> Security is important
The argument that this is actually a security benefit is a farce. It doesn't do anything. If the device is compromised then it's going to capture your password and send it to the attacker without attempting any attestation. So the only time the attestation is attempted is when the device isn't compromised.
Yes, if it was a measure of device security they would revoke attestation of devices that are behind on security updates. But no, a 5 year old device that never got security updates is A-OK according to Google but a completely up to date custom ROM is not.
It's clearly not about real security. It is about control. You follow the rules and get Google's blessing or no SafetyNet for you. These rules include things like ensuring that the user can't access their own data without the controlling app's permission.
> Yes, if it was a measure of device security they would revoke attestation of devices that are behind on security updates.
The new attestation system Google introduced recently (which I think also more strongly forces hardware-based attestation for phones that support it and is therefore more difficult to bypass) actually does that – the very highest attestation level requires running a security update not older than one year if I remember correctly.
What remains to be seen how much that'll get used in practice – users with rooted phones or custom ROMs are rare enough that a lot of vendors seemingly have no qualms excluding them, whereas users with outdated phones are probably a somewhat more sizeable number.
I think you are right that it is about control.
Let me offer another perspective. The OS vendor actually has significant control over your device. They could plant backdoors in different layers of the OS.
Therefore, in their defense, if the OS doesn't come from a trusted source (in the bank's or Google's point of view), your bank's credentials are essentially compromised.
You could argue that there are backdoors either way. They are just controlling which party gets to plant the backdoors, after all.
> Therefore, in their defense, if the OS doesn't come from a trusted source (in the bank's or Google's point of view), your bank's credentials are essentially compromised.
"Compromised" means that someone has them who will use them for unauthorized activity. When your device is infected with malware because it's running the same version of Android it came with that hasn't received a security update in several years, entering your credentials into that device will cause them to be compromised. When your device has a custom ROM that isn't sending your credentials to anyone it isn't supposed to, they are not compromised.
But the first device passes attestation and the second one doesn't. Moreover, that is the common case -- the version of Android that came with the device is likely to be older and have more vulnerabilities than a custom version installed later. Which means that passing attestation isn't just uncorrelated with uncompromised devices, it's actually anti-correlated with them. Requiring it is forcing users to keep and use the older OS with known vulnerabilities on that device.