【某软件消息的加解密分析】
首先来熟悉一下ida的使用。
首先找到打开ida，点击"debugger"-> “run” -> “local windows debugger"后，从Application中找到程序并点击"ok”，程序停在入口处。
因为我们要调试的是接收数据包的加解密过程，一般来说可以从recv，WSARecv这几个常用网络API入手，这时在右边的"Module"窗口处，输入ws2查找过滤模块ws2_32.dll：
鼠标双击选中ws2_32.dll后，可以在Module窗口中双击需要查看的模块中的API函数，比如recv函数，这时主窗口显示的就是recv的反汇编代码了。
此时可以通过鼠标点击或者菜单下断点调试了。
同时，开启wireshark抓包，可以看到登录过程产生如下数据包：
通过对recv的反复调试，在某种执念驱使下，多次低水平重复和一点一点的推进，中间经过了多次的调试和放松，最终确定了发现数据包的处理主要在一下函数中：
这里要说明2点：
- 因为程序是动态加载的，所以地址并不一定跟本文的图中相同。
- 本文是叙述性的，有很多片段是不可描述的细节总结，不可能还原全过程的所有细节。读万卷书行万里路，只看文字是无法描绘所有场景的，某些事只能在行动中定义。
recv后数据的走向如下函数所示：
int __thiscall sub_9E3A40(int this, int a2)
{
volatile signed __int32 *v3; // ebx
volatile signed __int32 *v4; // ebx
_DWORD *v5; // eax
int v6; // ebx
int v7; // ecx
int v8; // eax
int v9; // eax
_DWORD *v10; // eax
int result; // eax
int v12; // edx
int Error; // eax
int v14; // edi
LONG v15; // eax
int v16; // ecx
unsigned int v17; // [esp-4h] [ebp-20090h]
char v18; // [esp+0h] [ebp-2008Ch] BYREF
int v19; // [esp+14h] [ebp-20078h]
int pExceptionObject[4]; // [esp+28h] [ebp-20064h] BYREF
int v21; // [esp+38h] [ebp-20054h] BYREF
char *v22; // [esp+3Ch] [ebp-20050h] BYREF
_DWORD v23[4]; // [esp+40h] [ebp-2004Ch] BYREF
_DWORD *v24; // [esp+50h] [ebp-2003Ch]
char v25[8]; // [esp+58h] [ebp-20034h] BYREF
LPVOID lpMem[3]; // [esp+60h] [ebp-2002Ch] BYREF
int v27; // [esp+6Ch] [ebp-20020h] BYREF
int v28; // [esp+70h] [ebp-2001Ch]
unsigned int v29; // [esp+74h] [ebp-20018h]
char v30[131072]; // [esp+78h] [ebp-20014h] BYREF
char *v31; // [esp+2007Ch] [ebp-10h]
int v32; // [esp+20088h] [ebp-4h]
v31 = &v18;
v3 = *(volatile signed __int32 **)(this + 336);
*(_DWORD *)(this + 336) = 0;
v22 = (char *)this;
*(_DWORD *)(this + 332) = 0;
if ( v3 )
{
if ( !_InterlockedExchangeAdd(v3 + 1, 0xFFFFFFFF) )
{
(**(void (__thiscall ***)(volatile signed __int32 *))v3)(v3);
if ( !_InterlockedExchangeAdd(v3 + 2, 0xFFFFFFFF) )
(*(void (__thiscall **)(volatile signed __int32 *))(*v3 + 4))(v3);
}
}
v4 = *(volatile signed __int32 **)(this + 348);
*(_DWORD *)(this + 348) = 0;
*(_DWORD *)(this + 344) = 0;
if ( v4 )
{
if ( !_InterlockedExchangeAdd(v4 + 1, 0xFFFFFFFF) )
{
(**(void (__thiscall ***)(volatile signed __int32 *))v4)(v4);
if ( !_InterlockedExchangeAdd(v4 + 2, 0xFFFFFFFF) )
(*(void (__thiscall **)(volatile signed __int32 *))(*v4 + 4))(v4);
}
}
v21 = 1;
v29 = this - 12;
v29 = sub_9E5210(sub_9E4410, 0, &v21);
v32 = 1;
v24 = 0;
v5 = operator new(0x28u);
v6 = (int)v5;
if ( !v5 )
