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Overview

Muun Wallet supports biometric authentication as a convenient alternative to PIN entry for unlocking the app. Added in version 55.4, biometric support leverages Android’s BiometricPrompt API to provide secure, hardware-backed authentication.

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Supported biometric types

Muun supports all biometric types available through Android BiometricPrompt:
  • Fingerprint recognition (most common)
  • Face recognition (Android 10+)
  • Iris scanning (on supported devices)
The specific biometric methods available depend on device hardware and Android version.
Biometric authentication requires Android 6.0 (API level 23) or higher, with hardware support for at least one biometric type.

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How it works

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Authentication flow

  1. User enables biometrics in app settings
  2. Sensitive data encrypted with biometric-protected key
  3. On app unlock: BiometricPrompt shown
  4. Biometric verified by Android system
  5. Decryption key released by Android Keystore
  6. App unlocked with decrypted credentials

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Security model

Biometric authentication in Muun provides:
  • Hardware-backed security: Keys stored in Trusted Execution Environment (TEE) or Secure Enclave
  • Fallback to PIN: Users can always fall back to 4 or 6-digit PIN
  • No plaintext storage: PIN never stored unencrypted on device
  • Timeout protection: Biometrics disabled after extended inactivity
Important: Biometrics unlock the app but do not replace your PIN for transaction signing or recovery operations.

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Implementation details

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BiometricsController interface

The wallet implements biometric authentication through the BiometricsController:
BiometricsController.kt
interface BiometricsController {
    fun authenticate(
        activity: FragmentActivity,
        onSuccess: () -> Unit,
        onError: (BiometricsAuthenticationStatus) -> Unit
    )
    
    fun isAvailable(): Boolean
    fun isEnabled(): Boolean
    fun setEnabled(enabled: Boolean)
}

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Authentication status

Authentication can result in various statuses:
BiometricsAuthenticationStatus.kt
enum class BiometricsAuthenticationStatus {
    SUCCESS,
    FAILURE,
    CANCELLED,
    ERROR,
    LOCKOUT,
    PERMANENT_LOCKOUT,
    NOT_AVAILABLE,
    NOT_ENROLLED
}
Status meanings:
  • SUCCESS: Biometric verified successfully
  • FAILURE: Biometric not recognized (retry allowed)
  • CANCELLED: User cancelled the prompt
  • ERROR: System error occurred
  • LOCKOUT: Temporarily locked after too many attempts
  • PERMANENT_LOCKOUT: Biometric authentication disabled (requires device unlock)
  • NOT_AVAILABLE: No biometric hardware on device
  • NOT_ENROLLED: No biometrics enrolled in device settings

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Integration with Android BiometricPrompt

Muun uses Android’s BiometricPrompt API: 
val promptInfo = BiometricPrompt.PromptInfo.Builder()
    .setTitle("Unlock Muun")
    .setSubtitle("Verify your identity")
    .setNegativeButtonText("Use PIN")
    .setAllowedAuthenticators(
        BiometricManager.Authenticators.BIOMETRIC_STRONG
    )
    .build()

val biometricPrompt = BiometricPrompt(
    activity,
    executor,
    authenticationCallback
)

biometricPrompt.authenticate(promptInfo)
Muun requires BIOMETRIC_STRONG authenticators, which provides the highest security level and is backed by hardware security.

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User experience

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Enabling biometrics

1

Open settings

Navigate to Settings → Security in the Muun app
2

Enable biometric unlock

Toggle Biometric unlock option
3

Verify biometric

Authenticate with fingerprint or face to confirm setup
4

Set PIN fallback

Ensure you remember your PIN for fallback access

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Using biometrics

When biometrics are enabled:
  1. Open Muun app
  2. Biometric prompt appears automatically
  3. Authenticate with fingerprint/face
  4. App unlocks immediately on success
If biometric authentication fails:
  • Try again: Most devices allow 5 attempts
  • Use PIN: Tap “Use PIN” to enter PIN manually
  • Wait for timeout: Temporary lockout lifts after 30 seconds

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Security considerations

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When to use biometrics

Good use cases:
  • Convenient daily app access
  • Quick balance checks
  • Frequent small transactions
Not recommended for:
  • Shared devices (use PIN only)
  • Maximum security scenarios (disable biometrics)
  • Devices with weak biometric sensors

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Biometric data privacy

Privacy guarantee: Biometric data (fingerprints, face scans) never leaves the device’s secure hardware. Muun never receives or stores biometric data.
Biometric templates are:
  • Stored in hardware-protected storage (TEE/Secure Enclave)
  • Encrypted and inaccessible to apps
  • Never transmitted over network
  • Deleted when biometric enrollment is removed

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Fallback and recovery

Always maintain PIN access:
  • Biometric hardware can fail
  • Injuries may prevent biometric authentication
  • Device software updates may reset biometrics
  • Emergency access requires PIN
Critical: Never forget your PIN. Biometric authentication is a convenience feature that supplements but does not replace PIN security.

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Troubleshooting

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Biometric option not available

Cause: Device doesn’t support biometric authentication Solution:
  • Check device specifications for biometric hardware
  • Update Android to latest version
  • Enroll fingerprints/face in device settings

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Authentication always fails

Cause: Biometric template has degraded or hardware issue Solution:
  1. Re-enroll biometrics in device settings
  2. Clean fingerprint sensor or camera
  3. Use PIN as fallback
  4. Contact device manufacturer if problem persists

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Biometrics disabled after update

Cause: App or OS update reset biometric keys Solution:
  1. Re-enable biometrics in Muun settings
  2. Verify biometric authentication
  3. Test unlock before closing settings

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Best practices

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For users

  1. Enroll multiple fingerprints: Use 2-3 fingers for reliability
  2. Keep sensors clean: Dirty sensors cause authentication failures
  3. Remember your PIN: Always have fallback access
  4. Disable on shared devices: Use PIN-only on devices others can access
  5. Update biometrics: Re-enroll if authentication becomes unreliable

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For developers

  1. Handle all error cases: Gracefully handle lockouts and errors
  2. Provide clear prompts: Explain what biometric authentication unlocks
  3. Test edge cases: Lockouts, cancellations, not enrolled scenarios
  4. Respect user choice: Allow disabling biometrics anytime
  5. Implement rate limiting: Prevent brute force attempts

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Version history

  • v55.4 (January 2026): Biometric authentication support added
  • v55.3 (October 2025): Foundation work for biometric integration

Key Management

HD key management system

PIN Security

Challenge keys and PIN system

Auditing

Security audit guidelines

Changelog

Full version history

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