Certificate Authority Trustworthiness

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2024-12-01 05:30:04

The certificate authority (CA) system does an incredible job of solving an impossible challenge. Think about it. The CAs measure control of a domain name and then issue TLS certificates that pair cryptographic keys to those names. They do this on a global scale, often automatically. It’s impossible to do this perfectly, and unfortunately, they occasionally fail.

In this post I describe the challenges the CAs face, describe a history of failures, and explain the process we use to maintain confidence in the system in spite of it all.

The certificate authorities (CAs) solve a foundational key exchange problem for the Internet. They allow us to authenticate the TLS keys used by web servers, which they do by verifying control of domain names and signing certificates that associate public keys with these names. Authentication is a critical part of encrypting communications. Without authentication you may be encrypting with an attacker’s key, allowing them to eavesdrop on or tamper with your data in transit.

Methods like certificate pinning work for things like IoT or mobile applications that communicate with a single back-end server. The developer can hardcode the certificate fingerprint and push an update any time it changes. But pinning doesn’t scale for websites or email. We need something Internet-scale, and we’ve got the CAs.