Biometric Protection

Bolt21 uses advanced biometric security to protect your funds from unauthorized access, even if someone gains physical access to your device.

Payment Authorization

Large Payment Protection

Payments of 100,000 sats (~$100 USD) or more require biometric authentication:

• Face ID on supported iPhones
• Touch ID on supported devices
• Fingerprint on Android devices

This ensures that even if your phone is unlocked, significant payments require your explicit biometric approval.

Cumulative Tracking

We implemented a sophisticated protection against “split payment attacks” where an attacker might try to drain your wallet through multiple small payments:

Example Attack (BLOCKED):
- Payment 1: 99,000 sats ✓ (under threshold)
- Payment 2: 99,000 sats ✓ (under threshold)
- Payment 3: 99,000 sats → BIOMETRIC REQUIRED
  (cumulative: 297,000 sats in 5 minutes)

How it works:

1. We track all payments within a 5-minute rolling window
2. If cumulative payments approach 100,000 sats, biometric is required
3. The window resets after 5 minutes of no payments
4. This prevents attackers from draining funds via many small transactions

No PIN Fallback

Unlike many apps, Bolt21 uses biometricOnly mode:

• No PIN fallback for payment authorization
• Biometric failure = payment blocked
• This prevents shoulder-surfing attacks where someone watches you enter a PIN

What’s Protected

Screen Security

Additional protections when your app is in the background:

• Screenshot blocking on Android (FLAG_SECURE)
• Screen recording overlay on iOS
• App switcher blur hides sensitive data
• No screen capture of recovery phrases

Technical Details

• Biometric data never leaves your device
• We use platform-native APIs (LocalAuthentication on iOS, BiometricPrompt on Android)
• No biometric templates are stored by Bolt21
• Authentication is handled entirely by your device’s secure enclave

Source code: Payment Tracker Service