Lesson 2: tools and tricks of the trade


     When you break into a program you end up in portions of code
that are unfamiliar to you. It is also not uncommon for the
breakpoints to occur outside of the confines of the program you
want to crack. Getting your bearings is, in these cases, very
     One of the handiest utilities is the memory dump tool -it
tells you where all the device drivers and TSR are loaded, in
which memory locations the program you are cracking dwells, how
much memory is left and what the next program load point is. The
tools you use should report on the following:
-    the contents of interrupt vectors
-    the state of the BIOS data area, beginning at address 40:0
-    internal structures within DOS, such as the MCB chain, the
     SFT (System File Table) chain, the chain of installed
     device drivers, the PSPs and memory allocations associated
     with installed TSRs
-    memory allocation statistic from XMS and EMS drivers

     When seeking to understand a section of foreign code, you
must be especially careful to seek the real intent of the code.
Consider using a profiler prior to undertaking an analysis of an
unfamiliar program. This will help you by ensuring that you don't
waste time studying sections of the program that aren't even
involved in the protection scheme you are chasing down.
     Using a utility that charts a program's calling hierarchy
can give you an important perspective on how your babe conducts
its internal operations.

     First and foremost, your debugger must be designed for use
with resident modules (or must be itself a resident module).
Trying to crack with simplistic [] is a sure way to get
absolutely nowhere. We recommend Softice.exe from Nu-Mega
technologies (Version 2.6 [S-Ice.exe] has been cracked by MARQUIS
DE SOIREE and its vastly available on the Web). You could also
use [Periscope] or [Codeview] or Borland's Turbodebugger... all
these programs have been boldly cracked and/or distributed and
are now on the Web for free... learn how to use YAHOO and find
them. In emergency cases you could fix some quick crack using
[debug] or [symdeb], but, as said above, most of the time these
older debuggers won't do. I'll nevertheless ALWAYS give the final
crack procedure for [], in order to permit even lusers
to crack programs.
     When you first smell a protection, it can be tempting to
immediately begin your crack using invasive types of techniques.
While there is certainly nothing wrong with this approach,
provided that you are fairly familiar with the protection scheme
used, going in too deep too soon can be a problem when you don't
have a strong hunch. Most of the time you'll end up missing
important details. So first of all sit down and ponder... that's
the zen-way, the only one that really works.
     Single-stepping is expensive, not only because of the time
it requires but also because of the amount of detail with which
you must contend. Your immediate goal is to home in on the
protection scheme through a series of successively refined traps,
your broader aim is to get an overview idea of the program's
action... the wise use of breakpoints will condense these
minutiae into an understandable form.
     The first step is to try to identify the section of the
program where the protection scheme is snapping.
     Once you are able to isolate a certain section of a program,
breakpoints can be used to gather a trace history of the
program's execution. If your debugger sports a backtrace buffer,
logging window, or similar feature, by all means learn how to use
it. The debugger it's your best weapon, you must know all the
possibilities it offers and all the capabilities it possesses.
Having a debugger's display output echoed to a printer is another
     Using breakpoints is beneficial for two basic reasons: speed
and reduction of detail. Manual single-stepping is invaluable
when you are close to the protection scheme, but too much of it
will bore you to death.
     When selecting breakpoint locations and the types of
breakpoint to use, it is important to step back once more, drink
a cool Martini-Wodka (use only Moskovskaja: non-russian Wodkas
are appalling) and ask yourself: "What is this going to tell me?"
and "What else will I need to know once the break occurs?". MOST
IMPORTANT OF ALL: "Is my current cracking approach the simplest
and most direct?", coz you do not want to waste precious cracking
     When devising a set of breakpoints it is wise to consider
how "a trail of bread crumbs" can be left. Not allowing for an
execution chronicle from the start can mean having to restart a
cracking session.
     Setting breakpoints on certain software interrupt calls is
an excellent way to get an overview of a program's operations.
The INT_21 DOS services interrupt is probably the most universal
useful of these, with BIOS interrupts such as the INT_13 (BIOS
Disk services) and INT_16 (BIOS keyboard services) useful for
specific cracking.
     When working with a debugger, evaluative breakpoints are
usually your best shot. To avoid having to deal with a plethora
of calls, you would want to have a debugger capable of being told
to "break on any INT_21 call except where AH == 2C or AH == 0B".
     A real understanding of the working of a program is surely
important, but don't overdo it! To reverse-engineer even a small
program can involve many hours of analysis and documentation
work. If you'll not be able to use the zen-cracking techniques
described in this tutorial (sadly not everybody can) pace
yourself and make sure your chair is comfortable: you'll be
sitting for quite a spell.
     Much of the work involved in reverse-engineering consist of
chasing down tentacles. In order to understand the operations of
one function, you must understand what happens within each of the
functions it calls- its child functions. To understand these
child functions you must study their children; and so on down the
calling hierarchy tree. Then there is the data. Tracing tentacles
based on a program's calling hierarchy is a directed process.
Each function you encounter is basically a list of other
functions you must reckon with. When it comes to analyzing a
function's interrelationship with the program's data structure,
no such list is provided. You must have instinct, feeling and
     Data analysis requires more of a broad-based inquisition.
For each memory variable you are interested in, you must survey
all functions to determine which ones read and write that
variable. The use of memory conditional breakpoints and of a
disassembler that builds a cross-reference table can make this
task a lot easier. (Use Sourcer! It's a fairly good tool and
version 4.08 of [sr.exe] has been long ago cracked and
distributed on the Web).

