Cryptography is an implementation detail. When you connect to PayPal, how do you know it is actuality PayPal? Well, they show you a certificate saying that th

Cryptography is an implementation detail. When you connect to PayPal, how do you know it is actuality PayPal? Well, they show you a certificate saying that they are. Why would you trust that certificate? Well, it was issued by someone you trust already, some sort of authority. The authority can revoke certificates they issued before, that may happen for all sorts of reasons. Looks like this is what happened here.