Cracking the ShareLock Protection System (SHRLK20.DLL)
(A tale of hours of tracing with a surprising ending)
by XaVaX
(11 February 1997)
Programmer's corner
Courtesy of fravia's page
of reverse engineering
Well, A tale of hours of tracing with a surprising ending
describes well this very interesting essay by XaVaX: a new contributor and yet an old
cracker, as he wrote to me:
BTW I'm not new to reversing, just new to writing about
it - I've been reversing hardware & software for
several decades (usually in order to repair or improve
undocumented designs)
This target has a pretty strong protection scheme,
yet it could well win a prize for
the most stupid "demo release". Enjoy! (and please, please, please spare me work and use
the formamus.htm model when you send your essays! :-(
Cracking the ShareLock Protection System (SHRLK20.DLL)
(A lot of light can get into this scheme)
by XaVaX (A middle aged Anglo-Saxon cracker)
I used WEBZIP.EXE as a target for this study and, by
the way, found it to be a very useful utility. My
attack is on the protection scheme only - WEBZIP is an
innocent bystander.
Target WEBZIP13.EXE 928Kb 6/1/98
Tools WinIce
W32DSM89
Hex Workshop (any version)
Persistence
You may be thinking 'yet another serial number
treatise' but bear with me here - there is an
interesting point to this adventure
Read on
This protection does not use standard Windoze routines
for retrieving dialog box text entries etc (debugger
hostile?) - we'll see
Disassemble WEBZIP.EXE with W32DSM89
In the disassembly header you'll find the sharelock
entry:
Import Module 020: SHRLK20.DLL
Addr:000D9BDE hint(0000) Name: ShowAboutDialog
Addr:000D9BF0 hint(0000) Name: PassHandle
Addr:000D9BFE hint(0000) Name: InputUnlockCode <** note this
Addr:000D9C10 hint(0000) Name: GetTryNumber
Addr:000D9C20 hint(0000) Name: GetTrialPeriodRemaining
Addr:000D9C3A hint(0000) Name: CheckProtectionDLL <** & this
Load process & search for 'SHRLK20.'
Set breakpoints on all occurrences
Check 'Stop Auto on API' & all API documentation options
Hit F8 (step over) until we arrive here....
This call looks interesting - note Arg01's text reference
Is this a taunt for crackers? we'll see later!
:004B96FF E8CC0FF5FF call 0040A6D0
API NODOC Arg00 =
Local_Function(Arg01,Arg02,Arg03,Arg04,Arg05,Arg06,Arg07,Arg08)
API Address=004B96FF, API Return Address=004B9704
Arg01 = 00b21b48 ->(LPDWORD)57595542 or (LPSTR)"BUYWEBZIPNOWDUDESBUYWEBZIPNOWDUDES"
Arg02 = 0000001c
Arg03 = 00000000
Arg04 = 00000005
Arg05 = 00000000
Arg06 = 00000000
Arg07 = 007cfc70 ->(LPDWORD)007cfcbc or (LPSTR)"¼ü|"
Arg08 = 004b9760 ->(LPDWORD)f49f0be9 or (LPSTR)"é Ÿô(LPDWORD)00c90f9e or (LPSTR)""
Arg03 = 00b21b48 ->(LPDWORD)57595542 or (LPSTR)"BUYWEBZIPNOWDUDESBUYWEBZIPNOWDUDES"
Arg04 = 0000001c
Arg05 = 00000000
Arg06 = 00000005
Arg07 = 00000000
Arg08 = 00000000
and at:
:004B971B E870A9F4FF call 00404090
:004B9724 E867A9F4FF call 00404090
:004B972D E85EA9F4FF call 00404090
:004B9736 E855A9F4FF call 00404090
:004B973F E84CA9F4FF call 00404090
and finally at:
* Reference To: SHRLK20.CheckProtectionDLL, Ord:0000h
|
:004B9745 E87EF9FFFF Call 004B90C8
API NODOC Arg00 =
Local_Function(Arg01,Arg02,Arg03,Arg04,Arg05,Arg06,Arg07,Arg08)
API Address=004B9745, API Return Address=004B974A
Arg01 = 00b21b10 ->(LPDWORD)59454b48 or
(LPSTR)"HKEY_CURRENT_USER\Software\Microsoft\IFind"
Arg02 = 00b27f14 ->(LPDWORD)59454b48 or
(LPSTR)"HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Metrics"
Arg03 = 00b29b08 ->(LPDWORD)5a626557 or (LPSTR)"WebZIP"
Arg04 = 00b21af0 ->(LPDWORD)64697053 or (LPSTR)"Spidersoft"
Arg05 = 00b3d854 ->(LPDWORD)38312f36 or (LPSTR)"6/18/1997"
Arg06 = 00b21b48 ->(LPDWORD)57595542 or (LPSTR)"BUYWEBZIPNOWDUDESBUYWEBZIPNOWDUDES"
Arg07 = 0000001c
Arg08 = 00000000
Note Arg01 - this is where the encrypted key is stored
in the registry and Arg06 is beginning to nag us to
death by now.
