Secure Your BLE IoT Devices

TL;DR

Bluetooth Low Energy (BLE) devices are often targets for hackers because of their limited security features. This guide shows you how to protect your BLE IoT devices from being used as backdoors, covering pairing, encryption, firmware updates, and monitoring.

1. Understand the Risks

Hackers can exploit vulnerabilities in BLE devices to:

• Gain control of your device
• Steal sensitive data
• Use your device as a gateway to your network

Common attack vectors include weak pairing methods, unencrypted communication, and outdated firmware.

2. Secure the Pairing Process

1. Use Passkey Entry: Avoid ‘Just Works’ pairing whenever possible. This method requires a user to confirm a code on both devices, making it harder for attackers to intercept the connection.
2. Numeric Comparison: If passkey entry isn’t feasible, use numeric comparison where users verify a number displayed on both devices.
3. Out-of-Band (OOB) Pairing: This is the most secure method. It uses another channel (e.g., NFC, QR code) to exchange pairing information securely.

Example of checking BLE pairing status on Linux:

bluetoothctl info <MAC address>

3. Implement Strong Encryption

1. AES-CCM: Use Advanced Encryption Standard (AES) in Counter with CBC-MAC mode for data encryption. This is a widely accepted and secure algorithm.
2. Key Length: Employ at least 128-bit AES keys. Longer keys provide greater security.
3. Regular Key Rotation: Change your encryption keys periodically to limit the impact of potential compromises.

Note: Ensure your BLE stack supports and is configured for strong encryption algorithms.

4. Secure Firmware Updates

1. Code Signing: Digitally sign all firmware updates to ensure their authenticity and integrity. This prevents attackers from installing malicious code.
2. Secure Bootloader: Implement a secure bootloader that verifies the signature of the firmware before loading it.
3. Over-the-Air (OTA) Encryption: Encrypt the firmware update process to protect data in transit.
4. Rollback Protection: Prevent downgrading to older, vulnerable firmware versions.

Example of checking firmware version on ESP32:

idf.py flash --version

5. Monitor for Suspicious Activity

1. Log Pairing Attempts: Record all pairing attempts, including timestamps and MAC addresses.
2. Detect Anomalous Communication: Monitor data traffic for unusual patterns or unexpected destinations.
3. Intrusion Detection System (IDS): Consider using an IDS to detect and alert you to potential attacks.
4. Regular Security Audits: Conduct regular security audits of your BLE devices and infrastructure.

Tools like Wireshark can be used to capture and analyze BLE traffic for anomalies.

6. Limit Device Capabilities

1. Principle of Least Privilege: Only grant the device the minimum necessary permissions it needs to function.
2. Disable Unused Services: Turn off any Bluetooth services that are not required for your application.
3. Restrict Advertising: Limit the amount of information broadcasted by the device during advertising.

Example of disabling a BLE service on ESP32:

esp_bt_gap_disable(ESP_BT_GAP_SERVICE_UUID);

7. Keep Software Updated

Regularly update your BLE stack, operating system, and application software to patch security vulnerabilities.

8. Consider cyber security best practices

• Use a firewall: Protect your network from unauthorized access.
• Strong passwords: Use strong, unique passwords for all accounts associated with your devices.
• Two-factor authentication: Enable two-factor authentication whenever possible.