Security Device Microcontroller Encryption Coprocessor Key Protection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing security devices for long-lived products, such as vehicle control units, face challenges in protecting sensitive data due to the need for frequent redesigns of specialized circuits and the high cost and error vulnerability of generic, debuggable circuits that allow full access to microcontrollers, conflicting with the requirement to prevent key extraction by OEMs.
Innovation Solution
A security device design where a microcontroller can only access protection-worthy information for specific purposes, using a microcontroller connected to an encryption unit via a bus, with no direct access to keys, and only allowing encryption and decryption operations through the encryption unit, ensuring that the main key cannot be used for data decryption and is protected from overwrite or deletion, and keys can only be replaced in an encrypted form.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a special circuit with highly compact design is used for security purposes, then manufacturing cost is reduced and error resistance is improved, but service life is limited and adaptability deteriorates
Solution Approach 1:
The system is segmented into a generic microcontroller unit and a separate encryption coprocessor. The microcontroller handles general-purpose operations while the coprocessor is dedicated to cryptographic functions. This segmentation allows the microcontroller to be upgraded or modified independently while maintaining the security functions through the coprocessor, thus extending service life without sacrificing manufacturing efficiency.
Solution Approach 2:
The microcontroller is designed with universal functionality to handle various control tasks beyond just security operations. It can be programmed for different applications while the encryption coprocessor provides consistent security services. This multi-functionality extends the service life of the control unit compared to specialized security circuits.
2Ease of repair
If a debug interface is provided for software modification, then ease of repair and software updates are improved, but security deteriorates due to potential key access
Solution Approach 1:
The encryption coprocessor is extracted as a separate security module with its own protected memory space. Keys are stored exclusively in the coprocessor's secure memory, isolated from the main microcontroller's addressable memory space. This extraction ensures that even with full microcontroller debugging access, keys remain protected as they exist in a separate, secured environment.
Solution Approach 2:
The encryption coprocessor acts as an intermediary between the microcontroller and the protected data. All cryptographic operations must route through the coprocessor, which mediates access to keys and encrypted data. This intermediary architecture allows the microcontroller to be fully debuggable while maintaining key security through the coprocessor's controlled access interface.
3Adaptability or versatility
If full control of the microcontroller is enabled for debugging, then adaptability and software modification are improved, but key secrecy deteriorates
Solution Approach 1:
The system introduces a dimensional separation between the debuggable microcontroller space and the protected coprocessor space. The microcontroller operates in a fully accessible dimension for debugging and software updates, while the coprocessor exists in a separate protected dimension with restricted access. This dimensional separation allows full software flexibility in the microcontroller without compromising key secrecy in the coprocessor.
Solution Approach 2:
The control unit is segmented into two distinct functional domains: a generic microcontroller domain that is fully debuggable and adaptable, and a security coprocessor domain that maintains key secrecy. This segmentation enables the microcontroller to be freely modified for different applications while the coprocessor maintains isolated protection for cryptographic keys.
Data Source
AI summary
A method for operating a security device includes a microcontroller, a protected memory area, in which at least one item of protection-worthy information is stored, and a unit, the microcontroller being connected to the protected memory area via the unit, the at least one item of protection-worthy information being accessed by the microcontroller via the unit when the method is carried out.