160个CrackMe 002 Afkayas.1

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首先,同样的操作,PEID查壳:
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VB的程序,没有壳,OK,注意一下VB中的函数就可以了,这里推荐一个微博,总结了在逆向中常用到的VB的函数
VB程序逆向反汇编常见的函数

试着自己运行:
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OD运行起来,右键,查找,查找所有参考文本字符串,找到错误字符串的位置

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看到我们的错误字符串了,You Get Wrong,并且在上面还发现了应该是正确的字符串,两个字符串相距不远,嗯嗯,这个题目应该不难(至少跳转会少些..)

双击字符串进入位置,发现了跳转指令
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在跳转的位置F2下断,重新运行程序,输入我们瞎扯的字符串上去:
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好,停住,向上分析代码,找到及其关键的函数_vbastrcmp()字符串比较函数
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这样的话说明在这时的序列号已经生成了,所以对输入的name和生成的name比较,序列号生成代码就在这片汇编代码中
于是我丧心病狂的找到了这个函数的头部,F2下断:
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重新运行起来,F9到断点的位置,F8一步一步地调试,遇到重要的不认识的VB函数,就去博客上查,知道它是做什么用的就可以,具体分析的过程就不说了,耐心,很简单,分析源码:

00402409   > \8B95 50FFFFFF mov edx,dword ptr ss:[ebp-0xB0]
0040240F   .  8B45 E4       mov eax,dword ptr ss:[ebp-0x1C]                      ;  输入的name:12345
00402412   .  50            push eax                                             ; /String = 0000000A ???
00402413   .  8B1A          mov ebx,dword ptr ds:[edx]                           ; |
00402415   .  FF15 E4404000 call dword ptr ds:[<&MSVBVM50.__vbaLenBstr>]         ; \__vbaLenBstr   获得一个字符串的长度
0040241B   .  8BF8          mov edi,eax                                          ;  函数的返回值放在EAX寄存器中,本例为5
0040241D   .  8B4D E8       mov ecx,dword ptr ss:[ebp-0x18]
00402420   .  69FF FB7C0100 imul edi,edi,0x17CFB                                 ;  edi为name的长度乘以0x17CFB
00402426   .  51            push ecx                                             ; /String="1" 取出name的首字符
00402427   .  0F80 91020000 jo Afkayas_.004026BE                                 ; |
0040242D   .  FF15 F8404000 call dword ptr ds:[<&MSVBVM50.#rtcAnsiValueBstr_516>>; \rtcAnsiValueBstr 计算name首字符的Ascii值
00402433   .  0FBFD0        movsx edx,ax                                         ;  最终edi的值为name的长度乘以0x17cfb在加上第一个字符的ASCII码值
00402436   .  03FA          add edi,edx
00402438   .  0F80 80020000 jo Afkayas_.004026BE
0040243E   .  57            push edi                                             ;  msvbvm50.__vbaStrCat
0040243F   .  FF15 E0404000 call dword ptr ds:[<&MSVBVM50.__vbaStrI4>]           ;  msvbm50._vbaStrI4 edi中值16进制转成10进制
00402445   .  8BD0          mov edx,eax                                          ;  得到正确serila的数字部分
00402447   .  8D4D E0       lea ecx,dword ptr ss:[ebp-0x20]
0040244A   .  FF15 70414000 call dword ptr ds:[<&MSVBVM50.__vbaStrMove>]         ;  msvbvm50.__vbaStrMove
00402450   .  8BBD 50FFFFFF mov edi,dword ptr ss:[ebp-0xB0]
00402456   .  50            push eax
00402457   .  57            push edi                                             ;  msvbvm50.__vbaStrCat
00402458   .  FF93 A4000000 call dword ptr ds:[ebx+0xA4]
0040245E   .  85C0          test eax,eax
00402460   .  7D 12         jge short Afkayas_.00402474
00402462   .  68 A4000000   push 0xA4
00402467   .  68 5C1B4000   push Afkayas_.00401B5C
0040246C   .  57            push edi                                             ;  msvbvm50.__vbaStrCat
0040246D   .  50            push eax
0040246E   .  FF15 04414000 call dword ptr ds:[<&MSVBVM50.__vbaHresultCheckObj>] ;  msvbvm50.__vbaHresultCheckObj
00402474   >  8D45 E0       lea eax,dword ptr ss:[ebp-0x20]
00402477   .  8D4D E4       lea ecx,dword ptr ss:[ebp-0x1C]
0040247A   .  50            push eax
0040247B   .  8D55 E8       lea edx,dword ptr ss:[ebp-0x18]
0040247E   .  51            push ecx
0040247F   .  52            push edx
00402480   .  6A 03         push 0x3
00402482   .  FF15 5C414000 call dword ptr ds:[<&MSVBVM50.__vbaFreeStrList>]     ;  msvbvm50.__vbaFreeStrList
00402488   .  83C4 10       add esp,0x10
0040248B   .  8D45 D4       lea eax,dword ptr ss:[ebp-0x2C]
0040248E   .  8D4D D8       lea ecx,dword ptr ss:[ebp-0x28]
