CrackMe破解之Delphi
CrackMe破解之Delphi
安恒网络空间安全讲武堂
发布于 2018-08-17 17:47:29
发布于 2018-08-17 17:47:29
刚开始学逆向，先学了OD的使用，学了个大概之后就开始了实践，边学习边实践，破解一些crackme，因为是刚开始入门，所以有些算法还是不理解，无法逆向出算法，但是爆破，去nag是没问题的，这里有个crackme，试着破解并逆向它的算法。
这是个crackme程序，程序详细信息以及运行情况如下：
是个Delphi写的程序，无壳，程序要求把"OK"和"Cancella"按钮隐藏掉，以便看到 logo; 因为这是Delphi写的程序，所以用专业Delphi反编译工具Dark分析一下
以上代码先检查Cancella按钮是否隐藏，如果是就将ok按钮激活，否则检查用户名和密码是否匹配，匹配就激活按钮，否则禁用，关键call的代码如下：
00442E04 /. 55 push ebp ; 用户名改变函数
00442E05 |. 8BEC mov ebp,esp
00442E07 |. 6A 00 push 0x0
00442E09 |. 6A 00 push 0x0
00442E0B |. 53 push ebx
00442E0C |. 8BD8 mov ebx,eax
00442E0E |. 33C0 xor eax,eax
00442E10 |. 55 push ebp
00442E11 |. 68 9B2E4400 push aLoNg3x_.00442E9B
00442E16 |. 64:FF30 push dword ptr fs:[eax]
00442E19 |. 64:8920 mov dword ptr fs:[eax],esp
00442E1C |. 8B83 D0020000 mov eax,dword ptr ds:[ebx+0x2D0]
00442E22 |. 8078 47 00 cmp byte ptr ds:[eax+0x47],0x0 ;右边按钮是否隐藏,0为隐
00442E26 |. 75 0F jnz short aLoNg3x_.00442E37
00442E28 |. B2 01 mov dl,0x1
00442E2A |. 8B83 CC020000 mov eax,dword ptr ds:[ebx+0x2CC] ; ok按钮的ID
00442E30 |. 8B08 mov ecx,dword ptr ds:[eax]
00442E32 |. FF51 60 call dword ptr ds:[ecx+0x60] ;激活按钮
00442E35 |. EB 49 jmp short aLoNg3x_.00442E80 ;若隐藏了,直接激活左边按钮
00442E37 |> 8D55 FC lea edx,[local.1]
00442E3A |. 8B83 E0020000 mov eax,dword ptr ds:[ebx+0x2E0]
00442E40 |. E8 7B04FEFF call aLoNg3x_.004232C0
00442E45 |. 8B45 FC mov eax,[local.1]
00442E48 |. 50 push eax
00442E49 |. 8D55 F8 lea edx,[local.2]
00442E4C |. 8B83 DC020000 mov eax,dword ptr ds:[ebx+0x2DC]
00442E52 |. E8 6904FEFF call aLoNg3x_.004232C0
00442E57 |. 8B45 F8 mov eax,[local.2] ; 输入的用户名
00442E5A |. 5A pop edx
00442E5B |. E8 DCFBFFFF call aLoNg3x_.00442A3C;用户名密码匹配比较
00442E60 |. 84C0 test al,al
00442E62 |. 74 0F je short aLoNg3x_.00442E73 ;匹配就激活
00442E64 |. B2 01 mov dl,0x1
00442E66 |. 8B83 CC020000 mov eax,dword ptr ds:[ebx+0x2CC]
00442E6C |. 8B08 mov ecx,dword ptr ds:[eax]
00442E6E |. FF51 60 call dword ptr ds:[ecx+0x60] ;激活按钮
00442E71 |. EB 0D jmp short aLoNg3x_.00442E80
00442E73 |> 33D2 xor edx,edx
00442E75 |. 8B83 CC020000 mov eax,dword ptr ds:[ebx+0x2CC] ; 按钮ID
00442E7B |. 8B08 mov ecx,dword ptr ds:[eax]
00442E7D |. FF51 60 call dword ptr ds:[ecx+0x60] ;禁用按钮
00442E80 |> 33C0 xor eax,eax
