this post was submitted on 16 Oct 2024
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I'm not gonna lie I still don't understand how passkeys work, or how they're different from 2fa. I'm just entering a PIN and it's ok somehow? I don't get it.
It uses asymmetric cryptography. You sign a login request with the locally stored private key and the service verifies the signature with their stored public key. The PIN on your device is used to unlock access to the private key to sign the login request.
So isn't the pin now the weakest link and shorter than a password
Typically in most situations where a PIN is used on a modern device, it is not just the number you enter but some kind of hardware backing that is limited to the local device and also does things like rate limiting attempts.
The passkey stored locally in some kind of hardware backed store on your device or in your password manager is the first factor: something you have.
The PIN/password or fingerprint/face to unlock the device and access the stored passkey is the second factor: something you know or something you are, respectively.
Two factors gets you to 2FA.
If you've ever used ssh it's very similar to how ssh keys work. You create a cryptographic key for the site; this is the passkey itself. When you go to "log in" the client and server exchange cryptographic challenges, which also verifies the site's identity (so you can't be phished...another site can't pretend to be your bank, and there are no credentials to steal anyway). Keys are stored locally and are generally access restricted by various methods like PIN, passphrase, security key, OTP, etc. When you're entering your PIN it's how the OS has chosen to secure the key storage. But you've also already passed one of the security hurdles just by having access to that phone/computer. It is "something you have".
So one password to access them all basically?
That's quite a weakness.
It''s really up to the end device (and the user of said device) to decide how much security to put around the local keys. But importantly, it also requires access to the device the passkeys are stored on which is a second factor. And notably many of the implementations of it require biometrics to unlock.
The "one password" thing is also true of password managers, of course. One thing about having one master passphrase is that if you do not have to remember 50 of them, then you can make that passphrase better then you otherwise might, plus it should be unique, which prevents one of the most common attack vectors.
That's essentially how all password managers work currently though?
True, I hoped for something better :-/
If it makes you feel better, most PINs on modern devices are hardware backed in some way (TPM, secure enclave, etc) and do things like rate limiting. They'll lock out using a PIN if it's entered incorrectly too many times.
If you get my master keepass password, you have all my passwords, too.
As I said to Spotlight7573 yes true, I just hoped for something better.
If you're paranoid about this, go buy a yubikey and use that to secure your device/access to your passkeys. Being able to secure your own data instead of relying on the admin who may or may not know what they're doing to secure the server is an advantage of passkeys.