Software Security and Reverse Engineering
What is reverse engineering?
Today the market of software is covered by an incredible number of protected
applications, which don't allow you to use all features of programs if you
aren't a registered user of these. Reverse engineering is simply the art of removing
protection from programs also known as “cracking”.
In Some other words cracking is described as follows: - “When you create a program
you engineer it, in fact you build the executable from the source-code. The reverse
engineering is simply the art of generate a source-code from an executable. Reverse
engineering is used to understand how a program does an action, to bypass protection etc.
Usually it's not necessary to disassemble all code of the application not only the part of
the application that we are interested must be reversed. Reverse engineering used by a
cracker to understand the protection scheme and to break it, so it's a very important thing
in the whole world of the crack.”
In short: - "Reverse Engineering referred to a way to modify a program such that it
behaves as the way a reverse engineer wish."
“Cracking is a method of making a software program function other than it was
Originally intended by means of investigating the code, and, if necessary, patching It.”
A Little bit of history
Reveres egg. Most probably start with the DOS based computer games. The aim is that a
player has full life and armed in the final stage of the game. So what a reverse egg. Do is
just find the memory location where the life and number of weapons are store and then
modify this values. They used memory-cheating tools such as game hack etc. So that they
have full life and armed in the last stage of the program. But in today’s world with the
advent of the shareware concept more and more software author releases the shareware
versions. Hence with this reverse engineering become more tedious, more complex, and
trickier.
Today to protect the software a programmer use various kind of technique, some of them
are old, bad repetitive techniques but some are new. We will discuss them in next section.
Various Protection schemas
Following are the most commonly used schemas
1) Hard coded serial
2) Serial number, name protection
3) Nag screen
4) Time trial
5) Dongle (hardware protection)
6) Commercial protection
7) Other (cd rom check, keyfiles, disabled function etc.)
Let’s study this in detail
1) Hard coded serial: -This is the simple protection as compared to other. In this kind of
protection we have to enter only a serial number and this serial number is same for all
users. Serial numbers entered are compared to the original serial through an algorithm
and if a user entered correct serial then the software registered.
2) Serial number - name protection:-In this kind of protection we have to enter a name
and a serial number. Then our serial no is compared with the original serial, no which is
derived from our name using some algorithm. This protection is some time easy and
some times hard, based on the algorithm a programmer use. Example of this type
protection is most widely used software "WinZip."
3) Nag screen :-In this kind of protection a screen come each time a user start the
application, to remained such that how many days are left or your software are
unregistered or any other message. This is a littlie hard to remove. And most of the
newcomers found it difficult as a new programmer to understand pointers (i.e. –WinZip).
But if a reverse has enough knowledge of windows API then he can easily remove the
nag screen.
4) Time Trial: - According to +ORC This kind of protection has any of following
protection or combination of following protection schema: -
a) To a predetermined amount of days, say 30 days, starting with the first day of
installation. This is referred as "CINDERELLA protection".
b) To a predetermined period of time (ending at a specific fixed date)
independently from the start date... 'BEST_BEFORE a given date' protection.
c) To a predetermined amount of minutes and/or seconds each time you fire
them... 'COUNTDOWN' TIME PROTECTIONS' example of this kind of
programs are some games and audio video player which allows an unregistered
user to play game for some amount of time say 5 minutes etc.
d) To a predetermined amount of 'times' you use them, say 30 times. Strictly
speaking these protections are not 'time' dependent. But they depend only on thing
"HOW MANY TIMES YOU EXICUTE THEM"
5) Dongle Protection: - this kind of protection is supposed to be toughest protection to
crack. This protection is consisting of an EPROM, which was connected with a port on
computer. The program which is protected by this is first cheeks the presence of this and
then cheeks that the program is registered or not all though it implementation is too hard
and hence this kind of protection is not very widely used. This is used in Big Protected
shareware’s. This protection is used by a I/O LPT port (hardware) You will need the
registration Card attached To your PC's parallel port Or other in order to make The
program fully work, otherwise it will be Expired after xxDays / xxUses /rippled or it
won’t work at all. Dongles such as: HASP / Sentinel are most commonly used. Dongles
uses DLLs/VxD to check the "is registered"
Dongle API is also used for some checks.
Example of programs, which uses this kind of protection, included some version of CAD
etc.
6) Commercial protection: - Most of the software programmer don’t want to spend
there precious time in deciding which kind of protection they used to protect there
software. Because they think that instead of the spending there time on designing the
security algorithm of there programs, why not they spend time to improving the
functionality of there program??? And here comes the concept of commercial protection.