00442E82 |. 5A pop edx
00442E83 |. 59 pop ecx
00442E84 |. 59 pop ecx
00442E85 |. 64:8910 mov dword ptr fs:[eax],edx
00442E88 |. 68 A22E4400 push aLoNg3x_.00442EA2
00442E8D |> 8D45 F8 lea eax,[local.2]
00442E90 |. BA 02000000 mov edx,0x2
00442E95 |. E8 4209FCFF call aLoNg3x_.004037DC
00442E9A \. C3 retn
00442E9B .^ E9 D803FCFF jmp aLoNg3x_.00403278
00442EA0 .^ EB EB jmp short aLoNg3x_.00442E8D
00442EA2 . 5B pop ebx
00442EA3 . 59 pop ecx
00442EA4 . 59 pop ecx
00442EA5 . 5D pop ebp
00442EA6 . C3 retn用户名的长度要大于5，然后根据下面的一套规则计算出一个值保存在ebx中，然后ebx-密码=0x29A就可以激活ok按钮。
接下来看右边的按钮单击事件，代码如下：
00442A3C /$ 55 push ebp 关键call
00442A3D |. 8BEC mov ebp,esp
00442A3F |. 83C4 F8 add esp,-0x8
00442A42 |. 53 push ebx
00442A43 |. 56 push esi
00442A44 |. 8955 F8 mov [local.2],edx
00442A47 |. 8945 FC mov [local.1],eax
00442A4A |. 8B45 FC mov eax,[local.1]
00442A4D |. E8 9611FCFF call aLoNg3x_.00403BE8
00442A52 |. 8B45 F8 mov eax,[local.2] ; 密码
00442A55 |. E8 8E11FCFF call aLoNg3x_.00403BE8
00442A5A |. 33C0 xor eax,eax
00442A5C |. 55 push ebp
00442A5D |. 68 E52A4400 push aLoNg3x_.00442AE5
00442A62 |. 64:FF30 push dword ptr fs:[eax]
00442A65 |. 64:8920 mov dword ptr fs:[eax],esp
00442A68 |. 8B45 FC mov eax,[local.1] ; 用户名
00442A6B |. E8 C40FFCFF call aLoNg3x_.00403A34 ; 用户名长度
00442A70 |. 83F8 05 cmp eax,0x5 ; 要大于5
00442A73 |. 7E 53 jle short aLoNg3x_.00442AC8
00442A75 |. 8B45 FC mov eax,[local.1] ; 用户名
00442A78 |. E8 B70FFCFF call aLoNg3x_.00403A34 ; 长度
00442A7D |. 8BD8 mov ebx,eax
00442A7F |. 8B45 FC mov eax,[local.1] ; 用户名
00442A82 |. E8 AD0FFCFF call aLoNg3x_.00403A34
00442A87 |. 8BD0 mov edx,eax
00442A89 |. 4A dec edx
00442A8A |. 85D2 test edx,edx ; 长度大于1
00442A8C |. 7E 20 jle short aLoNg3x_.00442AAE
00442A8E |. B8 01000000 mov eax,0x1
00442A93 |> 8B4D FC /mov ecx,[local.1]
00442A96 |. 0FB64C01 FF |movzx ecx,byte ptr ds:[ecx+eax-0x1]
00442A9B |. 8B75 FC |mov esi,[local.1] ; 用户名
00442A9E |. 0FB63406 |movzx esi,byte ptr ds:[esi+eax]
00442AA2 |. 0FAFCE |imul ecx,esi
00442AA5 |. 0FAFC8 |imul ecx,eax
00442AA8 |. 03D9 |add ebx,ecx ; user32.767A78F4
00442AAA |. 40 |inc eax
00442AAB |. 4A |dec edx
00442AAC |.^ 75 E5 \jnz short aLoNg3x_.00442A93
00442AAE |> 8B45 F8 mov eax,[local.2] ; 密码
