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Joined 11 months ago
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Cake day: June 6th, 2023

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  • You are not wrong, but you we should understand what class of attacks we are protecting against. Will biometrics stop your maid from using your device? Probably less. Will it stop the FBI? Not so sure.

    Now, you may say, an FBI raid is not what you worry about on a daily basis. Agree.

    If you are trying to keep the photos on your device safe from snooping, your good. Attacker needs the device and your fingerprint.

    When we talk online accounts, I’d count device+fingerprint as one factor. Sure, the maid from the example above can’t login into your gmail without your fingerprint, but most attacks are online. Your device sends a token to gmail, a cookie, a String; that’s like a password. One factor.

    Technically, it’s slightly better than a password, because this token can be short-lived (although often it’s not), could be cryptographic signature to be used exactly once (although…), you cannot brute-force guess the token… But IF the token leaks, the attacker has full access (or enough to cause damage).

    That’s why I would suggest an independent second factor, such as password. Yes, a password. Not for your daily routine (biometrics+device is much better), but maybe for high-risk operations.


  • Well

    The biometrics only unlock the device

    Yes

    and give access to the security key

    This is the goal, sure, but what does this actually mean on device that’s mostly governed by software?

    There’s a chip (like a yubikey) in the device that can hold cryptographic keys.

    That’s good because the key cannot (easily) be extracted from the device.

    That’s good as long as no one has physical access to your device.

    With physical access, you hope that the device’s unlock mechanism is reasonably secure. That’s biometrics OR password/pin.

    The ‘or’ is the problem. For practical reasons you don’t want exactly one method hard-wired. You have a fingerprint scanner (good enough), the secure element (good enough) and lots of hard- and software in between (tricky).

    I’m not against biometrics (to unlock a device) because it’s convinient and much better than not locking the device at all. I’m also not against device trust (which you need if you want to store crypto keys sonewhere without separate hardware), but the convience of a single-device solution (laptop or phone) comes with a risk.

    If an attacker can bypass the unlock method or trick you into unlocking or compromise the device, your secrets are at risk. Having the key stored in the secure enclave (and not in a regular file on the hard disk) prevents copying the key material, but it does not prevent using the key when the attacker has some control over the (unlocked) device.

    A yubikey is more secure because it’s tiny and you can carry it on your keychain. The same chip inside your laptop is more likely to fall into the hands of an attacker.