Today some software company’s designs only security algorithm for various software.
Also they provide general software, which converts fully functional software in to
unregistered version and after paying the registration.
This software gets converted back in to the fully functional registered software after
entering the registration details. some of the companies which uses commercial
protection for there software are macromedia, Symantec etc and some companies which
provides this type of protection are preview systems (vbox protection) etc..
Although this kind of protection has high security because they are professionally
designed but they also have some disadvantages. One major disadvantage is that "if a
person cracks only one program which is protected using this protection, then he has
cracked the entire program which uses this kind of protection!!!!".
For example if a cracker has cracked the flash mx (which is protected by vbox) then he
was able to crack easily all the macromedia software such as dream waver mx etc.,
because all these programs are based on only one kind of protection!
And in the real world there is no protection, which is still uncracked.
7) Other protections: - There are many other techniques which are used to protect
software. These are generally used in computer games. Such as cd rom protection,
disabled function etc. I think most of computer user are familiar with this protection and
already seen this kind of protection. For example: - If a user doesn’t have cd for a
particular game then he cannot be able to play the game directly from hard disk. Because
when one runs the program then the program checks for the cdrom.
Also some protection schemes have disabled functions such as you cannot save your
work or you cannot use any particular function etc.
So I hope now you understand all the protection schemas, which used to protect software.
Ok let’s study how reverse engineering is done. The first thing to keep in mind that
cracker always works with the disassembly and they are familiar with the windows API.
Now all of us computer user knows that computer only understands binary nothing else.
So first we create a program and then compile it now what compiler does is check for
syntax, any error and then he generate the .obj file. As in high level language some
function are prewritten which are stored in library file hence after this we used linker
which links the programs with the library file and then after linking we get an exe file
hence exe file we use is nothing but the collection of instruction in binary formats.
Now to reverse engineer there are different tools available.
TOOLS OF THE TRADE
The popularity of Windows and the ease of creating programs for this platform have lead
to the development of thousands of shareware programs. Crackers usually work with the
assembly code, reverse engineering it, and have an excellent grasp of the Windows APIs
as well.
There is no one particular method to crack a program. Depending upon the program and
the kind of protection it has, crackers employ different techniques to get into the program.
But there are some common tools that crackers employ to start cracking the program.
These programs are perfectly legal and useful by themselves.
They are: -
1) Debugger
2) Dissembler
3) Hex-editor
4) Unpacker
5) File Analyzers
6) Registry monitor
7) File monitor
This is the tools, which a cracker used to reverse engineer any software. Let we have take
a detail look on them.
1) Debugger: -all of us know that debugger is a utility to debug the program. A
programmer use debugger to find bugs in their program. Debugger is only tool by which
we can trace/break a function or code live. There are many debuggers available in the
market. We all know how to debug any program, first we put a breakpoint on the required
statement and then we run the program. When this instruction is near to be executed the
program stops and we can see values! This thing is directly related with cracking.
Generally software programmer uses windows API function to get the serial number or to
create nag screen or dialog boxes. Now if a debugger support breakpoint on execution of
ape then a cracker easily set a breakpoint on API such as "getwindowtexta" and then after
tracing only some lines of code he can easily find the algorithm to used the generate key
and the key itself!!!
There are many debuggers available in the market but one of the most popular and a
powerful debugger is SOFTICE from NUMEGA CORPORATION. This debugger is so
powerful that earlier version of this debugger used to crack himself!!!! Almost all the
cracker in this world is using this debugger. So after seeing its misuse Numega
Corporation has kept some restriction on the sale of this great debugger and a buyer must
show that he will not use this debugger for illegal activities. But cracked copy of this
debugger is freely available on the net. This is a system level debugger, which works
directly between a computer's hardware and windows. We cannot load this debugger
within windows. We must load this debugger before windows loads in to the memory. It
can monitor every process, threads silently in memory until we call it up using hotkeys.
It allow us to patch memory at runtime (not permanently and hence we have to use hex
editor.) viewing the contents of the register, contains at memory address etc.
