razzia's tutorial for crippled programs
(The beautiful creation of the "RazziaPad")

by razzia

(19 August 1997)


Courtesy of Reverser's page of reverse engineering

Well, once more I'm amazed: Razzia's essays are always outstanding, but this one will make history in the scene: he's showing us with a very easy to follow example the road to the most sublime advanced cracking that you can dream of: ADDING functionality to ANY target you fancy... that's exactly what our aim should always be: they speak (falsely) of "object" oriented programming, as if the toy languages they use could really be used to integrate smoothly completely different compiled code (try to integrate visualbasic with visual c++ and you'll see what I mean) and Razzia throw them all possible eggs in the face DEMONSTRATING here, under your privileged eyes, dear readers of my page, how (relatively) easy it is to do such "novelties" and "modernities" using good old "obsolete" assembly.
I have no words: Razzia is a great cracker (as if we did not know it already) he may join the +HCU anytime he wishes, I'm sure +ORC would love this essay (hope you are reading this from wherever you are now, Master!).

So, once more, READ this essay, by all means, HEAD what Razzia teaches and try this out on other targets until you master this. Here you'll go, right now, from "dilettante" to "advanced" crackers, here and now!



razzia's tutorial for crippled programs
Introduction I think every cracker knows the feeling when you download a program and it turns out to be crippleware. We feel disappointed because we didn't even get a fair chance in the fight. But in this tutorial i want to show you that the fight doesnt necessarily have to end there. There is a good chance we can add the missing code to the program. It will not be easy, and a good deal of knowledge about windows is needed, but the satisfaction of a crack will in such cases be greater. Tools and References Before you start an operation like this you will need to know how windows programs work, and how windows exe files are construc- ted. You will need to study the following documents : - http://www.microsoft.com/win32dev/base/pefile.htm A document about the structure of the PE header (Win32 files are called PE files). - Vlad magazine #6 This virus magazine explains in this issue how they made the first win95 virus called Bizatch, souce code is included. This issue also has another document about the PE header. In the past this document was included in the microsoft win32 SDK package. But somehow (!) microsoft stopped doing that. - Reverser's tutorials about Taskman and Filemon This will give you a good understanding about how windows programs look when they have been compiled to assembly. - Wap32 example that comes with Tasm 5. This example will show you how to make win32 programs in assembly. This program is also used as the host for Bizatch, so you will find its source also in Vlad #6. - A windows programming book The tools i have used in this case are Softice 3.0, Tasm 5, Hiew 5.65, IDA PRO 3.6 and pedump (19585 bytes). A few words about Win32 programs Every win95 executable file consists of 2 parts : the PE header and the sections. The PE header contains all kind of information for the os about how to threat this file. The sections are grouped by their functionality. For example there is one section for the programs code, one for its data, one with its resources, one with the table of imported functions and a few more. Now, what happens when win95 loads a program is this: First an environment is created for the program where it gets its own virtual address-space. Then win95 has to decide where in this virtual address-space it should place the program. That information is avail- able in the PE header. The PE header contains the desired imagebase of the program, this is the adress the program wants to be loaded at. Then windows takes all the sections and places them in memory beginning at the imagebase (default imagebase is 400000h). Where exactly it places the sections is also stated in the PE header. Every section has its own so called RVA (Relative Virtual Address). This is just an offset relative to the imagebase. Once the sections are in memory, windows has to know how to threat those sections. It has to know which section contains a stucture with the resources, which one has the scructure of the import table etc. That is also stated in the PE header with RVA's to the beginning of the various so called data directories. Then finally windows has to jump to the programs code. This entrypoint is in the PE header as the entrypoint RVA. The above words about the PE header is not meant as a replacement for the PE document i mentioned at the beginning of this tutorial. I would recommend to every (win32) cracker to study the PE header thoroughly. It will give you a much better understanding of win95 programs. Our target : Notepad I dont program much, but when i do they are small programs most of the time, ie keygens, patches. To edit my code i like to use Note- pad. But one disadventage of Notepad is that it doesn't show linenumbers. So when the compiler gives an error with linenumber, i have to load another editor to find the line with the error. Therefore it would be nice if i could add some code that shows me the current line of the cursor. The reason i chose Notepad as an example in this tutorial is that it is small and simple. So its perfect for learning purposes. I dont know if Notepad.exe is the same on every version of win95, the one i have is 35.328 bytes long. Strategy Well, its time now to think about the 'crack'. We want to add some code to a program and want that code to interact with the existing code. We can do it in two steps. First we have to find out what code we are gonna add. Then we will have to append this code to the file and patch the file at some places so it will jump to the new code at the right times. Part 1 : find out what code we need In order to find out what code we have to add we will need to do some investigation on the target program. The 'heart' of every windows program is its WndProc procedure. This procedure is called by windows everytime the user has interacted with the programs window. Windows passes to this procedure a few variables, like a windows message, so that WndProc knows what happened and can perform what needs to be done to keep the window updated. In the case of notepad the main program generates a childwindow of the 'edit' class (to get more information about this class check your windows programming books).The edit childwindow gets the size of the mainwindow all the time. In order to print our own text to the mainwindow we will have to reduce the size of the 'edit' childwindow so it wont cover the complete mainwindow area. Everytime the user changes the size of the mainwindow, windows calls the WndProc functions with the WM_SIZE message. The WndProc procedure then can react to this event, ie adjust the size of the 'edit' childwindow to the new size of the mainwindow. Lets locate this WndProc procedure and see how it handles the WM_SIZE message. You can do that either with Softice or IDA. Lets chose the more relaxed way, and do it with IDA. Run IDA and load Notepad.exe. There are a lot of ways to get to WndProc procedure, but the easiest way is via the RegisterClass function. You see, at the beginning of every windows-program the main window is 'registered' to windows. The parameter to RegisterClass is a variable of WNDCLASS, which contains a pointer to the WndProc function (check your winAPI reference). So, press control-l in IDA and press return on the RegisterClassExA function (notepad uses this variation of RegisterClass). IDA will show you: 00402B16 lea eax, [ebp-30h] 00402B19 mov dword ptr [ebp-08h], offset aNotepad 00402B20 mov dword ptr [ebp-28h], offset loc_401AAD ;<- WndProc ! 00402B27 mov dword ptr [ebp-10h], 6 00402B2E mov dword ptr [ebp-2Ch], 1000h 00402B35 push eax 00402B36 mov [ebp-24h], edi 00402B39 mov [ebp-20h], edi 00402B3C call ds:RegisterClassExA Easily we see that loc_401AAD is the location of the WndProc proce- dure. At loc_401AAD IDA shows : 00401AAD loc_401ADD: ;WndProc 00401AAD push ebp 00401AAE mov ebp, esp 00401AB0 push esi 00401AB1 push edi 00401AB2 mov esi, [ebp+0Ch] 00401AB5 cmp esi, 5 ;beware that WM_SIZE = 5 00401AB8 ja short loc_401ACE 00401ABA jz loc_401BC6 ;jump here for WM_SIZE 00401AC0 cmp esi, 2 00401AC3 jz loc_401BB9 00401AC9 jmp loc_401B51 We see that here the program checks to see which message it is dealing with and branches accordingly. To find out which value corresponds to WM_SIZE you can look it up in the header files that come with a win32 c++ compiler (there is a free one at www.cygnus.com)'or you can do '? wm_size' in softice,
or you can download right now winuser.h from the Watcom C/C++ (version 11) package... the compiler you should buy, btw... courtesy of reverser :-)


  We also see that for a WM_SIZE msg the program branches to


loc_401BC6. If you examine the code at that location you will see a 


call to this procedure:





0040113F sub_40113F	 proc near		


0040113F	 push	 1


00401141	 mov	 eax, ds:dword_406004


00401146	 push	 0


00401148	 push	 eax


00401149	 call	 ds:InvalidateRect


0040114F	 push	 1


00401151	 mov	 eax, ds:dword_406004


00401156	 push	 dword ptr [esp+0Ch]  ;Height


0040115A	 push	 dword ptr [esp+0Ch]  ;Width


0040115E	 push	 0


00401160	 push	 0


00401162	 push	 eax                  ;handle of 'edit' win


00401163	 call	 ds:MoveWindow        ;Update size of 'edit' win


00401169	 retn	 8


00401169 sub_40113F	 endp





  Note that the handle of the 'edit' child window is apparently stored


in (virtual) address 406004.


