12.1Mbps highspeedTGXf download decode in Linux
hsTGXf is a browser driven ThruGlassXfer tool that enables high-speed uploads (1Mbps to 1Gbps or more) through the End-User-Compute display.
A file has been encoded in the highspeed version of the Through Glass Transfer protocol (TGXf). Here the HDMI intercepted video (RGB data saved in an uncompressed 10 bit-per-channel AVI file, converted to an RGB 24 bits-per-pixel « lossless » MOV file) is being decoded by the receiving tool. The video is being played back frame by frame, with analysis of the screen for pixels in a certain location.
In this version of the TGXf protocol, the receiver first looks for the location frame where the entire hsTGXf display space (in this case 1240×650 pixels) is rendered red. Once found (3 seconds into the video) the receiver notes the bounding box and renders a red line around it from that point on. The receiver will decode pixels within this bounded region as TGXf packets. At three bits-per-pixel (BPP), the colour channels (Red, Green, Blue) in each pixel are evaluated. A colour channel that is « substantially light » is regarded as a binary 1, while « substantially dark » colour channel is regarded as binary 0.
A small group of control packets (single row of pixels almost invisible in this video) provide the Filename, File Size, Frames Per Second and the Bytes per Frame detail for this transfer (the summary of this information is displayed 7 seconds into the video).
Following a successful control sequence the receiver processes the video frame by frame, assessing the bounded region for data. At a resolution of 1240 pixels by 650 pixels with data encoded at 3 bit-per-pixel (BPP) and 10 frames-per-second (FPS) the bounded region creates an effective datagram/packet size of 300,250 bytes (1240x650x3/8) and an effective throughput of 12.1Mbps (the throughput should be higher but isn’t due to an off calculation in the Javascript timer on the client).
As each frame is processed the text window displays the « — [Frame] — » marker. A CRC32 was added to the hsTGXf version of the TGXf protocol to replace the CRC that was provided by the original QR Code datagram layer. In this example each frame is a cleanly parsable frame (where the calculated CRC matches the one in the packet), due to the higher quality video capture device – Black Magic Design’s DeckLink 4K Extreme 12G product. Frames that contain no debugging information are duplicates, that is, they’ve already been cleanly parsed with the subsequent frames of the same packet being silently ignored.
At 15 seconds the hsTGXf transfer completes with a final control packet providing the CRC32 for the entire file, which the receiver validates against the stored binary.
The transferred file is the 2014 white paper published on the ThruGlassXfer site.
This is a proof of concept that shows data can be exfiltrated (downloaded) in binary formats through remote enterprise desktop sessions via the screen, without the need for a binary client or the use of QR codes.
Music: None
Video: Midnight Code (http://midnightcode.org)
Application: hsTGXf (http://thruglassxfer.com)
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