Cross-Device Passkey Authentication: Hybrid Flow Implementation

Cross-device passkey authentication allows users to log in to an application using a passkey created on one device on another device without needing to enter a password. This method leverages WebAuthn, a standard for strong, secure authentication, enabling seamless and secure access across multiple devices.

What is Cross-Device Passkey Authentication?

Cross-device passkey authentication simplifies the login process by allowing users to authenticate using a passkey generated on one device (like a smartphone) to sign in on another device (like a laptop). This eliminates the need for remembering passwords and enhances security by relying on cryptographic keys instead of passwords.

How does WebAuthn enable cross-device passkey authentication?

WebAuthn is a W3C standard that provides a secure way to authenticate users without passwords. It supports public-key cryptography, ensuring that authentication is secure and resistant to phishing attacks. By using WebAuthn, you can create passkeys on one device and use them on another, enhancing the user experience while maintaining high security standards.

What are the benefits of using cross-device passkey authentication?

Using cross-device passkey authentication offers several benefits:

• Enhanced Security: Passkeys are cryptographic keys stored securely on the user’s device, making them much harder to compromise compared to passwords.
• Improved User Experience: Users can log in without remembering passwords, reducing friction and improving usability.
• Phishing Resistance: Since passkeys rely on cryptographic operations, they are immune to phishing attacks that attempt to steal passwords.

What are the steps to implement cross-device passkey authentication using a hybrid flow?

To implement cross-device passkey authentication using a hybrid flow, follow these steps:

Registering a passkey

First, you need to register a passkey on the user’s primary device. This involves creating a public-private key pair and storing the private key securely on the device.

Code example: Registering a passkey

async function registerPasskey() {
    const publicKey = {
        rp: {
            name: "Example Corp",
            id: "example.com"
        },
        user: {
            id: new Uint8Array([1, 2, 3, 4]), // Unique user ID
            name: "[email protected]",
            displayName: "John Doe"
        },
        pubKeyCredParams: [{ alg: -7, type: "public-key" }], // ES256
        attestation: "direct",
        challenge: new Uint8Array([5, 6, 7, 8]), // Random challenge
        timeout: 60000,
        authenticatorSelection: {
            authenticatorAttachment: "platform",
            residentKey: "required",
            userVerification: "required"
        }
    };

    try {
        const credential = await navigator.credentials.create({ publicKey });
        console.log("Passkey registered:", credential);
    } catch (error) {
        console.error("Registration failed:", error);
    }
}

Authenticating with a passkey

Once the passkey is registered, the user can authenticate using it on any device. The authentication process involves verifying the user’s identity using the passkey.

Code example: Authenticating with a passkey

async function authenticateWithPasskey() {
    const publicKey = {
        challenge: new Uint8Array([9, 10, 11, 12]), // Random challenge
        allowCredentials: [{
            type: "public-key",
            id: new Uint8Array([1, 2, 3, 4]) // Registered passkey ID
        }],
        timeout: 60000,
        userVerification: "required"
    };

    try {
        const assertion = await navigator.credentials.get({ publicKey });
        console.log("Authentication successful:", assertion);
    } catch (error) {
        console.error("Authentication failed:", error);
    }
}

Handling cross-device authentication

To enable cross-device authentication, you need to ensure that the passkey can be used on different devices. This typically involves storing the passkey ID and other necessary information in a secure manner and making it accessible to all devices.

Code example: Storing passkey information

function storePasskeyInfo(credential) {
    const passkeyInfo = {
        id: Array.from(new Uint8Array(credential.rawId)),
        publicKey: Array.from(new Uint8Array(credential.response.getPublicKey())),
        transports: credential.response.transports
    };

    // Store passkeyInfo securely, e.g., in a database or secure storage
    console.log("Stored passkey info:", passkeyInfo);
}

Validating user presence

During authentication, it’s crucial to verify the user’s presence to prevent unauthorized access. This can be done using biometric sensors or other user verification methods supported by the device.

