Script for solving the Words Church challenge in the 2021 h@cktivitycon CTF

words_church.py

#!/usr/bin/env python3

import socket, time


directions = [(0, -1), (1, -1), (1, 0), (1, 1), (0, 1), (-1, 1), (-1, 0), (-1, -1)]

def parse_grid(txt):
    return [l[l.find('|')+1:].strip().replace(' ', '') for l in txt.split('\n')[2:]]


def calculate_coords(grid, start, direction, i):
    x, y = start[0] + i * direction[0], start[1] + i * direction[1]
    if y < 0:
        y += len(grid)
    if y >= len(grid):
        y -= len(grid)
    if x < 0:
        x += len(grid[y])
    if x >= len(grid[y]):
        x -= len(grid[y])
    return (x, y)


def is_word_present(grid, start, word, direction):
    for i in range(len(word)):
        x, y = calculate_coords(grid, start, direction, i)
        if grid[y][x] != word[i]:
            return False
    return True


def find_word(grid, word):
    start = None
    direction = None
    for y in range(len(grid)):
        for x in range(len(grid[y])):
            s = (x, y)
            for d in directions:
                if is_word_present(grid, s, word, d):
                    start = s
                    direction = d
                    break
            if start is not None:
                break
        if start is not None:
            break
    coords = []
    for i in range(len(word)):
        coords.append((start[0] + i * direction[0], start[1] + i * direction[1]))
    return coords

def send(s, txt):
    print(txt)
    s.sendall(bytes(txt, 'utf-8'))
    time.sleep(.5)
    resp = ""
    while True:
        try:
            resp += s.recv(4096).decode('utf-8')
        except:
            break
        for l in resp.split('\n'):
            if "flag{" in l:
                return resp
        if ': >' in resp.split('\n')[-1]:
            break
    return resp


def _main():
    grid = None
    s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    s.settimeout(2)
    s.connect(("challenge.ctf.games", 30838))
    time.sleep(2)
    print(s.recv(4096).decode("utf-8"), end = " ")
    resp = send(s, "play")
    print(resp, end=" ")
    while True:
        lines = resp.split('\n')
        new_grid_start = -1
        for i in range(len(lines)):
            if lines[i].startswith('Wordsearch #'):
                new_grid_start = i
                break
        if new_grid_start >= 0:
            new_grid_lines = lines[new_grid_start + 1:new_grid_start+19]
            grid = parse_grid('\n'.join(new_grid_lines))
        word = None
        if ": >" in lines[-1]:
            word = lines[-1][:lines[-1].find(':')]
        if word is None:
            break
        coords = find_word(grid, word)
        resp = send(s, str(coords))
        print(resp, end="")
    s.close()


if __name__ == "__main__":
    _main()