逆向 crackme6

关键代码段分析:

00401528  |. 68 00010000    PUSH 100                                                  ; /Count = 100 (256.)
0040152D  |. 8D85 00FFFFFF  LEA EAX,DWORD PTR SS:[EBP-100]           ; |  eax = ebp -100;  // 在栈上申请100DWord的数组空间,存放name
00401533  |. 50             PUSH EAX                                

00401534  |. 6A 65          PUSH 65                                                         ; |ControlID = 65 (101.)
00401536  |. FF75 08        PUSH DWORD PTR SS:[EBP+8]                        ; |hWnd
00401539  |. E8 FA010000    CALL <JMP.&USER32.GetDlgItemTextA>       ; \GetDlgItemTextA

// 把参数压入栈中,调用 GetDlgItemTextA 函数  转换成高级语言是:

// GetDlgItemTextA(hwnd, 0x65/*IDC_BUTTON*/, buffer, 100/*sizeof(bufffer)*/ );


0040153E  |. 89C3           MOV EBX,EAX                                                            //ebx = eax = GetDlgItemTextA的返回值  , 取得的字符串的长度
00401540  |. 09DB           OR EBX,EBX                                                              //判断长度是否为空
00401542  |. 75 04          JNZ SHORT unpacked.00401548                                 //用户名不空就跳,否则就挂
00401544  |. 31C0           XOR EAX,EAX                                                           //          
00401546  |. EB 50          JMP SHORT unpacked.00401598                                  //函数结束的地址。


00401548  |> BF BC020000    MOV EDI,2BC                             
0040154D  |. BE 30000000    MOV ESI,30
00401552  |. B8 48000000    MOV EAX,48
00401557  |. 99             CDQ
00401558  |. F7FB           IDIV EBX                                                       //ebx 存放的是Namelength
0040155A  |. 29C6           SUB ESI,EAX
0040155C  |. 8D34B6         LEA ESI,DWORD PTR DS:[ESI+ESI*4] 
0040155F  |. 29F7           SUB EDI,ESI
00401561  |. 6BFF 6B        IMUL EDI,EDI,6B
00401564  |. 81EF 6CCF0000  SUB EDI,0CF6C

 //EDI=(2bc-(30-48/namelen)*5)*6b-cf6c,得出的EDI必须在190-2300之间,否则就挂
0040156A  |. 81FF 00230000  CMP EDI,2300                          

00401570  |. 7F 08          JG SHORT unpacked.0040157A                      .
00401572  |. 81FF 90010000  CMP EDI,190                             
00401578  |. 7D 04          JGE SHORT unpacked.0040157E
0040157A  |> 31C0           XOR EAX,EAX

 //  edi  > 190  && edi <=2300

明天继续


 

原文地址:https://www.cnblogs.com/herso/p/1427560.html