Unidirectional USB Interface Circuit for Secure Data Transfer
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Solution Overview
Problem
Current USB interfaces are bidirectional, preventing direct connection and data transmission between two USB hosts, which is necessary for secure unidirectional data transfer, such as downloading files from a high-security device like an election machine without allowing modifications.
Innovation Solution
A circuit with converter chips that convert USB signals to protocols like RS-232, allowing data transmission from one USB host to another while disabling the reverse direction, using separate transmission paths to prevent data flow back.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a bidirectional USB interface is used, then communication flexibility is improved, but data security is worsened because both hosts can transmit data to each other
Solution Approach 1:
The bidirectional USB interface is segmented into two separate unidirectional paths: one path (D+ to D-) allows data transmission from Host A to Host B, while the other path (D- to D+) is disabled to prevent reverse transmission. This segmentation enables selective activation of transmission directions to ensure security while maintaining communication capability.
Solution Approach 2:
The USB interface configuration is made asymmetric by disabling one transmission direction (D- to D+) while keeping the other direction (D+ to D-) active. This asymmetric configuration ensures that data can flow securely from Host A to Host B without allowing Host B to transmit data back to Host A, thus resolving the security concern.
2Ease of operation
If direct connection between two USB hosts is enabled, then ease of operation is improved, but protocol compatibility is worsened because USB hosts cannot directly communicate
Solution Approach 1:
A USB-to-RS-232 converter circuit is introduced as an intermediary device between two USB hosts. The converter translates USB protocol signals from Host A into RS-232 signals that can be received by Host B's USB interface through its built-in serial communication capability. This intermediary enables direct connection and communication between hosts that would otherwise be incompatible.
3Object-affected harmful factors
If USB half-duplex differential signaling is used, then noise resistance is improved, but transmission direction control is worsened because bidirectional communication is automatic
Solution Approach 1:
One transmission direction (D- to D+) is extracted and removed from active service while keeping the other direction (D+ to D-) operational. By taking out the reverse transmission path, the system maintains noise-resistant differential signaling for the active direction while achieving unidirectional control without adding complex direction management circuitry.
Data Source
AI summary
A circuit interfaced between a first USB host and a second USB host for providing unidirectional transmission of data signals from the first USB host to the second USB host is provided. A first converter circuit is operable to receive data signals from the first USB host and convert them from a USB protocol to a second communications protocol. A second converter circuit is operable to receive the converted data signals from the first converter circuit and convert them from the second communications protocol to the USB protocol for transmission to the second USB host. The first and second converter circuits are electrically connected to each other in such a manner as to provide a transmission path from the first USB host to the second USB host and to disable a transmission path from the second USB host to the first USB host.