Recently, Let's Encrypt launched free wildcard certificates. While this is good news in and of itself, as it removes one of the last remaining reasons for expensive commercial certificates, I've unfortunately seen a lot of people dangerously misunderstand what wildcard certificates are for.
Therefore, in this brief post I'll explain why you probably shouldn't use a wildcard certificate, as it will put your security at risk.
It's generally pretty poorly understood (and documented!) how TLS ("SSL") works, so let's go through a brief explanation of the parts that are important here.
The general (simplified) idea behind how real-world TLS deployments work, is that you:
