Cracking Visual Basic Applications

              Introduction     

  Lately more and more programs come out that are programmed in VB.
Since VB programs are still unknown material for most crackers they
ignore them and label it as ‘uncrackable’. In this document i will show
you that that is not true for text based protections (serials/reg#’s).

  For tools we will need only soft-ice and in one case hiew. Further-
more i assume that the reader is somewhat familiar with cracking. For
absolutely beginners i recommend the great tutorials made by +orc and
ed!son’s good windows tutorial. But i will try my best to make the text
understandable for everyone who has a litle knownledge about cracking.

  
               Getting ourselves prepared

  Before i start bombing you with asm listings lets take a moment to
think about what we are dealing with.
  We are dealing with exe’s that dont have code themselves but instead
they make calls to a library with standard functions.
  What does this mean? It means that this is a big disadventage to
protect programs written in VB. Why? Do you think that the writers of
the VB dll made 10 different functions that you can use to compare 2
strings? No, ofcourse not. They made the dll to be as efficient as
possible, as small as possible.
  So therefore a good guess is that there will be only 1 or 2 places
in the dll where it can compare two strings. And that turns out to be
the case as you will see if you finish reading this document.
  Does the litle lamp already begin to glow in your head ? ;–)
Wouldnt it be great if we knew where in the dll 2 strings get compared?
Yes, it would be great. It would reduce VB cracking to a boring job of
setting a single breakpoint at the right place. Continue reading for
the details.   

               Strategy

 
  Before we continue it would be wise to set out a strategy (like its
the case with every other case of cracking).

  Lets think about the protection …
You enter a string of text , you hit enter or press ‘OK’ or whatever.
Then windows gives the data you entered to the VB dll. The VB dll then
does whatever it needs to know if that data is right or wrong. And you
get a msg saying you entered a good/wrong code.

  So what would be the weak link in the chain? The answer is where
windows gives the data you entered to the VB dll. Thats our entry point.
We can make softice break there. And then we are at the source of the
protection-chain. With the aid of breakpoints we can then monitor what
happens with our text.

  I think that we now have enough background information to crack a
first example.

               Case 1 : The Collector v2.1

  The collector is an utility for creating and maintaining your
image/photo collection. Not bad for a VB program.
  More info about this program :

  Name       : The Collector v2.1
  Where      : http://intranet.ca/~logic/collectr.html
  Size       : collectr.exe = 246.047 bytes
  Protection : serial
  DLL        : uses VB3 dll 
   
  I find it easier to explain things in steps. So therefor i will
split the cracking process in smaller chunks :

  Step 1 : Run The Collector – right at startup it will ask you for a
serial #

  Step 2 : Enter a dummy serial like ‘9876543210’. Now press control-d
to enter softice. In softice enter ‘bpx hmemcpy’ to place a breakpoint
on the hmemcpy function of the kernel.
         (Intermezzo : What is hmemcpy ?
          Windows uses hmemcpy alot in operations concerning
          strings. In this case it will be used to copy the buffer
          with the text we entered to the memory space of the VB dll.        
          Remember when i said that we were gonna break when
          windows gave the string we entered to the VB dll?)

  Step 3 : Leave softice with control-d. And press ‘OK". This will
make softice break right at the beginning of hmemcpy.

  Step 4 : Now we will continue with tracing further into the hmemcpy
function to find out where the string we entered will be stored. Keep
pressing F10 untill you see this :
        
         JMP   9E9F       
         PUSH  ECX           ;these lines copy the
         SHR   ECX,02        ;string at ds:si to es:di
         REPZ  MOVSD
         POP   ECX
         AND   ECX,03
         REPZ  MOVSB
         XOR   DX,DX
   
  Step 5: Right before REPZ MOVSD do a ‘ed si’. You will the text you
entered, in my case its shows ‘0987654321’. Do a ‘ed es:di’ and you will
see nothing (yet). But if you press F10 and get passed the REPZ MOVSB
you will see the text getting copied to this new location where the
VB dll can access it.     
 
  Step 6: Now we know where the text is located. Lets review our
strategy here. Our plan was to find out where the VB dll kept our
serial, then put a breakpoint on that memory location and find out
with what it got compared. So, lets set a bpr (breakpoint on range)
at the location with our string. Since the REPZ MOVS(D/B) instructions
increased the pointer in di (it now points to the end of our string)
we do ‘bpr es:di-8 es:di-1 rw’. Dont hit enter yet – read step 7 first.

