VolgaCTF 2017 Quals: Transformer

链接： https://ctftime.org/task/3695

题目：transformer

We’ve got a file that was processed with a binary called transformer. We really need the contents of this file. Can you help?

开始探索

在Mac上执行程序：

使用file 查看 文件属性
[Transformer] file transformer transformer: ELF 64-bit LSB pie executable, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, for GNU/Linux 2.6.32, BuildID[sha1]=3ba9baed5d1738eef040f333ec9c4707c3aeabf4, with debug_info, not stripped

发现是 64 位 Linux 二进制文件，拿到Linux系统下运行

➜ Transformer git:(main) ✗ ./transformer Usage: transformer <input_file> <output_file>

使用ldd 看看调用的库
➜ Transformer git:(main) ✗ ldd ./transformer linux-vdso.so.1 (0x00007ffc0c1ed000) libdl.so.2 => /lib/x86_64-linux-gnu/libdl.so.2 (0x00007fdccaf82000) librt.so.1 => /lib/x86_64-linux-gnu/librt.so.1 (0x00007fdccaf77000) libpthread.so.0 => /lib/x86_64-linux-gnu/libpthread.so.0 (0x00007fdccaf55000) libgcc_s.so.1 => /lib/x86_64-linux-gnu/libgcc_s.so.1 (0x00007fdccaf3b000) libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007fdccad76000) /lib64/ld-linux-x86-64.so.2 (0x00007fdccb1f5000)

我们尝试调用一下这个程序，构造一个输入文件:

➜ Transformer git:(main) ✗ ./transformer input.txt output.txt ➜ Transformer git:(main) ✗ cat input.txt output.txt 123456 uV���7�#

123456 输入，输出的内容看不懂，有乱码， 文件类型为data，文件大小由7 bit变成了12 bit

用IDA打开二进制文件