2) Disassembler: - As an executable file is in binary format so a normal user cannot
understand the instruction in this file. Also any exe or executable is generally in PE
format (which is a standard format for exe file, decided by the committee of software
companies like MICROSOFT, IBM, and AT&T. For more about exe search any virus
related site or /simply search your favorite search engines.) Hence a cracker first
disassemble the program .now a Disassembler converts the binary file in its equitant
assembly language instruction’s most of program is written in high level language hence
size of the disassembly goes in millions (or even larger) of lines and hence it is not
possible for any cracker to understand this code. And hence cracker generally looking for
strings in this disassembly such as; -"your 30 day trial period has expired." Or "the
serial no you entered is not valid!!!" Etc.
Then they trace the assembly code some lines and simply reverse the jumps. (For
example one to jump) so that control did not come on this string and go to the statement
such as "thanks for registration!!!"(We will see later how this can be done but currently
this info is enough for you..)
Now there are many dissembler available. But two of them, which are most commonly
used, are WIN32DASM and IDA .IDA is a powerful debugger then WIN32DASM and
used for advanced cracking. But WIN32DASM is most widely used debugger by
newcomer and intermediate crackers. This debugger allows you to disassemble any file
which is in PE format, we can save disassembly .it can tell us which function is imported,
which function is exported, we can execute jump, call, find string data reference and
dialog reference easily and many more facilities it provides like we can executes the exe
file, step in to it, step over and blah, blah.
3) Hex Editor: -as I mention above that softice can change the value at memory location
only at the run time. Now this is not useful or not a good cracking if we have to change
the value each time we run the program. Therefore we use hex editors. A hex editor
allows us to change the contents of any file in hex format. It displays the contents of the
file in hex format. We can simply have to change the value at memory location which we
find using softice. Now there are a lot of hex editor available such as ultredit, biew, hiew
and a lot (I think many c, c++ programmers has developed it).
But the most popular among these is HIEW. Which stands for “Hacker's vIEW". This
little program offers a lot of facilities such as editing in hex or ASCII format, searching
any string in hex or ASCII format. There is another good facility which makes it different
from others is that, it offers you to write the assembly code and it can automatically
convert this code in to equitant hex format. This is helpful for the crackers who don’t
know equitant hex value of assembly instruction. (For example: - if we have to change
the jump to nope at any memory location then after pressing F7 key then we can only
write nope and it will automatically convert it to its hexequilant which is 90.) There are
other hex editors also but it is the most widely used.
4) Unpacker/PE Editor: - sometimes programmers used file compressor such as UPX,
ASPACK to minimize the size of the program. This is called a file packer. Now what a
packer do is using any algorithm he reduce he size of the file and append it code in to the
exe file and at run time, first the code of the unpacker is executed and after that it
decompress or unpack the program in memory. Since the program we have to crack is
unpacked in the memory only hence a cracker cannot simply disassembles and patch the
program. User can only patch it runtime. Therefore to un-pack the exe file permanently
we use unpacked. Which unpack the exe file and we can store this unpack file to the disk.
If a program is using a packer then its exe header will changed. There are various
techniques available to manually unpack the exe by modifying the exe header but those
are high level techniques and don’t want to discuss them here because I think most of the
newsiest find difficult to understand it. The most widely used unpacker is procdump. This
software has ability to unpack different kind of packer stand-alone. It also allows
changing or viewing the header of exe files.
5) File Analyzers: - To identify which packer is used to pack file cracker uses this kind
of programs. By using this, a cracker can know which compiler or packer is used to
protect the shareware. This software simply works on signature byte. With the help of
this you can find what compiler or in which language the program has written. There are
many this kind of program are available such as file inspector, File Info etc.
6) Registry monitor: -Some program uses registry keys to store their registration
information. Hence, ‘Registry Monitor’ is a software which works in background and
traps all the registry access by the all process, which is currently running.
7) File monitor: -some program also uses key file or they have there security algorithm
in different file and hence file monitor is use to see which application is using what file.
Bypassing the protection
How programs are Reverse engineered
In my pervious article I discussed about the different protection schema and tools used
for cracking. In this article I show u how cracker past all these protections.
There are different ways to crack. These approaches are determinate from
different knowledge, different type of cracker, different personal preferences.
An example can be more useful than thousand of words. There are three type of
approaches in cracking shareware programs that need serial number to register or have
nag screens.
They are
1) Serial fishing
2) Bypassing of the check also called patching
3) To make a key generator.
The first method is simplest and fastest and can be used by normal cracker. The last one
is more complex. In fact, you need to understand all the serial number check routine and
then u have to code a program based on this which generates the key according to input.