  Step 7: Before you hit enter i will tell you what to expect. Softice
will break everywhere where that block of memory with the string is
read or written to.
  For example you will break inside the function strlen where the
lenght of the string is calculated.
  And you will break where the string is copied to another place in
memory (for example with REPZ MOVSW). When this happens place a new
bpr at the new location with the string.
  It will also break when the string or part of it gets deleted. If
not the whole string gets deleted do not remove the corresponding bpr.
Only remove it when the complete string gets written over by something
else.
  Also you will break again in hmemcpy. Hmemcpy will read another echo
of the string in the dll’s memory. Place a bpr there too.  
  And finally you will break at the part of the code that does the
comparing (the instruction you will see is REPZ CMPSB).
  When i reached that part of code i had 4 breakpoints set. One
breakpoint for hmemcpy and 3 bpr’s on 3 echos of the string (or parts
of it).

  Step 8: Now we found the code where the VB3 dll does comparing
we can place a breakpoint there and disable the other breakpoints. We
wont need them anymore. We found the place where things get compared
in VB3. What you see is this :

   : 8BCA         mov cx, dx
   : F3A6         repz cmpsb  ;<- here the strings in ds:si and es:di
   : 7401         je 8CB6     ;   are being compared
   : 9F           lahf
   : 92           xchg ax,dx
   : 8D5E08       lea bx, [bp+08]
   : E80E06       call 92CB

  Just before the REPZ CMPSB if you do a ‘ed si’ and a ‘ed es:di’, you
will see what is compared with what. In this case the second and third
character of the string we entered gets comared with ‘V8’. So if you
restart the program and enter 0V87654321 it will register.

  Step 9: We are not finished yet. The contrary is true, the important
part is what we do now. Next time we meet a VB3 program we want to place
a breakpoint at the location with the code above and read out the right
serial.
How do we do that ? Lets try it real quick with The Collector.
    -Start The Collector and enter a dummy serial.
    -Enter softice and place a breakpoint on hmemcpy.
    -Leave softice and press ‘OK’, this will put you back
     in softice.
    -Now, get out of the kernel and and get in the code of VBRUN300
     (press F11 and F10 untill you get there)
    -Now do a search for the pattern :
     8B,CA,F3,A6,74,01,9f,92,8D,5E,08,E8,0E,06
     (s 0 l ffffffffff 8B,CA,F3,A6,74,01,9f,92,8D,5E,08,E8,0E,06)   
    -Place a breakpoint at the adress that gets returned
     (bpx <seg:offset>)
    -press F5 and you will land in the middle of the above comparing
     code.
    -Only thing left to do is check out the pointers in es:di and ds:si
  

               Case 2 : Minimize Magic 1.2.4
 

  Minimize Magic is an utility that you can use to minimize your
programs to the traybar.

  More info about this program:

  Name       : Minimize Magic 1.2.4
  Where      : http://www.genesoft.demon.co.uk/
  Size       : minimagic.exe =  159.744 bytes
  Protection : password based on key 
  DLL        : uses VB4 dll 

  To crack this program you can do the same as we did with The
Collector. Starting with hmemcpy working your way to the code that
compares the string you entered. Important thing to know is that the
VB4 dll always converts strings to the WideChar format before it does
anything with them. So instead of using hmemcpy you can set a
breakpoint on MultiByteToWideChar to break. Check your windows API
reference to learn more about this function.

  I have done all the hard work for you and found the VB4 dll code
that compares two strings (in WideChar format !).
  Heres the listing :

 : 56            push esi
 : 57            push edi
 : 8B7C2410      mov edi, [esp + 10]
 : 8B74240C      mov esi, [esp + 0C]
 : 8B4C2414      mov ecx, [esp + 14]
 : 33C0          xor eax, eax
 : F366A7        repz cmpsw  ;<– here the (WideChar) strings at ds:esi
 : 7405          je 0F79B362 ;    and es:edi get compared
 : 1BC0          sbb eax, eax
 : 83D8FF        sbb eax, FFFFFFFF
 : 5F            pop edi
 : 5E            pop esi
 : C20C00        ret 000C

  Now we know enough of the VB4 dll to crack Minimize Magic:

  Step 1: Start Minimize Magic and chose Register from the menus.
You will be asked for a Name and a Password. Enter a name and a
dummy password. Dont press ‘OK’ yet, continue with next step.

