Scrambled CDM Touch Screen Overlay Attack Prevention
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Solution Overview
Problem
Touch screen terminals, particularly Point of Sale (PoS) terminals, are vulnerable to overlay attacks where a fraudulent layer captures sensitive information by mimicking the original touch screen, making it difficult to protect user inputs such as passwords and payment card numbers.
Innovation Solution
Implementing a scrambled Code Division Multiplexing (CDM) technique that generates orthogonal encoded drive signals, which are applied simultaneously to multiple drive lines, making it difficult for attackers to decode the exact location of touch inputs without access to the scrambled code patterns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional touch screen drive signals are used, then the touch screen is easy to operate and decode, but it becomes vulnerable to overlay attacks that can intercept and steal sensitive information
Solution Approach 1:
The patent applies parameter changes by transforming the drive signals through scrambling operations that modify the signal parameters (code patterns, sequences) without changing the fundamental touch screen operation. This makes the signals unreadable to overlay attacks while maintaining functionality for the legitimate controller
Solution Approach 2:
The patent introduces scrambled code patterns as an intermediary layer between the touch controller and the overlay attack. This intermediary scrambling mechanism prevents direct interception of touch information by overlay screens while allowing the legitimate controller to decode through the use of corresponding unscrambled codes
2Reliability
If scrambled CDM drive signals are applied to multiple drive lines simultaneously, then overlay attacks are prevented, but the signal processing complexity increases
Solution Approach 1:
The patent segments the drive signals into multiple orthogonal code patterns that are applied simultaneously to different drive lines. Each code pattern is scrambled independently, creating a segmented encoding scheme that enhances security while maintaining manageable complexity through systematic code generation
Solution Approach 2:
The patent employs periodic action through the use of orthogonal code patterns that repeat in systematic sequences. The scrambled codes are applied periodically to drive lines, creating a rhythmic signal structure that is difficult to intercept but can be systematically processed by the legitimate controller
Data Source
AI summary
A method to obtain a codeword scrambled based, in part, on a code division multiplexing (CDM) pattern; generate a drive signal encoded with the scrambled codeword; and stimulate drive lines of a touch sensor in a touch screen over multiple measurement frames utilizing different patterns of the scrambled codeword for respective ones of the multiple measurement frames.