BUUCTF通关之路 - Misc Part 15

#提取数据到文件
zsteg -e "b8,rgb,lsb,xy" attachment.png > file 

md5sum flag.zip 
17f5b08342cf65f6dc08ed0b4c9bd334  flag.zip

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

Good eyes! Here is your flag:
https://www.splitbrain.org/services/ook

+++++ ++++[ ->+++ +++++ +<]>+ +++++ .<+++ [->-- -<]>- .<+++ [->-- -<]>-
.<+++ +[->+ +++<] >+.<+ ++[-> ---<] >---- -.<++ +++++ [->++ +++++ <]>++
++.-- --.<+ +++[- >---- <]>-- ----. +++++ +++.< +++[- >---< ]>-.+ ++.++
+++++ .<+++ [->-- -<]>- .+++. -.... --.++ +.<++ +[->+ ++<]> ++++. <++++
++++[ ->--- ----- <]>-- ----- ----- --.<+ +++[- >++++ <]>+. +...< +++++
+++[- >++++ ++++< ]>+++ +++++ +++.. .-.<

连起来就是flag{c84bb04a-8663-4ee2-9449-349f1ee83e11}

#!/usr/bin/env python3
'''
deepsound2john extracts password hashes from audio files containing encrypted
data steganographically embedded by DeepSound (http://jpinsoft.net/deepsound/).

This method is known to work with files created by DeepSound 2.0.

Input files should be in .wav format. Hashes can be recovered from audio files
even after conversion from other formats, e.g.,

    ffmpeg -i input output.wav

Usage:

    python3 deepsound2john.py carrier.wav > hashes.txt
    john hashes.txt

This software is copyright (c) 2018 Ryan Govostes <rgovostes@gmail.com>, and
it is hereby released to the general public under the following terms:
Redistribution and use in source and binary forms, with or without
modification, are permitted.
'''

import logging
import os
import sys
import textwrap


def decode_data_low(buf):
  return buf[::2]

def decode_data_normal(buf):
  out = bytearray()
  for i in range(0, len(buf), 4):
    out.append((buf[i] & 15) << 4 | (buf[i + 2] & 15))
  return out

def decode_data_high(buf):
  out = bytearray()
  for i in range(0, len(buf), 8):
    out.append((buf[i] & 3) << 6     | (buf[i + 2] & 3) << 4 \
             | (buf[i + 4] & 3) << 2 | (buf[i + 6] & 3))
  return out


def is_magic(buf):
  # This is a more efficient way of testing for the `DSCF` magic header without
  # decoding the whole buffer
  return (buf[0] & 15)  == (68 >> 4) and (buf[2]  & 15) == (68 & 15) \
     and (buf[4] & 15)  == (83 >> 4) and (buf[6]  & 15) == (83 & 15) \
     and (buf[8] & 15)  == (67 >> 4) and (buf[10] & 15) == (67 & 15) \
     and (buf[12] & 15) == (70 >> 4) and (buf[14] & 15) == (70 & 15)


def is_wave(buf):
  return buf[0:4] == b'RIFF' and buf[8:12] == b'WAVE'


def process_deepsound_file(f):
  bname = os.path.basename(f.name)
  logger = logging.getLogger(bname)

  # Check if it's a .wav file
  buf = f.read(12)
  if not is_wave(buf):
    global convert_warn
    logger.error('file not in .wav format')
    convert_warn = True
    return
  f.seek(0, os.SEEK_SET)

  # Scan for the marker...
  hdrsz = 104
  hdr = None

  while True:
    off = f.tell()
    buf = f.read(hdrsz)
    if len(buf) < hdrsz: break

    if is_magic(buf):
          hdr = decode_data_normal(buf)
          logger.info('found DeepSound header at offset %i', off)
          break

    f.seek(-hdrsz + 1, os.SEEK_CUR)

  if hdr is None:
    logger.warn('does not appear to be a DeepSound file')
    return

  # Check some header fields
  mode = hdr[4]
  encrypted = hdr[5]

  modes = {2: 'low', 4: 'normal', 8: 'high'}
  if mode in modes:
    logger.info('data is encoded in %s-quality mode', modes[mode])
  else:
    logger.error('unexpected data encoding mode %i', modes[mode])
    return

  if encrypted == 0:
    logger.warn('file is not encrypted')
    return
  elif encrypted != 1:
    logger.error('unexpected encryption flag %i', encrypted)
    return

  sha1 = hdr[6:6+20]
  print('%s:$dynamic_1529$%s' % (bname, sha1.hex()))


if __name__ == '__main__':
  import argparse

  parser = argparse.ArgumentParser()
  parser.add_argument('--verbose', '-v', action='store_true')
  parser.add_argument('files', nargs='+', metavar='file',
    type=argparse.FileType('rb', bufsize=4096))
  args = parser.parse_args()

  if args.verbose:
    logging.basicConfig(level=logging.INFO)
  else:
    logging.basicConfig(level=logging.WARN)

  convert_warn = False

  for f in args.files:
    process_deepsound_file(f)

  if convert_warn:
    print(textwrap.dedent('''
    ---------------------------------------------------------------
    Some files were not in .wav format. Try converting them to .wav
    and try again. You can use: ffmpeg -i input output.wav
    ---------------------------------------------------------------
    '''.rstrip()), file=sys.stderr)

python .\deepsound2john.py .\final_flag.wav > hash.txt
john hash.txt

0_1s_4lwayS_Th3_S4me}

20555 : The next is a8242a234560a0d3cf121864ee34d7fb.txt

import os

hexdata = ''
with open('./files/start.txt', 'r') as f:
    cont = f.read()
    nexttxt = cont[-36:]
    hexdata += format(int(cont[:cont.find(':')-1]), '04x')
    
while True:
    path = f'./files/{nexttxt}'
    if not os.path.exists(path):
        break
    with open(path, 'r') as f:
        cont = f.read()
        nexttxt = cont[-36:]
        hexdata += format(int(cont[:cont.find(':')-1]), '04x')

with open('flag.zip', 'wb') as f:
    f.write(bytes.fromhex(hexdata))

#很久之前的项目了，必须用python2否则一堆报错
python2 lsb.py extract attachment.png output.txt lovekfc

PVSF{vVckHejqBOVX9C1c13GFfkHJrjIQeMwf}

Welcome to QCTF

hint1:把给出的keyword放到前面试试

hint2：一种把关键词提前的置换

lovekfcabdghijmnpqrstuwxyz

# -*- coding:utf-8 -*-
import string

ciphertext = 'PVSF{vVckHejqBOVX9C1c13GFfkHJrjIQeMwf}'
secretkey = 'lovekfcabdghijmnpqrstuwxyz'
plaintext = ''

for letter in ciphertext:
    if letter in string.ascii_lowercase:
        index = secretkey.lower().index(letter)
        plaintext += string.ascii_lowercase[index]
        continue
    if letter in string.ascii_uppercase:
        index = secretkey.upper().index(letter)
        plaintext += string.ascii_uppercase[index]
        continue
    plaintext += letter

print(plaintext)

.. -. ... .- -.--. -- ----- .-. ..... ...-- ..--.- .-- .---- .-.. .-.. ..--.- -. ...-- ...- ...-- .-. ..--.- ....- --. ...-- -.-.-- -.--.-