Scan Chain Output Encryption for Secure SoC Diagnostics
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Solution Overview
Problem
Diagnosing errors in complex system-on-chip (SoC) devices in the field is challenging due to the difficulty in reproducing errors in the test environment, and existing methods for securing scan dumps expose confidential information and create security risks.
Innovation Solution
Implementing encryption circuits on the SoC to encrypt scan chain data using a session key generated by the SoC, which is further encrypted with the manufacturer's public key, and disabling scan input during output to protect against unauthorized access, allowing secure collection and transmission of encrypted scan dumps to the manufacturer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Difficulty of detecting and measuring
If scan chain output is permitted for diagnostic purposes, then error diagnosis capability is improved, but confidential information security deteriorates
Solution Approach 1:
An encryption circuit is introduced as an intermediary between the scan chain output and the external diagnostic equipment. This encryption circuit encrypts the scan chain output data using an encryption key before output, and the corresponding encrypted data can be decrypted only by authorized parties possessing the decryption key. This mediator mechanism enables diagnostic data transmission while preventing unauthorized access to confidential information.
2Object-affected harmful factors
If encryption is applied to scan chain output, then security is improved, but device complexity deteriorates
Solution Approach 1:
The encryption function is extracted as a separate, dedicated encryption circuit module within the scan testing apparatus. This modular extraction allows the encryption functionality to be implemented independently using standardized cryptographic components, rather than integrating encryption logic throughout the entire scan chain infrastructure. This reduces overall system complexity while maintaining security.
3Object-affected harmful factors
If scan input is disabled during output, then unauthorized access prevention is improved, but diagnostic flexibility deteriorates
Solution Approach 1:
The scan input enabling/disabling operation is implemented as a periodic, controlled action synchronized with the scan output process. The scan input is disabled during the scan output phase to prevent unauthorized access, and can be re-enabled in subsequent phases when security is not a concern. This periodic control mechanism maintains security during critical operations while preserving diagnostic flexibility overall.
Data Source
AI summary
Scan chain data of a system-on-chip (SoC) is protected from unauthorized access by an encryption circuit disposed on the SoC. A test access port (TAP) is coupled to the scan chain and is configured to shift data through the scan chain. The encryption circuit is coupled to the TAP and is configured to encrypt the data into encrypted data for output from the SoC.