被加密的生产流量

题目链接：[CISCN 2023 初赛]被加密的生产流量 | NSSCTF

某安全部门发现某涉密工厂生产人员偷偷通过生产网络传输数据给不明人员，通过技术手段截获出一段通讯流量，但是其中的关键信息被进行了加密，请你根据流量包的内容，找出被加密的信息。
得到的flag使用NSSCTF{}格式提交。

初步分析

拿到附件看名称为modbus.pcap，再打开流量包看其内容，发现有很多modbus协议，于是过滤modbus协议

image-20260215204210488

发现modbus协议中length为73和66的伴随出现，并且发现每个length=66的流量后面都有两个可疑字符

image-20260215204550799

image-20260215204630042

可疑字符提取

这里我采用的是人力提取，也可以写写脚本提取，不过脚本运行可能会遇到tshark路径不正确报错的问题，报错问题可以看看这个博主彻底解决 pyshark 库 TShark not found_pyshark.tshark.tshark.tsharknotfoundexception: tsh-CSDN博客

其实追踪tcp流就可以直接看到所有可以字符image-20260215205229905

提取出来的字符如下

1
MMYWMX3GNEYWOXZRGAYDA===

base32解码

提取出来的字符串有明显的base32特征，解码得到最后的加密信息

1
c1f_fi1g_1000

image-20260215205646744

一道简单的流量

题目来源：PolarCTF【2024秋季个人挑战赛】

初步分析

题目给了一个hint.txt附件，内容为

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2
小明是一名黑客，他在使用扫描器日站的时候发现了一个有意思的东西，请你找到这个文件
flag为解密后到文本直接套上flag{}

打开流量包http过滤后依旧还有90000多条，直接尝试字符串检索

依次查看检索的内容，看到有flag.txt和存在PK开头，尝试http流提取出来，注意一定要用raw导出，不然可能不完整。

image-20260215212545522

还原压缩包

将导出的压缩包数据放入cyberchef里面生成.zip

image-20260215213005007

打开压缩包后发现是base64+base32组合

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一把梭解码

把这一大串丢进PuzzleSolver一键解码得到Base_sixty_four_point_five

image-20260215213310178