00442AB1 |. E8 BA4BFCFF call aLoNg3x_.00407670 密码转十六进制
00442AB6 |. 2BD8 sub ebx,eax
00442AB8 |. 81FB 9A020000 cmp ebx,0x29A
00442ABE |. 75 04 jnz short aLoNg3x_.00442AC4
00442AC0 |. B3 01 mov bl,0x1
00442AC2 |. EB 06 jmp short aLoNg3x_.00442ACA
00442AC4 |> 33DB xor ebx,ebx
00442AC6 |. EB 02 jmp short aLoNg3x_.00442ACA
00442AC8 |> 33DB xor ebx,ebx
00442ACA |> 33C0 xor eax,eax
00442ACC |. 5A pop edx
00442ACD |. 59 pop ecx
00442ACE |. 59 pop ecx
00442ACF |. 64:8910 mov dword ptr fs:[eax],edx
00442AD2 |. 68 EC2A4400 push aLoNg3x_.00442AEC
00442AD7 |> 8D45 F8 lea eax,[local.2]
00442ADA |. BA 02000000 mov edx,0x2
00442ADF |. E8 F80CFCFF call aLoNg3x_.004037DC
00442AE4 \. C3 retn
00442AE5 .^ E9 8E07FCFF jmp aLoNg3x_.00403278
00442AEA .^ EB EB jmp short aLoNg3x_.00442AD7
00442AEC . 8BC3 mov eax,ebx ebx不为0
00442AEE . 5E pop esi
00442AEF . 5B pop ebx
00442AF0 . 59 pop ecx
00442AF1 . 59 pop ecx
00442AF2 . 5D pop ebp
00442AF3 . C3 retn以下代码检查用户名与密码是否满足条件，如果满足就隐藏Cencela按钮并且激活OK按钮；
00442AF4 /$ 55 push ebp
00442AF5 |. 8BEC mov ebp,esp
00442AF7 |. 83C4 F8 add esp,-0x8
00442AFA |. 53 push ebx
00442AFB |. 56 push esi
00442AFC |. 8955 F8 mov [local.2],edx
00442AFF |. 8945 FC mov [local.1],eax
00442B02 |. 8B45 FC mov eax,[local.1]
00442B05 |. E8 DE10FCFF call aLoNg3x_.00403BE8
00442B0A |. 33C0 xor eax,eax
00442B0C |. 55 push ebp
00442B0D |. 68 902B4400 push aLoNg3x_.00442B90
00442B12 |. 64:FF30 push dword ptr fs:[eax]
00442B15 |. 64:8920 mov dword ptr fs:[eax],esp
00442B18 |. 8B45 FC mov eax,[local.1]
00442B1B |. E8 140FFCFF call aLoNg3x_.00403A34 ;用户名长度
00442B20 |. 83F8 05 cmp eax,0x5 ;用户名长度要大于5
00442B23 |. 7E 53 jle short aLoNg3x_.00442B78
00442B25 |. 8B45 FC mov eax,[local.1]
00442B28 |. 0FB640 04 movzx eax,byte ptr ds:[eax+0x4] ;用户名第五个字符串ASCII码
00442B2C |. B9 07000000 mov ecx,0x7 ; ecx=7
00442B31 |. 33D2 xor edx,edx
00442B33 |. F7F1 div ecx ;eax =eax /ecx
00442B35 |. 8BC2 mov eax,edx
00442B37 |. 83C0 02 add eax,0x2
00442B3A |. E8 E1FEFFFF call aLoNg3x_.00442A20
00442B3F |. 8BF0 mov esi,eax
00442B41 |. 33DB xor ebx,ebx
00442B43 |. 8B45 FC mov eax,[local.1]
00442B46 |. E8 E90EFCFF call aLoNg3x_.00403A34
00442B4B |. 85C0 test eax,eax
00442B4D |. 7E 16 jle short aLoNg3x_.00442B65
00442B4F |. BA 01000000 mov edx,0x1
