Secure Data Transmission (0x84) in UDS Protocol Explained with Examples

Hello, fellow automotive tech enthusiasts! In this blog post, I’m excited to introduce you to Secure Data Transmission (0x84) in UDS – one of the advanced and essential s

ervices in the UDS protocol: Secure Data Transmission (0x84). This service plays a crucial role in ensuring that sensitive information is transmitted safely between ECUs. Whether you’re working on vehicle diagnostics, ECU flashing, or secure communication, understanding 0x84 is key. I’ll walk you through what this service does, how it works, and where it’s used. We’ll also explore real-world examples to make things clearer. By the end of this post, you’ll have a solid grasp of Secure Data Transmission in UDS. Let’s dive into the world of secure automotive data!

Introduction to Secure Data Transmission (0x84) Service in UDS Protocol

Welcome to this deep dive into the Secure Data Transmission (0x84) service in the UDS (Unified Diagnostic Services) protocol. In modern vehicles, protecting data during communication between Electronic Control Units (ECUs) is more important than ever. That’s where the 0x84 service comes in it ensures sensitive data is transmitted securely and reliably. This service is especially critical when handling security keys, vehicle configuration data, or software updates. In this article, we’ll break down how Secure Data Transmission works, its typical use cases, and how it fits into the UDS framework. Whether you’re a beginner or a seasoned automotive developer, you’ll find this guide valuable. Let’s explore how UDS keeps vehicle communication safe!

What is Secure Data Transmission (0x84) Service in UDS Protocol?

The Secure Data Transmission (0x84) service is a specialized service defined in the UDS (Unified Diagnostic Services) protocol, primarily used in automotive systems to protect the confidentiality and integrity of sensitive data exchanged between diagnostic tools and Electronic Control Units (ECUs).

Purpose:

The main goal of this service is to securely transfer critical data such as encryption keys, security credentials, or proprietary calibration data across a potentially insecure communication network (like CAN, Ethernet, or FlexRay).

Why do we need Secure Data Transmission (0x84) Service in UDS Protocol?

In today’s connected vehicles, Electronic Control Units (ECUs) communicate and share critical data over internal networks like CAN, FlexRay, or Ethernet. These networks are not always secure, especially during diagnostics, flashing, or over-the-air (OTA) updates. This creates potential risks, such as:

1. Protection Against Eavesdropping

When sensitive data like encryption keys, security tokens, or configuration settings are transmitted over a vehicle network, they can be intercepted by unauthorized tools or attackers if left unencrypted. The 0x84 service ensures this data is securely encrypted during transmission. This encryption makes the data unreadable to any third party snooping on the communication bus. Without it, malicious users could gain access to confidential system parameters and misuse them. Secure transmission helps safeguard both the user and the vehicle.

2. Preventing Data Tampering

Tampering with diagnostic data during transmission can lead to dangerous outcomes, such as reprogramming ECUs with faulty values or bypassing safety features. The 0x84 service uses a Message Authentication Code (MAC) or similar integrity checks to ensure the data received is exactly the same as what was sent. If any bit is altered in transit, the ECU will detect the mismatch and reject the message. This prevents hackers from injecting fake or manipulated data into the communication. It’s a key feature for maintaining trust in the data flow.

3. Blocking Replay Attacks

Replay attacks occur when an attacker captures a valid message and sends it again later to the ECU to perform unauthorized actions, like unlocking doors or triggering diagnostic routines. To stop this, the 0x84 service uses sequence counters, timestamps, or session-specific tokens. These mechanisms help the ECU recognize whether a message is new or a repeat of a previously received one. If the message is detected as a replay, it is discarded. This adds another important layer of security to the protocol.

4. Safeguarding Vehicle Functions

Many vehicle features like engine control, braking systems, or ADAS (Advanced Driver Assistance Systems) depend on accurate and trusted data communication. Any interference in this communication could lead to safety risks or ECU malfunction. Secure Data Transmission helps ensure that only authorized and verified data is processed by the ECUs. This minimizes the chance of system failures due to false or malicious inputs. It’s vital for maintaining the safety and reliability of modern vehicles.

5. Enabling Secure Remote Operations

With the rise of connected cars, remote diagnostics and Over-The-Air (OTA) updates are becoming more common. These operations involve transmitting sensitive software and calibration data over external networks. Without protection, this data could be exposed or altered during transit. The 0x84 service ensures that all remote communication is encrypted and authenticated before it reaches the ECU. This helps OEMs provide remote services without compromising the security of the vehicle systems.

6. Compliance with OEM Security Standards

Automotive OEMs are required to follow strict cybersecurity standards like ISO 21434 and UNECE WP.29. These standards mandate secure communication between diagnostic tools and ECUs, especially for critical functions. Using Secure Data Transmission (0x84) fulfills these requirements by enabling encryption, integrity checks, and anti-replay measures. It also allows manufacturers to meet regulatory demands while protecting their intellectual property. This service is an essential part of a compliant and secure UDS implementation.

7. Protecting Intellectual Property and Proprietary Data

Automotive manufacturers often use custom configurations, calibration values, and algorithms that represent years of research and development. If this proprietary data is transmitted without protection, it becomes vulnerable to reverse engineering or theft by unauthorized parties. The 0x84 service encrypts such valuable data before transmission, ensuring it can only be understood by the intended ECU with the correct decryption keys. This helps safeguard a company’s intellectual property and maintains a competitive edge in the industry.

Syntax of 0x84 SID Request Message Frame Format

The security sub-layer generates the application layer Secured Data Transmission request message parameters.

Data Byte	Parameter Name	Byte Value
#1	Secured Data Transmission Request SID	0x84
#2 : #n	Security Data Request Record[] = [                          security Data Parameter#1                                                                :                          security Data Parameter#m ]	0x00 – 0xFF : 0x00 – 0xFF

Request Message Data-Parameter

securityDataRequestRecord

This parameter contains data processed by the Security Sub-Layer.

Syntax of 0x84 SID Positive Response Message Frame Format

Data Byte	Parameter Name	Byte Value
1	Secured Data Transmission +Ve Response SID	0xC4
2 : n	Security Data Response Record[] =[                     security Data Parameter#1                                                                    :                     security Data Parameter#m]	0x00 – 0xFF : 0x00 – 0xFF

Response Message Data-Parameter

securityDataResponseRecord

This parameter contains the data as processed by the Security Sub-Layer.

Syntax of 0x84 SID Negative Response Message Frame Format

Data Byte	Parameter Name	Byte Value
1	Secured Data Transmission –Ve Response SID [ byte#1 ]	0x7F
2	Requested SID [ byte#1 ]	0x84
3	Negative Response Code [ byte#1 ]	NRC

Supported Negative Response Codes (NRCs) of 0x84 SID

NRC	Description
0x13	Incorrect Message Length Or Invalid Format The server shall use this response code, if the length of the request A_PDU is not correct.
0x38 – 0x4F	Reserved By Extended Data Link Security Document This range of values is reserved by extended data link security.

Example of Secure Data Transmission (0x84) Service in UDS Protocol

Following are the Examples of Secure Data Transmission (0x84) Service in UDS Protocol:

Example of Request Upload (0x84) SID Request Frame Format

PCI Length	Request SID	DTC
0x03	0x84	A1	A2

Example of Request Upload (0x84) SID Positive Response Frame Format

PCI Length	Response SID	DTC
0x03	0xC4	B1	B2

Example of Request Upload (0x84) SID Request Frame Format

PCI Length	Request SID	DTC
0x06	0x14	0xFF	0xFF	0x33

Example of Request Upload (0x84) SID Negative Response Frame Format

PCI Length	Response SID	SID	NRC
0x03	0x7F	0x84	13

Advantages of Secure Data Transmission (0x84) Service in UDS Protocol

Here are the Advantages of Secure Data Transmission (0x84) Service in UDS Protocol:

1. Ensures Data Confidentiality: Data is encrypted before transmission, preventing unauthorized parties from intercepting and understanding it. This ensures that sensitive information, such as security keys and configuration settings, remains protected throughout the transmission process. Encryption ensures only authorized recipients with decryption rights can access the data. Without it, there’s a risk of data theft, which could be exploited maliciously.
2. Maintains Data Integrity: The 0x84 service uses Message Authentication Codes (MACs) to verify that data remains unaltered during transmission. Any modification, even by a single bit, would be detected, ensuring that the data received is identical to what was sent. This guarantees that the vehicle’s systems act on accurate and untampered information. It’s essential for ensuring safe and reliable vehicle operations.
3. Prevents Unauthorized Access: By using cryptographic keys for communication, only authorized diagnostic tools or systems can access or interact with the ECU. Unauthorized access attempts are blocked, reducing the risk of malicious actors gaining control over critical vehicle functions. This protection is vital for preventing unauthorized personnel from tampering with vehicle systems, ensuring the integrity of the vehicle’s software.
4. Protects Against Replay Attacks: The service uses sequence counters, timestamps, or session tokens to prevent attackers from re-sending previously captured valid messages. These mechanisms ensure that each message is unique and cannot be reused maliciously to trigger the same action repeatedly. Replay attacks can be a significant vulnerability, and blocking them helps maintain the system’s security and operational integrity.
5. Improves Vehicle Cybersecurity: Secure Data Transmission bolsters the overall cybersecurity of vehicle networks by encrypting and authenticating communication between ECUs and diagnostic systems. It helps prevent unauthorized manipulation, ensuring that the car’s software functions as intended without interference. With increasing connectivity in vehicles, securing data becomes crucial to defend against evolving cyber threats.
6. Supports Compliance with Automotive Security Standards: Using 0x84 helps manufacturers comply with international standards like ISO 21434 and UNECE WP.29, which mandate secure communications in vehicles. By adhering to these regulations, manufacturers ensure their vehicles meet legal requirements and maintain trust with customers and regulatory bodies. It’s a crucial aspect of ensuring that automotive systems are both secure and legally compliant.
7. Enables Secure OTA Updates and Remote Diagnostics: The 0x84 service allows secure communication for Over-The-Air (OTA) software updates and remote diagnostics. Data remains protected even when transmitted over public or third-party networks, reducing the risk of man-in-the-middle attacks. This capability allows manufacturers to update vehicles without requiring them to visit a service center, enhancing convenience and reducing costs.
8. Safeguards Manufacturer’s Intellectual Property: Manufacturers often need to transmit proprietary data, such as algorithms, tuning parameters, or system configurations. Secure Data Transmission ensures that this intellectual property is encrypted and protected during communication. This prevents competitors or unauthorized third parties from stealing or reverse-engineering sensitive information, helping maintain a competitive advantage.
9. Reduces Risk of Data Manipulation: By using encryption and authentication mechanisms, the 0x84 service ensures that the data cannot be modified by malicious entities during transmission. This prevents attackers from altering diagnostic commands, ECU firmware, or vehicle settings, which could lead to unsafe or unintended vehicle behavior. It adds a layer of protection against data manipulation that could compromise safety.
10. Enhances Trust in Remote Services: As remote services like diagnostics and firmware updates become more common, trust in these services is essential. The 0x84 service ensures that these operations are secure and that the vehicle’s systems are only modified by trusted entities. This builds confidence among vehicle owners and service providers, knowing that the remote operations are safe and secure.

Disadvantages of Secure Data Transmission (0x84) Service in UDS Protocol

Here are the Disadvantages of Secure Data Transmission (0x84) Service in UDS Protocol:

1. Increased ECU Complexity: Implementing secure communication protocols like 0x84 requires additional hardware and software resources in the ECU. Developers must integrate encryption algorithms, key management systems, and validation logic, making the ECU design more complex. This can increase development time and potential for bugs or security loopholes if not handled properly.
2. Higher Computational Load: Encryption and decryption processes consume significant processing power and memory. ECUs with limited hardware capabilities may struggle to handle cryptographic functions efficiently. This can slow down diagnostics or software updates, especially in real-time or low-latency systems where performance is critical.
3. Increased Development Time and Cost: Developing a secure communication stack involves cryptographic libraries, key exchanges, and compliance with standards. This requires skilled engineers, longer testing cycles, and possibly licensing of third-party security components. As a result, the overall cost and time-to-market for vehicle software increases.
4. Key Management Challenges: Handling and distributing cryptographic keys securely is a complex task. Any compromise in the key storage or exchange mechanism can break the entire security system. Automotive suppliers must implement robust key lifecycle management, which adds to project complexity and requires continuous maintenance.
5. Compatibility Issues: Not all diagnostic tools or third-party devices may support secure transmission. This can lead to compatibility problems when using legacy tools or working in mixed environments. As a result, manufacturers may need to maintain both secure and non-secure communication paths, adding overhead.
6. Difficulty in Debugging: Encrypted communication makes it harder to analyze and debug message flows using standard tools like CAN analyzers. Developers cannot inspect the actual data unless they have decryption keys, making fault isolation more complicated. This can slow down development and increase maintenance efforts.
7. Potential for Misconfiguration: Improper configuration of security parameters like encryption keys, authentication methods, or session handling can lead to failed communication or security loopholes. Even small errors in setup can render the secure channel non-functional or insecure, requiring thorough testing and validation.
8. Performance Bottlenecks in Large Networks: In vehicles with multiple ECUs communicating simultaneously, secure data transmission can introduce noticeable delays. The time taken for cryptographic operations and authentication checks adds latency, which may affect time-sensitive applications like ADAS or infotainment systems.
9. Risk of Denial-of-Service (DoS) Attacks: Attackers can flood the system with repeated secure session requests, forcing the ECU to perform expensive cryptographic operations repeatedly. This could drain resources and make the system temporarily unavailable. Without proper rate limiting or security checks, the system becomes vulnerable.
10. Complex Compliance Verification: Proving that the secure communication implementation meets industry standards like ISO 21434 or AUTOSAR Security is not easy. It requires extensive documentation, audits, and security testing, which can be time-consuming and resource-intensive, especially for small or mid-sized suppliers.

Future Development and Enhancement of Secure Data Transmission (0x84) Service in UDS Protocol

Following are the Future Development and Enhancement of Secure Data Transmission (0x84) Service in UDS Protocol:

1. Integration with Post-Quantum Cryptography: As quantum computing evolves, current encryption algorithms may become vulnerable. Future updates may incorporate post-quantum cryptographic methods to ensure long-term security against powerful quantum attacks, making the UDS protocol future-proof and highly secure.
2. Standardized Key Management Infrastructure: Efforts are underway to develop standardized, centralized, and scalable key management systems across the automotive industry. This will simplify the process of key generation, storage, distribution, and revocation, making secure communication easier to implement and maintain.
3. Enhanced Real-Time Performance: Future ECUs will likely use hardware accelerators or optimized cryptographic engines to process secure messages faster. This will reduce latency and improve the performance of secure diagnostics and OTA updates, especially in safety-critical systems like braking and steering.
4. Dynamic Security Policy Adaptation: Upcoming implementations may allow the ECU to dynamically adjust security levels based on context, threat level, or operating conditions. For example, stricter encryption can be used during remote access sessions while local access may use lighter protection, improving efficiency and security.
5. Broader Toolchain Support: Future diagnostic and testing tools will increasingly support secure data transmission natively. This will ensure better compatibility, smoother integration in workshops, and improved debugging and validation environments for developers and service providers.
6. Secure Multi-ECU Communication: As vehicle architectures become more centralized or zonal, there will be a need for secure communication not just between tester and ECU but among ECUs themselves. The 0x84 service could evolve to support secure end-to-end communication across multiple domains.
7. Increased Support for Over-The-Air Security: Future enhancements will better support secure OTA operations, including encrypted firmware delivery, secure flashing, and rollback protection. This ensures that updates remain trusted and vehicles receive only authentic, verified software versions.
8. AI-Driven Intrusion Detection Integration: Secure transmission may be combined with machine learning or AI-based anomaly detection systems that monitor communication patterns. These systems can flag suspicious secure session usage or identify trends indicating an attempted attack or malfunction.
9. Improved Compliance and Certification Processes: New frameworks and tools will emerge to simplify the verification of compliance with ISO 21434 and UNECE WP.29. These will automate auditing and certification of secure UDS implementations, helping OEMs and Tier-1s meet regulatory needs faster.
10. Unified Security Frameworks Across Protocols: Secure data transmission mechanisms like 0x84 may be integrated into broader automotive security frameworks that unify diagnostics, communication, and boot security. This harmonization will enhance interoperability and simplify secure system design.