解除某下载软件的注册限制

PEID查壳为NeoLite v2.0，这壳很简单，本文就不多说了，直接脱壳并修复。

脱壳后反汇编得到如下信息：

:0040F490 8BC3   mov eax, ebx
:0040F492 E879030000   call 0040F810  //看看下面提示语句就知道很经典的，让我们跟进这个Call
:0040F497 84C0   test al, al
:0040F499 7460   je 0040F4FB   //跳则死
:0040F49B 6A00   push 00000000

* Possible StringData Ref from Data Obj ->”感谢您，您已经注册成功!
重新启动系统，注册将会”
->”生效!”
|
:0040F49D BA15E24E00   mov edx, 004EE215
:0040F4A2 66C746102C00   mov [esi+10], 002C
:0040F4A8 8D45E4   lea eax, dword ptr [ebp-1C]
:0040F4AB E864350C00   call 004D2A14
:0040F4B0 FF461C   inc [esi+1C]
:0040F4B3 8B10   mov edx, dword ptr [eax]
:0040F4B5 52   push edx
:0040F4B6 6A02   push 00000002
:0040F4B8 6A00   push 00000000
:0040F4BA 8D4DBA   lea ecx, dword ptr [ebp-46]
:0040F4BD 51   push ecx
:0040F4BE E885940B00   call 004C8948
:0040F4C3 83C40C   add esp, 0000000C
:0040F4C6 8D45BA   lea eax, dword ptr [ebp-46]
:0040F4C9 804DBA04   or byte ptr [ebp-46], 04
:0040F4CD 668B08   mov cx, word ptr [eax]
:0040F4D0 58   pop eax
:0040F4D1 B202   mov dl, 02
:0040F4D3 E8E8310700   call 004826C0
:0040F4D8 FF4E1C   dec [esi+1C]
:0040F4DB 8D45E4   lea eax, dword ptr [ebp-1C]
:0040F4DE BA02000000   mov edx, 00000002
:0040F4E3 E8C8360C00   call 004D2BB0
:0040F4E8 C7833402000001000000   mov dword ptr [ebx+00000234], 00000001
:0040F4F2 8BC3   mov eax, ebx
:0040F4F4 E83BAB0600   call 0047A034
:0040F4F9 EB58   jmp 0040F553

* Referenced by a (U)nconditional or (C)onditional Jump at Address:
|:0040F499(C)
|
:0040F4FB 6A00   push 00000000

* Possible StringData Ref from Data Obj ->”注册码错误!请重新输入!”
|
:0040F4FD BA49E24E00   mov edx, 004EE249
:0040F502 66C746103800   mov [esi+10], 0038

—————–来自 0040F492 E879030000   call 0040F810—-

:0040F810 55   push ebp
:0040F811 8BEC   mov ebp, esp
:0040F813 83C4A8   add esp, FFFFFFA8
:0040F816 53   push ebx
:0040F817 56   push esi
:0040F818 57   push edi
:0040F819 8BD8   mov ebx, eax
:0040F81B 8D75B8   lea esi, dword ptr [ebp-48]
:0040F81E B8B0E64E00   mov eax, 004EE6B0
:0040F823 E83C940B00   call 004C8C64
:0040F828 8BC3   mov eax, ebx
:0040F82A E8BD030000   call 0040FBEC
:0040F82F 66C746100800   mov [esi+10], 0008
:0040F835 33D2   xor edx, edx
:0040F837 33C9   xor ecx, ecx
:0040F839 8955FC   mov dword ptr [ebp-04], edx
:0040F83C 33C0   xor eax, eax
:0040F83E FF461C   inc [esi+1C]
:0040F841 8D933C030000   lea edx, dword ptr [ebx+0000033C]
:0040F847 66C746101400   mov [esi+10], 0014
:0040F84D 66C746102000   mov [esi+10], 0020
:0040F853 894DF8   mov dword ptr [ebp-08], ecx
:0040F856 FF461C   inc [esi+1C]
:0040F859 66C746101400   mov [esi+10], 0014
:0040F85F 66C746102C00   mov [esi+10], 002C

