Locking Down Your Mobile App: A Guide to Secure Biometric Authentication 🔒

AI-generated image with Gemini

Biometric authentication is a fantastic way to boost user experience in mobile apps, offering a quick and easy login process. But, if not implemented correctly, it can open a Pandora’s Box of security vulnerabilities. I’ve seen too many developers make the critical mistake of storing user credentials directly on the device — a huge no-no! 🚫 This article outlines a secure approach to biometric authentication, avoiding this dangerous practice.

The Golden Rule: Never Store User Credentials on the Device! 🙅‍♀️

Instead of storing sensitive information, we’ll use a more robust method involving hashes and device IDs. Here’s the breakdown:

1. Generate and Securely Store a Hash 🔑

This is the foundation of our secure system:

• When users opt for biometric login, we generate a unique hash specifically for their account. Think of it as a digital fingerprint. 👆
• This hash is then encrypted and securely stored. On iOS, this is done using the Keychain; on Android, it’s the Keystore. For Flutter developers, the Flutter Secure Storage package provides a seamless solution. 📦
• Critically, this encrypted hash is also sent to your backend server for secure storage. This is where the real security lies. 🛡️

2. Setting Up a Secure Biometric Login Endpoint 📡

Your backend needs a dedicated endpoint for biometric logins. This endpoint should accept two crucial pieces of information:

• The encrypted hash (the unique account identifier).
• The device ID (to verify the device being used).

3. Validation During Subsequent Logins ✅

When the user tries to log in using biometrics:

a. The app fetches the encrypted hash from secure storage. b. This hash, along with the device ID, is sent to the backend’s biometric login endpoint.

On the backend, thorough validation takes place:

I. Hash Match: Does the received hash match the securely stored for this account? 🤔 II. Device ID Match: Does the received device ID match the one associated with the user’s account? 📱

4. Handling Edge Cases Gracefully ⚠️

Robust error handling is essential:

• Successful Login: If both the hash and device ID match, grant the user access to the app. 🎉
• Incorrect Hash: If the hash doesn’t match, reject the login. ❌
• Incorrect Device ID: This requires a bit more nuance:
• If the new device ID isn’t associated with any account, allow the user to register the device and proceed. This could be a new phone or a fresh install. 🆕
• If the new device ID is associated with another account, reject the login. This prevents unauthorized access. ⛔

Why This Matters 🤔

Biometric authentication is all about convenience, but security should never be compromised. By using hashes and device IDs, we ensure that actual login credentials are never stored on the device, significantly reducing the risk of data breaches. This approach provides a robust and secure biometric login experience. 💪

What are your thoughts? Do you use any other methods for secure biometric authentication? I’d love to hear your insights! 👇

Credit: Initial publication by Ikenna Umeh on LinkedIn. Improved and revised.