00442B54 |> 8B4D FC /mov ecx,[local.1]
00442B57 |. 0FB64C11 FF |movzx ecx,byte ptr ds:[ecx+edx-0x1]
00442B5C |. 0FAFCE |imul ecx,esi
00442B5F |. 03D9 |add ebx,ecx
00442B61 |. 42 |inc edx
00442B62 |. 48 |dec eax
00442B63 |.^ 75 EF \jnz short aLoNg3x_.00442B54
00442B65 |> 2B5D F8 sub ebx,[local.2] ;ebx-密码
00442B68 |. 81FB 697A0000 cmp ebx,0x7A69
00442B6E |. 75 04 jnz short aLoNg3x_.00442B74
00442B70 |. B3 01 mov bl,0x1
00442B72 |. EB 06 jmp short aLoNg3x_.00442B7A
00442B74 |> 33DB xor ebx,ebx
00442B76 |. EB 02 jmp short aLoNg3x_.00442B7A
00442B78 |> 33DB xor ebx,ebx
00442B7A |> 33C0 xor eax,eax
00442B7C |. 5A pop edx
00442B7D |. 59 pop ecx
00442B7E |. 59 pop ecx
00442B7F |. 64:8910 mov dword ptr fs:[eax],edx
00442B82 |. 68 972B4400 push aLoNg3x_.00442B97
00442B87 |> 8D45 FC lea eax,[local.1]
00442B8A |. E8 290CFCFF call aLoNg3x_.004037B8
00442B8F \. C3 retn
00442B90 .^ E9 E306FCFF jmp aLoNg3x_.00403278
00442B95 .^ EB F0 jmp short aLoNg3x_.00442B87
00442B97 . 8BC3 mov eax,ebx
00442B99 . 5E pop esi
00442B9A . 5B pop ebx
00442B9B . 59 pop ecx
00442B9C . 59 pop ecx
00442B9D . 5D pop ebp
00442B9E . C3 retn将ebx与密码作差看是否等于0x7A69，如果是就可以实现右侧按钮单击时隐藏了，如下：
下一步隐藏"OK"按钮就可以了，检查条件的关键CALL如下：
00442BA0 /$ 55 push ebp
00442BA1 |. 8BEC mov ebp,esp
00442BA3 |. 6A 00 push 0x0
00442BA5 |. 6A 00 push 0x0
00442BA7 |. 6A 00 push 0x0
00442BA9 |. 53 push ebx
00442BAA |. 56 push esi
00442BAB |. 8BF2 mov esi,edx
00442BAD |. 8945 FC mov [local.1],eax
00442BB0 |. 8B45 FC mov eax,[local.1]
00442BB3 |. E8 3010FCFF call aLoNg3x_.00403BE8
00442BB8 |. 33C0 xor eax,eax
00442BBA |. 55 push ebp
00442BBB |. 68 672C4400 push aLoNg3x_.00442C67
00442BC0 |. 64:FF30 push dword ptr fs:[eax]
00442BC3 |. 64:8920 mov dword ptr fs:[eax],esp
00442BC6 |. 33DB xor ebx,ebx
00442BC8 |. 8D55 F8 lea edx,[local.2]
00442BCB |. 8BC6 mov eax,esi
00442BCD |. E8 6E4AFCFF call aLoNg3x_.00407640
00442BD2 |. 8D45 F4 lea eax,[local.3]
00442BD5 |. 8B55 F8 mov edx,[local.2] ;密码
00442BD8 |. E8 730CFCFF call aLoNg3x_.00403850
00442BDD |. 8B45 F8 mov eax,[local.2]
00442BE0 |. E8 4F0EFCFF call aLoNg3x_.00403A34 ;密码长度
00442BE5 |. 83F8 05 cmp eax,0x5
00442BE8 |. 7E 60 jle short aLoNg3x_.00442C4A 不能跳
00442BEA |. 8B45 F8 mov eax,[local.2]
