Python solution for solving PicoCTF 2017 - Just Keyp Trying

keyboard_pcap.py

"""
shahril:pico$ python keyboard_pcap.py -f data.pcap
flag{pr355_0nwards_a4263f07}c
"""

from scapy.all import *
from argparse import ArgumentParser
from sys import argv
from collections import OrderedDict

# USB HID Keyboard scan codes
# https://gist.github.com/MightyPork/6da26e382a7ad91b5496ee55fdc73db2
key_hid = {
    0x00 : ['', ''], # no key pressed
    0x04 : ['a', 'A'],
    0x05 : ['b', 'B'],
    0x06 : ['c', 'C'],
    0x07 : ['d', 'D'],
    0x08 : ['e', 'E'],
    0x09 : ['f', 'F'],
    0x0a : ['g', 'G'],
    0x0b : ['h', 'H'],
    0x0c : ['i', 'I'],
    0x0d : ['j', 'J'],
    0x0e : ['k', 'K'],
    0x0f : ['l', 'L'],
    0x10 : ['m', 'M'],
    0x11 : ['n', 'N'],
    0x12 : ['o', 'O'],
    0x13 : ['p', 'P'],
    0x14 : ['q', 'Q'],
    0x15 : ['r', 'R'],
    0x16 : ['s', 'S'],
    0x17 : ['t', 'T'],
    0x18 : ['u', 'U'],
    0x19 : ['v', 'V'],
    0x1a : ['w', 'W'],
    0x1b : ['x', 'X'],
    0x1c : ['y', 'Y'],
    0x1d : ['z', 'Z'],
    0x1e : ['1', '!'],
    0x1f : ['2', '@'],
    0x20 : ['3', '#'],
    0x21 : ['4', '$'],
    0x22 : ['5', '%'],
    0x23 : ['6', '^'],
    0x24 : ['7', '&'],
    0x25 : ['8', '*'],
    0x26 : ['9', '('],
    0x27 : ['0', ')'],
    0x2d : ['-', '_'],
    0x2e : ['=', '+'],
    0x2f : ['[', '{'],
    0x30 : [']', '}'],
    0x31 : ['\\', '|'],
    0x32 : ['Non-US #', '~'],
    0x33 : [';', ':'],
    0x34 : ["'", '"'],
    0x35 : ['`', '~'],
    0x36 : [',', '<'],
    0x37 : ['.', '>'],
    0x38 : ['/', '?'],

}

def main():

    parser = ArgumentParser(description='Automatically extract ASCII key from capture USBPcap file')
    parser.add_argument('-f', '--file', help='USBPcap file', required=True)

    if len(argv) == 1:
        parser.print_help()
        exit()

    args = parser.parse_args()
    packets = rdpcap(args.file)

    flag = ""
    
    for each in packets:

        data = str(each)

        # https://docs.mbed.com/docs/ble-hid/en/latest/api/md_doc_HID.html#keyboard
        input_report = OrderedDict()
        input_report['modifier'] = ord(data[-8])
        input_report['reserved'] = ord(data[-7])
        input_report['Key1']     = ord(data[-6])
        input_report['Key2']     = ord(data[-5])
        input_report['Key3']     = ord(data[-4])
        input_report['Key4']     = ord(data[-3])
        input_report['Key5']     = ord(data[-2])
        input_report['Key6']     = ord(data[-1])

        flag += key_hid[input_report['Key1']][ 1 if input_report['modifier']==32 else 0 ]

    print(flag)

if __name__ == '__main__':
    main()