Microcomputer Key Management via Debug Port Disabling
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing methods for securely writing and managing individual keys in microcomputers, especially in low-cost IC cards and manufacturing processes, are inadequate as they lack robust multilevel key management and are vulnerable to internal fraudulent threats, with simple encryption methods being insufficient.
Innovation Solution
A communicating device with a storage unit, debugging unit, random-number generating unit, public-key encrypting unit, and individual-key writing unit is used to securely write and manage individual keys by disabling debugging, generating and encrypting random numbers, and decrypting encrypted keys from a key issuing server, ensuring secrecy and integrity during manufacturing and operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the debug port is disabled after writing the secret key to prevent external access, then external security is improved, but internal fraudulent persons can still access the secret key in plain text during the manufacturing process
Solution Approach 1:
The patent applies preliminary action by disabling the debug port before the secret key is written to memory. The sequence is reversed from conventional methods: first the debug port is disabled, then the secret key is written in encrypted form directly to memory. This preliminary disabling prevents both external and internal access during the key writing process, as the debugging unit cannot access memory after being disabled.
Solution Approach 2:
The patent applies preliminary anti-action by preemptively neutralizing the debugging unit's potential harmful effect. By disabling the debug port before key writing, the system prevents the debugging unit from being used for fraudulent key extraction. The initializing program automatically disables the debug port, creating a counter-measure against internal fraud before the vulnerability can be exploited.
2Ease of manufacture
If simple encryption is applied to write data in low-price microcomputers, then cost is reduced, but security against fraudulent key extraction is insufficient without multilevel key management
Solution Approach 1:
The patent applies segmentation by dividing the encryption process into multiple stages with different key levels. First, a first encryption key encrypts the secret key, then a second encryption key (stored in non-writable memory) encrypts the already-encrypted data. This multilevel segmentation provides strong security even in low-cost devices, as each layer requires its own key, and the debugging unit is disabled to prevent key extraction.
Solution Approach 2:
The patent applies the nested doll principle by creating nested encryption layers. The secret key is first encrypted with a first key, then the resulting ciphertext is encrypted again with a second key, forming a nested structure where one encryption is contained within another. This nested approach provides robust security while remaining implementable in cost-sensitive applications.
3Ease of operation
If the secret key is handled in plain text during the manufacturing process for simplicity, then ease of operation is improved, but vulnerability to internal fraudulent persons increases
Solution Approach 1:
The patent applies preliminary action by disabling the debug port before the secret key is written to memory. The initializing program automatically performs this disabling action, ensuring that even if someone attempts to access the key during manufacturing, the debugging unit is already inactive. This eliminates the need for complex manual security procedures while maintaining simplicity in operation.
Solution Approach 2:
The patent applies self-service by making the system automatically disable its own debug port through the initializing program. The device itself performs the security action of disabling the debugging unit without requiring external intervention or complex manual procedures. This self-service approach maintains operational simplicity while effectively preventing internal fraud.
Data Source
AI summary
The debugging unit writes a public key of the key issuing server and an initializing program given from outside, to the storage unit. The instruction executing unit reads and executes the initializing program stored in the storage unit. The debug disabling unit disables the debugging unit. The public-key encrypting unit encrypts the random number by the public key in the storage unit, the random number generated by the random number generating unit after the debugging unit is disabled. The transmitting unit transmits the encrypted random number to the key issuing server. The receiving unit receives an individual key encrypted by the random number from the key issuing server. The individual-key writing unit decrypts the encrypted individual key by the random number to obtain the individual key and write the individual key to the storage unit.