struct Packet
{
    int size;
    int type;
    int errorcode;
    int digest;
    int state;
    char Message[];
};

Packet *msg;

void __declspec(naked) DecryptMsg(Packet *Crypted)
{
    __asm {
        mov eax, [esp + 4];
        mov ecx, [eax];
        sub ecx, 4;
looplabel:
        test ecx, ecx;
        jz retnlabel;
        mov dl, [eax + ecx + 3];
        ror dl, 3;
        not dl;
        mov [eax + ecx + 3], dl;
        dec ecx;
        jmp looplabel;
retnlabel:
        retn;
    }
}