Transponder Metal Shield Switch for Relay Attack Prevention
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Solution Overview
Problem
Contactless chip cards and NFC-enabled devices are vulnerable to uncontrolled reading and relay attacks, particularly due to their susceptibility to external magnetic fields, which can lead to unauthorized data access and misuse in applications like payments.
Innovation Solution
A transponder design featuring a metal shielding with interruptions bridged by a switch, creating a closed circuit when not actuated, preventing external addressing and allowing controlled reading only when the user interacts to open the circuit, combined with a mechanically stable structure to withstand mechanical influences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a metallic shield surrounds the antenna coil to protect against external magnetic fields, then shielding effectiveness is improved, but the transponder becomes vulnerable to relay attacks and uncontrolled reading
Solution Approach 1:
The patent applies the dynamics principle by making the metallic shield's electrical continuity controllable rather than static. A switch element is integrated into the shield structure, allowing it to transition between conductive and non-conductive states. When the switch is in the first position, the shield forms a closed loop providing magnetic shielding. When switched to the second position, the shield becomes electrically open, preventing relay attacks while maintaining structural integrity.
Solution Approach 2:
The patent employs parameter changes by modifying the electrical conductivity parameter of the metallic shield through the switch mechanism. The shield's conductivity is changed from continuous (when switch is in first position) to discontinuous (when switch is in second position), thereby altering its electromagnetic properties dynamically to address different security requirements.
2Object-affected harmful factors
If the metallic shield forms a closed loop to provide shielding, then magnetic coupling protection is improved, but current flows in the shield that acts back on the antenna coil
Solution Approach 1:
The switch element enables dynamic control of the shield's electrical continuity. In the first position, the shield forms a closed loop for optimal magnetic shielding. In the second position, the switch opens the circuit, eliminating current flow and preventing back-action on the antenna coil while maintaining the shield's physical structure.
Solution Approach 2:
The shield's electrical continuity is periodically switched between closed and open states through the switch mechanism. This periodic action allows the system to alternate between shielding mode (closed loop) and anti-relay-attack mode (open circuit), providing both protective functions at different times.
3Ease of operation
If the transponder is designed to be readable remotely through materials like bags, then convenience of use is improved, but unauthorized reading and data security are compromised
Solution Approach 1:
The switch element provides dynamic control over the transponder's readability. When switched to the first position, the shield is conductive allowing legitimate reading operations. When switched to the second position, the shield becomes non-conductive, blocking unauthorized reading attempts while maintaining the same physical structure that enables convenient contactless operation.
4Reliability
If a switch is introduced to control shield conductivity, then security against unauthorized reading is improved, but device complexity increases
Solution Approach 1:
The switch element is merged with the metallic shield structure itself, forming an integrated component rather than a separate addition. The switch is positioned within the shield's conductor path, combining the shielding function and the switching function into a single unified structure, thereby minimizing the increase in device complexity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The transponder is robust against mechanical influences and resistant to unauthorized reading, ensuring secure data access only through user-initiated interaction, effectively mitigating relay attacks and uncontrolled data access.
Implementation Method 1
a metallic shield with at least one interruption (24)... surrounds at least one antenna coil (6)... The at least one interruption (24) in the metallic shield is bridged by at least one switch (10) in its unactuated state... a current is induced in the winding as a result of the electromagnetic waves emitted by the reader, which generates a magnetic field, thus preventing the IC card from being read
Implementation Method 2
a current is induced in the winding as a result of the electromagnetic waves emitted by the reader
Data Source
Figure 1~2
Figure 3
Figure 4
AI summary
The transponder (2) has a metallic shield (4) with an interruption, while an antenna coil (6) is provided with a winding. The antenna coil is surrounded by the metallic shield, where a chip (8) is connected to the antenna coil. A switch (10) is arranged to bridge the interruption to the non-actuated state, so that a closed circuit is formed in the metallic shield and the transponder is not accessed from the outside. The metallic shield has a circular shape, and is provided as a metallic pipe with the ends opposite to the point of interruption without electrical contact. An independent claim is included for a method for manufacturing the transponder.