     Remember that if the program you are cracking was written
in assembler in the first place (very unlikely knowing the
laziness of to_days programmers), system calls are probably made
directly from the functions which need them. But when a program
is developed in a high-level language, it is more likely that
common library functions will be used for many operations
involving system calls. When a program makes all of its INT_21
calls from the same location, you know that this is certainly the
     Now, what happens sometimes is that the programmers write
the whole application in a overbloated language like C++, but are
afterwards compelled to "speed up" critical sections of the code
writing them in assembler. And loo! A section where you
repeatedly find assembler crafted patches is precisely the
protection scheme! So you could have a program with all INT_21
calls from the same location but for one or two calls which are
coming out of the section where the morons have "hidden" their
protection strategy. By just "looking" at the dead code of a
program, you should be capable to tell wich parts have been
"added on" in a later phase. They presents themselves as
unevenness and irregularities, especially if you use an utility
that represents graphicallly the code of a program. Protections
are often added on at the end of the development.
     Should you determine that the system calls relevant to your
cracking are made from common library functions, all is not lost.
The specific function from which these library calls were made,
the function you are seeking to locate, is executing at some
point in between these calls. Break in with your debugger at the
end of the first system call, just where it is returning to the
point of call. From there, trace through the remainder of the
common library routine until it returns to its caller. In short
order, you should find yourself in the function you need to see.
The trick is to be able to identify it for what it is.

     In the interest of gaining an overall familiarity with the
program you want to crack, it can be enlightening to use a hex
dump utility to examine the message strings contained within the
program's binary modules. If the program happens to load its
message strings from separate files, your search has just been
     Your debugger's memory-dumping feature is one tool that can
be useful for this type of exploration. You could also construct
a filtering program, which would read a binary file and output
all sequences of bytes that are comprised of displayable
characters and are over a certain minimum length (the best
cracker tools are often the ones you write yourself).
     When a protection scheme is marked by the issuance of a
specific message on the screen, you could go into the program and
locate the code that emits this message, and then determine what
triggers it. A good way to start the location process is to see
if a system call is used to display the string. Interrupt INT_21,
INT_10 or INT_29 are usually used to display text messages to the
     When the message's display is not a result of one of these
system calls, direct video writing is probably being used. If you
know the screen location used, and if that part of video memory
is not used for anything else at the time (a big if), a memory
write breakpoint could be set on the video buffer address
corresponding to the first character's position. If this won't
work, use the step-over/step-around tracing technique while
watching for the message to appear.
     Now you found it: from a disassembled listing, you locate
the address of the message string and then survey the reminder
of the file for any instructions that reference this address.
[Sourcer] can generate labels for specific memory locations and
a cross-reference table showing where these labelled locations
are referenced. Otherwise, load the disassembled listing file
into your editor and use its search capabilities. Manually
searching for such things in a listing will make you old before
your time.

     When stepping through code at the assembler level, watch out
for interrupt calls that are followed by data. Sometimes you will
find an interrupt call, typically within the range INT_34 to
INT_3F, where several bytes immediately following the interrupt
instruction will be data rather than code.
     Be especially suspicious of this type of code-and-data
mixture when your debugger's disassembly output of the
instructions immediately following an interrupt call doesn't make
sense. Sometimes you  can determine the offset of the next true
instruction by inspecting the following code and data. In other
cases, you will have to trace through the interrupt call to see
how it accesses the data following the interrupt call instruction
and how it manipulates the return address on the stack.

