[LitCTF 2023]snake

使用pycdc工具反编译的时候，发现会报错，

在hex改变魔数，根据题目提示可知是3.7版本的，找python对应版本的魔数，改变

反编译成功

分析代码：

# Source Generated with Decompyle++
# File: game.cpython-37.pyc (Python 3.7)

'''\xe8\xb4\xaa\xe5\x90\x83\xe8\x9b\x87'''
import random
import sys
import time
import pygame
from pygame.locals import *
from collections import deque
SCREEN_WIDTH = 600
SCREEN_HEIGHT = 480
SIZE = 20
LINE_WIDTH = 1
SCOPE_X = (0, SCREEN_WIDTH // SIZE - 1)
SCOPE_Y = (2, SCREEN_HEIGHT // SIZE - 1)
FOOD_STYLE_LIST = [
    (10, (255, 100, 100)),
    (20, (100, 255, 100)),
    (30, (100, 100, 255))]
LIGHT = (100, 100, 100)
DARK = (200, 200, 200)
BLACK = (0, 0, 0)
RED = (200, 30, 30)
BGCOLOR = (40, 40, 60)

def print_text(screen, font, x, y, text, fcolor = ((255, 255, 255),)):
    imgText = font.render(text, True, fcolor)
    screen.blit(imgText, (x, y))


def init_snake():
    snake = deque()
    snake.append((2, SCOPE_Y[0]))
    snake.append((1, SCOPE_Y[0]))
    snake.append((0, SCOPE_Y[0]))
    return snake


def create_food(snake):
    food_x = random.randint(SCOPE_X[0], SCOPE_X[1])
    food_y = random.randint(SCOPE_Y[0], SCOPE_Y[1])
    while (food_x, food_y) in snake:
        food_x = random.randint(SCOPE_X[0], SCOPE_X[1])
        food_y = random.randint(SCOPE_Y[0], SCOPE_Y[1])
    return (food_x, food_y)


def get_food_style():
    return FOOD_STYLE_LIST[random.randint(0, 2)]


def main():
    pygame.init()
    screen = pygame.display.set_mode((SCREEN_WIDTH, SCREEN_HEIGHT))
    pygame.display.set_caption('\xe8\xb4\xaa\xe5\x90\x83\xe8\x9b\x87')
    font1 = pygame.font.SysFont('SimHei', 24)
    font2 = pygame.font.Font(None, 72)
    (fwidth, fheight) = font2.size('GAME OVER')
    b = True
    snake = init_snake()
    food = create_food(snake)
    food_style = get_food_style()
    pos = (1, 0)
    game_over = True
    start = False
    score = 0
    orispeed = 0.5
    speed = orispeed
    last_move_time = None
    pause = False
    while None:
        for event in pygame.event.get():
            if event.type == QUIT:
                sys.exit()
                continue
            if event.type == KEYDOWN or event.key == K_RETURN or game_over:
                start = True
                game_over = False
                b = True
                snake = init_snake()
                food = create_food(snake)
                food_style = get_food_style()
                pos = (1, 0)
                score = 0
                last_move_time = time.time()
                continue
                if not event.key == K_SPACE or game_over:
                    pause = not pause
                    continue
                    if not (event.key in (K_w, K_UP) or b) and pos[1]:
                        pos = (0, -1)
                        b = False
                        continue
                        if not (event.key in (K_s, K_DOWN) or b) and pos[1]:
                            pos = (0, 1)
                            b = False
                            continue
                            if not (event.key in (K_a, K_LEFT) or b) and pos[0]:
                                pos = (-1, 0)
                                b = False
                                continue
                                if not event.key in (K_d, K_RIGHT) and b and pos[0]:
                                    pos = (1, 0)
                                    b = False
                                screen.fill(BGCOLOR)
                                for x in range(SIZE, SCREEN_WIDTH, SIZE):
                                    pygame.draw.line(screen, BLACK, (x, SCOPE_Y[0] * SIZE), (x, SCREEN_HEIGHT), LINE_WIDTH)

        for y in range(SCOPE_Y[0] * SIZE, SCREEN_HEIGHT, SIZE):
            pygame.draw.line(screen, BLACK, (0, y), (SCREEN_WIDTH, y), LINE_WIDTH)

        if not game_over:
            curTime = time.time()
            if not curTime - last_move_time > speed and pause:
                b = True
                last_move_time = curTime
                next_s = (snake[0][0] + pos[0], snake[0][1] + pos[1])
                if next_s == food:
                    snake.appendleft(next_s)
                    score += food_style[0]
                    speed = orispeed - 0.03 * (score // 100)
                    food = create_food(snake)
                    food_style = get_food_style()
                elif next_s[0] <= next_s[0] or next_s[0] <= SCOPE_X[1]:
                    pass
                else:
                    SCOPE_X[0]
            elif next_s[1] <= next_s[1] or next_s[1] <= SCOPE_Y[1]:
                pass
            else:
                SCOPE_Y[0]
        elif next_s not in snake:
            snake.appendleft(next_s)
            snake.pop()
        else:
            game_over = True
        if not game_over:
            pygame.draw.rect(screen, food_style[1], (food[0] * SIZE, food[1] * SIZE, SIZE, SIZE), 0)
        for s in snake:
            pygame.draw.rect(screen, DARK, (s[0] * SIZE + LINE_WIDTH, s[1] * SIZE + LINE_WIDTH, SIZE - LINE_WIDTH * 2, SIZE - LINE_WIDTH * 2), 0)

        print_text(screen, font1, 450, 7, f'''\xe5\xbe\x97\xe5\x88\x86: {score}''')
        if score > 1000:
            flag = [
                30,
                196,
                52,
                252,
                49,
                220,
                7,
                243,
                3,
                241,
                24,
                224,
                40,
                230,
                25,
                251,
                28,
                233,
                40,
                237,
                4,
                225,
                4,
                215,
                40,
                231,
                22,
                237,
                14,
                251,
                10,
                169]
            for i in range(0, len(flag), 2):
                flag[i] = flag[i + 1] ^ 136
                flag[i + 1] = flag[i] ^ 119

            print_text(screen, font2, (SCREEN_WIDTH - fwidth) // 2, (SCREEN_HEIGHT - fheight) // 2, bytes(flag).decode(), RED)
            pygame.display.update()
        if game_over and start:
            print_text(screen, font2, (SCREEN_WIDTH - fwidth) // 2, (SCREEN_HEIGHT - fheight) // 2, 'GAME OVER', RED)
        pygame.display.update()

if __name__ == '__main__':
    main()

?

flag = [
        30,
        196,
        52,
        252,
        49,
        220,
        7,
        243,
        3,
        241,
        24,
        224,
        40,
        230,
        25,
        251,
        28,
        233,
        40,
        237,
        4,
        225,
        4,
        215,
        40,
        231,
        22,
        237,
        14,
        251,
        10,
        169]
for i in range(0, len(flag), 2):
    tmp=flag[i]
    flag[i] = flag[i + 1] ^ 136
    flag[i + 1] = tmp ^ 119
for i in flag:
    print(chr(i),end="")
# LitCTF{python_snake_is_so_easy!}