>For example, Chrome Desktop, Firefox, and IE did not enforce HPKP if they encountered a cert from a user-added CA. Why does Android do the opposite? I don't se

>For example, Chrome Desktop, Firefox, and IE did not enforce HPKP if they encountered a cert from a user-added CA. Why does Android do the opposite? I don't see the threat model they are addressing. From what I understand in the post, desktop Chrome and Android Chrome are the same. If you add the user-added CA to the user store, it doesn't need CT. If you add the user-added CA to the system store, it does need CT. On desktop, everyone adds them to the user store. On Android, most reverse engineers added them to the system store, which causes the problem. > I don't see the threat model they are addressing. The idea is that if it's in the system store, Chrome thinks it must be a real CA and thus needs to follow real CA rules, whereas if it's in the user store, it's a weird CA that the user likes and wants to be treated specially, so the CA doesn't need to follow the rules. To focus more in on threats: a system CA is a big juicy target for hackers or malicious governments, because it can issue a cert that any device will trust, so it needs lots of oversight, like CT. As opposed to a user CA, which is something tiny, that likely only this specific user trusts, so it's not a big target for hackers, and thus doesn't need to follow CT. This whole thing breaks down if the user adds a cert into the system store, because then Chrome thinks it's a big target and needs a lot of oversight, when actually it's a tiny target and doesn't. Disclosure: Google employee