00442BED |. E8 420EFCFF call aLoNg3x_.00403A34
00442BF2 |. 8BF0 mov esi,eax
00442BF4 |. 83FE 01 cmp esi,0x1
00442BF7 |. 7C 2F jl short aLoNg3x_.00442C28
00442BF9 |> 8D45 F4 /lea eax,[local.3]
00442BFC |. E8 0310FCFF |call aLoNg3x_.00403C04
00442C01 |. 8D4430 FF |lea eax,dword ptr ds:[eax+esi-0x1]
00442C05 |. 50 |push eax
00442C06 |. 8B45 F8 |mov eax,[local.2]
00442C09 |. 0FB64430 FF |movzx eax,byte ptr ds:[eax+esi-0x1]
00442C0E |. F7E8 |imul eax
00442C10 |. 0FBFC0 |movsx eax,ax
00442C13 |. F7EE |imul esi
00442C15 |. B9 19000000 |mov ecx,0x19
00442C1A |. 99 |cdq
00442C1B |. F7F9 |idiv ecx
00442C1D |. 83C2 41 |add edx,0x41
00442C20 |. 58 |pop eax
00442C21 |. 8810 |mov byte ptr ds:[eax],dl
00442C23 |. 4E |dec esi
00442C24 |. 85F6 |test esi,esi
00442C26 |.^ 75 D1 \jnz short aLoNg3x_.00442BF9
00442C28 |> 8B45 F4 mov eax,[local.3] 可变字符串
00442C2B |. 8B55 FC mov edx,[local.1] 用户名
00442C2E |. E8 110FFCFF call aLoNg3x_.00403B44
00442C33 |. 75 17 jnz short aLoNg3x_.00442C4C
00442C35 |. 8B45 FC mov eax,[local.1]
00442C38 |. 8B55 F4 mov edx,[local.3]
00442C3B |. E8 040FFCFF call aLoNg3x_.00403B44 关键call
00442C40 |. 75 04 jnz short aLoNg3x_.00442C46
00442C42 |. B3 01 mov bl,0x1
00442C44 |. EB 06 jmp short aLoNg3x_.00442C4C
00442C46 |> 33DB xor ebx,ebx
00442C48 |. EB 02 jmp short aLoNg3x_.00442C4C
00442C4A |> 33DB xor ebx,ebx
00442C4C |> 33C0 xor eax,eax
00442C4E |. 5A pop edx
00442C4F |. 59 pop ecx
00442C50 |. 59 pop ecx
00442C51 |. 64:8910 mov dword ptr fs:[eax],edx
00442C54 |. 68 6E2C4400 push aLoNg3x_.00442C6E
00442C59 |> 8D45 F4 lea eax,[local.3]
00442C5C |. BA 03000000 mov edx,0x3
00442C61 |. E8 760BFCFF call aLoNg3x_.004037DC
00442C66 \. C3 retn
00442C67 .^ E9 0C06FCFF jmp aLoNg3x_.00403278
00442C6C .^ EB EB jmp short aLoNg3x_.00442C59
00442C6E . 8BC3 mov eax,ebx
00442C70 . 5E pop esi
00442C71 . 5B pop ebx
00442C72 . 8BE5 mov esp,ebp
00442C74 . 5D pop ebp
00442C75 . C3 retn从这个代码里可以看到，在后面有一个和某个字符串对比的call，如果用户名是这个字符串就可以通过了，而这个字符串是上面的循环中根据密码字符串计算得到，因此只要输入的用户名和密码对应就可以了。
到此程序破解完毕，虽然成功了，但是有些地方还是模糊，不能很流畅的去分析程序，需要多接触一些算法，多做题，多实践
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原始发表：2018-08-14，如有侵权请联系 cloudcommunity@tencent.com 删除
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