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README.md
intercept_3dcea34fd7056a4cc2c1934dd07e4d1fed0bc0683b05b24741a999d1273339da.pcapng
solve.py Added Python Script for solution, README fix coming soon Aug 26, 2016

README.md

IceCTF 2016

Intercepted Part One

Solution By: duck

Solution (copied from solve.py)

The pcap is a capture of a USB keyboard.

The proper way to tell is by finding the VID/PID combination during enumeration then looking up the device from that.

The easy way is just to have looked at enough USB stuffs to recognize that it's a keyboard. :)

The keyboard data exists in the USB Leftover section. tshark is our friend for extracting this.

tshark -r ./intercept.pcapng -T fields -e usb.capdata -Y usb.capdata 2>/dev/null

This has some trailing data that we don't care about it, so use tail to skip the beginning 6 lines.

tshark -r ./intercept.pcapng -T fields -e usb.capdata -Y usb.capdata 2>/dev/null | tail -n +6

The output looks like:

00:00:00:00:00:00:00:00
20:00:00:00:00:00:00:00
20:00:0a:00:00:00:00:00
20:00:00:00:00:00:00:00
00:00:00:00:00:00:00:00
...

The first byte is a bit field of modifier keys (shift, ctrl, alt, etc.). 0x20 means shift

The third byte is a keycode. More keycodes can be in the later bytes, but this isn't the case this time.

A line of all 00's means that all keys have been released.

The keycodes can be found here

Except, it's not actually a QWERTY keyboard. It's (mostly) Dvorak. Luckily for me, I actually use Dvorak.

Treating it as pure Dvorak doesn't work either because some of the symbols aren't actually changed as expected. Truthfully, I didn't save the key, and I did some unswapping by hand, so I don't know if this final script is fully correct. It's at least really close. (may need to swap ':' with 'Z')

tshark -r ./intercept.pcapng -T fields -e usb.capdata -Y usb.capdata 2>/dev/null | tail -n +6 | python usbcap_to_ascii.py