Decryption Key Protection via Consistency Check Circuits
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Solution Overview
Problem
Programmable logic circuits are vulnerable to attacks that aim to discover decryption keys through differential power analysis, as attackers can monitor power consumption to identify operations and determine the decryption key, especially during decryption processes.
Innovation Solution
A decryption system that includes a decryptor circuit and a consistency check circuit, which decrypts the data stream using a key and checks for inconsistencies before completing decryption. If inconsistencies are found, a tampering signal is generated, and an alternative key or data stream is used to prevent key exposure, thereby masking the true key from attackers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the decryption key is stored in the programmable IC and used to decrypt the bitstream, then the design is protected from unauthorized copying, but the key becomes vulnerable to power analysis attacks that can reveal the key through monitoring power consumption variations
Solution Approach 1:
The patent performs consistency checks on decrypted data before the decryption process is complete, specifically checking early portions of the decrypted bitstream against expected values. This preliminary verification allows the system to detect attacks and switch to alternative keys before the full decryption reveals the master key through power analysis
Solution Approach 2:
The system dynamically changes the decryption key parameter during operation. When an inconsistency is detected that suggests a power analysis attack, the system switches from the master decryption key to alternative keys, thereby changing the cryptographic parameter to prevent key extraction while maintaining the ability to decrypt legitimate data
2Reliability
If consistency checks are performed during decryption to detect attacks, then key security is improved, but the decryption process becomes more complex and time-consuming
Solution Approach 1:
The patent performs consistency checks on only a portion of the decrypted data (specifically, early portions of the bitstream) rather than verifying the entire decryption output. This partial verification provides sufficient security against power analysis attacks while minimizing the additional complexity and time required compared to full verification
3Reliability
If the system switches to alternative keys upon detecting inconsistencies, then the master key is protected from exposure, but the decryption process requires additional key management and switching mechanisms
Solution Approach 1:
The patent extracts the master decryption key from the direct decryption path and stores it separately in secure memory. Instead of using the master key directly for decryption operations, the system uses alternative keys for actual decryption while the master key remains isolated and protected. This extraction approach protects the master key from exposure during decryption operations while minimizing the complexity of key management
Data Source
AI summary
An embodiment of a method is disclosed for protecting a key from discovery during decryption of a data stream. This embodiment of the method includes decrypting the data stream with the key. Before completing decryption of the data stream, the method checks consistency between a decrypted portion of the data stream and expected data using a circuit arrangement. In response to an inconsistency between the decrypted portion and the expected data, a tampering signal is generated to indicate tampering is suspected.