The advantage of this method is that the serial number can be used for further versions of
the program or for different computers or for different user. So, the choice is determined
from the level of knowledge, the time the cracker has and his style of cracking.
Let’s have a detail look on them.
1) Serial fishing: -serial fishing is supposed to be the cleanest method to crack any
program. This method is also known as live cracking because in this we find the correct
serial only at run time. It means we find the serial when program is executing. Serial
fishing deals with finding the correct serial and then registering software using this serial
number. In serial fishing we don’t have to modify the code but simply we have to inspect
or analyze the code.
In serial fishing first we enter any fake i.e. wrong serial number of our choice say 123456
.now this serial number is compared with the correct serial and hence we have to only
find the memory location or register where our correct serial number is stored. The
general routine in high-level language to compare the serial number is as follows: -
If (entered serial=correct serial) then
Register program (do some modification in program or store the registration information)
Message box (“successfully registered”)
Else
Message box (“sorry!! Your serial number is not valid”)
And in assembly the general routine is as follows: -
In assembly all the data is stored in registers or stored in any memory location. Suppose
eax register store the fake serial and ebx stores the correct serial.
Now the routine is: -
100aa : Cmp eax,ebx
100bb : Jz 100xx jump if our serial is correct
100cc : Mov ax,yyyy
100dd: other code….
100xx : code for message box successfully registered
100yy : code…
Where 100xx is memory locations.
Here what is happening that both serial numbers is compared using the cmp instruction
and if the two serials are equal then control jumps to the message that we have entered
the correct serial. Otherwise controls transfer to next statement, which is 100% sure like
this “you have entered a invalid serial”
Although this is not necessary that always cmp is used. But mostly it is used to compare
the serial. Now the programmer uses windows APIs such as GetWindowTextA or
GetDlgItemTextA to get the serial numbers.
Now as I mentioned SOFTICE allows us to set or put a breakpoint on windows API.
Hence a cracker simply puts the breakpoint on such API and when after entering the
serial number program breaks on this breakpoint then a cracker simply trace the
disassembled code to find the correct serial. Crackers while tracing is simply search the
conditional jump such as jne or jz or jae after a cmp instruction. In short they checks the
routine I mentioned above and in this way a cracker can find the whole algorithm and
correct key with the simple softice command such as: -
D eax
Or
? eax
Well here D eax simply display contains of the register eax in hex format. And? eax
display contains of eax in ASCII format. (All these are softice commands).
And after finding correct key he can easily register the software and if he want to
distribute the key for every user then he simply creates a keygenrator after analyzing the
whole algorithm. Because we know that in serial number-name protection for each name
there will be a different key. Some program also uses various techniques such as
appending ur hard drive serial number to the end of serial and etc in this case serial
number is different for each computer and hence a cracker simply writes the key
generator after analyzing the whole protection schema.
By using this technique a cracker can easily defeat the first two protections I mentioned
in my previous article (hard coded and name-serial number combination.)
2) Patching: - if a program is showing the nag screen and don’t have any option to
register then we use patching. Patching is also referred as dead cracking. Using patching
is not supposed to be a good crack. most crackers avoid to use this technique until they
don’t have other option then this. In case of nag screen programmer simply uses the
windows API such as DialogBoxParam or MessageBoxa etc. now a cracker sets the
breakpoint on these API calls and run the program. Now when the program calls this
function then softice pauses the execution of program and a cracker have to deal with the
assembly snippets. The simple structure of calling a nag screen in high-level language is
as bellow: -
If (program is not registered) then
Display the nag screen
Else
Execute the program
And in assembly the structure is as follows: -
Suppose that first program checks for the registration and return the value in eax register.
(If eax=1 then register and eax=0 mean unregistered)
Now this compared as
dddd: Cmp eax,1
aaaa: Jz xxxx
bbbb: Mov ax,02
cccc: Call yyyy this is for calling the nag screen
Xxxx: Rest of the program…
Here aaaa ,bbbb etc are called offset or memory locations.
So whats happening here is that first program checks that if it is registered .the
registration status of program is put in to eax. Now this eax is compared with 1 if eax is
one then program is registered and we don’t have to show the nag screen else we have to
show the nag screen.
So we have to only reverse the jump (jz to jnz). So that the nag screen does not appear. In
this case we use hex editor such as hiew to patch the exe file of programs.
Patching is also used to remove the time trial protections. Suppose we have a program,
which expires after 30 executions. Now it is clear that when we run the program it
compares that is 30 executions are over or not. If not then it increases the number of total
execution by 1 and store this value somewhere but if 30 executions are over then it shows
the message that ur program has expired.
