167 lines
7.9 KiB
Markdown
167 lines
7.9 KiB
Markdown
过检测，修bug
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先晒方法：
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```
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*文件偏移
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8DD: 80->E3
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8DE: 82->E3
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8DF: 80->E3
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8E0: 85->E3
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```
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细节：
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EP进来先跳第一个检测
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```assembly
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00401007 | E9 03010000 | jmp bugged.40110F |
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```
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这里会对401000~4010F8代码进行求和校验
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```assembly
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0040110F | 60 | pushad |
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00401110 | 33DB | xor ebx,ebx |
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00401112 | B8 00104000 | mov eax,<bugged.OptionalHeader.AddressOfEn |
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00401117 | 90 | nop |
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00401118 | 90 | nop |
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00401119 | 90 | nop |
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0040111A | 90 | nop |
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0040111B | 90 | nop |
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0040111C | 90 | nop |
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0040111D | 90 | nop |
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0040111E | 0318 | add ebx,dword ptr ds:[eax] |
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00401120 | 83C3 04 | add ebx,4 |
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00401123 | 83C0 04 | add eax,4 |
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00401126 | 3D F8104000 | cmp eax,bugged.4010F8 |
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0040112B | 75 EA | jne bugged.401117 | 循环0x3E次，对EP开头这段进行求和校验
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0040112D | 3B1D FA304000 | cmp ebx,dword ptr ds:[4030FA] | 004030FA:"煼愚"
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00401133 | 0F84 D3FEFFFF | je bugged.40100C |
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00401139 | 6A 30 | push 30 |
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0040113B | 68 1C214000 | push bugged.40211C | 40211C:"Bad checksum!!"
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00401140 | 68 2B214000 | push bugged.40212B | 40212B:"A virus or a cracker ;-) has corrupted the program, please reinstall it."
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00401145 | 6A 00 | push 0 |
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00401147 | E8 DCFEFFFF | call <JMP.&_MessageBoxA@16> |
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0040114C | E9 CEFEFFFF | jmp bugged.40101F |
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```
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校验无误后会一路跳：
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```
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0040100D | EB 7E | jmp bugged.40108D |
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```
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这段好像没啥用：
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```
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0040108D | 60 | pushad |
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0040108E | 40 | inc eax |
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0040108F | 48 | dec eax |
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00401090 | 33C9 | xor ecx,ecx | ecx:EntryPoint
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00401092 | 83E9 02 | sub ecx,2 | ecx:EntryPoint
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00401095 | 41 | inc ecx | ecx:EntryPoint
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00401096 | 41 | inc ecx | ecx:EntryPoint
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00401097 | 8BD9 | mov ebx,ecx | ecx:EntryPoint
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00401099 | 85DB | test ebx,ebx |
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0040109B | 75 82 | jne bugged.40101F |
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0040109D | 61 | popad |
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0040109E | EB 37 | jmp bugged.4010D7 |
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```
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接下来是释放最后的检查代码：
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```
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004010D7 | 60 | pushad |
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004010D8 | B8 8D104000 | mov eax,bugged.40108D |
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004010DD | BB C0304000 | mov ebx,4030C0 |
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004010E2 | 33C9 | xor ecx,ecx | ecx:EntryPoint
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004010E4 | 8A13 | mov dl,byte ptr ds:[ebx] |
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004010E6 | 80C2 02 | add dl,2 |
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004010E9 | 80F2 75 | xor dl,75 |
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004010EC | 8810 | mov byte ptr ds:[eax],dl |
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004010EE | 40 | inc eax |
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004010EF | 43 | inc ebx |
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004010F0 | 41 | inc ecx | ecx:EntryPoint
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004010F1 | 83F9 3A | cmp ecx,3A | ecx:EntryPoint, 3A:':'
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004010F4 | 75 EE | jne bugged.4010E4 | 循环0x3A次，释放新的检查代码到上个检查
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004010F6 | 61 | popad |
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004010F7 | EB 94 | jmp bugged.40108D |
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```
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可以看出从4030C0位置开始3A大小内容是被加密的（再后面好像是前面的校验值，不过用不上）
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```
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13 44 AC F4 B4 75 FC BC F4 9A 75 11 44 B3 33 FC
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AB 3C FC B4 CC 21 73 73 73 80 84 80 83 80 82 80
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85 12 1D 33 1B 73 43 33 73 1B 65 43 33 73 1D 73
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9B 11 88 88 88 9A 3B 88 88 88
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```
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经过解密`+0x2，xor 0x75`，可以得到：
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```
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60 33 DB 83 C3 02 8B CB 83 E9 02 66 33 C0 40 8B
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D8 4B 8B C3 BB 56 00 00 00 F7 F3 F7 F0 [F7 F1 F7 ←
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F2] 61 6A 40 68 00 30 40 00 68 12 30 40 00 6A 00
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E8 66 FF FF FF E9 48 FF FF FF
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```
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文件先摆着，反正等会儿也要执行这块代码
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这是解密的代码
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```assembly
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0040108D | 60 | pushad |
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0040108E | 33DB | xor ebx,ebx |
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00401090 | 83C3 02 | add ebx,2 |
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00401093 | 8BCB | mov ecx,ebx | ecx:EntryPoint
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00401095 | 83E9 02 | sub ecx,2 | ecx:EntryPoint
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00401098 | 66:33C0 | xor ax,ax |
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0040109B | 40 | inc eax |
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0040109C | 8BD8 | mov ebx,eax |
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0040109E | 4B | dec ebx |
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0040109F | 8BC3 | mov eax,ebx |
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004010A1 | BB 56000000 | mov ebx,56 | 56:'V'
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004010A6 | F7F3 | div ebx |
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004010A8 | F7F0 | div eax |
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004010AA | F7F1 | div ecx | <--
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004010AC | F7F2 | div edx | <--
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004010AE | 61 | popad |
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004010AF | 6A 40 | push 40 |
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004010B1 | 68 00304000 | push bugged.403000 | 403000:"Congratulations!!"
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004010B6 | 68 12304000 | push 403012 | 403012:"Bug anihilated/destroyed/defated. :p. Coded a little in Masm32 and more in hex editor."
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004010BB | 6A 00 | push 0 |
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004010BD | E8 66FFFFFF | call <JMP.&_MessageBoxA@16> |
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004010C2 | E9 48FFFFFF | jmp bugged.40100F |
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```
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其中`004010AA`、`004010AC`会出现问题（/0），NOP掉
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`F7 F1 F7 F2`这块换成`90 90 90 90` (也就是上边解密的二进制内容[]指出部分)
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更换后重新加密回去`xor 0x75, -0x2`，最后可得到
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```
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13 44 AC F4 B4 75 FC BC F4 9A 75 11 44 B3 33 FC
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AB 3C FC B4 CC 21 73 73 73 80 84 80 83 [E3 E3 E3
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E3] 12 1D 33 1B 73 43 33 73 1B 65 43 33 73 1D 73
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9B 11 88 88 88 9A 3B 88 88 88
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```
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用你的hex编辑器打开exe文件，转到文件偏移`0x8C0`处
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```
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8DD: 80->E3
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8DE: 82->E3
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8DF: 80->E3
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8E0: 85->E3
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```
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(可选) 有时候好像过不去这个文件校验？直接Patch成`jmp bugged.40100C`
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```
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00401133 | 0F84 D3FEFFFF | je bugged.40100C |
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```
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