00402491   .  8D55 DC       lea edx,dword ptr ss:[ebp-0x24]
00402494   .  50            push eax
00402495   .  51            push ecx
00402496   .  52            push edx
00402497   .  6A 03         push 0x3
00402499   .  FF15 F4404000 call dword ptr ds:[<&MSVBVM50.__vbaFreeObjList>]     ;  msvbvm50.__vbaFreeObjList
0040249F   .  8B06          mov eax,dword ptr ds:[esi]
004024A1   .  83C4 10       add esp,0x10
004024A4   .  56            push esi
004024A5   .  FF90 04030000 call dword ptr ds:[eax+0x304]
004024AB   .  8B1D 0C414000 mov ebx,dword ptr ds:[<&MSVBVM50.__vbaObjSet>]       ;  msvbvm50.__vbaObjSet
004024B1   .  50            push eax
004024B2   .  8D45 DC       lea eax,dword ptr ss:[ebp-0x24]
004024B5   .  50            push eax
004024B6   .  FFD3          call ebx                                             ;  msvbvm50.__vbaStrMove; <&MSVBVM50.__vbaObjSet>
004024B8   .  8BF8          mov edi,eax
004024BA   .  8D55 E8       lea edx,dword ptr ss:[ebp-0x18]
004024BD   .  52            push edx
004024BE   .  57            push edi                                             ;  msvbvm50.__vbaStrCat
004024BF   .  8B0F          mov ecx,dword ptr ds:[edi]
004024C1   .  FF91 A0000000 call dword ptr ds:[ecx+0xA0]
004024C7   .  85C0          test eax,eax
004024C9   .  7D 12         jge short Afkayas_.004024DD
004024CB   .  68 A0000000   push 0xA0
004024D0   .  68 5C1B4000   push Afkayas_.00401B5C
004024D5   .  57            push edi                                             ;  msvbvm50.__vbaStrCat
004024D6   .  50            push eax
004024D7   .  FF15 04414000 call dword ptr ds:[<&MSVBVM50.__vbaHresultCheckObj>] ;  msvbvm50.__vbaHresultCheckObj
004024DD   >  56            push esi
004024DE   .  FF95 40FFFFFF call dword ptr ss:[ebp-0xC0]                         ;  msvbvm50.741CC368
004024E4   .  50            push eax
004024E5   .  8D45 D8       lea eax,dword ptr ss:[ebp-0x28]
004024E8   .  50            push eax
004024E9   .  FFD3          call ebx                                             ;  msvbvm50.__vbaStrMove
004024EB   .  8BF0          mov esi,eax
004024ED   .  8D55 E4       lea edx,dword ptr ss:[ebp-0x1C]
004024F0   .  52            push edx
004024F1   .  56            push esi
004024F2   .  8B0E          mov ecx,dword ptr ds:[esi]
004024F4   .  FF91 A0000000 call dword ptr ds:[ecx+0xA0]
004024FA   .  85C0          test eax,eax
004024FC   .  7D 12         jge short Afkayas_.00402510
004024FE   .  68 A0000000   push 0xA0
00402503   .  68 5C1B4000   push Afkayas_.00401B5C
00402508   .  56            push esi
00402509   .  50            push eax
0040250A   .  FF15 04414000 call dword ptr ds:[<&MSVBVM50.__vbaHresultCheckObj>] ;  msvbvm50.__vbaHresultCheckObj
00402510   >  8B45 E8       mov eax,dword ptr ss:[ebp-0x18]
00402513   .  8B4D E4       mov ecx,dword ptr ss:[ebp-0x1C]
00402516   .  8B3D 00414000 mov edi,dword ptr ds:[<&MSVBVM50.__vbaStrCat>]       ;  msvbvm50.__vbaStrCat
0040251C   .  50            push eax
0040251D   .  68 701B4000   push Afkayas_.00401B70                               ;  UNICODE "AKA-"
00402522   .  51            push ecx                                             ; /String = 80020004 ???
00402523   .  FFD7          call edi                                             ; \__vbaStrCat
00402525   .  8B1D 70414000 mov ebx,dword ptr ds:[<&MSVBVM50.__vbaStrMove>]      ;  msvbvm50.__vbaStrMove
0040252B   .  8BD0          mov edx,eax
0040252D   .  8D4D E0       lea ecx,dword ptr ss:[ebp-0x20]
00402530   .  FFD3          call ebx                                             ;  msvbvm50.__vbaStrMove; <&MSVBVM50.__vbaStrMove>
00402532   .  50            push eax                                             ;  "AKA-487704"
00402533   .  FF15 28414000 call dword ptr ds:[<&MSVBVM50.__vbaStrCmp>]          ;  msvbvm50.__vbaStrCmp
00402539   .  8BF0          mov esi,eax                                          ;  比较结果存在EAX中,是FFFFFFFF,说明失败了