unknown_libname_325();
v17 = v29;
*v5 = std::_Func_impl<std::_Callable_obj<nbase::WeakCallback<std::_Bind<1,void,std::_Pmf_wrap<void (__thiscall nbiz::LinkSocket::*)(int),void,nbiz::LinkSocket,int>,nbiz::LinkSocket * const &,int &>>,0>,std::allocator<std::_Func_class<void,>>,void,>::`vftable';
sub_57E2A0(v17);
v24 = (_DWORD *)v6;
LOBYTE(v32) = 3;
v7 = v19;
if ( v19 && !_InterlockedDecrement((volatile signed __int32 *)(v19 + 8)) )
(*(void (__thiscall **)(int))(*(_DWORD *)v7 + 4))(v7);
v8 = sub_52C600(v25, v23);
LOBYTE(v32) = 4;
sub_52C680(v8);
LOBYTE(v32) = 3;
sub_52AFC0(v25);
v9 = *(_DWORD *)(sub_936F30() + 176);
if ( v9 >= 15 )
{
if ( v9 > 240 )
v9 = 240;
}
else
{
v9 = 15;
}
v10 = (_DWORD *)sub_54DA90(v9, v9 >> 31);
sub_8EBCB0(*v10, v10[1]);
LOBYTE(v32) = 5;
result = (*(int (__thiscall **)(int, char *, int, _DWORD))(*(_DWORD *)(this + 64) + 20))(this + 64, v30, 0x20000, 0);
v12 = result;
if ( result == -1 )
{
result = sub_9E2950();
v12 = result;
}
v32 = 3;
if ( v12 == -1 )
{
Error = WSAGetLastError();
v14 = Error;
if ( Error == 10035 || Error == 10036 )
return sub_52F090(v23);
v15 = sub_8EB5B0();
if ( (unsigned int)(*(int (__thiscall **)(LONG))(*(_DWORD *)v15 + 16))(v15) >= 2 )
{
v27 = 2;
v28 = 37;
v29 = (unsigned int)"E:\\14_svn_branch\\src\\biz/network/socket_wrapper.h";
sub_8EB730(&v27, "[nbiz::WouldBlock] err_code:%d", v14);
}
result = sub_9E3770(this - 12);
v16 = *(_DWORD *)(this + 4);
if ( v16 )
result = (*(int (__thiscall **)(int, int))(*(_DWORD *)v16 + 4))(v16, 1);
}
else if ( v12 > 0 )
{
if ( !*(_BYTE *)(this + 24) )
{
sub_8EA440(2, "core\\link_socket_asyncsockex.cpp", 286, "Receive Message While Not Encrypted", v18);
v22 = "Receive Message While Not Encrypted";
std::exception::exception((std::exception *)pExceptionObject, (const char *const *)&v22);
pExceptionObject[0] = (int)&nbase::NException::`vftable';
pExceptionObject[3] = 5004;
_CxxThrowException(pExceptionObject, (_ThrowInfo *)&_TI3_AVNException_nbase__);
}
v29 = 15;
v28 = 0;
LOBYTE(lpMem[0]) = 0;
LOBYTE(v32) = 7;
(*(void (__thiscall **)(_DWORD, char *, int, LPVOID *))(**(_DWORD **)(this + 8) + 24))(
*(_DWORD *)(this + 8),
v30,
v12,
lpMem);
sub_55D4C0((_DWORD *)(this + 188), lpMem, 0, 0xFFFFFFFF);
LOBYTE(v32) = 3;
if ( v29 >= 0x10 )
opus_repacketizer_destroy(lpMem[0]);
sub_9E4220((_DWORD *)(this - 12));
return sub_52F090(v23);
}
v32 = -1;
if ( v24 )
return (*(int (__stdcall **)(bool))(*v24 + 16))(v24 != v23);
return result;
}
