Passkeys / FIDO2: Public-Key Registration &…

What Passkeys / FIDO2 Are

Passkeys are a form of authentication that leverages public-key cryptography for secure login processes. Unlike traditional password-based methods, passkeys do not store or transmit sensitive information such as passwords or biometric data directly; instead, they rely on the generation and use of unique key pairs stored locally on devices.

The FIDO2 standard, developed by the FIDO Alliance, defines protocols for secure authentication using public-key cryptography. This includes the WebAuthn (Web Authentication) API, which enables web applications to authenticate users based on their passkeys.

Why It Matters

Passkeys significantly enhance security by reducing the risk of password leaks and phishing attacks. Since no sensitive data is stored or transmitted in plaintext, even if a user’s device is compromised, the attacker cannot use the passkey to log into other accounts.

Additionally, passkeys offer a seamless user experience with fewer steps compared to traditional multi-factor authentication (MFA) methods, making them more likely to be used consistently by users.

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How Passkeys Work

During the registration process, a device generates a public/private key pair locally. The public key is sent to the server for future authentication purposes, while the private key remains securely stored on the device. This ensures that even if the public key is intercepted, it cannot be used without the corresponding private key.

For login, the server sends a random challenge to the user’s device. The device uses its private key to sign this challenge, and the resulting signature is sent back to the server for verification against the stored public key. If the signature matches, the authentication is successful.

Phishing Prevention

The simulation includes a phishing button that demonstrates how passkeys prevent attacks by ensuring that signatures are only valid within their intended domain. When attempting to log in from a spoofed origin, the signature fails verification due to the mismatch between the expected and actual domains.

This feature is crucial because it prevents attackers from using stolen public keys to gain unauthorized access to user accounts.

Frequently asked questions

How does passkey authentication protect against phishing attacks?

Passkeys prevent phishing by ensuring that the signature generated during login is only valid within the intended domain. If a user attempts to log in from an unexpected origin, the signature will fail verification, blocking unauthorized access.

Can passkeys be used with any device?

Passkeys can be used with various devices that support FIDO2 standards, including smartphones, laptops, and tablets. The key pair is generated locally on these devices to ensure security.

Is it possible to lose access to my passkey if I forget the device?

Yes, losing a device means losing access to your passkey unless you have additional recovery methods set up through your account settings or backup options provided by your service provider.

Can passkeys be used without internet connectivity?

Passkeys can still function offline as long as the user has previously registered their key with a server. The authentication process relies on locally stored keys and does not require an active internet connection for successful login.

Try it live

Everything above runs in your browser — open Passkeys / FIDO2: Public-Key Registration & Challenge-Response Login and change the parameters while it is running. Nothing is installed, nothing is uploaded, the whole model lives in one tab.

▶ Open Passkeys / FIDO2: Public-Key Registration & Challenge-Response Login simulation