Smart Card Data Integrity Verification via Intermediary Checksum
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Solution Overview
Problem
Smart card data transfers are vulnerable to electromagnetic disturbances, allowing fraudulent access and modification of sensitive data due to ineffective detection methods that can be circumvented by attackers applying the same disturbances during copying and verification.
Innovation Solution
A method where the integrity of source data is calculated and verified by comparing it with an integrity value passed through the data bus during verification, rather than the data itself, making it impossible for attackers to apply the same disturbances during both phases effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If data transfer verification is performed by comparing transferred data with source data, then data integrity can be checked, but the verification process can be circumvented by attackers who apply the same electromagnetic disturbances during both copying and verification phases
Solution Approach 1:
The patent introduces an intermediary verification mechanism using a checksum value. Instead of directly comparing the data itself during verification (which can be fooled by consistent disturbances), the system compares a checksum calculated from the transferred data with a pre-stored checksum. This intermediary verification approach ensures that even if disturbances affect the data transfer, the verification process detects anomalies because the checksum comparison reveals inconsistencies in the disturbed data.
Solution Approach 2:
The patent applies preliminary action by pre-calculating and storing checksum values for data elements before they are transferred. These preliminary checksums are stored in non-volatile memory alongside the data. During verification, the system recalculates the checksum from the transferred data and compares it with the pre-stored checksum, enabling detection of disturbances without requiring re-transfer of the entire data set.
2Ease of manufacture
If traditional byte-by-byte comparison is used for verification, then simple implementation is achieved, but it cannot detect disturbances that affect both copying and verification operations
Solution Approach 1:
The patent uses a checksum as an intermediary verification mechanism that simplifies the verification process while improving reliability. Instead of complex byte-by-byte comparison that can be circumvented, the system uses a single checksum value that encapsulates the integrity of the data. This intermediary approach maintains implementation simplicity while providing robust detection capability against consistent disturbances.
Solution Approach 2:
The patent changes the verification parameter from direct data comparison to checksum value comparison. By transforming the verification process into a parameter-based comparison (comparing checksums rather than raw data bytes), the system achieves both simplicity in implementation and effectiveness in detecting disturbances, as the checksum parameter captures any modification in the data.
Data Source
Figure 1~2
AI summary
The invention relates to a method for the secure transfer of data, that comprises comparing source data stored in a source memory (NV_MEM) with transferred data (COPY_ELT_X_V_MEM) copied from the source memory (NV_MEM) into a so-called destination memory (V_MEM). The method comprises reading in the source memory (NV_MEM) an integrity value (PI_ELT_X) associated with an element (ELEMENT_X_NV_MEM) such as a file containing the source data, calculating the integrity of a reconstituted element formed by the transferred data (COPY_ELT_X_V_MEM) and optionally completed by data of the source element (ELEMENT_X_NV_MEM), different from the transferred data, and deciding that the transferred data (COPY_ELT_X_V__MEM) is identical to the source data when the integrity calculation gives a value identical to the integrity value of the source element (PI_ELT_X). The invention can be used for transferring data between the components of a chip in a smart card.