no-strings-attached writeup

no-strings-attach writeup

1、程序分析

 主函数如图所示，关键函数在authenticate中，进入函数。

 分析可得，decrypt代码段为关键代码段，进入关键函数decrypt。

2、解题脚本 

可以看到，des指针指向地址处存放的值应该就是flag了，直接静态分析应该可以得到，但是会比较吃力，这时候，我们可以打开gdb，查看一下对应内存处的值。

 断点设在add esp,0x34处。

 查看内存地址处的值，提取出来，写一个简单脚本跑一下。

ls=[0x39,0x34,0x34,0x37,0x7b,0x79,0x6f,0x75,0x5f,
    0x61,0x72,0x65,0x5f,0x61,0x6e,0x5f,0x69,0x6e,
    0x74,0x65,0x72,0x6e,0x61,0x74,0x69,0x6f,0x6e,
    0x61,0x6c,0x5f,0x6d,0x79,0x73,0x74,0x65,0x72,
    0x79,0x7d,0x0,0x57,0x1]
flag=""
for a in ls:
    flag+=chr(a)

print(flag)