其中的"result = (*(int (__thiscall **)(int, char , int, _DWORD))((_DWORD *)(this + 64) + 20))(this + 64, v30, 0x20000, 0);"即跳转到recv函数中，
而" (*(void (__thiscall )(_DWORD, char *, int, LPVOID *))((_DWORD **)(this + 8) + 24))(
*(_DWORD *)(this + 8),"这一行，即进入以下函数中执行:
通过在接收数据的缓冲区地址中设置数据读写断点，发现最终程序经过多次跳转，进入如下函数：
_DWORD *__cdecl sub_7B4CB0(_DWORD *a1, unsigned int a2, _BYTE *a3, _BYTE *a4)
{
_DWORD *result; // eax
int v5; // ecx
char v6; // bl
int v8; // esi
int v10; // ecx
int v11; // edx
int v12; // esi
int v13; // ebx
int v14; // ecx
int v15; // edx
int v16; // esi
int v17; // ebx
int v18; // ecx
int v19; // edx
int v20; // esi
int v21; // ebx
int v22; // ecx
int v23; // edx
int v24; // esi
int v25; // ebx
int v26; // ecx
int v27; // edx
int v28; // esi
int v29; // ebx
int v30; // ecx
int v31; // edx
int v32; // esi
int v33; // ebx
int v34; // ecx
int v35; // edx
int v36; // esi
int v37; // ebx
int v38; // edx
int v39; // ebx
int v40; // edx
int v41; // ebx
bool v42; // zf
int v43; // edx
int v44; // ebx
int v45; // edx
int v46; // ebx
int v47; // edx
int v48; // ebx
int v49; // edx
int v50; // ebx
int v51; // edx
int v52; // ebx
int v53; // edx
int v54; // ebx
int v55; // edx
int v56; // ebx
unsigned int v57; // [esp+14h] [ebp+4h]
int v58; // [esp+14h] [ebp+4h]
int v59; // [esp+14h] [ebp+4h]
int v60; // [esp+14h] [ebp+4h]
int v61; // [esp+14h] [ebp+4h]
int v62; // [esp+14h] [ebp+4h]
int v63; // [esp+14h] [ebp+4h]
int v64; // [esp+14h] [ebp+4h]
int v65; // [esp+14h] [ebp+4h]
result = a1;
v5 = *a1;
v6 = a2;
v8 = a1[1];
v57 = a2 >> 3;
if ( a2 >> 3 )
{
do
{
v10 = (unsigned __int8)(v5 + 1);
v11 = result[v10 + 2];
v12 = (unsigned __int8)(v11 + v8);
v13 = result[v12 + 2];
result[v10 + 2] = v13;
result[v12 + 2] = v11;
*a4 = *a3 ^ LOBYTE(result[(unsigned __int8)(v11 + v13) + 2]);
v14 = (unsigned __int8)(v10 + 1);
v15 = result[v14 + 2];
v16 = (unsigned __int8)(v15 + v12);
v17 = result[v16 + 2];
result[v14 + 2] = v17;
result[v16 + 2] = v15;
a4[1] = a3[1] ^ LOBYTE(result[(unsigned __int8)(v15 + v17) + 2]);
v18 = (unsigned __int8)(v14 + 1);
v19 = result[v18 + 2];
v20 = (unsigned __int8)(v19 + v16);
v21 = result[v20 + 2];
result[v18 + 2] = v21;
result[v20 + 2] = v19;
a4[2] = a3[2] ^ LOBYTE(result[(unsigned __int8)(v19 + v21) + 2]);
v22 = (unsigned __int8)(v18 + 1);
v23 = result[v22 + 2];
v24 = (unsigned __int8)(v23 + v20);
v25 = result[v24 + 2];
result[v22 + 2] = v25;
result[v24 + 2] = v23;
a4[3] = a3[3] ^ LOBYTE(result[(unsigned __int8)(v23 + v25) + 2]);