  We also see that for every WM_SIZE message the 'edit' childwindow gets 


updated with a call to MoveWindow with the new size of the mainwindow.


But we dont want the edit childwindow to be the full size of the 


mainwindow. 


  In order to get a smaller heigth  we have to place a jump to our


own code at the line with (virtual) adress 00401156. Such a jump takes


5 bytes, so our return adress will have to be 0040115E. For the code


that gets overwritten we will make up in our code. 





  Own our code will look like :


      


Own_Code_1:            


      sub    esp,8	


      push   ebx                      ;Save ebx temporarily





      mov    ebx,[esp+0Ch+4]          ;Get heigth


      sub    ebx,20                   ;Substract 20                  


      mov    [esp+4+4],ebx            ;Push heigth


             


      mov    dwHeight,ebx             ;Save Height





      mov    ebx,[esp+0Ch]            ;Get width


      mov    [esp+4],ebx              ;Push width 


	      	


      pop    ebx                      ;Restore ebx	                                    


      jmp    0040115E                 ;Return to where we left       


      dwHeigth      dd    0 


              


  One note here is appropiate. We save the Height because we will need 


this value in the printing part of our code, as you will see if you


continue reading my essay.





  Ok, one down, one more to go (as you will see). We want to print 


some text on the mainwindow. Everytime a window needs to get 


'repainted', for example when another window overlapped it or when 


the user changed the windows size, windows will call the WndProc


procedure with WM_PAINT. This means we have to 'trap' the WM_PAINT


msg in the WndProc function and make a jump to our own routine, the


one that prints text. 


  We will also need to print every time the vertical position 


of the cursor has changed. The easiest way to do that is by ignoring 


all the possible messages that inform about a change in the cursor


position, and instead compare the new cursor position with the old


one.


  If you examine the WndProc code you will see it doesnt do anything 


with the WM_PAINT message. So, at the beginning of the WndProc procedure


we have to insert a jump to our own code.


   


  The beginning of WndProc procedure looked like this:





00401AAD loc_401ADD:			    ;WndProc	 


00401AAD	 push	 ebp


00401AAE	 mov	 ebp, esp


00401AB0	 push	 esi		    ;<- good place for jump


00401AB1	 push	 edi


00401AB2	 mov	 esi, [ebp+0Ch]     


00401AB5	 cmp	 esi, 5         ;<- return here


00401AB8	 ja	 short loc_401ACE


00401ABA	 jz	 loc_401BC6         


00401AC0	 cmp	 esi, 2


00401AC3	 jz	 loc_401BB9


00401AC9	 jmp	 loc_401B51





 


  A nice place to put the jump to our code for processing WM_PAINT


will be at the line with (virtual) adress 00401AB0. And again, the 


jumping code occupies 5 bytes, so it will return at adress 00401AB5. 


 


  Our own code for the WM_PAINT msg will look like this :   





Our_Code_2:


      push    esi


      push    edi


      mov     esi, [ebp+0Ch]      ; Esi contains current message now


     


      push    0


      push    -1


      push    EM_LINEFROMCHAR 


      push    [406004]            ; (Handle of 'edit' child win)


      call    SendMessageA        ; After this call EAX will have 


                                  ; the y position of cursor





      cmp     eax,dwLine          ; Has cursor pos changed ?


      jnz     update_line_num     ; If yes, print the new line num      





      cmp     esi,0Fh             ; Is the current msg a WM_PAINT ?


