WebAuthn

WebAuthn (Web Authentication) is a W3C standard that allows users to log in to websites and applications using public-key cryptography instead of a traditional password. It is the core technical specification behind FIDO2, a broader framework for passwordless authentication. When a user registers with a service, their authenticator—such as a security key (e.g., YubiKey), a platform authenticator (e.g., Windows Hello, Touch ID), or a smartphone—generates a unique cryptographic key pair. The public key is stored by the relying party (the website), while the private key remains securely stored on the user's device and is never shared.

The authentication process is initiated by the relying party sending a challenge to the user's browser. The authenticator signs this challenge with the user's private key, and the resulting signature is sent back for verification using the stored public key. This process provides strong authentication by proving the user possesses the required credential without transmitting secrets over the network. Crucially, WebAuthn credentials are scoped to a specific origin (the website's domain), making them inherently resistant to phishing attacks because a credential created for example.com cannot be used on a fake examp1e.com site.

A key architectural component is the Authenticator Model, which separates the authenticator from the client platform. Authenticators are categorized as roaming (cross-platform devices like security keys) or platform (built into a device like a laptop or phone). The standard also defines levels of user verification (e.g., PIN, biometrics) and attestation, which allows a relying party to receive cryptographic proof of the authenticator's make and model, aiding in policy enforcement. This model enables a consistent experience whether using a hardware key or a device's built-in biometric sensor.

For developers, integration is facilitated through the Web Authentication API, a JavaScript API exposed by modern browsers. The primary operations are navigator.credentials.create() for registration and navigator.credentials.get() for authentication. The API handles communication with the authenticator via an underlying client-to-authenticator protocol (CTAP), part of the FIDO2 suite. This allows the web application to request authentication without managing the complex details of the cryptographic operations or direct hardware communication.

The primary benefits of WebAuthn are enhanced security—eliminating risks associated with password databases, replay attacks, and phishing—and improved user experience by removing the need to create, remember, and manage passwords. It is a foundational technology for a passwordless future and is increasingly adopted for securing high-value accounts in finance, enterprise, and government services. Its standardization ensures interoperability across browsers, operating systems, and a wide range of authenticator devices.

WebAuthn (Web Authentication) is a W3C standard that allows users to log into online services using public-key cryptography instead of a password. The protocol enables authentication via authenticators—hardware security keys (like YubiKeys), platform biometrics (Touch ID, Windows Hello), or mobile phones. During registration, the authenticator generates a unique public-private key pair for the website (the relying party), storing the private key securely and sending the public key to the server. This establishes a cryptographically secure, phishing-resistant credential bound to both the user and the specific website.

The authentication flow begins when a user attempts to log in. The relying party sends a challenge—a cryptographically random string—to the user's browser. The browser prompts the user to activate their authenticator, for example, by touching a security key or scanning a fingerprint. The authenticator then uses its stored private key to sign the challenge, creating an assertion. This signed assertion is sent back to the server, which verifies it using the corresponding public key stored during registration. Successful verification proves the user possesses the correct private key without the key itself ever leaving the device.

A critical security feature of WebAuthn is origin binding. The browser cryptographically signs the website's origin (e.g., https://example.com) as part of the assertion. This prevents phishing attacks where a malicious site impersonates a legitimate one, as the authenticator's signature will not validate for the wrong domain. Furthermore, WebAuthn supports user verification (like a PIN or biometric) and user presence (a physical tap), enabling strong multi-factor authentication in a single step. The protocol's design ensures that credentials are not shared between sites and cannot be extracted from the authenticator.

WebAuthn (Web Authentication) is a W3C standard that defines a browser and platform API allowing servers to register and authenticate users using public-key cryptography instead of passwords. It is the client-side component of the broader FIDO2 project, which also includes the CTAP (Client to Authenticator Protocol). When a user attempts to log in, the relying party (e.g., a website) sends a challenge. The browser, via the WebAuthn API, communicates with an authenticator—such as a hardware security key, platform biometrics (like Windows Hello or Touch ID), or a mobile phone—to generate a cryptographic signature proving possession of a private key. This signature is sent back to the server for verification, completing the authentication without exposing a shared secret.

The protocol's security model is built on public-key cryptography and attestation. During registration, a new cryptographic key pair is generated on the authenticator; the private key never leaves the secure hardware, while the public key is registered with the server. Subsequent logins require the authenticator to sign a unique challenge from that specific server, making stolen credentials useless elsewhere and effectively neutralizing phishing attacks. Attestation provides optional metadata about the authenticator's origin and type (e.g., a certified security key vs. a software authenticator), allowing relying parties to enforce policy-based trust.

WebAuthn's integration into the FIDO2 ecosystem is seamless. While WebAuthn handles the browser-to-server communication, CTAP manages the low-level protocol between the client device and external authenticators, such as USB, NFC, or Bluetooth security keys. This division of labor means a website implementing the WebAuthn API can support a wide range of authenticators without needing device-specific code. The user experience is standardized: a browser prompt requests user verification, which could be a biometric scan, PIN, or a button press on a hardware key, providing a consistent interface across different services.

For developers and CTOs, adopting WebAuthn significantly reduces risks associated with credential storage, database breaches, and account takeover attacks. Implementation involves adding WebAuthn API calls to existing authentication flows—navigator.credentials.create() for registration and navigator.credentials.get() for authentication. Major platforms and browsers have native support, and backend libraries exist for all major server-side languages to handle the cryptographic verification. The shift represents a move from what the user knows (a password) to what the user has (an authenticator) and what the user is (a biometric), fundamentally upgrading security postures.