Remember this structure - it will be useful later
(The key will contain registration info including
install and expiry date)
I followed the encryption method and its a simple
rolling byte technique which, as we'll see later, does
not require any reversing to beat this scheme.
OK - now it's time for WinIce
Edit WINICE.DAT and include the following line under:
; ***** Examples of export symbols that can be included for Windows 95 *****
EXP=c:\windows\system\shrlk20.dll
(Lets us break on all exported functions by name)
Restart with winice and set breakpoints on the shrlk20.dll export:
bpx shrlk20!InputUnlockCode
Now we're ready - get your Wodka(s) and/or cigarette(s)
close at hand
Fire up WEBZIP.EXE
Enter any name & number and hit OK - we'll break at:
(addresses will be offset by ~+160000h from the ones
I've shown as the snippets are copied directly from
W32DSM89)
Exported fn(): InputUnlockCode - Ord:000Bh
:00429C38 55 push ebp
:00429C39 8BEC mov ebp, esp
:00429C3B 6A00 push 00000000
:00429C3D 6A00 push 00000000
:00429C3F 6A00 push 00000000
:00429C41 53 push ebx
:00429C42 56 push esi
:00429C43 57 push edi
:00429C44 33C0 xor eax, eax
:00429C46 55 push ebp
:00429C47 68A09C4200 push 00429CA0 <** initializing
:00429C4C 64FF30 push dword ptr fs:[eax]
:00429C4F 648920 mov dword ptr fs:[eax], esp
:00429C52 8D45FC lea eax, dword ptr [ebp-04]
:00429C55 8B5510 mov edx, dword ptr [ebp+10]
:00429C58 E80397FDFF call 00403360 <** initializing
:00429C5D 8B45FC mov eax, dword ptr [ebp-04]
:00429C60 50 push eax
:00429C61 8D45F8 lea eax, dword ptr [ebp-08]
:00429C64 8B550C mov edx, dword ptr [ebp+0C]
:00429C67 E8F496FDFF call 00403360 <** initializing
:00429C6C 8B45F8 mov eax, dword ptr [ebp-08]
:00429C6F 50 push eax
:00429C70 8D45F4 lea eax, dword ptr [ebp-0C]
:00429C73 8B5508 mov edx, dword ptr [ebp+08]
:00429C76 E8E596FDFF call 00403360 <** initializing
:00429C7B 8B45F4 mov eax, dword ptr [ebp-0C]
:00429C7E 5A pop edx
:00429C7F 59 pop ecx
:00429C80 E8B7D7FFFF call 0042743C <** TRACE THIS CALL
:00429C85 33C0 xor eax, eax
:00429C87 5A pop edx
:00429C88 59 pop ecx
:00429C89 59 pop ecx
:00429C8A 648910 mov dword ptr fs:[eax], edx
:00429C8D 68A79C4200 push 00429CA7
:00429C92 8D45F4 lea eax, dword ptr [ebp-0C]
:00429C95 BA03000000 mov edx, 00000003
:00429C9A E8B595FDFF call 00403254
:00429C9F C3 ret
:00429CA0 E9E791FDFF jmp 00402E8C
:00429CA5 EBEB jmp 00429C92
:00429CA7 5F pop edi
:00429CA8 5E pop esi
:00429CA9 5B pop ebx
:00429CAA 8BE5 mov esp, ebp
:00429CAC 5D pop ebp
:00429CAD C20C00 ret 000C
The calls to 403360 perform checks on the input strings
(length etc)
Note: this code is very messy as it performs no calls
to the standard Windoze API functions (eg getdlgitemtext etc)
The call to 0042743C does all the manipulation and
comparison with many movements of the strings,
converting to upper case etc
Breakpoint all copy ranges and keep tracing until we
end up here:
:004274B0 E88B2F0000 call 0042A440
:004274B5 8BD0 mov edx, eax
:004274B7 83EAFF sub edx, -01 <** increment edx
:004274BA 7410 je 004274CC <** bad jump if 0
:004274BC 4A dec edx <** -1
:004274BD 7426 je 004274E5 <** bad jump if 0
:004274BF 4A dec edx <** -1
:004274C0 81EA6D010000 sub edx, 0000016D <** -16d
:004274C6 720A jb 004274D2 <** bad jump if -ve
:004274C8 7411 je 004274DB <** looks good
:004274CA EB15 jmp 004274E1 <** else bad
The only jump on an exact match is je 4274DB, this
'feels' like a possibility so change the 1st jump at
4274BA to a JMP 4274DB to bypass the other tests ie:
:004274B0 E88B2F0000 call 0042A440
:004274B5 8BD0 mov edx, eax
:004274B7 83EAFF sub edx, -01
:004274BA EB1F jmp 004274DB <** always a good jump
:004274BC 4A dec edx
We could also have modified the code to force eax to
the correct value in the call to 42A440 ie 0000016E but
this is not required here (luck!)
