Passkeys are the reverse password you never need to remember. 

Instead of having your username and password stored on the server and it letting you in if you can make it match, the passkeys instead rely on your device to unlock a secret key, and only if the keys match mathematically, will the authentication be granted. 

The benefits:  

You can't be tricked! The website/app is coming to you clearly identifying itself and providing their version of the 'key'. Your private key will only work with its corresponding key held by the true website. 

It's more secure! You need to prove you are you (using biometrics such as a fingerprint or face scan on your phone or a device) and will need to actually have the device on you to first unlock your private key and it never leaves your device. If the server is hacked, then it's basically useless information. 

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