v26 = (unsigned __int8)(v22 + 1);
v27 = result[v26 + 2];
v28 = (unsigned __int8)(v27 + v24);
v29 = result[v28 + 2];
result[v26 + 2] = v29;
result[v28 + 2] = v27;
a4[4] = a3[4] ^ LOBYTE(result[(unsigned __int8)(v27 + v29) + 2]);
v30 = (unsigned __int8)(v26 + 1);
v31 = result[v30 + 2];
v32 = (unsigned __int8)(v31 + v28);
v33 = result[v32 + 2];
result[v30 + 2] = v33;
result[v32 + 2] = v31;
v34 = (unsigned __int8)(v30 + 1);
a4[5] = a3[5] ^ LOBYTE(result[(unsigned __int8)(v31 + v33) + 2]);
v35 = result[v34 + 2];
v36 = (unsigned __int8)(v35 + v32);
v37 = result[v36 + 2];
result[v34 + 2] = v37;
result[v36 + 2] = v35;
a4[6] = a3[6] ^ LOBYTE(result[(unsigned __int8)(v35 + v37) + 2]);
v5 = (unsigned __int8)(v34 + 1);
v38 = result[v5 + 2];
v8 = (unsigned __int8)(v38 + v36);
v39 = result[v8 + 2];
result[v5 + 2] = v39;
result[v8 + 2] = v38;
LOBYTE(v38) = a3[7] ^ LOBYTE(result[(unsigned __int8)(v38 + v39) + 2]);
a3 += 8;
a4[7] = v38;
a4 += 8;
--v57;
}
while ( v57 );
v6 = a2;
}
v58 = v6 & 7;
if ( (v6 & 7) != 0 )
{
v5 = (unsigned __int8)(v5 + 1);
v40 = result[v5 + 2];
v8 = (unsigned __int8)(v40 + v8);
v41 = result[v8 + 2];
result[v5 + 2] = v41;
result[v8 + 2] = v40;
v42 = v58 == 1;
v59 = v58 - 1;
for ( *a4 = *a3 ^ LOBYTE(result[(unsigned __int8)(v40 + v41) + 2]);
!v42;
*a4 = *a3 ^ LOBYTE(result[(unsigned __int8)(v55 + v56) + 2]) )
{
v5 = (unsigned __int8)(v5 + 1);
v43 = result[v5 + 2];
v8 = (unsigned __int8)(v43 + v8);
v44 = result[v8 + 2];
result[v5 + 2] = v44;
result[v8 + 2] = v43;
v42 = v59 == 1;
v60 = v59 - 1;
a4[1] = a3[1] ^ LOBYTE(result[(unsigned __int8)(v43 + v44) + 2]);
if ( v42 )
break;
v5 = (unsigned __int8)(v5 + 1);
v45 = result[v5 + 2];
v8 = (unsigned __int8)(v45 + v8);
v46 = result[v8 + 2];
result[v5 + 2] = v46;
result[v8 + 2] = v45;
v42 = v60 == 1;
v61 = v60 - 1;
a4[2] = a3[2] ^ LOBYTE(result[(unsigned __int8)(v45 + v46) + 2]);
if ( v42 )
break;
v5 = (unsigned __int8)(v5 + 1);
v47 = result[v5 + 2];
v8 = (unsigned __int8)(v47 + v8);
v48 = result[v8 + 2];
result[v5 + 2] = v48;
result[v8 + 2] = v47;
v42 = v61 == 1;
v62 = v61 - 1;
a4[3] = a3[3] ^ LOBYTE(result[(unsigned __int8)(v47 + v48) + 2]);
if ( v42 )
break;
v5 = (unsigned __int8)(v5 + 1);
v49 = result[v5 + 2];
v8 = (unsigned __int8)(v49 + v8);
v50 = result[v8 + 2];
result[v5 + 2] = v50;
result[v8 + 2] = v49;
v42 = v62 == 1;
v63 = v62 - 1;
a4[4] = a3[4] ^ LOBYTE(result[(unsigned __int8)(v49 + v50) + 2]);
if ( v42 )
break;
v5 = (unsigned __int8)(v5 + 1);