OK - one test down and hours out of the way - let's go
on
After much, much more fiddling of the strings in every
imaginable way we arrive at the following test:
:004034E1 8B0E mov ecx, dword ptr [esi] <** our (modified) number
:004034E3 8B1F mov ebx, dword ptr [edi] <** what's this?
:004034E5 39D9 cmp ecx, ebx <** same ?
:004034E7 7558 jne 00403541 <** TEST FAILED!
:004034E9 4A dec edx <** counter
:004034EA 7415 je 00403501 <** done if 0
:004034EC 8B4E04 mov ecx, dword ptr [esi+04]
:004034EF 8B5F04 mov ebx, dword ptr [edi+04]
:004034F2 39D9 cmp ecx, ebx <** test next 4
:004034F4 754B jne 00403541 <** TEST FAILED!
:004034F6 83C608 add esi, 00000008 <** adjust pointers
:004034F9 83C708 add edi, 00000008
:004034FC 4A dec edx
:004034FD 75E2 jne 004034E1 <**loop till edx=0
:004034FF EB06 jmp 00403507 <** ALL PASSED
This test may be circumvented by nopping the two jne
403541's (or equivalent 'nothing' opcodes) ie the test
never fails.
By the way, the 'good' string at [edi] is not the
full correct string - it has 3 characters missing
We may be concerned at this point that the
'CheckProtectionDLL' routine will 'spit the dummy' with
the above patches if it performs a checksum test on the
DLL code but this is not the case.
At this point, make a backup of SHRLK20.DLL
Anyway, apply the patches using the offsets supplied by
W32DSM89 with a hex editor and run WEBZIP.EXE again
(disable breakpoints 1st)
The 'Time Expired - Register' dialog comes up as usual
but any name/number combination is accepted as valid
now, only problem is that this is required every time
the prog is run - could we possibly make a key
generator to permanently register it? well possibly.
At this point I started investigating the ShareLock
system further and downloaded a 'demo' SHRLK201.ZIP for
this purpose.
The "demo" kit includes a KEY GENERATOR!!
Surely this 'demo' model is not compatible with the
full version?
Believe it or not, IT IS!
Remember that nag string
'BUYWEBZIPNOWDUDESBUYWEBZIPNOWDUDES'?
We've seen quite a lot of it by now
This is the key for the key generator which, when
processed with the entered name, creates the correct
unlock code - try it!.
So our long cracking session was NOT NECESSARY!
We can now delete our painfully patched and crippled
SHRLK20.DLL and restore the original, plus any software
protected by this system can be fully registered in
about 5 minutes. Its a shame really to see this
reasonably well crafted protection undone by the eternal
quest for the almighty dollar - it happens so often.
The programmers who have invested in this protection
system should be more than a little upset with this
situation where the protection vendor is giving away
the keys freely - I don't expect to see it for much
longer.
As always, if the software performs adequately the task
you intended and you use it regularly, it is worth the
price being asked (quite reasonable in this case for a
good net utility). I certainly would not part with any
cash for the 'protection' of ShareLock.
All credit goes to the +HCU for inspiration
(c) 1998 XaVaX All rights reversed
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