What would be the best way to protect a file from being disassembled, or from getting the source from the PE file? Is there a way to encode the file so it would be really difficult or impossible?
Posted on 2000-12-15 14:41:00 by dork
It's impossible to encode a file some way that it could never be disassembled... you could toughen it up by packing it (ex:Aspack.com) but this won't prevent unpacking it tho :( There are some common anti-disassembler tricks but these are quickly anhilated too... btw: how do you get the source from an pe-file?
Posted on 2000-12-15 16:05:00 by JimmyClif
try encrypting the file an decrypting in run-time , if you dissasembled the file you will se the decryption routine and encrypted program ... include also some anti-emulation/debuggin rotines to fuck up the emulators/unpackers/tracers ... it is impossible a 'perfect protection' but you can make it harder ;). search for more tricks on the net.
Posted on 2000-12-15 18:05:00 by unknow
I know ASPack is eaisly decoded, does anyone have any expirence or know how to protect against disassembly? Is there any software or websites that would help?
Posted on 2000-12-15 18:58:00 by dork
Yah what are some of the common tricks used? Like a high percentage of disassembled programs are disassembled by newbie wanna-be hackers, who don't know much. And anyone with the experience to do anything real won't want to hack my programs anyhow so the basics should be fine. I've heard some things, like using a hew editor to put illegal values in the resource area of the exe so resource editors can't get it. I've also heard of putting illegal instruction codes in places on purpose which you jump over but the average newbie won't figure out. Or an invalid opcode. Does anyone have any advice? Even the simplest most easy stuff? Thanks, Ben
Posted on 2000-12-15 23:16:00 by cyberben
i have been cracking for over a year an yea only wanna-be's will want to attack somthing really easy. I'll i have to say is if you want to learn to crack and just solve crack me's to get an idea of cool pertections. the best crackme site i can find is http://crackmes.cjb.net/ nothing better than using what you learned. hope it helps -rage9
Posted on 2000-12-16 14:39:00 by rage9
Futur belongs to open sources. The best way to preserve your marvelous work from others sight is to keep it for yourself only and publish nothing at all. betov.
Posted on 2000-12-17 15:04:00 by Betov
Ehm... I announced the anti-disassembler tricks but forgot to provide the link (*DOH*) Here it is: http://www.woodmann.com/fravia/snatfo.htm Of course... have a look around here too :) : http://www.woodmann.com/fravia/protecti.htm JimmyC
Posted on 2000-12-17 15:37:00 by JimmyClif
With PE files, a memory dump will beat most packers/crypters, it is useful to get the PE header directly from the PE file on disk as it can easily be changed once the file is loaded. Most anti disassembly tricks get beaten over time so all you buy is a little time, PE files are understood very well these days so there is not much that cannot be done with them. Anakin has a novel PE cryptor on Kaparo's tools site which encrypts the import table so a memory dump does not get the imports but it gets the rest. It really depends on how much work you want to do and how much time you want to buy but most will be broken by someone who knows what they are doing. Regards, hutch@pbq.com.au
Posted on 2000-12-18 04:48:00 by hutch--
You could have self-modifying code. One anti-cracker technique I thought was neat came from the DOS era... For example, you could have int 13h (in hex it would be: CD 13) You could do something like change the 13 to some other number like 21. Then, once your program runs, it could replace that one modified byte with 13! In the world of Win32, you could do similar stuff. One trick I thought of (but never tried) is to mess with the indirect calls. For example, you could import a bunch of DLL functions. One line of code could be: CALL You could change the address refered to by that CALL to point to some other DLL function import. Then, when viewed under a disassembler/debugger, it would appear to be: CALL I wonder if anybody's actually tried this trick before. If your program is infested with tons of code that are modified in this fashion, it could make it pretty hard for an impatient newbie cracker to deal with. --------------------------- Team2k PC development team: http://ppilot.homepage.com
Posted on 2000-12-20 03:23:00 by Al Leitch
I agree with the last post -- SMC is a good strategy. Disassemblers like IDA can't cope with SMC. They'll just replace the old asm instructions with the new ones corresponding to the new code, the old code having been overwritten. As a result, the asm listing will omit all information not contained in the latest "go". Make your code section(s) writable and use a block of code that you overwrite many many times. Calls to system dll functions are unrestricted, but make sure that the current block doesn't call any of your own routines that are not already resident in the block. In practice, this means writing in-line code where possible. Also, you wouldn't want to split For or While loops etc. between blocks (too inefficient, you might have to reload code back and forth hundreds of times). What I do is analyze my own asm code to package the crucial parts into self-contained blocks. When one block has executed, it is overwritten in place by the next block (possibly of a different size). This analysis can be tricky, requires some modification of the code, and has to be done by hand (there's no straightforward way to automate it), but it becomes easier if you appropriately adjust your coding practices.
Posted on 2000-12-20 12:00:00 by A Mason
mmh, i tryed to do something like a exucutable that encrypts itself everytime it it started with a different encryption key. at the first run it decrypts itself with xor_code 0 so you could paste your code without any problems, then it will increment the xor key after every start with 8. i still stuck on writing to the running exe and i have no clue why this could be prohibited in windows... whatever, the second problem is to relocate the writing address, i think you can do this with the help of the innstruction pointer but i don't know exactly. if someone could tell me how to gain write access to the running executable i would be very lucky (in dos this was possible without any problems because the data is transfered into mem at start...)
.DATA dummy db 0 old dd PAGE_EXECUTE .DATA? thisfile db 300 dup (?) filehandle dd ? written dd ? .CODE start: call real_prog real_prog proc pop esi ;current ip lea eax,end_of_code sub eax,offset start invoke VirtualProtect,addr start,eax,PAGE_EXECUTE_READWRITE,addr old return: lea edi,start_of_code lea ecx,end_of_code sub ecx,edi mov al,xor_key decrypt: xor byte ptr ,al inc edi loop decrypt cmp dummy,1 jz exit jmp start_of_code xor_key db 0 start_of_code: ;----------------------- ;REAL code goes here... mov dummy,1 add xor_key,8 jmp return end_of_code: ;----------------------- invoke GetModuleFileName,NULL,addr thisfile,SIZEOF thisfile invoke CreateFile,addr thisfile,GENERIC_WRITE,0,NULL,OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL,NULL cmp eax,INVALID_HANDLE_VALUE jz exit mov filehandle,eax invoke SetFilePointer,filehandle,0441h,NULL,FILE_BEGIN ;don't know if 0441h is right i used a hexeditor for this ;maybe esi should come into the game here lea eax,end_of_code sub eax,offset xor_key invoke WriteFile,filehandle,offset xor_key,eax,addr written,NULL invoke CloseHandle,filehandle exit: invoke ExitProcess,NULL real_prog endp END start
Posted on 2001-01-05 12:52:00 by drcmda
Another anti-dissasemling trick is to 'hide' your instruction code inside other opcodes i.e jmp @F BYTE 43 @@: mov eax,Offset MemVar Dissasmbly: 00401000 EB01 jmp loc_00401003 00401002 2BB800204000 sub edi, It is intresting and it works. Of course any half awake person would notice the jump to the middle of the instruction stream so a better implication would be nesscery or it would be noticed 'to' easy. This combined with a good encyption of the code section will make things more difficult. But you have to remember, the only real protection against cracking, dissambling, whatever....is to take the only copy of your app, and burn the computer it resides on, simple as.
Posted on 2001-01-05 23:30:00 by 870621345
a nifty little trick to add to SMC is to use the "unused" (in .EXE files atleast) .reloc section for thedecryption routine...;) kinda like encrypting your .reloc section win 0x123456-0x4000000 (or whatever) then changing you base adress in the header to 123456 umm here's the article i found about it... virus related but usefule..;) Encryptation through relocs Until now relocs section (.reloc) has been very useful (curiously by useless) for virus coders. Why? Virus coders overwrite it to hide an increase of size after the infection. Nothing to worry because when Windows loads an executable it gives a new virtual address space and it will be loaded into the base address indicated in his header and it's not necessary to apply the relocs. That's the reason why by default some compilers don't include the .reloc section except if you tell the contrary. Of course, it doesn't happen the same with DLLs since it's more common they have their base already busy (at least it's already loaded the executable and usually there will be other DLLs) then it will must to be loaded into other base address and applied new relocs based in the new base. Let's see what happens when a module is loaded into another different base of the indicated in the header and it's needed to apply relocs; each entry in the relocs table point to the addresses of the module that are needed to be reseted. To the content of each of these addresses is subtracted the indicated base in the header (since it's already reseted respect to that base) and it's added the base where it has been loaded really. Other fact we will use is that if to an executable we put a base where we know it will not be loaded, Windows by default tries to load it at 0x400000. Taking care of all these, we are going to get encrypted a virus and the own Windows will decrypt it, i mean, it will not be needed any decryption routine. First, we need the host having his base at 0x400000 and we need to null his relocs (if it has any). Now we change the base to the executable for one we know Windows will not accept, per example we take 0x12345678. With this we will get Windows loading the executable at 0x400000 and applying the relocs; It's due to that we have nulled the relocs of the host since finally it's being loaded his choosed base. Now we create a new .reloc section pointing each DWORD from the body of the virus and we encrypt every DWORD of the virus in the next way: DWORD virus + 0x12345678 - 0x400000 We do that since when Windows loads the executable at 0x400000 what it will do will be subtract the header of the base (0x12345678) and add the real base (0x400000). This way: (virus + 0x12345678 - 0x400000) - 0x12345678 + 0x400000 = virus; We've gotten Windows finally decrypting our virus and then it's different to how it was in disk without execute any instruction (it's only needed whereupon it has been loaded into a debugger per example :-) In NT there are limitations to the use of this method since it doesn't want to load the executable if it finds a strange base (i believe it must to be multiple of 64KB). Tcp/29A
Posted on 2001-01-06 23:47:00 by NervGaz