v51 = result[v5 + 2];
v8 = (unsigned __int8)(v51 + v8);
v52 = result[v8 + 2];
result[v5 + 2] = v52;
result[v8 + 2] = v51;
v42 = v63 == 1;
v64 = v63 - 1;
a4[5] = a3[5] ^ LOBYTE(result[(unsigned __int8)(v51 + v52) + 2]);
if ( v42 )
break;
v5 = (unsigned __int8)(v5 + 1);
v53 = result[v5 + 2];
v8 = (unsigned __int8)(v53 + v8);
v54 = result[v8 + 2];
result[v5 + 2] = v54;
result[v8 + 2] = v53;
v42 = v64 == 1;
v65 = v64 - 1;
a4[6] = a3[6] ^ LOBYTE(result[(unsigned __int8)(v53 + v54) + 2]);
if ( v42 )
break;
v5 = (unsigned __int8)(v5 + 1);
v55 = result[v5 + 2];
v8 = (unsigned __int8)(v55 + v8);
v56 = result[v8 + 2];
result[v5 + 2] = v56;
result[v8 + 2] = v55;
v42 = v65 == 1;
v59 = v65 - 1;
}
}
result[1] = v8;
*result = v5;
return result;
}
至此，我们以比较大的把握猜测，加解密函数算法是一个rc4算法。我们知道，rc4函数需要一个初始化密钥，于是在进入加解密函数之前设置断点，我在内存中找到了这个密钥，并手动抄了出来。初始的密钥如下：
const int DecryptKey[260] =
{
0x00,0x00,0x34,0x6a,
0x81,0xD4,0xEA,0x47,
0xBC,0xC1,0x24,0xCA,
0x7B,0x19,0x70,0x2F,
0x1A,0x2A,0x68,0x62,
0xB7,0x4E,0xFB,0x53,
0x50,0x04,0x3A,0xD3,
0x48,0xDD,0x71,0x4D,
0x32,0x77,0x3F,0xEB,
0x55,0x02,0x14,0xB6,
0x93,0xA1,0xAB,0x03,
0x11,0x8F,0xF1,0x57,
0xB1,0xEE,0x52,0xB2,
0xAC,0x7A,0xAE,0x06,
0x86,0xF3,0x82,0xAA,
0xBD,0x85,0xF7,0xD9,
0x22,0xB0,0x8E,0x8A,
0x79,0xF4,0x6C,0xE7,
0xA4,0x9F,0xE3,0x96,
0xFC,0x7C,0xBA,0x2C,
0x4C,0xA3,0x80,0x98,
0x65,0x5E,0xE6,0xAF,
0xCB,0x58,0x67,0x1C,
0x08,0x4F,0x3C,0x44,
0xC9,0x6B,0xE4,0x7E,
0x1E,0x3D,0xE8,0xA6,
0xBB,0x5F,0x6F,0x59,
0x97,0x9E,0xB4,0x30,
0x2D,0x2B,0xF2,0x6E,
0x0A,0xA7,0xE9,0x5D,
0x29,0x5C,0x33,0xEF,
0x91,0xE5,0x39,0x36,
0x17,0xDF,0x31,0x45,
0x8D,0x5B,0x05,0xF0,
0xC8,0x09,0xA5,0xF9,
0x84,0xC7,0x1B,0xB5,
0xC6,0x9B,0xE2,0xC5,
0x89,0xE0,0x9A,0x27,
0xC4,0x40,0x0D,0x20,
0x66,0x7F,0xA9,0xC3,
0x07,0xB3,0x2E,0x49,
0xFA,0xD5,0xAD,0xE1,
0x83,0x6D,0x0E,0x43,
0x28,0x78,0x42,0x64,
0x8B,0x16,0x74,0x88,
0xD8,0x1F,0xA0,0x3E,
0x63,0x60,0xFD,0xA8,
0xD7,0x76,0x72,0x18,
0xDC,0x56,0xFE,0xD0,
0x90,0xD1,0x9D,0xDB,
0x94,0x8C,0xDA,0xDE,
0xBE,0xCD,0xCF,0xC2,
0x1D,0x51,0xCE,0xBF,
0x73,0x35,0x00,0x92,
0x7D,0xC0,0x12,0x69,
0x26,0x38,0x4B,0xFF,
0xED,0x9C,0x13,0xF5,
0x15,0xD2,0xEC,0xF8,
0xB9,0x46,0xA2,0x41,
0xF6,0x99,0x75,0x95,
0x87,0x23,0x10,0x61,
0x25,0xB8,0x37,0xCC,
0x0C,0xD6,0x01,0x0F,
0x21,0x4A,0x54,0x3B,
0x5A,0x0B,0x00,0x00
};
现在还有一个问题，因为我不知道这个初始化密钥来自何处，所以就面临一个问题，这个密钥是多变的吗？是否是客户指纹产生的动态密钥呢？如果是的话，那么这个密钥将毫无用处。另外，发送函数也是这样加解密的吗？于是我注册了两个账号，最终经过验证，发现该密钥是都一样的！
忘了说一声，该软件的名字叫做某网的某信，版本号4.4.1280。
因为没法上传工程文件和wireshark的抓包文件，故所有测试代码这在这里，如下所示：
#include