What is 'passwordless authentication via passkeys' and what underlying standard does it use?

• A.Passkeys use email magic links stored in a cloud service instead of passwords
• B.Passkeys are SMS-based tokens that use a phone number as the second factor
• C.Passkeys are an implementation of FIDO2/WebAuthn that creates platform-backed cryptographic credentials stored in the device's secure element (TPM, Secure Enclave). During registration, a public/private key pair is created for the specific website (bound to the origin). During authentication, the device signs a challenge from the server using the private key - the server verifies with the stored public key. Passkeys are phishing-resistant (origin-bound), sync across devices via iCloud/Google Password Manager, and replace passwords entirely
• D.Passkeys are hardware tokens (like YubiKey) that must be physically purchased and provisioned