Debug Protection Circuit for Chip Security
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Solution Overview
Problem
Debugging channels in chips, such as SWD or JTAG interfaces, pose a security risk after chip development, as they can be exploited by hackers to access confidential information or tamper with the device, leading to potential unauthorized functions or device damage.
Innovation Solution
A debug system incorporating a chip under test with a debug protection circuit that enables or blocks communication between the debug access circuit and the chip under test based on a protection function, which is controlled by a write message from the debug controller, using a comparator to authenticate debug keys and store them in one-time programmable memory to prevent unauthorized access.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a debugging channel is incorporated in the chip to enable debugging access, then debugging capability is improved, but security risk increases due to potential unauthorized access after chip development
Solution Approach 1:
The debug protection circuit dynamically switches between enabling and blocking the debugging channel based on the protection function state. When the protection function is enabled, the circuit blocks all communication between the debug access circuit and the first circuit under test. When disabled, normal debugging communication is restored. This dynamic control allows the system to adapt between debugging mode and secure operation mode.
Solution Approach 2:
The debug protection circuit acts as an intermediary component inserted between the debug access circuit and the first circuit under test. It interceptates all communication attempts and selectively permits or blocks them based on the protection function state and authentication results. This intermediary structure allows the debugging channel to remain physically present for ease of access while adding a security layer that prevents unauthorized access.
2Object-affected harmful factors
If the debug protection circuit blocks communication to prevent unauthorized access, then security is improved, but debugging access becomes difficult when protection is enabled
Solution Approach 1:
The system changes the authentication parameter (debug key) to control access. The debug protection circuit compares the provided debug key with a stored reference key. When the keys match, the protection function is disabled and debugging access is granted. When they don't match or no key is provided, the protection function remains enabled and access is blocked. This parameter-based control allows secure restriction of access while enabling debugging when proper authentication is provided.
3Object-affected harmful factors
If the debug protection circuit always blocks communication to ensure security, then information security is improved, but debugging functionality is lost
Solution Approach 1:
The debug protection circuit implements dynamic control of the protection function rather than a static always-block mode. The circuit can switch between two states: blocking communication when the protection function is enabled, and permitting communication when the protection function is disabled through successful authentication. This dynamic behavior allows the system to maintain information security during normal operation while restoring full debugging functionality when needed and authorized.
Solution Approach 2:
The authentication mechanism performs preliminary verification before allowing debugging access. The debug protection circuit first checks whether the provided debug key matches the stored reference key before enabling the debugging channel. This preliminary action ensures that only authorized debugging sessions can access the circuit under test, maintaining security while enabling necessary debugging functionality.
Data Source
AI summary
A debug system includes a chip to be tested and a debug controller. The chip to be tested includes a circuit to be tested, a debug access circuit and a debug protection circuit. When a protection function is not enabled, the debug protection circuit enables a communication between the debug access circuit and the chip to be tested, the debug controller accesses the data of the chip to be tested via the debug access circuit for debugging the circuit to be tested. When the protection function is enabled, the debug protection circuit blocks the communication between the debug access circuit and the chip to be tested, the debug controller transmits a message to the debug protection circuit via the debug access circuit, and the debug protection circuit determines whether to disable the protection function according to the message.