其中在这个位置的函数_VbaStrI4()

 0040243E   .  57            push edi
    0040243F   .  FF15 E0404000 call dword ptr ds:[<&MSVBVM50.__vbaStrI4>]           ;  msvbm50._vbaStrI4 edi中值16进制转成10进制
    00402445   .  8BD0          mov edx,eax                                          ;  得到正确serila的数字部分
    00402447   .  8D4D E0       lea ecx,dword ptr ss:[ebp-0x20]

它的作用我简单查了一下,没有找到(当然我努力找肯定能找到),但是
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和第一题一样的套路...16进制转10进制字符串

将本例的结果试验一下:
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成功!
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算法分析:
最终生成的serial是
AKA-((name的长度)*0x17CFB+第一个字符的ASCII码值)转成10进制字符串)

OK,写注册机,我要用python

str1=raw_input(‘input your name:‘)
length=str1.__len__()
c=ord(str1[0])
serial=length*97531+c
print ‘serial:‘
print ‘AKA-‘+str(serial)

最后还有的几个JO命令的地方是判断是否溢出的,溢出就直接ERROR。这个我心算了一下...,应该很难溢出,就不考虑了..

这题目还可以用VB的反汇编工具,例如:VB Decompiler
直接看VB源码:
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这个是不是很简单

源码:

Private Sub OK_Click() ‘402310
  Dim var_24 As TextBox
  Dim var_B0 As TextBox
  loc_0040237A: var_C0 = CrackMe.RegSerial ‘Ignore this
  loc_00402387: Set var_2C = CrackMe.RegSerial
  loc_00402394: var_B0 = var_2C
  loc_0040239A: var_C4 = CrackMe.Text1 ‘Ignore this
  loc_004023A7: Set var_24 = var_2C
  loc_004023B6: var_18 = Text1.Text
  loc_004023D3: call var_C4(Me, Me, Me, edi, Me, var_24)
  loc_004023ED: var_1C = Text1.Text
  loc_00402420: Len(var_1C) = Len(var_1C) * 97531
  loc_00402436: Len(var_1C) = Len(var_1C) + Asc(var_18)
  loc_0040243F: call var_4040E0(Len(var_1C))
  loc_0040244A: var_20 = var_4040E0(Len(var_1C))
  loc_00402458: Text1.Text = var_20
  loc_004024C1: var_18 = Serial.Text
  loc_004024DE: call var_C0(Me, Me)
  loc_004024F4: var_1C = Serial.Text
  loc_00402530: var_20 = "AKA-" & var_1C
  loc_0040254A: esi = (var_18 = var_20) + 1
  loc_0040258B: If (var_18 = var_20) + 1 = 0 Then GoTo loc_004025E5
  loc_004025AB: var_34 = "You Get It" & "vbCrLf" & "KeyGen It Now"
  loc_004025E3: GoTo loc_0040263B
  loc_004025E5: ‘Referenced from: 0040258B
  loc_00402600: var_34 = "You Get Wrong" & "vbCrLf" & "Try Again"
  loc_0040263B: ‘Referenced from: 004025E3
  loc_00402652: GoTo loc_0040269E
  loc_0040269D: Exit Sub
  loc_0040269E: ‘Referenced from: 00402652
  loc_0040269E: Exit Sub
End Sub

相比汇编,这个很容易看懂了,不过借助工具终究是外力,总有工具是有限制的,唯一能改变这点的就是自己NB,谁都骗不过你喽(我还是新手,勿喷).

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