BLE Security: 5.0 vs. 4.2

TL;DR

Bluetooth Low Energy (BLE) 5.0 offers significant security improvements over BLE 4.2, primarily through enhanced encryption and connection management. While 4.2 is still usable with careful implementation, upgrading to 5.0 provides a stronger foundation for secure devices. This guide details the key differences and how to improve your BLE security.

1. Understanding the Core Differences

Both BLE 4.2 and 5.0 use encryption, authentication, and pairing mechanisms, but 5.0 introduces features that make attacks harder. Here’s a breakdown:

• Encryption: Both versions support AES-CCM encryption. However, 5.0 encourages the use of larger key sizes (128-bit or more) for stronger protection.
• Authentication: Both use pairing methods like Passkey Entry and Just Works. 5.0 adds Numeric Comparison which is more secure than Just Works.
• Connection Management: BLE 5.0 introduces Connection Subintervals, allowing faster connection intervals without sacrificing security.
• Privacy: 5.0 has improved privacy features with Resolvable Private Addresses (RPA) and Address Rotation, making tracking devices more difficult.

2. Security Weaknesses in BLE 4.2

BLE 4.2 is vulnerable to several attacks if not implemented correctly:

• Man-in-the-Middle (MITM) Attacks: Without proper authentication, attackers can intercept and modify communication between devices.
• Eavesdropping: Unencrypted or weakly encrypted connections allow attackers to listen in on sensitive data.
• Passkey Entry Vulnerabilities: If the passkey entry process isn’t secure (e.g., displaying the code on both devices), it can be compromised.
• Just Works Pairing: This method offers no authentication and is highly susceptible to attacks. Avoid using it if possible.

3. How BLE 5.0 Improves Security

BLE 5.0 addresses these weaknesses through several key features:

• LE Secure Connections: This is the biggest improvement. It uses Elliptic-curve Diffie–Hellman (ECDH) key exchange for more secure pairing and encryption.
• Requires both devices to support LE Secure Connections.
• Provides forward secrecy, meaning past communications remain secure even if a key is compromised later.
• Numeric Comparison: This method requires users to verify a number displayed on both devices before pairing, preventing MITM attacks.
• Privacy Features (RPA & Address Rotation): Makes it harder to track devices by frequently changing the Bluetooth address used for communication.

4. Implementing Secure BLE Connections (General Steps)

These steps apply to both 4.2 and 5.0, but are *crucial* for 4.2 and best practice for 5.0.

1. Use LE Secure Connections (if possible): This is the most important step. Check if your hardware supports it.
2. Avoid “Just Works” Pairing: Always use a more secure pairing method like Passkey Entry or Numeric Comparison.
3. Implement Proper Authentication: Verify the identity of connecting devices before exchanging sensitive data.
4. Encrypt All Communication: Use AES-CCM encryption with at least 128-bit keys.
5. Regularly Update Firmware: Security vulnerabilities are constantly being discovered, so keep your device’s firmware up to date.
6. Consider Privacy Features: Enable RPA and Address Rotation if supported by your hardware.

5. Code Example (Illustrative – Pairing Process)

This is a simplified example of how pairing might be initiated in C using a BLE library. Actual implementation will vary depending on the specific library used.

// Simplified pairing initiation code
bool initiatePairing(BLEDevice *device) {
  // Check if LE Secure Connections is supported.
  if (device->supportsSecureConnections) {
    // Initiate secure pairing process using ECDH key exchange.
    pairingResult = device->startSecurePairing();
    if (pairingResult == SUCCESS) {
      return true;
    } else {
      // Handle pairing failure.
      return false;
    }
  } else {
    // Fallback to Passkey Entry or Numeric Comparison if Secure Connections is not supported.
    // Implement appropriate security measures for the chosen method.
    pairingResult = device->startPasskeyPairing(); // Or startNumericComparisonPairing()
    if (pairingResult == SUCCESS) {
      return true;
    } else {
      // Handle pairing failure.
      return false;
    }
  }
}

6. Tools for Security Testing

• Bluetooth Sniffers: Tools like Ubertooth One or Ellisys Bluetooth Explorer can capture and analyze BLE traffic to identify vulnerabilities.
• Security Audits: Hire a cybersecurity firm to perform a thorough security audit of your device.
• Fuzzing: Use fuzzing tools to test the robustness of your BLE implementation against unexpected inputs.