     Seeing what interrupt intercepts already exist within a
system before running the program you want to crack, as well as
what interrupt handlers are established by the target program,
can provide useful clues. For example, if a protection
establishes an INT_09 intercept just before the snapping of a
keyboard verification routine, your range of suspects has just
been narrowed significantly.
     To study the interrupt vector activities of an application,
a vector dump map utility is useless. It can't be run while
running the application you want to crack. One solution is to run
the program under a debugger and watch for system calls to INT_21
functions 25h (set interrupt vector) and 35h (get interrupt
vector), but in the event that the program  reads and writes
interrupt vectors directly, this method will not give you a
complete picture. Normally you'll use a spy, trace or "step"
TO THE ENTIRE TABLE is another way to deal with this.
     Note that some sort of direct vector writing must be
occurring if a vector change is detected between system calls.
     If a vector change is detected during a system call but it
isn't function 25h of INT_21, suspect that an IRQ handler may be
effecting the change.

*    determining interrupt vector addresses ****************
     How do you determine the interrupt vector addresses? As
example let's find the address of the INT_21 interrupt vector.
Since the interrupt vector table starts at address 0000:0000
(easy to remember, isn't it?) and there are four bytes per
vector, the basic process is to multiply the interrupt number
four times and use the result at the offset (on segment zero).
21h + 21h = 42h                         42h + 42h = 84h
The int_21 vector is located at address 0000:0084
You could also use a calculator, for instance, the address of
INT_63 is 63h*4=18ch               ->   0000:018C 
* address conversion ***************************************
     After a painstaking cracking session, you have finally
determined that a byte of memory at address 6049:891C is the
trigger. But when you isolate the offending instruction, you find
that the address it is generating when the protection occur is
different, being 6109:7D1C instead! How can this be?
     An 80x86 type CPU, when running in real or VM86 mode, uses
what is known as segment:offset type addressing. One side effect
of this addressing method is that one physical address can be
equivalent to many different segment:offset addresses.
     To find the PHYSICAL ADDRESS for a given segment:offset do
the following:
- convert the segment portion of the address to a 1-based number
by multiplying it by 16 (x10)... it's easy: add 0 at the right
end of the number!... 
     6049 -> 60490
     6109 -> 61090
now all you have to do is to add this value to the offset value
     60490+891C  -> 68DAC     
     61090+7D1C  -> 68DAC          <-   Got it?

And the other way round? If you have a physical address, say
19AC3, and you want to obtain a segment:offset address you must
first of all decide in which segment you want the address... if,
say, you choose segment 16CC, you proceed as follows:
     16CC           -> 16CC0
     19AC3-16CC0    =  2E03 (offset)
     address for 19AC3 in segment 16CC = 16CC:2E03

Before starting this section, for those of you that do not know
anything, here is the ARCHIE way you get all the program that do
EXIST on the planet: e-mail following
1) (address) 
I use this french archie, but you can get a worldwide list using
the metacommand "servers"
2) (text)      set search sub      <- anywhere in string
               set maxhits 140     <- (100-1000)
               set maxhitspm 15    <- not just 1 file all over
               find stepdos        <- search e.g. this file
Wait two hours, get your post and ftp the file you wanted (and
YES!, you 'll find also EVERYTHING else for free on the Web).
You could, instead of using archie, also learn how to use YAHOO.

     One of the most fascinating tools that I have ever seen is
a (very old) program: MEMSCAN.EXE.
This program was originally written in 1988 by Scott A. Mebust,
running in CGA. It's a "visual" utility: it enables you to see
graphically the 1-meg of PC memory in 8 kbyte chunks. It's a
powerful tool in order to locate quickly bit mapped graphics and
other 'objects' in memory, like program data tables, stack areas,
code areas, available RAM, etc. I used this great idea to create
(in C) my own tools: a "dead_programs scanner" and an ameliorate
version of Memscan itself. Looking at the VISUAL STRUCTURE of a
program it's a great help when you'll crack higher levels.

     A very good tool by James W.Birdsall, tracks memory usage
of programs (EMS, XMS, conventional).

     "THE" scancode lister, by the code_masters from clockwork
software. The must utility for crackers that do not learn all
scancodes by heart.

     Actually "MAP2", THE memory mapper from the code_masters at
clockwork software. It's a very good tool and an interesting one
too, coz you get it with the "Nigel" nag screens. They are not
difficult to remove (a "passletter" protection scheme, you'll
learn how to find and remove it from [Map.exe] in LESSON 3.2).