…….省略基本无关初始化的语句，来到下面的计算注册码的核心代码：
* Possible StringData Ref from Data Obj ->”0x”
|
:0040F9C6 B8F2E24E00   mov eax, 004EE2F2
:0040F9CB E828350C00   call 004D2EF8
:0040F9D0 8D45E4   lea eax, dword ptr [ebp-1C]
:0040F9D3 8B00   mov eax, dword ptr [eax]
:0040F9D5 E89AD00A00   call 004BCA74
:0040F9DA 8945B0   mov dword ptr [ebp-50], eax
:0040F9DD 8955B4   mov dword ptr [ebp-4C], edx
:0040F9E0 FF4E1C   dec [esi+1C]
:0040F9E3 8D45E4   lea eax, dword ptr [ebp-1C]
:0040F9E6 BA02000000   mov edx, 00000002
:0040F9EB E8C0310C00   call 004D2BB0
:0040F9F0 FF4E1C   dec [esi+1C]
:0040F9F3 8D45E8   lea eax, dword ptr [ebp-18]
:0040F9F6 BA02000000   mov edx, 00000002
:0040F9FB E8B0310C00   call 004D2BB0
:0040FA00 66C746101400   mov [esi+10], 0014
:0040FA06 33DB   xor ebx, ebx
:0040FA08 EB6E   jmp 0040FA78

————— 以上作用主要是把机器码转为16进制数，即0x…… —————-

* Referenced by a (U)nconditional or (C)onditional Jump at Address:
|:0040FAA4(C)
|
:0040FA0A 837DFC00   cmp dword ptr [ebp-04], 00000000 <—[ebp-04]保存的是我们填入的E-mail。判断是否为空
:0040FA0E 7408   je 0040FA18
:0040FA10 8B45FC   mov eax, dword ptr [ebp-04] <—E-mail 地址
:0040FA13 8B50FC   mov edx, dword ptr [eax-04] <—E-mail 字符位数
:0040FA16 EB02   jmp 0040FA1A

* Referenced by a (U)nconditional or (C)onditional Jump at Address:
|:0040FA0E(C)
|
:0040FA18 33D2   xor edx, edx

* Referenced by a (U)nconditional or (C)onditional Jump at Address:
|:0040FA16(U)
|
:0040FA1A 3BDA   cmp ebx, edx <— ebx初始值为0 ，并判断该计算E-mail字符位数是否大于已经循环的次数
:0040FA1C 7D3B   jge 0040FA59 <— 若大于已经循环的次数，则转到0040FA59进行处理
:0040FA1E 8D7B01   lea edi, dword ptr [ebx+01]
:0040FA21 57   push edi
:0040FA22 8D45FC   lea eax, dword ptr [ebp-04]
:0040FA25 50   push eax
:0040FA26 E8652F0C00   call 004D2990
:0040FA2B 83C408   add esp, 00000008
:0040FA2E 8D45FC   lea eax, dword ptr [ebp-04]
:0040FA31 E8D2320C00   call 004D2D08
:0040FA36 037DFC   add edi, dword ptr [ebp-04]
:0040FA39 4F   dec edi
:0040FA3A 0FBE07   movsx eax, byte ptr [edi]
:0040FA3D 99   cdq <—–CDQ指令以方便做64位运算
:0040FA3E 52   push edx
:0040FA3F 50   push eax
:0040FA40 8B45B0   mov eax, dword ptr [ebp-50] <—保存机器码后 8 位计算的累计结果
:0040FA43 8B55B4   mov edx, dword ptr [ebp-4C] <—保存机器码前 8 位计算的累计结果
:0040FA46 E8D1BE0B00   call 004CB91C

———————-call 004CB91C—start————————–
|:0040F1DE , :0040FA46 , :0040FA66
|
:004CB91C 52   push edx
:004CB91D 50   push eax
:004CB91E 8B442410   mov eax, dword ptr [esp+10]
:004CB922 F72424   mul dword ptr [esp]
:004CB925 8BC8   mov ecx, eax
:004CB927 8B442404   mov eax, dword ptr [esp+04] <—[esp+04]：原始机器码前 8 位
:004CB92B F764240C   mul [esp+0C] <—[esp+0c]保存E-mail码地址的ASCII的值或00:A1
并与原始机器码前 8 位相乘，结果保存在EDX（符号）和EAX（数值）
:004CB92F 03C8   add ecx, eax <—ECX保存中间结果
:004CB931 8B0424   mov eax, dword ptr [esp] <—[Esp]：原始机器码后 8 位
:004CB934 F764240C   mul [esp+0C] <—[esp+0c]保存E-mail码地址的ASCII的值或00:A1
并与原始机器码后 8 位相乘，结果保存在EDX（符号）和EAX
:004CB938 03D1   add edx, ecx <—EDX为上步运算结果的符号位，并与ECX相加
:004CB93A 59   pop ecx
:004CB93B 59   pop ecx
:004CB93C C20800   ret 0008
———————-call 004CB91C—End—————————