The structure is same as the nag screen: -
aaaa : cmp eax,1e (1E in hex=30 in decimal)
bbbb : jea xxxx jump if greater then or equal to 30
cccc : ax,02
dddd: call yyyy this is for calling the nag screen
eeee: ret stop execution and exit
Xxxx: Rest of the program…
Here what’s the program is doing is that it comparing the number of times we use with 30
if it is equal or above then it display the message and exit. so what we do here is simply
change the jea to jmp. so that program always jump irrespective of that if it is registered
or not.
3)Key generator:-this technique is supposed a little harder. in this technique a cracker
need to understand all the serial number check routine and understand all the conditions.
such as a serial number can contain ‘–‘ symbol or size of serial number must be 11
character long or user name must not be blank etc. this techniques simply needs that a
cracker must understand the assembly language very well and analyzes the code very
carefully. he must be careful to analyze each line of code. because a small mistake in
understanding the code can result in unexpected results.
Now lets see how crackers past the commercial protection.
Well today many of the commercial protection are using different techniques to fool the
tools of cracking such as anti dissembler code. Anti softice tricks and etc. hence this
protections are harder to crack for a newcomer. First lets see how this program protects
the software: -
There are common dll or say binary file for all the software which uses a particular
commercial protection such as the entire macromedia product uses the same protection
‘vbox’ and all the files related with vbox is stored in the c:\programfiles\comman\vbox
directory. Now when a user runs the program then first the vbox files are executed.
Which check that if program is registered or not. If program is not registered then it
checks the 30 days trial period and if trial not expired then executes the program.
Commercial protection included many checks so a cracker cannot easily patch the
program. The most popular trend in between the cracker is that they simply BYPASS this
kind of protection. it means as I mentioned that the vbox changed the header of exe file
and for this reason all files related with vbox is executed before the actual exe file of
program is executed. Now what a cracker does is simply find the original entry point of
the exe. It means a cracker only have to find that from which point the original program
starts its execution. For this a cracker puts breakpoint on windows API such as
GetProcAddress etc and then run the program. Now when program executed then first
vbox code is executed and therefore vbox calls the API GetProcAddress and SOFTICE
pauses the execution of program. Now a cracker have the assembly snippets. The rest is
purely depends on a crackers ability and experience. After tracing some lines from the
vbox files a cracker can find the original program entry point.
After finding the entry point a cracker simply modify the exe header and IAT.
So now onwards program has nothing to deal with commercial protection because
cracker has bypassed the protection!!!!
For each commercial protection there is a different way to crack. The method I discussed
here is only related with vbox protection.
So this are all the techniques generally used in cracking world. Nowadays there are
several cracking groups specialized in reverse web scripts. There is nothing of new in this
because the web pages are written in java or CGI scripts or something else. So, they can
be considered as small programs. Consequently, this is only another type of crack.
The web cracker usually reverses the protection schemes of web pages creating
cracked passwords, which are distributed on the web.
To end this article I would like to mention these lines of a cracker:-
“There is a crack, a crack in every thing. That is how the light gets in.”
Hope it tells the psychology of a cracker.
If you have a symbian phone and you have forgotten your memory card then you can easily get your password by using this simple trick.This trick works only on nokia symbian phones not on the java phones.Before starting the tutorial on “Tricks To Reset Memory card Password In Nokia” Here are the the requirements
Total Video Converter is a very usefull software for converting any audio or video file . if you have use this software then you can convert media file in high speed .
This attractive, superthin laptop has everything you need and more--assuming that you're not an audiophile.
If the display was higher resolution and offered better off-axis viewing angles, this would be our favorite Ultrabook.
Sony demonstrates cutting-edge design in this surprisingly powerful but unfortunately expensive laptop.
Though pricey for a 12.5-inch laptop, this ultraportable delivers in performance and battery life.
The U300s ameliorates its high price and slightly slow performance with a classy and very usable design.
Gorgeous looks plus a great interface and display overcome the Envy 14 Spectre's slightly higher weight.
The Zenbook UX31E is almost perfect, except for its mediocre touchpad.
This laptop not only gets the job done, but also has a lot of thoughtful features that harried businesspeople will appreciate
This ultraportable's appeal lies in its outstanding toughness and its easy access to components.
Thicker and heavier than the average ultrabook, the Folio 13 may actually be a more sensible option for many users.
