+HCU's special Project: 'Our protections'

by +RCG

(slightly edited by reverser+, 18 January 1998)
Courtesy of reverser's page of reverse engineering
The following essay by our +colleague and "Uberprotector" +RCG is VERY interesting for many aspects, it deals for instance with the "delayed" protection scheme, that we have already discussed in the "programmer corner" section, a "delayed" revenge which is already implemented in some very recent protection schemes, but I'm sure that the whole part about "How to take Softice on a boat ride" will indeed prove to be a very interesting reversing reading for all our protectors and crackers friends.
In fact the idea of COUPLING softice detection and self-patching promises to deliver us very ineteresting challenges in the future :-)

HOW TO PROTECT BETTER ~ Part II Purpose of the "Our protection" section The "delayed" protection scheme of the future The Port 70/71 trick How to take Softice on a boat ride Softice breakpoint magic explained and defeated by +RCG 18 January 1998

Hi all!!!! I see that my "heavy" protection has been severely criticised... I know that an encrpytion xoring values is pretty stupid... but in my opinion the idea behind this section is to introduce and implement new ideas, and not really to create a whole uncrackable program, which as we all know is impossible anyway. I believe that we will very soon be confronted with much tougher protection schemes, because the programmers and the protectionists ARE learning assembly, notwithstanding the widespread belief of the countrary. I have been thinking about all this and I have concluded that the best solution is to use the VxD to perform only critical actions. That is, let the program, usually written in an "higher" language create the more or less complex encription algorithms that you need in order to protect and THEN use the VxD to move the decripted function to its place. Do you agree with me that this would be a much better solution? Yes, my previous protections have been quickly defeated, yet you must think that these programs of mine are only "probes": they are very very short programs, and their protection schemes are not hidden at all, quite the contrary actually: they are in front of you. Actually you should only examine the idea that I have implemented and find solutions or problems for the scheme. I'm sure that the perfect protection doesn't exist, it's like the final weapon... a very clever protection to-day will be very easy to defeat to-morrow. But we can do nevertheless our best: we can for instance use two or three protection schemes at the same time, for example, 1) encryption with 2) antiSoftice tricks, and 3) some other things we have already seen on this page. Imagine all these schemes bundled together with a little intelligence into an ovebloated multimega huge program! That will cause an headache to most crackers, even if it will be -maybe- easily solved, by real "zen" +crackers. Indeed, most of today "key" protection schemes are very easy to crack because the programmer thinks that a simple check is more that enough, which is stupid to say the least. Think for example that mostly we only have to patch a conditional jne with a 'compelled' jmp, and the program thinks that it is registered. Moment: thinks that it is registered... or let us think that he thinks that it is registered? :-) Yes! Now suppose you are using your "cracked" program and suddenly it crashes, or does not let you make something... say a couple of days AFTER your supposedly easy crack... It's very difficult follow this kind of "delayed" protection tracing or dead listing your target. Where, inside the whole program is this kind of protection implemented? Think: imagine that somewhere in the middle of the normal execution code the target performs a check. You don't perceive it at all, because there is NO NEED to alert the user about this verifying. And then, imagine, the target patches some code on the fly or checks for code modifications... man, I understand now what +ORC always teached us with his "be careful not to nop with nops" doctrine... he foresaw the development of our protections TWO YEARS ago... but the protectionists probably never read his tutorial and I have until now still to see a target checking for our nops instead of having a simple CRC-type check :-( But you get the idea, don't you? You will never understand what happened because that code, patched by the target can be itself encrypted. I don't agree with colleagues that say that this protection way is just like all the others. This kind of tricks, if implemented, would let us make much more other things, and at the very least would for sure prevent the "30 seconds" cracking. OUR VXD. LETS BEGIN AGAIN Basical Functions. 1. Blitter (block memory transfer) 2. Port IO 3. SoftIce remover 4. Device_Service_Hooker 5. Int_Hooker 6. Api_Hooker 7. GP_hooker (General Protection Exception) and more... Comments about the implementation of these functions.
