The Death of the Password: Step-by-Step Implementation of Passkeys and WebAuthn

Passwords have outlived their security value. They rely on humans to generate, memorize, and manage complex credentials across dozens of services. The result is predictable: credential stuffing, phishing, reuse, and widespread account takeovers.

Passkeys, which are based on the WebAuthn standard and the FIDO2 framework, are a way of moving beyond knowledge-based authentication (something you know) to a possession-based, cryptographically enforced authentication (something you have). With the help of public-key cryptography, asymmetric key pairs, and hardware-backed secure enclaves, Passkeys are completely resistant to remote phishing and credential leaks.

Core Concepts and Entities

• Passkey: A set of two cryptographic keys (public and private). The private key is kept locked on the user’s device and the public key is stored on the application server.
• WebAuthn (Web Authentication API): W3C (Web 3 Consortium) standard built into web browsers so that web applications and services can communicate directly with local device authenticators.
• Authenticator: The component of the hardware or system to manage the keys, such as Apple Touch ID/Face ID, Windows Hello, Android Biometrics, or hardware security keys like YubiKeys.
• Relying Party (RP): The application server that issues challenges, stores public keys and provides access.

Step 1: User Registration Flow

Registration is the process of associating a public key with an account profile, and leaving the corresponding private key on the local device.

1. Initiate Request: User clicks on “Create Passkey” in his/her account settings.
2. Challenge Generation: The server generates a unique, randomized string (a cryptographic challenge) linked to the user’s current session, alongside domain constraints (Relying Party ID).
3. Hardware Prompt: Browser passes challenge parameters to the native OS authenticator prompt screen, which asks the user for biometrics and/or a PI.
4. Key Generation: When the authenticator validates, it generates a brand new unique asymmetric key pair particular to that domain.
5. Signing & Payload Creation: Using the newly created private key, the authenticator signs the challenge sent by the server, and creates a payload with the public key metadata (attestation).
6. Server Verification & Storage: The server checks the cryptographic signature for validity with respect to the original challenge. If it is confirmed, it will be stored along with the user’s account entry the public key and credential ID.

Step 2: User Authentication Flow

Logins bypass traditional credential checks by proving ownership of the private key.

1. Request Login Options: The user triggers a passkey login or selects an existing passkey prompt.
2. Issue New Challenge: The server responds with a brand-new cryptographic challenge bound to that specific authentication attempt.
3. Authenticator Interaction: The browser passes the challenge to the local device. The device prompts the user for biometric approval (Touch ID, Face ID, or PIN) to unlock access to the stored private key.
4. Assertion Signing: The private key signs the server challenge to produce an authentication assertion proof.
5. Cryptographic Verification: The server uses the stored public key to decode and verify the incoming assertion. If the signature matches the challenge and domain rules, the server establishes a valid user session.

Production Security and Edge Cases

Moving passkeys to production requires planning for real-world application demands and device limitations.