工具：ollyDBg1.09,W32Dasm10,Caspr110脱壳工具。
假设：
用户编号：222961388
注册码：654321
一、先脱壳，查找出错信息。
* Referenced by a (U)nconditional or (C)onditional Jump at Address:
|:0047A05C(C)
|
:0047A19F 6830000400 push 00040030
:0047A1A4 B908A24700 mov ecx, 0047A208
* Possible StringData Ref from Code Obj ->"注册码无效！"
|
:0047A1A9 BA6CA24700 mov edx, 0047A26C
:0047A1AE A1E8794B00 mov eax, dword ptr [004B79E8]
:0047A1B3 8B00 mov eax, dword ptr [eax]
:0047A1B5 E8A22AFDFF call 0044CC5C
:0047A1BA 8B86E8020000 mov eax, dword ptr [esi+000002E8]
:0047A1C0 8B10 mov edx, dword ptr [eax]
:0047A1C2 FF92CC000000 call dword ptr [edx+000000CC]
向上看：
0047A053 8B55F8 mov edx, dword ptr [ebp-08]＝＝＞在这下断
:0047A056 58 pop eax
:0047A057 E8489EF8FF call 00403EA4
:0047A05C 0F853D010000 jne 0047A19F=========>
:0047A062 6840000400 push 00040040
:0047A067 B908A24700 mov ecx, 0047A208
* Possible StringData Ref from Code Obj ->"注册成功！请保留好您的注册码，谢谢！"
|
二、用ollydbg载入，动态分析。
0047A002 |. 8B1D 28784B00 MOV EBX,DWORD PTR DS:[4B7828] ; unpacked.004B8930
0047A008 |. 33C0 XOR EAX,EAX
0047A00A |. 55 PUSH EBP
0047A00B |. 68 FBA14700 PUSH unpacked.0047A1FB
0047A010 |. 64:FF30 PUSH DWORD PTR FS:[EAX]
0047A013 |. 64:8920 MOV DWORD PTR FS:[EAX],ESP
0047A016 |. 6A 00 PUSH 0
0047A018 |. 6A 1B PUSH 1B
0047A01A |. E8 A9FDFFFF CALL unpacked.00479DC8 ; 用户编号十六进制值入eax,此eax=0D4A1EEC
0047A01F |. 2D 1F17F601 SUB EAX,1F6171F ; eax减1F6171F，eax=B5407CD
0047A024 |. 83DA 00 SBB EDX,0
0047A027 |. E8 44C5F8FF CALL unpacked.00406570 ; B5407CD值乘以1b，此eax=131DCD29F
0047A02C |. 52 PUSH EDX ; /Arg2
0047A02D |. 50 PUSH EAX ; |Arg1
0047A02E |. 8D45 FC LEA EAX,DWORD PTR SS:[EBP-4] ; |
0047A031 |. E8 6AE9F8FF CALL unpacked.004089A0 ; \把串31DCD29F转换为十进制，即为5131522719
0047A036 |. 8B45 FC MOV EAX,DWORD PTR SS:[EBP-4]
0047A039 |. 50 PUSH EAX
0047A03A |. 8D55 F4 LEA EDX,DWORD PTR SS:[EBP-C]
0047A03D |. 8B86 E8020000 MOV EAX,DWORD PTR DS:[ESI+2E8]
0047A043 |. E8 444AFBFF CALL unpacked.0042EA8C ; 取输入注册码
0047A048 |. 8B45 F4 MOV EAX,DWORD PTR SS:[EBP-C]
0047A04B |. 8D55 F8 LEA EDX,DWORD PTR SS:[EBP-8]
0047A04E |. E8 9DE7F8FF CALL unpacked.004087F0
0047A053 |. 8B55 F8 MOV EDX,DWORD PTR SS:[EBP-8] ; 输入注册码，此为edx=654321
0047A056 |. 58 POP EAX ; 真码入eax
0047A057 |. E8 489EF8FF CALL unpacked.00403EA4 ; 关键比较unpa
0047A05C |. 0F85 3D010000 JNZ unpacked.0047A19F ; 不等就跳npac
0047A062 |. 68 40000400 PUSH 40040
总结：
1、用户编号转为十六进制：222961388－＞D4A1EEC
2、十六进制值减1F6171F：D4A1EEC-1F6171F=B5407CD
3、第二步的值乘1b:B5407CD＊1b=131DCD29F
4、第三步的值转为十进制就是注册码：131DCD29F－＞5131522719
所以我的注册码如下：
用户编号：222961388
注册码：5131522719