Understanding Trusted Applications in Automotive Cybersecurity

Trusted applications in automotive cybersecurity are secure programs that run in an isolated part of the vehicle’s processor. They protect critical functions like digital key verification, secure updates, and tamper-proof data storage from unauthorized access or attacks.

You tap your phone, and your car unlocks.

No key, no buttons, just a secure handshake between devices. Or at least, that is the idea.

Behind that instant unlock is a delicate chain of trust. Your phone sends a digital credential, the vehicle authenticates it, checks its validity, ensures it has not been tampered with or replayed, and only then do the doors respond.

But how does the car really know the request is genuine? How does it prevent an attacker from faking that handshake, replaying an old unlock signal, or injecting a malicious update into the system?

That assurance does not come from the app on your phone or the infotainment OS. It comes from deeper within the system, in a secure zone of the vehicle’s processor. This is where Trusted Applications operate. Running inside the Trusted Execution Environment, they handle the most sensitive operations-validating keys, guarding firmware and enforcing access rules.

In this article, we explore the crucial role the trusted applications play in automotive cybersecurity and why they are essential for building trust in the age of connected vehicles.

Trusted Apps in Action: A Closer Look at Execution Flow

Execution of Trusted Applications in cybersecurity follows a simple rule: critical operations must only run in a secure and verifiable space away from untrusted software and potential threats.

In connected vehicles, software is everywhere. It plays music, monitors sensors, manages charging, and even controls the engine. But not all software is equally sensitive. Some operations like verifying cryptographic keys, approving over-the-air (OTA) updates, or accessing safety critical systems demand a higher level of protection.

These operations are handled by specialized applications that execute inside a Trusted Execution Environment (TEE) a secure zone within the vehicle’s processor. This environment is completely isolated from the main operating system (Linux, QNX, Android Automotive), ensuring that even if the rest of the system is compromised, these core applications remain secure.

Before any secure application is allowed to run inside the TEE, it must go through a strict verification process. Each binary is digitally signed and checked for authenticity. Only validated code is allowed to execute. Nothing else gets through.

Once running, these applications, often referred to as secure services or isolated logic units, do exactly what they are designed to do. Nothing more, nothing less.

• Their data is protected.
• Their memory is inaccessible from outside.
• Their logic cannot be altered or inspected.

This approach creates strong, hardware enforced boundaries. It ensures that only trusted inputs reach critical systems, and that unauthorized access is simply not possible.

Now that we’ve covered the basics, let’s dive deeper into the architecture and execution flow behind secure execution in vehicle ECUs.

Let’s break down how applications run in a trusted execution environment:

1. Secure Boot and Root of Trust
• At power-on, the system initiates a secure boot process.
• The processor verifies each software component in a chain of trust, starting from immutable hardware (like ROM or a hardware security module).
• This chain extends to the TEE OS, which loads only if its signature is valid.
• The Trusted Applications themselves are also verified before being allowed to execute, typically through X.509 certificates and RSA/ECC signatures.
2. Isolated Execution Environment
• The TEE runs in secure world mode (via TrustZone), separate from the rich execution environment, where the main OS (Linux, QNX, Android Automotive) operates.
• Trusted Applications are executed entirely within this secure context and are inaccessible from the outside world, both in terms of memory and system calls.
• Memory regions used by TAs are protected by the MMU and hardware, any access attempt from normal world processes results in an exception or is silently dropped.
3. Secure Communication with the Rich Execution Environment (REE)
• Applications in the REE (called Client Applications, or CAs) can request services from a TA using a defined API, usually the GlobalPlatform TEE Client API.
• The request goes through a TEE driver in the normal world, which marshals the data and forwards it to the TEE kernel.
• The TEE kernel performs basic validation on incoming requests, such as checking parameter types and interface conformance. Once validated, the request is routed to the appropriate Trusted Application (TA) for access control or permission checks.