     There are hundred of file dump utilities, coz file dumping
is one of the first exercise they learn you at C-school. is 558 bytes long, Tdump.exe 120.704, pick the one
you like better or write your own (even better).,
by Daniel M.O'Brien, 1046 bytes long, it's nice.

     That's a good crack utility indeed! This 1989 program by
Daniel M.O'Brien gives you a "post-mortem" picture of your
memory. You redirect it to <myfile> and study it at ease. It's
difficult to say how many hours of cracking it did spare me (you
should study the program, only 252 bytes long, and will have to
modify it a bit, coz it's pretty primitive, in the original
version, for instance, the redirection to the printer works only
if there is NO SPACE between "spray" and ">").

     A good EXE files analyzer, useful for windows programs too
(see --> LESSON 7). Some of its functions are present in
TDUMP.EXE too. This 1991 program by S.Krupa it's sometimes very

     A must to study the "calling hierarchy" of an unknown
program. KGB.EXE, a 1992 program by Petr Hor…k could easily be
the best one, and comes with source code(!). I'll teach you how
to crack without any of them (you do not need them if you zen-
crack), but they can nevertheless be very useful in some
situations. Stepdos.exe, by Mike Parker, is a excellent program:
a pleasure to crack in order to use it for slightly different
purposes :=)
     SR.EXE can be used for sourcering unknown programs. It's a
fairly good sourcering tool. Version 4.08 has been cracked (it's
a "ORIGINAL NUMBERCODE" protected program) and distributed on the
Web, so you should easily find it. This said, you should NEVER
use such a brute force approach, unless you are really desperate:
I'll teach you how to crack without sourcering (you don't need
to sourcer if you zen-crack). 
Every idiot has written at least one hexeditor, and you can find
very bad tools everywhere (the SIMTEL collection, on the Web,
lists at least 35 hexeditors). I suggest you write your own and
contribute to the flood, or (better) get PSEDIT.EXE, a good 1990
program by Gary C. Crider (Parity Solutions, 1903 Pavia Ct.
Arlington, TX 76006... sometimes even americans can write good
programs). If you do use it (as you should) disapt the nag screen
as small exercise in cracking.

     Your best friend in cracking, your weapon, your hidecloak...
I suggest [Softice.exe] from Nu-Mega technologies (Version 2.6
has been cracked by MARQUIS DE SOIREE and its vastly available
on the Web). You could also use [Periscope] or [Codeview] or
Borland's Turbodebugger... all these programs have been boldly
cracked and/or distributed and are now on the Web for free...
learn how to use ARCHIE and YAHOO in order to find them. Your
debugger is the only tool you 'll REALLY need, believe me. So
choose your weapon wisely and learn how to use backtrace ranges
and (FOREMOST!) breakpoint on user written qualifications
routines. You 'll be able to crack almost EVERYTHING using these
features in the right way. 

     You should get all the programs mentioned above (all the
programs that EXIST for that matter) for free on the Web. Use
them, but also modify them recklessly! REMEMBER THAT YOU ARE
(GOING TO BE) A CRACKER! The first programs you should crack and
modify are therefore your very tools! So steal the code of the
best tools you find! Snatch the best routines and change them for
the better! That's the whole point in cracking: a mission to
IMPROVE the best accomplishments of humanity's genius :=)

     You 'll learn, beginning with next lesson, how to crack
systematically the different protection schemes: paper & password
protections, time protections, access protections. At the end of
the "methodolocical" part, you'll be able to deprotect programs,
but you still wont be a cracker. In order to crack higher you
must use what I call (lacking a better definition) "zen-
cracking". I 'll give you right now an example of this, so that
you know what I'm talking about, but -unless you are already
capable- you'll have to finish this tutorial part for "normal"
cracking before attempting this techniques. Let's zen-crack
together a password protection scheme (aka "paper protection",
coz you need the original manual of the program in order to
answer). This protection is based on the typing, at the nag
screen, of the correct sequence of numbers. Our example is a game
for the reasons explained in lesson 1, but you 'll find the SAME
protection scheme in the access protection procedure of some old
Tapestry networks... so do not frown upon games protections.

