NepCTF2023--部分wp

Q1ng_chuan

已于 2023-08-14 16:23:47 修改

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文章标签： python 开发语言

于 2023-08-14 16:17:06 首次发布

本文链接：https://blog.youkuaiyun.com/qing_chuan_/article/details/132278546

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文章介绍了NepCTF2023中的一个编程挑战，涉及Huffman编码的使用，包括压缩和解压缩数据，以及解码包含Morse码和十六进制的隐藏信息。还提到了与安全漏洞相关的pwn和CVE问题的解决过程。

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NepCTF2023–部分wp

在这里插入图片描述

Misc:

Check in

NepCTF{H4ve_Fun_1N_This_Game}

与AI共舞的哈夫曼

需要在原本附件里自带的py文件修改一下即可

import heapq
import os

class HuffmanNode:
  def __init__(self, char, freq):
    self.char = char
    self.freq = freq
    self.left = None
    self.right = None

  def __lt__(self, other):
    return self.freq < other.freq

def build_huffman_tree(frequencies):
  heap = [HuffmanNode(char, freq) for char, freq in frequencies.items()]
  heapq.heapify(heap)

  while len(heap) > 1:
    left = heapq.heappop(heap)
    right = heapq.heappop(heap)
    merged = HuffmanNode(None, left.freq + right.freq)
    merged.left = left
    merged.right = right
    heapq.heappush(heap, merged)

  return heap[0]

def build_huffman_codes(node, current_code, huffman_codes):
  if node is None:
    return

  if node.char is not None:
    huffman_codes[node.char] = current_code
    return

  build_huffman_codes(node.left, current_code + '0', huffman_codes)
  build_huffman_codes(node.right, current_code + '1', huffman_codes)

def compress(input_file, output_file):
  with open(input_file, 'rb') as f:
    data = f.read()

  frequencies = {}
  for byte in data:
    if byte not in frequencies:
      frequencies[byte] = 0
    frequencies[byte] += 1

  root = build_huffman_tree(frequencies)
  huffman_codes = {}
  build_huffman_codes(root, '', huffman_codes)

  compressed_data = ''
  for byte in data:
    compressed_data += huffman_codes[byte]

  padding = 8 - len(compressed_data) % 8
  compressed_data += '0' * padding

  with open(output_file, 'wb') as f:
    \# Write frequency information
    f.write(bytes([len(frequencies)]))
    for byte, freq in frequencies.items():
      f.write(bytes([byte, (freq >> 24) & 0xFF, (freq >> 16) & 0xFF, (freq >> 8) & 0xFF, freq & 0xFF]))

    \# Write compressed data
    for i in range(0, len(compressed_data), 8):
      byte = compressed_data[i:i+8]
      f.write(bytes([int(byte, 2)]))


def build_huffman_tree_from_bytes(frequencies):
  heap = [HuffmanNode(byte, freq) for byte, freq in frequencies.items()]
  heapq.heapify(heap)

  while len(heap) > 1:
    left = heapq.heappop(heap)
    right = heapq.heappop(heap)
    merged = HuffmanNode(None, left.freq + right.freq)
    merged.left = left
    merged.right = right
    heapq.heappush(heap, merged)

  return heap[0]

def decompress(input_file, output_file):
  with open(input_file, 'rb') as f:
    frequencies_count = ord(f.read(1))
    frequencies = {}

    for _ in range(frequencies_count):
      byte = ord(f.read(1))
      freq = (ord(f.read(1)) << 24) + (ord(f.read(1)) << 16) + (ord(f.read(1)) << 8) + ord(f.read(1))
      frequencies[byte] = freq

    root = build_huffman_tree_from_bytes(frequencies)

    huffman_codes = {}
    build_huffman_codes(root, '', huffman_codes)
    reverse_huffman_codes = {v: k for k, v in huffman_codes.items()}

    decompressed_data = bytearray()
    code = ''
    while True:
      byte = f.read(1)
      if len(byte) == 0:
        break

      byte = ord(byte)
      for i in range(7, -1, -1):
        if byte & (1 << i):
          code += '1'
        else:
          code += '0'

        if code in reverse_huffman_codes:
          decompressed_data.append(reverse_huffman_codes[code])
          code = ''

  with open(output_file, 'wb') as f:
    f.write(decompressed_data)


if __name__ == "__main__":
  \# input_file = 'input.txt'
  compressed_file = 'compressed.bin'
  decompressed_file = 'decompressed.txt'

  \# 压缩文件
  \# compress(input_file, compressed_file)

  \# 解压缩文件
  decompress(compressed_file, decompressed_file)

小叮弹钢琴

下载拿到piano.bin，是个音频文件，拉进Audacity看一下，发现有频谱，通过放大缩小频谱发现有字符串，将字符串抄写下来，钱一部分是摩斯密码，后部分是16进制

1011 111 001 000 0000 111 001 0100 100 001 000 0 1 0000 00 000 1 111 1001 111 010 000 111 11 0 1 0000 00 10 110

0x370a05303c290e045005031c2b1858473a5f052117032c39230f005d1e17

对摩斯面解码发现：

YOUSHOULDUSETHISTOXORSOMETHING

提示应该有异或，但暂时不知道是什么，

后来试了半天与16进制转字符串异或

codes

#include <stdio.h>

extern char **en\
viron;
int main()
{
    int i = 0;
    while (en\
viron[i] != NULL)
    {
        printf("%s\n", en\
viron[i]);
        i++;
    }
    return 0;
}