Re:Let's Encrypt Has Issued a Billion Certificates
by tialaramex on Thursday February 27, 2020 @04:24PM
(#22438089)
Pinning can be used with anything in the chain not just your leaf.
Some pinning strategies assume a particular CA is trustworthy and pin the public key for that CA, so that they don't need to update with new pins just because they got a new certificate. Obviously you do need to stay on your toes (if you pinned Symantec and then it got distrusted... need to get new pins pronto) but that's true for any pinning strategy. Laziness plus pinning is a bad combination. Like er... keeping tigers as pets and having a toddler maybe?
In X.509, the CA never sees the private key associated with a certificate. So while a state actor could always manufacture a “legitimate CA-signed” replacement cert and MITM you with it, they can’t do anything about modern defense-in-depth security approaches like certificate pinning, since it’s the particular public key of the original cert being pinned, not the CA’s authority + CN.