For example, let’s consider that a Client App in the IVI system wants to perform a secure cryptographic operation. Instead of accessing keys directly, it sends a request to a TA called crypto_service.ta via a Trusted API. The TA performs the operation and returns only the result (not the key) back to the client.

4. Access Control and Policy Enforcement
• Services inside the TEE are purpose-built and have minimal, defined access privileges.
• Each component is granted access only to specific memory regions, peripherals, or cryptographic modules.
• Any request outside the predefined scope is automatically denied by the TEE kernel or the processor’s security controller.
5. Cryptographic Key Management
• Secure key lifecycle management involves generating, storing, using, and retiring cryptographic keys in a way that prevents unauthorized access or leakage. This is handled entirely within a protected environment, isolated from the vehicle’s main operating system.
• Keys used for vehicle authentication, firmware signing, and secure communication are never exposed outside the secure execution zone, ensuring confidentiality and integrity.
• This secure zone also serves as a trusted link to Hardware Security Modules (HSMs) or Secure Elements, creating a layered and tamper-resistant architecture for key protection.
6. Secure Updates and Version Control
• Updates to Trusted Applications go through a signed and verified OTA mechanism.
• The update package is signed by the OEM, validated by the TEE, and installed only if all checks are passed.
• Version rollbacks are often prevented to mitigate downgrade attacks.

Use Case: Anti-Rollback and Immutable Data Storage Using Hard/Soft OTP Application

Small, trusted applications are critical components of cybersecurity framework. Let’s understand this by an example – An automobile stores various data points such as odometer reading, vehicle diagnostic data, firmware version history, etc.

This is important for:

• Warranty enforcement
• Safety and compliance
• Supporting predictive maintenance
• Fraud prevention (e.g., odometer rollback)
• Accurate diagnostics across servicing events

The challenge is to ensure that this data cannot be rolled back to an older state by flashing outdated software or manipulating non-volatile memory. In traditional storage systems, this rollback is difficult to detect and even harder to prevent without secure, hardware-backed enforcement.

How Trusted Execution of OTP TA helps prevent data roll back?

A specialized trusted application developed for preventing roll back works on hard and soft OTP (one-time programmable) mechanism.

What Happens Behind the Scenes of Hard/Soft OTP TA?

When a new value is written, such as a firmware version or odometer reading, the trusted execution logic compares it against the existing value stored securely within the Trusted Execution Environment.

• If the new value is higher, it is accepted and saved.
• If it is lower or already used, the update is rejected.

This mechanism ensures that system data progresses in only one direction and cannot be rolled back.

This is managed by trusted applications through two mechanisms commonly used in cybersecurity: soft OTP and hard OTP.

• In case of soft OTP, the TEE manages counters or state variables in secure memory, completely isolated from the main operating system. The logic is tamper proof and inaccessible to untrusted software.
• Hard OTP allows trusted applications to extend security down to the hardware layer.
  It enables programming of irreversible values into one-time programmable elements like eFuses, commonly used revoke cryptographic keys. Once written, these values are permanent and cannot be modified.

By combining both soft and hard OTP mechanisms, immutability of critical data is ensured. It blocks the installation of outdated software, prevents tampering with diagnostic logs, and ensures all system changes follow a strict forward-only rule.

This capability is foundational for secure and compliant vehicle operation, especially in scenarios that require reliable service history, authentic firmware records, and tamper-evident diagnostics.

Conclusion

The role of trusted applications in automotive cybersecurity may be small, but it is the foundation of securing connected vehicles. It may not be visible in the main driving experience, but it silently controls access to the most sensitive operations.

From verifying digital keys to protecting firmware updates and preventing rollback attempts, trusted applications play pivotal role in implementation of automotive cybersecurity.

Looking ahead, the role of such applications will go beyond isolated protection. It will support secure in-vehicle payments, personalized user environments, intelligent edge-based decision making, and encrypted data exchange across entire vehicle fleets.