[[SWPU 2019]Network](https://www.nssctf.cn/problem/35)

Problem: [SWPU 2019]Network

思路

• 解题大致思路
  二进制提取前两位：发现是zip的文件头

​

后面就是写个解密脚本 （base64和32轮流）

import base64
import re


def is_base64(s):
	"""检查字符串是否为有效的base64编码"""
	try:
		# 尝试解码并重新编码来验证
		if isinstance(s, str):
			s_bytes = s.encode('utf-8')
		else:
			s_bytes = s
		decoded = base64.b64decode(s_bytes, validate=True)
		re_encoded = base64.b64encode(decoded)
		# 去除填充字符后比较
		return s_bytes.rstrip(b'=') == re_encoded.rstrip(b'=')
	except (Exception, ValueError, TypeError):
		return False


def is_base32(s):
	"""检查字符串是否为有效的base32编码"""
	try:
		if isinstance(s, str):
			s_bytes = s.encode('utf-8')
		else:
			s_bytes = s
		decoded = base64.b32decode(s_bytes, validate=True)
		re_encoded = base64.b32encode(decoded)
		# 去除填充字符后比较
		return s_bytes.rstrip(b'=') == re_encoded.rstrip(b'=')
	except (Exception, ValueError, TypeError):
		return False


def decode_recursive(encoded_data, round_count=1):
	"""递归解码base64/base32编码的数据"""
	print(f"\n=== 第 {round_count} 轮解码 ===")
	
	# 尝试base64解码
	if is_base64(encoded_data):
		try:
			decoded = base64.b64decode(encoded_data)
			print("使用 Base64 解码")
			print(f"解码结果: {decoded}")
			return decode_recursive(decoded, round_count + 1)
		except:
			pass
	
	# 尝试base32解码
	if is_base32(encoded_data):
		try:
			decoded = base64.b32decode(encoded_data)
			print("使用 Base32 解码")
			print(f"解码结果: {decoded}")
			return decode_recursive(decoded, round_count + 1)
		except:
			pass
	
	# 如果都无法解码，返回最终结果
	print("无法继续解码 - 最终结果")
	try:
		# 尝试以UTF-8解码显示
		final_result = encoded_data.decode('utf-8')
		print(f"最终文本: {final_result}")
	except:
		print(f"最终二进制数据: {encoded_data}")
	
	return encoded_data


def main():
	# 读取文件内容
	try:
		with open('./flag.txt', 'r', encoding='utf-8') as file:
			content = file.read().strip()
	except:
		with open('./flag.txt', 'rb') as file:
			content = file.read()
	
	print("原始文件内容:")
	print(content)
	
	# 开始递归解码
	if isinstance(content, str):
		content_bytes = content.encode('utf-8')
	else:
		content_bytes = content
	
	final_result = decode_recursive(content_bytes)


if __name__ == "__main__":
	main()
​

EXP

• 具体攻击代码

总结

• 对该题的考点总结