Hola!

Te recomiendo leer este tutorial.

Saludos!

PD: El OEP sale sencillo! 

Well, I need to practice my english, so:

1) I recommend you to use Olly 1.10 and StrongOD plugin. Also, always tray to unpack using Windows XP SP3 (a Virtual Machine is pretty handy for this).
2) In this case, OEP is at 702742h. To get to the OEP:
 - At the EP (C1F400) put a BPM in the .text section and hit F9. When Olly stops, you'll be at C33C95:
 
If you watch the code, you'll see that the LOOP at 00C33CAB goes to the JMP at 00C33CAF and that JMP goes up. BUT the JMP between both (00C33CAD) goes to the RETN.
Now, Put a BP on that RETN (00C33CB4) and hit F9. When Olly stops, put a BPM in the .text section and hit F9. When Olly stops, you'll be at OEP:


Now you can dump and rebuild IAT with ImpRec. You'll have 4 bad entries in the IAT. The first is ExitProcess (the same as the tutorial).
The other 3 are used by the program to comunicate with the packer. You'll have to wach what happens in each of those 3 (what registers are modified and what is modified in the stack).
In fact, only 2 functions are important. Both MUST return 0 in EAX, but they also return data in the stack, so be careful with that.

And that should be enough to remove the packer...

Cheers!

EDIT:

I forgot to tell you to check all the exceptions, so they are passed to the packer!

Hi MCKSys,

Sorry for bothering you but I have tried to rebuild the IAT but without success. If you don't mind I have some questions.

I did what you said and dumped the unpacked proccess.

Set the Image Base 00400000 and Entry point 00302742.

I am using ImpREC to rebuild the IAT. I am reading some tutorials how to unpack Armadillo manually as this packer removes the IAT and is a good exercise on how to rebuild it from scratch.

I'll describe the steps I am following.

-select the exe process;
-set OEP to 00302742;
-press IAT auto search;
-ImpREC finds the IAT at 003F2000;
-I checked this address(007F2000) in Olly to make sure it is the IAT;

CPU Dump
Address   Value      Comments
007F2000   76EBC55A  ; ADVAPI32.RegDeleteValueA
007F2004   76EA11A8  ; ADVAPI32.RegQueryValueExA
007F2008   76EA1197  ; ADVAPI32.RegOpenKeyExA
007F200C   76EBC527  ; ADVAPI32.RegEnumKeyExA
007F2010   76EBC5D6  ; ADVAPI32.RegEnumValueA
007F2014   76EBD023  ; ADVAPI32.GetFileSecurityA
007F2018   76EE10CE  ; ADVAPI32.SetFileSecurityA
...


Seems to be the IAT. And size (B20) seems to be correct too.

-click Get Imports and Imprec rebuild the IAT;

-click show invalid and as you mentioned I have 4 bad entries in IAT.


CPU Dump
Address   Value      Comments
007F2280   774EC83C  ; KERNEL32.RtlUnwind
007F2284   00C39B1A  -----> 1
007F2288   774EC318  ; KERNEL32.GetModuleHandleExW

007F254C   76E138D5  ; OLEAUT32.VariantClear
007F2550   00000000
007F2554   00C2D3D6  -----> 2
007F2558   00C2C7F0  -----> 3
007F255C   00C2C4BF  -----> 4
007F2560   00000000
007F2564   75C0F9E7  ; SHELL32.SHAppBarMessage

-I set a break point in 007F2284 trying to trace the jump.
-Run the proccess (F9). Doesn't hit the breakpoint.
-I exit the proccess then Olly hits the breakpoint.

The code seems to be using some kind of overlapping instruction obfuscation. Is that right? If that is the case is there a way to fix that? Am I doing something wrong?

CPU Disasm
Address                    Hex dump                     Command                                                    Comments
00C39B17                       00                       DB 00
00C39B18                       00                       DB 00
00C39B19                       00                       DB 00
00C39B1A                       60                       DB 60                                                      ; CHAR '`'  ------->landed here.
00C39B1B                       EB                       DB EB                                                      ; CHAR 'ë'
00C39B1C                       01                       DB 01
00C39B1D                       E3                       DB E3                                                      ; CHAR 'ã'
00C39B1E                       EB                       DB EB                                                      ; CHAR 'ë'
00C39B1F                       01                       DB 01
00C39B20                       D4                       DB D4                                                      ; CHAR 'Ô'
00C39B21                       E8                       DB E8                                                      ; CHAR 'è'
00C39B22                       00                       DB 00
00C39B23                       00                       DB 00
00C39B24                       00                       DB 00
00C39B25                       00                       DB 00

I appreciate any help.  

Cheers,

PS:I forgot to mention that first I tried to cut and delete the invalid thunks just to check if the process would execute but it crashes...

Hi MCKSys,

Yes I knew that the first one was the ExitProccess I was just trying to figure out that by myself. I was trying to learn something from that.  Actually I don't need to patch that program I am just doing it for "fun" and learning purposes...

How do you know the first was the ExitProccess? I was trying to figure it out analysing the code and finding the jump to the ExitProccess but as you said it is all obfuscated...

Anyway I'll try to fix the 3rd and 4th calls and maybe bring some more questions. lol


Cheers mate,