      jnz     no_update_needed    ; If no , return to WndProc





update_line_num:


      mov     dwLine,eax          ; Save new y position of cursor


            


      inc     eax


      push    eax


      push    offset  szFormat


      push    offset  sLineNumber  


      call    wsprintfA           ; Convert number to ascii


 


      push    [406000h]           ; (Handle of main window)


      call    GetDC               ; Get the device context





      mov     theDC,eax           ; Save dc      





      push    0


      push    0


      push    0


      push    14


      push    sLineNumber


      push    0


      push    [dwHeigth]


      push    [theDC]


      call    TabbedTextOut      ; Print the text





      push    [theDC]


      push    [406000h]          ; (Handle of main window)


      call    ReleaseDC          ; Release the DC





no_update_needed:


      mov     esi, [ebp+0Ch]      


      jmp     0401AB5h           ; Return to WndProc      





      dwLine	    dd 0


      szFormat      db '%#05d',0


      sLineNumText  db '  line : '	


      sLineNumber   db  6 dup (?)


      theDC         dd  0      





  A few notes about the above code. First of all i used only api functions


that were already imported by Notepad.exe (check its import table). 


What if the API's functions we need were not in the import table? 


I will explain at the end of this tutorial how to solve this problem.


  Secondly, some functions need the handle of the main window as a 


parameter. You can find its (virtual) address with IDA if you look


where notepad stores it after the first call to CreateWindowExA.


  Finally, this code is not final. Consider it as a sketch, or a blueprint. 


Some minor, but very important, changes will be necessary.








                   Part 2 : Appending our code








  Now we are ready to start thinking about adding our code to 


notepad.exe. Our main concern will be to make code that is not 


dependant on the memory location it get placed. This is because our


code gets compiled independently of the notepad code. Therefore our


instuctions with addresses will not get relocated by the win32 loader.





  Lets start from the beginning and deal with the problems as they


occur on our path.


   


  The first question to deal with is where should we place our 


code inside the target. The easiest way is to append our code to the 


last section of notepad.exe. 


Let's examine the header of the last section, which happens to be 


the .reloc section.





  At the dos prompt type 'pedump notepad.exe > out.txt'. If you have 


downloaded pedump, this will make a file with the header information 


of notepad.





  The last section header shows :


           


06 .reloc    VirtSize: 0000091E      VirtAddr:  0000B000


      raw data offs:   00008000  raw data size: 00000A00


      relocation offs: 00000000  relocations:   00000000


      line # offs:     00000000  line #'s:      00000000


      characteristics: 42000040


      INITIALIZED_DATA  MEM_DISCARDABLE  MEM_READ


  


  We see that there is a space of A00h-91Eh = E2h bytes left in the


section. For me this was not enough, mainly because i am a bad coder 


and produce too big code. So, first thing that should be done is to 


increase the size of this section. I increased both Virtual Size and


raw data size to B00h.


  Our code needs also to write to its variables, so another thing we


have to do with this section is to add a MEM_WRITE property to its


flags.  


  An easy way to find the file-offsets of the places we want to change


is to load notepad.exe with Hiew. You will find the header easily 


because the first 8 bytes contain its name, ".reloc" in this case.





  This section header tells us also what the RVA of our code is going


to be. The RVA of the section itself is B000h , it has 91eh bytes, so 


that means the RVA of our code will be B91Eh. (As a reminder, a RVA 


is just an offset/distance to the image base)    


  This knowledge is needed for the jumps from notepad to our code and


vice versa. Knowing that in 32 bit programs all jumps get compiled to


relative jumps (opcode is E9), we can compile those jumps (total of 4)


in tasm with :


   


	jmp $+ (RVA_of_destination_code - RVA_of_current_instruction)    





  For example, we needed a jump from 00401156 to Our_code_1. 


We know the RVA of Our_code_1 is B91Eh. So we can produce the opcode


for this jump with : jmp $+(B91Eh - 1156h) . 