Code example: Verifying user presence

async function verifyUserPresence(publicKey) {
    try {
        const assertion = await navigator.credentials.get({ publicKey });
        if (assertion.response.userHandle) {
            console.log("User presence verified:", assertion);
        } else {
            console.error("User presence could not be verified");
        }
    } catch (error) {
        console.error("Verification failed:", error);
    }
}

What are the security considerations for cross-device passkey authentication?

Implementing cross-device passkey authentication requires careful attention to security to protect user data and prevent unauthorized access.

Protecting passkeys

Passkeys should be stored securely on the user’s device and never transmitted over the network in plaintext. Use secure storage mechanisms provided by the operating system to protect passkeys.

Preventing phishing attacks

Since passkeys rely on cryptographic operations, they are inherently resistant to phishing attacks. However, it’s still important to educate users about phishing attempts and encourage them to be cautious.

Validating user presence

Always validate user presence during authentication to ensure that the user is physically present and authorized to access the system. This can be done using biometric sensors or other user verification methods.

How do you handle errors during cross-device passkey authentication?

Errors can occur during the registration and authentication processes, and it’s important to handle them gracefully to provide a good user experience.

Common errors and solutions

• Registration failed: Ensure that the device supports WebAuthn and that the user has granted permission to use biometric sensors.
• Authentication failed: Verify that the passkey ID and other information are correct and that the user is present.

Code example: Handling registration errors

async function registerPasskey() {
    const publicKey = {
        rp: {
            name: "Example Corp",
            id: "example.com"
        },
        user: {
            id: new Uint8Array([1, 2, 3, 4]),
            name: "[email protected]",
            displayName: "John Doe"
        },
        pubKeyCredParams: [{ alg: -7, type: "public-key" }],
        attestation: "direct",
        challenge: new Uint8Array([5, 6, 7, 8]),
        timeout: 60000,
        authenticatorSelection: {
            authenticatorAttachment: "platform",
            residentKey: "required",
            userVerification: "required"
        }
    };

    try {
        const credential = await navigator.credentials.create({ publicKey });
        console.log("Passkey registered:", credential);
    } catch (error) {
        if (error.name === "NotAllowedError") {
            console.error("User denied permission to use biometric sensors");
        } else {
            console.error("Registration failed:", error);
        }
    }
}

Code example: Handling authentication errors

async function authenticateWithPasskey() {
    const publicKey = {
        challenge: new Uint8Array([9, 10, 11, 12]),
        allowCredentials: [{
            type: "public-key",
            id: new Uint8Array([1, 2, 3, 4])
        }],
        timeout: 60000,
        userVerification: "required"
    };

    try {
        const assertion = await navigator.credentials.get({ publicKey });
        console.log("Authentication successful:", assertion);
    } catch (error) {
        if (error.name === "NotAllowedError") {
            console.error("User denied permission to use biometric sensors");
        } else {
            console.error("Authentication failed:", error);
        }
    }
}

What are the best practices for implementing cross-device passkey authentication?

Following best practices ensures that your implementation is secure, efficient, and user-friendly.

Use secure storage

Store passkeys and other sensitive information securely on the user’s device. Avoid transmitting passkeys over the network in plaintext.

Validate user presence

Always validate user presence during authentication to ensure that the user is physically present and authorized to access the system.

Educate users

Educate users about phishing attempts and encourage them to be cautious. Provide clear instructions on how to use passkeys and troubleshoot common issues.

Test thoroughly

Thoroughly test your implementation to identify and fix any issues before deploying it to production. Test on multiple devices and browsers to ensure compatibility.

Comparison of different authentication methods

Quick Reference

Expanding the implementation

Step-by-step guide to implementing cross-device passkey authentication

Architecture diagram

Terminal output

Stat cards

Version badges

v2.0 NEW v1.5 DEPRECATED

Checklist

• Implement passkey registration - completed
• Implement passkey authentication - completed
• Store passkey information securely - pending
• Validate user presence - pending

Implementing cross-device passkey authentication using a hybrid flow enhances security and improves the user experience. By following the steps outlined in this guide, you can create a secure and efficient authentication system that leverages the power of passkeys. That’s it. Simple, secure, works.