  Step 2: Enter softice and place a breakpoint on hmemcpy. Leave
softice and press ‘OK’. You will land in softice.

  Step 3: Press F11 and F10 untill you are out of the kernel and in
the code of the VB40032.dll. Now we will search for the pattern of the
code above.
Do ‘s 0 l fffffffff 56,57,8b,7c,24,10,8b,74,24,0c,8b,4c,24,14’
and place a breakpoint at the adress that gets returned.

  Step 4: Press F5 to leave softice, but you will immediately break
again, right at the beginning of the above code. Here the password
you entered will be compared to the correct password. Trace untill
right before the REPZ CMPSW and do ‘ed es:edi’, this will show the
password you entered. If you do ‘ed esi’ you will see the correct
password.
(the strings will be in WideChar format – for example you could
see A T G H D E H D. That means your password is ATGHDEHD) 

  Ok, now you found a working password that will work only for the
version on your computer. If you give that password to somebody else,
the program wont accept it. The password is calculated from a Key
that is different on each computer. This key could be randomly
generated at setup or based on the info on your hd. Whichever one it
is, it will be hard to find out how its generated or where it is
stored.

  So how can we make a general crack ?
  We could use the ‘Magic Window’ trick here. We will ‘reprogram’
the VB40032.dll to show the correct password.
  The original code in the VB40032.dll looks like this :

 
:0F79B348 56         push esi
:0F79B349 57         push edi
:0F79B34A 8B7C2410   mov edi, [esp + 10] ; es:edi -> pw you entered
:0F79B34E 8B74240C   mov esi, [esp + 0C] ; esi -> correct pw
:0F79B352 8B4C2414   mov ecx, [esp + 14]
:0F79B356 33C0       xor eax, eax
:0F79B358 F366A7     repz cmpsw          ; compare them
:0F79B35B 7405       je 0F79B362
:0F79B35D 1BC0       sbb eax, eax
:0F79B35F 83D8FF     sbb eax, FFFFFFFF
:0F79B362 5F         pop edi
:0F79B363 5E         pop esi
:0F79B364 C20C00     ret 000C            ; end of this function
:0F79B367 57         push edi            ; the code below this adress
:0F79B368 8B7C2408   mov edi, [esp + 08] ; is not important, but we
:0F79B36C 8B4C2410   mov ecx, [esp + 10] ; will need its space
:0F79B370 8B44240C   mov eax, [esp + 0C]
:0F79B374 0BE4       or esp, esp
:0F79B376 F266AF     repnz scasw
:0F79B379 B800000000 mov eax, 00000000
:0F79B37E 7503       jne 0F79B383
:0F79B380 8D47FE     lea eax, [edi-02]
:0F79B383 5F         pop edi
:0F79B384 C20C00     ret 000C

  The code is located at offset 7a748 in the vb40032.dll file. So, to
make a general crack make a patch that turns the above code into:

:0F79B348 56           push esi
:0F79B349 57           push edi
:0F79B34a 8B7C2410     mov edi, [esp + 10] ;es:edi –> text you enter
:0F79B34E 8B74240C     mov esi, [esp + 0C] ;esi –> correct pw 
:0F79B352 813F70006300 cmp dword ptr [edi], 00630070 ;edi -> ‘PC" ?
:0F79B358 7527         jne 0F79B381                  ;if not – leave      
:0F79B35A 803E00       cmp byte ptr [esi], 00   |<- these lines    
:0F79B35D 7410         je 0F79B36F              |   put spaces
:0F79B35F 83C601       add esi, 00000001        |   between the chars
:0F79B362 C60620       mov byte ptr [esi], 20   |
:0F79B365 EB03         jmp 0F79B36A             |<–skip the ret
:0F79B367 C20C00       ret 000C            ;<– this to prevent crash
:0F79B36A 83C601       add esi, 00000001        |
:0F79B36D EBEB         jmp 0F79B35A             |<- back to the start
:0F79B36F 8B3DDCC47B0F mov edi, [0F7BC4DC]      *<– these lines
:0F79B375 8B74240C     mov esi, [esp + 0C]      *    call the
:0F79B379 6A00         push 00000000            *    MessageBoxA
:0F79B37B 56           push esi                 *    function to show
:0F79B37C 56           push esi                 *    the correct
:0F79B37D 6A00         push 00000000            *    password
:0F79B37F FFD7         call edi                 *
:0F79B381 5F           pop edi
:0F79B382 5E           pop esi
:0F79B383 90           nop
:0F79B384 C20C00       ret 000C