1. Blitter (block memory transfer). Not much to speak about. Very easy to program.
2. Port IO Yes, no more GetLocalTime function, now we can use Ports 70h and 71h. Cinderella-type protections will be not stupid and easy to defeat as they are now. SoftIce bpio has no effect wjatsoever if we read directly the port.
3. SoftIce remover I will show you a little trick to remove SoftIce from memory or to let it 'out of the game' during the execution of our program. How does Ice pops up? Either by a breakpoint or by Ctrl+D. (This is top secret info :-) If you dead list winice.exe, searching for the string "breakpoint" you will find the string 'No more breakpoint available'. Let's have a look at the surrounding code: :2E258 push ebx :2E259 push ecx :2E25A mov ecx, 000000FF ;256 breakps. max. :2E25F mov eax, 00000000 :2E264 cmp byte ptr [eax+4], 00 :2E26B je 0002E277 :2E26D add eax, 00000183 ;Every bp block is 183h bytes. :2E272 loop 0002E264 ;try next :2E274 stc ;Ret Error :2E275 jmp 0002E29F ;'No more breakps. aval.' :2E277 lea ebx, dword ptr [eax+0] ;ebx = 1st byte of block :2E27D call 0002E237 <== Is block corrupted? :2E282 jb 0002E29F <="=" Error return :2E284 push eax <="=" Next breakp. free pointer :2E285 push edi :2E286 mov ecx, 00000183 <="=" Clear 183h bytes area :2E28B sub ecx, 00000004 <="=" But no the 'TDJF' :2E28E sub ecx, 00000004 <="=" But no the 'TDJF' :2E291 lea edi, dword ptr [ebx+04] :2E294 xor al, al :2E296 repz :2E297 stosb :2E298 pop edi :2E299 pop eax :2E29A mov [ebx+05], 01 :2E29E clc <="=" Ret Success :2E29F pop ecx :2E2A0 pop ebx :2E2A1 ret Most rewarding and interesting! Every breakpoint block has a "structure" in order to check the conditions or the kind of breakpoint. Every block is a 183h byte structure like this: 0123456789ABCDEF TDJF???????????? . . .??????????????T DJF The 4th byte is the breakpoint type: 0>Free (this is the trick) 1=>bpint 2=>bpio 3=>bpm 4=>bpr 5=>bpx 6=>bmsg That's enough, as you'll see, to nuke the breakpoints, and now, lets snap (and shut) the Ctrl+D entrance too SoftIce sets its default Ctrl+D hotkey using the keyboard service Define_Hot_Key mov al, ScanCode mov ah, type mov ebx, ShiftState mov cl, flag mov esi, OFFSET32 HotKeyProc mov edx, OFFSET32 refdata mov edi, max_delay VxDcall VKD_Define_Hot_Key jc errorhandler BTW, if you try to define the same hotkey you will see that it has no effect (because softice prevents it). And the HotKeyProc is: 3392 mov ds:byte_66CD, 0 ;Active flag 3399 mov esi, offset loc_66CF+1 ;Offset of scancodes 339E mov eax, 400h 33A3 cmp ds:byte_66CE, 1Dh ;keyboard type 33AA jz short loc_33B6 33AC mov esi, offset loc_66D1+1 ;Offset of scancodes 33B1 mov eax, 800h 33B6 test eax, ecx 33B8 mov ecx, 1 ;1 scancode 33BD jz short loc_33C3 33BF inc ecx ;2 scancodes 33C0 dec esi 33C1 jmp short $+2 33C3 VxDcall VKD_Force_Keys VxDcall VKD_Force_Key mov esi, OFFSET32 ScanCodes mov ecx, num_ScanCodes VxDcall VKD_Force_Keys jc errorhandler If you write on the memory any value over "1D" and if you also remove all the breakpoints by putting zero on the 4th block byte (=free breakpoint), SoftIce will not pop up (unless a GPF happens). 1D identifies the keyboard type, and the scancodes needed to pop up, you also can modify the code in order to force other scancodes that will left the stupid cracker without its Ctrl+D (most stupid crackers wont even understand why softice doesn't snap any more. Notice that if your program detects 1) the presence of a softice session and 2) some modifications of its own code you can be 99% sure that you are running inside a cracker's machine :-) This may give some 'revenge' idea to the clever protectionists :-)
4. Device_Service_Hooker You can find the complete Service ID on the VxDMon file. When programming at Hook_Service the following is pretty important: ;Data area Real_Proc dd 0 ;Code Area Public VXD_Device_Exit BeginProc VXD_Device_Exit mov eax,Service mov esi,offset32 OurServiceFunct VMMcall Unhook_Device_Service clc ret EndProc VXD_Device_Exit BeginProc OurServiceFunct, Hook_Proc Real_Proc <== Don't forget that this is necesary to remove the hook on exit. Do something jmp dword ptr [Real_Proc] EndProc OurServiceFunct VXD_LOCKED_CODE_ENDS VXD_ICODE_SEG BeginProc VXD_Device_Init mov eax,Service mov esi,offset32 OurServiceFunct VMMcall Hook_Device_Service jc not_installed mov [Real_Proc],esi clc ret not_installed: stc ret EndProc VXD_Device_Init
5. Int_Hooker 6. Api_Hooker For points 5 and 6, please see my other examples
7. GP_hooker (General Protection Exception) Another +Hcuker is working on it (Good Luck _m)
rcg__@latinmail.com +rcg
(c) +RCG All rights reserved
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