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ASISCTF2017-ASIS secret letter-writeup

ASISCTF2017-ASIS secret letter-writeup
binwalk Stéganô

Task

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The face is the index of the mind, its ASIS secret letter!

Solution

题目提供了压缩包,解压后得到两张图片。用binwalk看一下。

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root@chybeta:~/Desktop/asis_letter# binwalk *
Scan Time: 2017-09-06 07:51:11
Target File: /root/Desktop/asis_letter/3baa358f6d671e86f17bc4439cc4062e
MD5 Checksum: 3baa358f6d671e86f17bc4439cc4062e
Signatures: 344
DECIMAL HEXADECIMAL DESCRIPTION
--------------------------------------------------------------------------------
0 0x0 JPEG image data, JFIF standard 1.01
30 0x1E TIFF image data, big-endian, offset of first image directory: 8
56 0x38 Zlib compressed data, default compression
Scan Time: 2017-09-06 07:51:11
Target File: /root/Desktop/asis_letter/e07d17ed7d8104590ff3e17bdf052057
MD5 Checksum: e07d17ed7d8104590ff3e17bdf052057
Signatures: 344
DECIMAL HEXADECIMAL DESCRIPTION
--------------------------------------------------------------------------------
0 0x0 PNG image, 4351 x 2812, 8-bit/color RGB, non-interlaced
41 0x29 Zlib compressed data, default compression

用命令binwalk -e *解压出文件,在图片3baa358f6d671e86f17bc4439cc4062e解压得到的文件夹中:

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root@chybeta:~/Desktop/asis_letter# cd _3baa358f6d671e86f17bc4439cc4062e.extracted/
root@chybeta:~/Desktop/asis_letter/_3baa358f6d671e86f17bc4439cc4062e.extracted# ls
38 38.zlib
root@chybeta:~/Desktop/asis_letter/_3baa358f6d671e86f17bc4439cc4062e.extracted# cat 38
OEorU2pDQWdabkp2YlNCQlUwbFRJSGRwZEdnZ2JHOTJaU3dnY0d4bFlYTmxJR1pwYm1RZ2MyVmpjbVYwSUcxbGMzTmhaMlVnWVc1a0lISmxjR3g1SUhOdmIyNHNJSEJ2ZDJWeVpXUWdZbmtnOEorUmlTQWdVM1REcVdkaGJzTzBJUENma1lnPQ==r

将上面的base64串进行解密,得到:

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>>> import base64
>>> base64.b64decode("OEorU2pDQWdabkp2YlNCQlUwbFRJSGRwZEdnZ2JHOTJaU3dnY0d4bFlYTmxJR1pwYm1RZ2MyVmpjbVYwSUcxbGMzTmhaMlVnWVc1a0lISmxjR3g1SUhOdmIyNHNJSEJ2ZDJWeVpXUWdZbmtnOEorUmlTQWdVM1REcVdkaGJzTzBJUENma1lnPQ==r")
'8J+SjCAgZnJvbSBBU0lTIHdpdGggbG92ZSwgcGxlYXNlIGZpbmQgc2VjcmV0IG1lc3NhZ2UgYW5kIHJlcGx5IHNvb24sIHBvd2VyZWQgYnkg8J+RiSAgU3TDqWdhbsO0IPCfkYg='

继续进行base64解密:

得到提示:Stéganô

在github上搜索,发现了一个项目:cedricbonhomme/Stegano

经过尝试,最后的命令如下:

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stegano-lsb-set reveal -i e07d17ed7d8104590ff3e17bdf052057 -g triangular_numbers

flag:

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ASIS{767ba85340d9e49fa0bb9c2b12037f08}

或者用python

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>>> from stegano import lsbset
>>> from stegano.lsbset import generators
>>> message = lsbset.reveal("./e07d17ed7d8104590ff3e17bdf052057", generators.triangular_numbers())
>>> message
'ASIS{767ba85340d9e49fa0bb9c2b12037f08}'

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本文标题:ASISCTF2017-ASIS secret letter-writeup

文章作者:chybeta

发布时间:2017年09月11日 - 21:09

最后更新:2017年09月12日 - 18:09

原始链接:http://chybeta.github.io/2017/09/11/ASISCTF2017-ASIS-secret-letter-writeup/

许可协议: 署名-非商业性使用-禁止演绎 4.0 国际 转载请保留原文链接及作者。