  Comments:
  We used the space of two routines, so to prevent a crash we have to
put a RET function at the beginning of the (original) second function
(see line 0F79B367).
  This part of the VB4 dll code is not only used to check the passwords.
It is used by other parts of the program as well. Therefor we need to
do something so that only something will be shown when we are dealing
with a password comparison. That is what the code at line 0F79B352 is
about. It checks to see if EDI points to the text "PC". So we can
use that to trigger the crack. To trigger the crack, "PC" has to be
entered for password when registering.
  The lines marked with | are there to put spaces between chars of the
string. Originally there would be a string of WideChar format. That
means that in memory there will be zero’s between the chars. And the
function we will use to show the text (MessageBoxA) translates a 0 to
end of string. So only 1 letter would be shown if we dont replace the
zeros with spaces.
  The lines marked with * are there to call the function MessageBoxA
to show the correct password. I ripped those commands from the VB4 dll.
Placed a breakpoint on MessageBoxA to see how VB4 called it.
 
  Well thats it for Minimize Magic. To make a general crack, a patch
could be written that patches the VB4 dll at offset 7a748 with the
above code. To use such a crack minimagic.exe and the vb40032.dll
should  be placed in a temp dir and the patch run there. Then start
minimize.exe from that temp dir, and use ‘PC’ for password. And voila,
a window will pop up with the correct password. Once the correct pw
is known, the temp files should be deleted and the password can be
used in the original Minimize Magic.

               Case 3 : Sub Station Alpha 2.02  

  Most of the VB4 programs can be cracked with the method described
in case 2, but i have encountered 2 programs which used a different
method of comparing. One of those programs is Sub Station Alpha 2.02.
It uses a protection that first converts a number you enter to its
hex value and then compares it with the correct number. Lets start to
crack Sub Station Alpha and things will get clearer.

  Info about this program:
  
  Name       : Sub Station Alpha 2.02
  Where      : http://www.eswat.demon.co.uk/index.html
  Size       : SUBSTN32.EXE = 629.248 bytes
  Protection : password based on user name  
  DLL        : uses VB4 dll 
  

  Earlier i mentioned that VB4 converts strings to the widechar format
before it does aything with them. Therefor we will use this function
as an entry point. Again we will do it step by step ;–)

  Step 1: Start Sub Station Alpha and chose register from the menus.
Enter a name and a dummy registration key.
 
  Step 2: Enter softice and place a breakpoint on MultiByteToWideChar
(with ‘bpx multibytetowidechar)

  Step 3: Now, leave softice and press "Register".

  Step 4: Softice will break at the beginning of MultiByteToWideChar,
press F11 to get out of it. You will see :
 
:FF1500C27B0F call [KERNEL32!MultiByteToWideChar]
:8BD8         mov ebx, eax
:83FEFF       cmp esi, FFFFFFFF
:7501         jne 0F738BCF
:4B           dec ebx
:53           push ebx
:6A00         push 00
:FF1518C97B0F call dword ptr [0F7BC918]
:8BE8         mov ebp, eax       
:85ED         test ebp, ebp
:0F845B260100 jz 0F74B23D
:43           inc ebx
:53           push ebx
:55           push ebp
:56           push esi
:57           push edi
:6A00         push 00
:6A00         push 00
:FF1500C27B0F call [KERNEL32!MultiByteToWideChar]
:8BC5         mov eax, ebp       ;<– do ‘ed ebp’ here
:5D           pop ebp
:5F           pop edi
:5E           pop esi
 
