Every Passkey Needs a Silent Partner

Passkeys provide phishing-resistant daily authentication through WebAuthn public-key cryptography, but they do not independently establish a user’s identity at account creation or offer a reliable recovery route after a user loses their last credential. The article proposes pairing passkeys with Vonage Verify API’s Silent Authentication, which verifies possession of a phone number through the SIM and carrier network without exposing an OTP or other secret to the user. In the recommended lifecycle, Silent Authentication validates the phone number during sign-up before the first passkey is registered, passkeys handle routine sign-ins, and Silent Authentication supports account recovery, new-device enrollment, or optional step-up checks for sensitive actions. The implementation involves initiating a Verify v2 workflow with silent authentication and an SMS fallback, opening the returned check URL over cellular data, confirming the carrier response through the backend, and then completing WebAuthn registration with discoverable credentials and verified biometric or PIN user verification. While the approach avoids reverting to phishable email links or codes for key lifecycle events, it still requires safeguards for phone-number recycling and SIM-swap risks, such as recovery monitoring, notifications, delays on high-value changes, and event logging.

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