates) operates two logs recognized by Chrome: Mammoth and Sabre. Both logs accept certificates from all public certificate authorities, and run SuperDuper, which is Google's original open source log implementation.

In addition to operating two open logs, Comodo CA runs, a search engine for certificates found in Certificate Transparency logs. has been an invaluable resource for the community when investigating misbehavior by certificate authorities.

Cloudflare is the latest log operator to join the ecosystem. They operate the Nimbus log set, which accepts certificates from all public certificate authorities and is split into four shards based on the expiration year of the certificate. Nimbus runs Trillian, Google's latest open source implementation, with some Cloudflare-specific patches.

Cloudflare is unique because unlike DigiCert and Comodo CA, they are not a certificate authority. DigiCert and Comodo have an obvious motivation to run logs: they need somewhere to log their certificates so they will be trusted by Chrome. Cloudflare doesn't have such a need, but they've chosen to run logs anyways.

DigiCert, Comodo CA, and Cloudflare should be lauded for running open Certificate Transparency logs. None of them have to do this. Even DigiCert and Comodo could have adopted the strategy of their competitors and waited for someone else to run a log that would accept their certificates. Their willingness to run logs shows that they are invested in improving the Internet for everyone's benefit.

We need more companies to step up and join these three in running public Certificate Transparency logs. How about some major tech companies? Although we all benefit from the success of Certificate Transparency, large tech companies benefit even more: they are bigger targets than the rest of us, and they have more to gain when the public feels secure conducting business online. Major tech companies are also uniquely positioned to help, since they already run large-scale Internet infrastructure which could be used to host Certificate Transparency logs. And what kind of tech company doesn't want the cred that comes from helping the Internet out?

If you're a big tech company that knows how to run large-scale infrastructure, why aren't you running a Certificate Transparency log too?


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