   The important place is right after the second call to MultiByte-
ToWideChar. Disable the first bp on MultiByteToWideChar and place
a new bp right after the second call to that function (on the line
with MOV EAX,EBP). On that line EBP will contain a pointer to a
string in WideChar format that was processed. It doesnt have to be the
string of the registration key. Therefor we will edit that breakpoint
so that it will only break when it is processing the registration key.
   How can we do that? Well, the MultiByteToWideChar function returns
the lenght of the string it processed plus 1 in EAX. So we will add a
conditional statement on the breakpoint. Do ‘bl’ to find out what the
number is of that breakpoint. Then do ‘bpe #’ and add
‘if al==<lengthOfKeyString+1>’ to the breakpoint. For example, if you
entered ‘212121’, lenghtOfKeyString would be 6 :–).
 

  Step 5: Now we will let the program run with F5. When softice breaks
do a ‘ed edp’ and see the WideChar form of the key you entered. We
place a bpr on the block of memory containing the string and we
continue (F5). What will happen is this. Softice will break on several
places. Whats important is that it will break in the code of OLEAUT32.
When that happens trace a litle further to see whats going on. The
first few times you will get out of the OLEAUT32 very quickly. But
eventually you will see this code :

( listing from OLEAUT32.DLL)
:6534B6B3 395C240C cmp [esp + 0C], ebx     ;  this is a loop that
:6534B6B7 7E14     jle 6534B6CD            ;  goes trough all
:6534B6B9 33C9     xor ecx, ecx            ;  the chars of a
:6534B6BB 8D0492   lea eax, [edx + 4*edx]  ;  string, in the end
:6534B6BE 8A0E     mov cl , [esi]          ;  edx will have the
:6534B6C0 46       inc esi                 ;  hex value of the string
:6534B6C1 4F       dec edi
:6534B6C2 FF4C240C dec [esp + 0C]
:6534B6C6 8D1441   lea edx, [ecx + 2*eax]
:6534B6C9 85FF     test edi, edi
:6534B6CB 7FE6     jg 6534B6B3
:6534B6CD 85FF     test edi, edi
:6534B6CF 7F4A     jg 6534B71B
  ………….
  ………….
:6534B6F2 8910     mov [eax], edx          ;  edx is saved
:6534B6F4 33C0     xor eax, eax
:6534B6F6 83C424   add esp, 00000024
:6534B6F9 C21000   ret 0010

  Step 6: We saw that the key is transformed into its hex value,
and saved to a place in memory. If you monitor this memory location,
you will end up here in the VB4 dll that compares it with another
value:
 
:0F7A2CE1 5A             pop edx             ; load edx
:0F7A2CE2 58             pop eax             ; load eax
:0F7A2CE3 2BC2           sub eax, edx        ; subtract them
:0F7A2CE5 83F801         cmp eax, 00000001
:0F7A2CE8 1BC0           sbb eax, eax
:0F7A2CEA 50             push eax
:0F7A2CEB 0FB706         movzx word ptr eax, [esi]
:0F7A2CEE 83C602         add esi, 00000002
:0F7A2CF1 FF2445F4997B0F jmp dword ptr [2*eax + 0F7B99F4]
:0F7A2CF8 E8BB000000     call 0F7A2DB8

  We see that EDX and EAX get loaded from the stack, and then
substracted. This is just an indirect way of comparing those two
values. If you check out the contents of EAX and EDX, you will see
that one has the number you entered and the other one will have the
correct registration number.

  Step 7: Now we found this location its wise to note the hex values
of the code, so you can find it back quickly when you suspect that 
another VB4 program uses this protection.

 

                 Final notes             

  Well, with the above 3 techniques i have been able to crack quite
some VB3/4 programs that used a text based protection. Sometimes
when you set a breakpoint at the comparing routine, softice will not
break. Try then to enter strings with a different length. Because
the program could be checking the length of the string you enter before
it compares the string itself. And other programs first isolate chars
from the string you enter and then compare those isolated chars, but
again they get compared at the locations stated in the examples above.
  With VB5 programs i havent much experience, i only cracked one of
them. It was called Hitlist Pro v3.0. By patching the VB5 dll, I could
remove its 30 day timelimit just like it was a regular program. Of
course, the VB5 dll had to be placed in the Hitlist Pro main dir,
this to prevent other VB5 programs using the patched DLL.
belgesi-992

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