INDIANAPOLIS 500, Papyrus software & Electronic Arts, 1989
It's a rather widespread program, you should therefore find it
pretty easily. The nag screen asks for data based on the
historical performances of race cars... that means that the
answers will consist in two to three digits. 
     Now, the normal way to crack such a program (described in
-> lesson 3.1) embodyes following steps:
-    snap save program memory areas before typing your answer
-    snap compare after typing, say, "666"
-    search for the sequence 36,36,36 (i.e. 666)
-    breakpoint on memory range for reading
-    look at the program part fetching your data
-    find the snap procedure
-    disable it.
     The above crack it's relatively quick and should be most of
the time fairly effective, but there is a better way: the "zen
way", the only one that can really enable you to crack high
protection schemes.
-    Run the program and break in at the nag screen
-    Answer consist of 2-3 digits? Search for "AC" (i.e. the
instruction LODSB, load digit of answer in AL) in the area 500
bytes BEFORE and 500 bytes AFTER your position. You'll get some
locations. (In the case of INDY 500 you get 6 such locations).
-    "feel" the locations (that's the tricky part).
-    OK, you already made it! Here is the protection strategy:
  8BBF28A5     MOV  DI,[BX+A528]<-- DI points to coded data area
  AC      LODSB          <-- load first digit of answer in AL
  B4FF    MOV  AH,FF     <-- load mask in AH
  2A25    SUB  AH,[DI]   <-- sub coded data from mask and get
                         real answer
  47      INC  DI        <-- ready to get next coded data
  3AC4    CMP  AL,AH     <-- user answer = real answer ?
  751A    JNZ  beggar_off_coz_false_answer
  0AC0    OR   AL,AL     <-- more numbers?
  75F2    JNZ  compare_loop
  59      POP  CX        <-- all OK, go on, nice guy
And if the protection scheme had been more far away? And if you
cannot "feel" the right one? And if my grandma had wheels? You'll
learn it, believe me.
Now let's quickly crack this crap.
CRACKING INDY.EXE (by +ORC, January 1996)

ren indy.exe indy.ded
symdeb indy.ded
-    s (cs+0000):0 Lffff B4 FF 2A 25 47 3A C4 75 1A
xxxx:yyyy           <-- this is the answer of the debugger
-    s (cs+1000):0 Lffff B4 FF 2A 25 47 3A C4 75 1A
(nothing, but you must be sure there isn't a mirror)
-    e xxxx:yyyy+8 00    <-- "JNZ 1A ahead" changes to "JNZ 0"
-    w
-    q
ren indy.ded indy.exe
Cracked: you just changed the JNZ beggar_off instruction in a JNZ
go_ahead_anyway. Nice, isnt'it?

     Strange as it may seem, the reasons for cracking are very
important for the success of our task. We (at least we old
crackers) crack AGAINST society, and OPPOSING laws and
conventions. We usually DO NOT crack for money or for other
"commercial" reasons (just sometimes, and we are expensive: I
have plenty of money already and my services are VERY expensive
if you need an aimed deprotection). But in general we don't care
much for money and -as you can see- I am giving away the basis
of what I know for free with this tutorial. The programs we crack
should be made free for everybody, even if we spent some of our
time deprotecting them. We could not care less of the commercial
value of a given program, not to mention the holy work of the
ethical programmers... we program ourselves, but only because we
LIKE it... if somebody does something only in order to gain
money, he does not deserve anything. It's the mind challenge that
counts, NEVER the profit! (Even if you can make good use of the
cracked programs and even if -as I said- there is at times a
personal profit). 
     This is an indispensable attitude! Only a non-mercantile
mind can leap forward to the "satori" knowledge that you
desperately need if you want to crack quickly and elegantly huge
iperbloated monstruosities that somebody else wrote and
protected, or if you want to gain access to some hidden
information, data that you would like to snoop but that somebody
declared "off limits", coz a stupid government, or useless
industry sector, or money oriented programmer or dirty lobby of
interest decided it. 
     If you do accept the society where we are compelled to live,
its awfully egoistic way of life and its dirty "profit" values,
you may eventually learn how to disable some simple protections,
but you'll never be able to crack in the "right" way. You must
learn to despise money, governments, televisions, trends,
opinion-makers, public opinion, newspapers and all this
preposterous, asinine shit if you want to grasp the noble art,
coz in order to be emphatic with the code you must be free from
all trivial and petty conventions, strange as it may sound. So
you better take a good look around you... you'll find plenty of
reasons to hate society and act against it, plenty of sparks to
crackle programs in the right way... Hope all this did not sound
too cretin. 

Well, that's it for this lesson, reader. Not all lessons of my
tutorial are on the Web.

     You 'll obtain the missing lessons IF AND ONLY IF you mail
me back (via with some tricks of the trade I may
not know that YOU discovered. Mostly I'll actually know them
already, but if they are really new you'll be given full credit,
and even if they are not, should I judge that you "rediscovered"
them with your work, or that you actually did good work on them,
I'll send you the remaining lessons nevertheless. