Fleet Key Management: Enhancing Security with Per-ECU Key Rotation

What is a Fleet Key Management System? 

Electronic Control Units (ECU) are important components of modern vehicles and machinery that are tandemly working advanced computers running operations seamlessly on wheels and connecting roadside infrastructure, cloud, and the ecosystem of other vehicles with the internal environment. 

These units communicate with, monitor, control, and regulate various electronic systems within the vehicle, such as vehicle control unit, telematics control unit, battery monitoring system, EV motor controller, automotive monitoring system, etc., by processing data from sensors, using algorithms, and adjusting parameters. This includes specific functions and safety features for vehicle reliability, such as airbags in the Supplemental Restraint System (SRS), transmission and emissions control, optimal engine and fuel performance, air conditioning, etc.  

Hacking of these units can lead to unauthorized software or firmware over-the-air (OTA) updates or remote diagnostics, threats to communication channels or external connections, unintended wireless vehicle unlocking or other human actions, data theft, loss, or breach of safety.  

To prevent this, vehicles are secured with mitigation mechanisms, such as cryptographic keys that can encrypt and decrypt messages, regulate vehicle authentication, techniques for access control, and code signing. Secure and centralized fleet key control systems assist in secure generation, injection, controlling, storage, tracking, and access management of these keys throughout the lifecycle of ECUs.  

These are digital tools that allow organizations to authenticate access to the keys in real-time and track their usage, thus ensuring operational security, efficiency, and accountability. These are one of many such automotive IT solutions, such as license plate recognition system, fleet management system, 360° camera for car, blind spot detection system, vehicle detection system, etc. 

The global market for fleet key management was valued at about US $1.24 billion in 2024 and is expected to surge to an approximate value of US $3.52 billion in 2033, registering a 12.3% CAGR during this forecast period. Let us explore the types, features, benefits, and challenges of implementing these systems in this blog. 

Source: Market.us 

Growing market size of digital key solutions for fleets from 2023 to 2033 forecast period 

Insights into Secure Fleet Key Management System 

Importance 

It is necessary to handle these cryptographic keys with utmost priority and importance, as loss, misplacement, or unauthorized use of the same can cause a surge in security risks, downtime, and operational expenses. This security practice involves communication of individual ECUs with their specific or respective encryption keys that are changed, rotated, or updated within a stipulated time or after a specific number of uses to enhance security.  

Whence a centralized and secure key management system is in place, traditional methods, such as manual logs, are no longer required, as smart key encryption, software tracking, and access control allow only authorized personnel to access them. The system thus provides round-the-clock visibility into vehicle usage, generates alerts and reports, and automates security to avoid unauthorized access of any sort.  

The fleet key management system allows a role-based lock access system per user, automatic, real-time digital logging, a completely searchable user and time-wise history, automated managerial alerts, live key status on the dashboard, and scalable features like ease of functioning across different locations and fleets.  

It eliminates time spent backtracking on unauthorized access, enhances ECU security, sends alerts for overdue keys, conducts in-depth audit trails, and reduces vehicle loss or misplacement risks, apart from enhancing access control and tracking. 

The practice is also important to follow as part of stringent cybersecurity regulations for the automotive industry, a specific recent example being the 2020 United Nations Economic Commission for Europe (UNECE) regulations R155 and R156. Both regulations lie in conjunction with the joint effort between the Society of Automotive Engineers (SAE) and the International Organization for Standardization (ISO).  

UNECE R155 and ISO/SAE 21424 postulate that every automated or connected vehicle requires a Cybersecurity Management System (CSMS). UNECE R156 in conjunction with ISO 24089 stresses the fact that the vehicles must also feature a Software Update Management System (SUMS) to avoid unauthorized data breaches. Thus, compliance with these regulations through sound and thoroughly secured software updates, distribution processes, and well-defined cyber risk management has become the need of the hour for efficient logistics. 

Types of Keys 

1. Symmetric Keys:

In this case, the data is encrypted and decrypted using the same key, that is, both the recipient and the sender need to have access to the same key. It is a faster and more efficient encryption method for large volumes of data and does not require computational overhead.  

It can be used in Hash-based Message Authentication Code (HMAC), where the shared key is used by both the recipient and the sender to create a hash that verifies that the message has not been tampered with. 

A few examples of such digital key management algorithms where symmetric keys are applied include Advanced Encryption Standard (AES), Data Encryption Standard (DES), Triple Data Encryption Standard (3DES), etc. Common security considerations involve the risk of data decryption during transmission or key sharing and secure channel establishment using an asymmetric key system to exchange symmetric keys for efficient key management. 

2. Asymmetric Keys:

In this case, a public key is used for encryption while a private key decrypts the data, and both the keys are mathematically related, although the latter cannot be easily derived from the former.  

A few examples of algorithms where symmetric keys are applied include Rivest-Shamir-Adleman (RSA), Elliptic Curve Cryptography (ECC), Digital Signature Algorithm (DSA), etc. In digital signatures, the sender signs the message with a private key, and the recipient verifies the authenticity of the same using the sender’s public key. 

The keys are also used for establishing trust in public key infrastructures; for example, in SSL/TLS a server’s public key is sent to the client during handshake for encrypting session keys and exchanged for further communication in fleet key control systems. 

Common security considerations involve man-in-the-middle attacks that are tackled using digital certification signatures of widely distributed public keys for authenticity issued by Certificate Authorities (CAs). Another concern is related to private keys, which can be decrypted, or signatures can be forged when accessed if not stored securely and confidentially. 

3. Hybrid Cryptosystem:

In this case, both symmetric and asymmetric encryption approaches are combined to ensure the integrity and authenticity of the message. For example, in an HTTPS connection, the server uses asymmetric encryption (RSA or ECC) to exchange a symmetric key (AES) with the client during the SSL/TLS handshake, which is then used to decrypt data for all further communication. 

Implementation of Digital Key Management 

Given below are the steps of managing fleet keys for enhancing vehicle security. 

Generation 

Key generation involves the creation of keys prior to being used for encryption, verification, and authentication of respective ECUs. This must be done using a Key Management System (KMS), a Hardware Security Module (HSM) or another secure hardware environment in lieu of any software tool of an unsecured ECU.  

A specific key must be generated for a particular purpose, such as communication, diagnostics, and more. ISO/IEC 18031 or NIST SP 800-9A standard-compliant high-entropy Random Number Generators (RNGs) must be used.  

Here IEC refers to the International Electrotechnical Commission, while NIST SP stands for the National Institute of Standards and Technology Special Publication. Both standards provide guidelines for cryptographic and non-cryptographic applications and related generation of high-quality random bits.  

In this case, high-entropy RNGs produce highly unpredictable random numbers for secure communication, digital signatures, key generation, session tokens, and to prevent attacks, such as brute force, replay, etc., that are difficult to replicate. Hybrid cybersecurity methods combine True Random Number Generators (TRNGs) or Pseudorandom Random Number Generators (PRNGs) for better efficiency. 

Flow diagram showcasing digital key management 

Injection 

Key injection involves securely loading or provisioning cryptographic keys generated using KMS or Hardware Security Module (HSM) into specific electronic control units during boot in a controlled industrial setup with stringent role-based access via secure and authenticated channels.  

Authenticated channels such as Mutual Transport Layer Security Internet Protocol Security (mTLS IPSec, certificate pinning) must be used to avoid leakage of the keys. These should be encrypted, stored inside Secure Hardware Extension (SHE), and not transferred in human-readable plain text form.  

Validation must occur through a Root of Trust (RoT) stored in HSMs or equivalent secure storage, post-injection of which operational keys and certifications are injected inside the ECU for software updates, secure boot, diagnostics, and encrypted communication.  

Here, HSM refers to dedicated hardware that is present inside an ECU for cryptographic processing, storage of keys, checks on runtime integrity, secure boot, and isolation of application logic and keys for compliance with ISO/SAE 21434. Also, SHE refers to affordable hardware modules that support the Message Authentication Code (MAC) generation, secure communication, and key management. 

All injection events involved in digital key solutions for fleets must be recorded in a traceable log for compliant audits. The keys must be stored using elements such as enforcement of least privilege, where particular functions of the ECU should require a key for access.  

Global keys or identical keys across multiple units must be avoided, and the keys must be protected at all costs against side-channel attacks such as timing attacks and power analysis that do not break the encryption algorithm and yet allow adversaries to infer cryptographic keys. 

Rotation 

Key updates or rotations involve replacement or refreshment of keys over time for long-term security purposes. Existing trusted keys must be used for authenticating updates, and cryptographic agility must be implemented.  

This includes the selection of strong key lengths and algorithms throughout the vehicle’s life span, which may range from 10 to 15 years, for example, RSA 3072-bit, ECC 256-bit, etc. Here is how per-ECU key rotation helps in resisting large-scale attacks and strengthening anti-theft mechanisms. 

• Rolling Code System: Key updates can be implemented while rolling or changing keys used for ignition to prevent replay attacks or key cloning against the ECU that verifies the stored code with the key code. As and when the key fob and ECU communicate, the code changes automatically, such that the same code cannot be used twice even after interception. 

• Tamper Detection: In case any unauthorized access to the vehicle, attempted tampering of the unit or fleet key control systems, hacking, bypassing, or predicting the key code, or reprogramming or duplication of the key is detected, the vehicle is secured using rotation of the encryption key to a new random code.  

• Dynamic Key Generation: The ECU generates unique and new encryption keys whenever a new session is initiated to prevent interception or reuse. It can also be done after specific or limited time intervals or events, including a particular threshold in regular functioning of the units, vehicle unlocking, ignition, startup, key fob interaction, repair, or incident. 

• Encryption Updates: Key rotation on a per-ECU basis may also be done after diagnostics, Electronic Periodical Technical Inspection (ePTI), maintenance, or resetting the ECU and its security settings to prevent hacking through multiple layers of rotating codes or duplication of a static key signal. 

Deletion 

Key deletion basically involves erasing a key from the electronic control unit in a secure manner, while revocation refers to invalidating an untrusted key. Keys must be revoked in case these are securely deleted and cannot be recovered using memory overwrite or resetting of secure elements. A revocation list mentioning certificates must be maintained, and compromised ECUs must not be reused. Offline mechanisms for revocation, such as use of USB at service centers, must be supported for vehicles that are unable to connect online. 

Drive Profits through KritiKal’s Fleet Key Control Systems 

KritiKal Solutions offers advanced cybersecurity and software update management systems for software-defined vehicles. Our systems support:  

• Tamper-evident audit logs 

• Threat Analysis and Risk Assessments (TARA) 

• Secure boot chain verification 

• Hardware serial binding 

• Incident handling and continuous improvement 

• We use cryptographic algorithms to avoid deprecated cryptography and support future advancements like polygonal geo-fencing, cloud-based management, predictive analytics, and mobile app-based digital keys. 

It presents various options for lifecycle management controls, such as maintenance of in-depth tamper-evident audit logs, including tracking of details like operator and key ID, injection timestamps, HSM signature, etc.  

We ensure compliance with ISO/SAE 21434 by performing thorough document processing while maintaining supply chain integrity and auditable key provisioning. We understand and are fully equipped to develop and deliver digital key solutions for fleet that can streamline vehicle distribution to enable fleet pooling and driver accountability.  

Our custom application development services present a strong impact against current challenges in key generation, distribution, storage, rotation, authentication, revocation, backup, recovery, scalability, compliance, resistance to quantum computing, confidentiality, tamper detection, transparency, supply chain traceability, and centralized key and logistics inventory management. All the while enhancing security, operational efficiency, accountability, user-friendliness with regards to human machine interface development, and reducing expenses and implementation time. Please get in touch with us at sales@kritikalsolutions.com to know more about our products and realize your automotive requirements. 

Mohamed Wasif

Mohamed Wasif currently works as an Associate Architect at KritiKal Solutions. He is an experienced software developer with a decade of work in C++, C, Linux Kernel, System Design, UML, alongside a proven track record of delivering results, leading teams and optimizing product performance. With his passion for innovation and commitment to continuous learning, he has helped KritiKal in delivering various major projects.