Google CTF 2018: Wired CSV solution

wired_csv.py

import csv

FILENAME = 'data.csv'
HSYNC = 1 / 15700
SCANCODES = ["L", "J", ";", "{F1}", "{F2}", "K", "+", "*", "O", "{NULL}", "P", "U", "{CR}", "I", "-", "=", "V", "Help", "C", "{F3}", "{F4}", "B", "X", "Z", "4", "{NULL}", "3", "6", "{Esc}", "5", "2", "1", ",", "{Spc}", ".", "N", "{NULL}", "M", "/", "{Inv}", "R", "{NULL}", "E", "Y", "{Tab}", "T", "W", "Q", "9", "{NULL}", "0", "7", "{BS}", "8", "<", ">", "F", "H", "D", "{NULL}", "Caps", "G", "S", "A"]

change_offsets = {0: [], 1: [], 2: [], 3: [], 4: [], 5: [], 6: [], 7: []}

def add_change_offset(line, time, value):
    if time == '' or time == ' ':
        return False
    time = float(time)
    change_offsets[line].append((time, int(value.strip())))
    return True

def read():
    with open(FILENAME) as csv_file:
        reader = csv.reader(csv_file)
        for idx, line in enumerate(reader):
            if idx == 0:
                continue
            _, _, _, timek0, k0, timek1, k1, timek2, k2, timek3, k3, timek4, k4, timek5, k5, timekr1, kr1, timekr2, kr2 = line
            
            if not add_change_offset(0, timek0, k0):
                break
            add_change_offset(1, timek1, k1)
            add_change_offset(2, timek2, k2)
            add_change_offset(3, timek3, k3)
            add_change_offset(4, timek4, k4)
            add_change_offset(5, timek5, k5)
            add_change_offset(6, timekr1, kr1)
            add_change_offset(7, timekr2, kr2)


def get_values(indices, time):
    values = []
    for i in range(len(change_offsets)):
        index = indices[i]
        while index < len(change_offsets[i]) and change_offsets[i][index][0] < time:
            index += 1
        indices[i] = index
        values.append(change_offsets[i][index - 1][1])
    return values
    

def parse_values(values):
    for i in range(8):
        # if i not in (3, 4):
        values[i] = 1 - values[i]
    kr1 = values[6]
    kr2 = values[7]
    scancode = 0
    for x in values[:6][::-1]:
        scancode = scancode * 2 + x
    return kr1, kr2, scancode


def run():
    time = 0
    indices = [0] * len(change_offsets)
    last_kr1 = 0
    last_scancode = 0
    answer = ''
    while time < 20:
        values = get_values(indices, time)
        kr1, kr2, scancode = parse_values(values)
        if last_kr1 == 0 and kr1 == 1:
            if last_scancode != scancode:
                print(f'Current time is {time}, values are {values}')
                print(f'kr1 = {kr1}, kr2 = {kr2}, scancode = {scancode}, char = {SCANCODES[scancode]}')
                answer += SCANCODES[scancode]
            last_scancode = scancode
        last_kr1 = kr1
        time += HSYNC
    print(answer)

if __name__ == '__main__':
    read()
    run()