:0040FA4B 83C001   add eax, 00000001 <—-后8位计算结果加1
:0040FA4E 83D200   adc edx, 00000000 <—-前8位计算结果加0（多此一举？*^_^*）
:0040FA51 8945B0   mov dword ptr [ebp-50], eax <—-保存前8位计算结果
:0040FA54 8955B4   mov dword ptr [ebp-4C], edx <—-保存后8位计算结果
:0040FA57 EB1E   jmp 0040FA77

* Referenced by a (U)nconditional or (C)onditional Jump at Address:
|:0040FA1C(C)
|
:0040FA59 6A00   push 00000000 <—–符号位
:0040FA5B 68A1000000   push 000000A1 <—–原始值
:0040FA60 8B45B0   mov eax, dword ptr [ebp-50]
:0040FA63 8B55B4   mov edx, dword ptr [ebp-4C]
:0040FA66 E8B1BE0B00   call 004CB91C <—–用00:A1代替原E-mail 地址的 ASCII码
依次与机器码前、后 8 位做相同运算
:0040FA6B 83C001   add eax, 00000001 —–
:0040FA6E 83D200   adc edx, 00000000 |—作用如前述。
:0040FA71 8945B0   mov dword ptr [ebp-50], eax |
:0040FA74 8955B4   mov dword ptr [ebp-4C], edx —–

* Referenced by a (U)nconditional or (C)onditional Jump at Address:
|:0040FA57(U)
|
:0040FA77 43   inc ebx <—计算标志，用于判断E-mail字符串运算是否结束。
若结束，则用A1代替E-mail字符串的ASC值进行运算

* Referenced by a (U)nconditional or (C)onditional Jump at Address:
|:0040FA08(U)
|
:0040FA78 837DFC00   cmp dword ptr [ebp-04], 00000000
:0040FA7C 7408   je 0040FA86
:0040FA7E 8B4DFC   mov ecx, dword ptr [ebp-04] <—E-mail 地址
:0040FA81 8B41FC   mov eax, dword ptr [ecx-04] <—E-mail 位数
:0040FA84 EB02   jmp 0040FA88

* Referenced by a (U)nconditional or (C)onditional Jump at Address:
|:0040FA7C(C)
|
:0040FA86 33C0   xor eax, eax

* Referenced by a (U)nconditional or (C)onditional Jump at Address:
|:0040FA84(U)
|
:0040FA88 8945AC   mov dword ptr [ebp-54], eax
:0040FA8B C745A808000000   mov [ebp-58], 00000008
:0040FA92 8B55A8   mov edx, dword ptr [ebp-58]
:0040FA95 3B55AC   cmp edx, dword ptr [ebp-54]
:0040FA98 7E05   jle 0040FA9F
:0040FA9A 8D4DA8   lea ecx, dword ptr [ebp-58]
:0040FA9D EB03   jmp 0040FAA2

* Referenced by a (U)nconditional or (C)onditional Jump at Address:
|:0040FA98(C)
|
:0040FA9F 8D4DAC   lea ecx, dword ptr [ebp-54]

* Referenced by a (U)nconditional or (C)onditional Jump at Address:
|:0040FA9D(U)
|
:0040FAA2 3B19   cmp ebx, dword ptr [ecx] <—ecx=8
:0040FAA4 0F8C60FFFFFF   jl 0040FA0A <—循环 8 次
:0040FAAA 66C746105000   mov [esi+10], 0050
:0040FAB0 FF75B4   push [ebp-4C] <—-保存最终后 8 位结果
:0040FAB3 FF75B0   push [ebp-50] <—-保存最终前 8 位结果
:0040FAB6 33D2   xor edx, edx
:0040FAB8 B808000000   mov eax, 00000008
:0040FABD 8955E0   mov dword ptr [ebp-20], edx

将前、后 8 位结果算出后的最终结果作为字符串简单相加即为注册码。

本软件的注册信息保存在注册表中，删除该键值就可以重新注册，也可以根据本文的算法写出内存注册机，这里就不写了。