环境
Windows xp sp3

工具
exeinfope
ollydbg

查壳
无壳的MFC程序

测试

字符串搜索：

004014F5  |.  E8 AA030000   call <jmp.&MFC42.#CWnd::GetWindowTextLengthA_>
004014FA  |.  8945 EC       mov [local.5],eax
004014FD  |.  837D EC 05    cmp [local.5],0x5                             ;  Name要大于5，不然就显示错误
00401501  |.  7F 05         jg Xcosh_3.00401508
00401503  |.  E9 BB000000   jmp cosh_3.004015C3
00401508  |>  8B4D E0       mov ecx,[local.8]
0040150B  |.  83C1 60       add ecx,0x60
0040150E  |.  E8 91030000   call <jmp.&MFC42.#CWnd::GetWindowTextLengthA_>
00401513  |.  8945 E8       mov [local.6],eax
00401516  |.  837D E8 05    cmp [local.6],0x5
0040151A  |.  7F 05         jg Xcosh_3.00401521                           ;  Serail也要大于5
0040151C  |.  E9 A2000000   jmp cosh_3.004015C3
00401521  |>  8B45 E0       mov eax,[local.8]
00401524  |.  05 E0000000   add eax,0xE0
00401529  |.  50            push eax
0040152A  |.  8B4D E0       mov ecx,[local.8]
0040152D  |.  81C1 A0000000 add ecx,0xA0
00401533  |.  E8 66030000   call <jmp.&MFC42.#CWnd::GetWindowTextA_3874>  ;  获取Name
00401538  |.  8B4D E0       mov ecx,[local.8]
0040153B  |.  81C1 E4000000 add ecx,0xE4
00401541  |.  51            push ecx
00401542  |.  8B4D E0       mov ecx,[local.8]
00401545  |.  83C1 60       add ecx,0x60
00401548  |.  E8 51030000   call <jmp.&MFC42.#CWnd::GetWindowTextA_3874>  ;  获取Serial
0040154D  |.  8B55 E0       mov edx,[local.8]
00401550  |.  81C2 E0000000 add edx,0xE0
00401556  |.  52            push edx
00401557  |.  8D4D E4       lea ecx,[local.7]
0040155A  |.  E8 39030000   call <jmp.&MFC42.#CString::operator=_858>
0040155F  |.  8B45 E0       mov eax,[local.8]
00401562  |.  05 E4000000   add eax,0xE4
00401567  |.  50            push eax
00401568  |.  8D4D F0       lea ecx,[local.4]
0040156B  |.  E8 28030000   call <jmp.&MFC42.#CString::operator=_858>
00401570  |.  33C0          xor eax,eax
00401572  |.  33DB          xor ebx,ebx
00401574  |.  33C9          xor ecx,ecx
00401576  |.  B9 01000000   mov ecx,0x1
0040157B  |.  33D2          xor edx,edx
0040157D  |.  8B45 E4       mov eax,[local.7]                             ;  name
00401580  |>  8A18          /mov bl,byte ptr ds:[eax]
00401582  |.  32D9          |xor bl,cl
00401584  |.  8818          |mov byte ptr ds:[eax],bl
00401586  |.  41            |inc ecx
00401587  |.  40            |inc eax
00401588  |.  8038 00       |cmp byte ptr ds:[eax],0x0
0040158B  |.^ 75 F3         \jnz Xcosh_3.00401580
0040158D  |.  33C0          xor eax,eax
0040158F  |.  33DB          xor ebx,ebx
00401591  |.  33C9          xor ecx,ecx
00401593  |.  B9 0A000000   mov ecx,0xA
00401598  |.  33D2          xor edx,edx
0040159A  |.  8B45 F0       mov eax,[local.4]                             ;  serial
0040159D  |>  8A18          /mov bl,byte ptr ds:[eax]
0040159F  |.  32D9          |xor bl,cl
004015A1  |.  8818          |mov byte ptr ds:[eax],bl
004015A3  |.  41            |inc ecx
004015A4  |.  40            |inc eax
004015A5  |.  8038 00       |cmp byte ptr ds:[eax],0x0
004015A8  |.^ 75 F3         \jnz Xcosh_3.0040159D
004015AA  |.  8B45 E4       mov eax,[local.7]
004015AD  |.  8B55 F0       mov edx,[local.4]                             ;  比较计算后的Name和Serial是否相同
004015B0  |>  33C9          /xor ecx,ecx
004015B2  |.  8A18          |mov bl,byte ptr ds:[eax]
004015B4  |.  8A0A          |mov cl,byte ptr ds:[edx]
004015B6  |.  3AD9          |cmp bl,cl
004015B8  |.  75 09         |jnz Xcosh_3.004015C3
004015BA  |.  40            |inc eax
004015BB  |.  42            |inc edx
004015BC  |.  8038 00       |cmp byte ptr ds:[eax],0x0
004015BF  |.^ 75 EF         \jnz Xcosh_3.004015B0
004015C1  |.  EB 16         jmp Xcosh_3.004015D9
004015C3  |>  6A 00         push 0x0
004015C5  |.  68 6C304000   push cosh_3.0040306C                          ;  ASCII "ERROR"
004015CA  |.  68 40304000   push cosh_3.00403040                          ;  ASCII "One of the Details you entered was wrong"
004015CF  |.  8B4D E0       mov ecx,[local.8]
004015D2  |.  E8 BB020000   call <jmp.&MFC42.#CWnd::MessageBoxA_4224>
004015D7  |.  EB 14         jmp Xcosh_3.004015ED
004015D9  |>  6A 00         push 0x0
004015DB  |.  68 34304000   push cosh_3.00403034                          ;  ASCII "YOU DID IT"
004015E0  |.  68 20304000   push cosh_3.00403020                          ;  ASCII "Well done,Cracker"

前两个函数用来确定Name和Serial的长度要大于5，然后取得Name的每个字符，分别于字符的位置异或。
Serial也是取每个字符，分别与每个字符的位置加0x9异或，比较两个字符串的异或结果是否相同，相同就显示正确的消息框，否则显示错误的消息框。

可以简单写出注册机：

    char Name[50];scanf("%s",Name);for(int i=0;i<strlen(Name);i++){printf("%c",Name[i]^(1+i)^(10+i));}