   Another point of concern is that our code makes use of 'local' 


variables, like "mov   dwHeigth,ebx". In order to be able to 


read/write to variables without needing relocation we can use the


same old good trick that all exe-protectors and virii have been 


using until today :


  


	call next_instruction


  next_instruction:  


	pop ebp


	sub ebp, offset next_instruction  ;ebp has now 'delta' offset


  


        mov [ebp + offset dwHeigth], ebx





  This code is independent from the memory location it gets placed at.





  There is just one more thing left to take cafe of : the calls to


the api functions. If you examine with Hiew the calls to api's from 


the original code of notepad, you will see that in reality they have


the form : 


         


	call [address_of_a_dword_var]





  So, they are infact indirect calls trough a dword variable which


contains the address of the api function in question.


  Win95 uses this method of calling api's because in this way it  


needs to put the address of the relevant api function at only one 


place. 


  So, for us to make use of an api function we need to find out the 


RVA of the dword variable that contains the address of the api


function we want to use. 


  This can be done by examining the operand of the inscruction in Hiew.


For example for a SendMessageA call Hiew shows :





	FF1554744000		call   SendMessageA ;USER32.dll





  Which in reality is 


  


	FF1554744000		call   [00407454]





  So, the RVA of this variable is 7454. To calculate the address of 


this variable in memory you still have to calculate the image base, 


which is : EIP_At_start_of_own_code - B91Eh. Then the address of the 


variable is ofcourse : image base + RVA.





  In practice : 





Our_code_1:                                ; <-- RVA = B91Eh  


  ...


  ...


	call next_instruction


next_instruction:  


	pop ebp


	sub ebp, offset next_instruction   ; ebp has now 'delta' offset


   ...  


   ...


        mov eax,ebp


        


        add eax,  offset Our_code_1        ; <-- EAX has now  the


                                           ;  the EIP at Our_code_1





        sub eax, B91eH                     ; <-- EAX has image base        





        add eax, 7454h                     ; <-- [EAX] has now the


                                           ;  address of SendMessageA 





        call [eax] 			   ; call SendMessageA	





  The same method can be used to address variables of the original


code of notepad, like the variable with (virtual) address 406000h that


contained the handle of the main window. 


  


 The complete source to patch notepad.exe and add the extra code 


is included with this tutorial. Also is included is the notepad.exe


that i have.
DOWNLOAD EVERYTHING razzia.zip HERE!
 


                        Final notes





 


  We have seen that we can add any code we want to any win32 


program. 


The question now is how we can know what code we have add to a 


crippled program ?





  Sometimes it is obvious. For example when we are dealing with a 


save disabled program and the file it should generate is a text file. 


If the output file is not a text file, it can be helpful to check


the Swag file format encyclopedia.


(available at http://www.gdsoft.com/swag/swag.html).


 


  Sometimes examining old versions of a program can help. Or examining 


'lite' versions of programs which are not crippled. 


  Also examining the load function can be helpful.





  Another question is what should we do if we need to use api functions 


which are not imported by our target. 


  The easiest solution to that is just to replace 2 entries in the 


import table with the kernel32 functions GetModuleHandle and 


GetProcAdress. With those two functions you can get the address of 


every function you fancy.


  If you also change the entry point RVA to let it point at some code 


that you have added, which will put the addresses of the two original 


functions at the places they were supposed to get, then there will be no


problem.


 


                         The Greetings





   I would like to take advantage of this oppurtunity and thank the


following persons for everything they thought me in the past :


 


  THE_OWL, rANDOM, aCP, madmax, lost_soul and xygorf.     


       


  Also i would like to greet the wonderfull ppl in #cracking,


#cracking4newbies and #Pc97 :


 


  Psychotrn, lordbyte, j0b, ThePharao, musashi, sharp, mailman, dwolf,


niabi, josephco, StarDogg Champion (Brain is fried dude ;--), tHATDUDE, 


cyberlatin, blorgth, sice_boy, jacky_x, teraphy and everybody


else i forgot..





 Finally my special thanks go to +ORC, reverser+ and +gthorne.





 august 1997 - razzia 





    
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