Securing SPI and Why It Matters

Serial Peripheral Interface (SPI), Inter-Integrated Circuit (I2C), and Improved Inter-Integrated Circuit (I3C) are critical for enabling communication between sensors, microcontrollers, memory devices, and other peripherals in countless applications. They are also some of the most widely used communication protocols in embedded systems.

However, SPI, I2C, and I3C were originally designed for efficiency and simplicity with minimal inherent security features. As a result, these communication protocols are now becoming points of vulnerability in connected systems.
 

Insecurity of SPI, I2C, and I3C

1. Lack of Built-in Security Features:

• SPI: This full-duplex protocol has no inherent mechanisms for authentication, encryption, or integrity verification. Devices communicating over SPI can be easily spoofed or tampered with if physical access is gained.

• I2C: Widely used for short-distance communication, I2C lacks encryption, authentication, and data integrity checks. It is susceptible to bus sniffing and injection attacks.

• I3C: While an improvement over I2C, I3C’s security features are still limited. It introduces some error-detection capabilities and in-band interrupts, but these are not sufficient to fully address modern security challenges.

2. Physical Vulnerabilities: The physical accessibility of these protocols—often exposed as traces on printed circuit boards (PCBs)—makes them easy targets for attackers with physical access to the hardware.

3. Growing Attack Surface: The more connected a system, the greater the risk of remote attacks exploiting insecure communications within it. This could allow attackers to manipulate sensors, extract sensitive data, or inject malicious commands.

Why Security Matters Now More Than Ever

The proliferation of connected automotive systems, medical devices, industrial automation, and the Internet of Things (IoT) has brought these protocols into environments where security is paramount. A breach in these systems could lead to:

• Data theft or leakage
• Malfunctioning or compromised devices
• Safety hazards in critical systems like vehicles or medical devices

Recommendations for Standardization Bodies

Organizations such as the MIPI Alliance (which governs I3C) and IEEE have a critical role to play in addressing these vulnerabilities. While these bodies have focused on optimizing performance, power efficiency, and backward compatibility, it is time to prioritize security as a fundamental requirement.
Recommendations include…

1. Develop Mandatory Security Specifications:

• Authentication: Standardize mechanisms for authenticating devices communicating over these protocols.

• Encryption: Require encryption for data in transit to prevent eavesdropping and tampering.

• Integrity Verification: Introduce checksum or cryptographic hash requirements to ensure data integrity.

2. Implement Secure Boot and Firmware Validation:

Establish guidelines for secure boot processes and firmware validation to protect against unauthorized code execution.

3. Define Physical Security Best Practices:

Include recommendations for PCB design, such as trace obfuscation, shielding, and secure connectors, to reduce the risk of physical attacks.

4. Encourage Adoption of Secure Hardware Modules:

Promote the use of hardware security modules (HSMs) or secure elements that can manage cryptographic keys and perform secure operations.

Best Practices for Developers and Organizations

While waiting for standardized security specifications, developers and organizations can take proactive steps to secure their systems.

• Encrypt Data: Use encryption libraries to protect data transmitted over SPI, I2C, or I3C.

• Authenticate Devices: Implement mutual authentication to ensure devices are communicating with trusted counterparts.

• Monitor Communication: Employ tools to detect anomalous behavior or unexpected transactions.

• Physically Secure Hardware: Protect sensitive traces and interfaces from unauthorized access.

Conclusion: Protocols Remain Vulnerable Unless Protected

The widespread use of SPI, I2C, and I3C in embedded systems makes their security a critical concern. Without built-in protections, these protocols remain vulnerable to a variety of attacks, endangering the safety and reliability of connected systems.

It is imperative that organizations such as the MIPI Alliance and IEEE develop comprehensive security specifications to safeguard these communication pathways. By addressing these vulnerabilities, we can ensure the continued growth and trustworthiness of embedded and connected systems in an increasingly digital world.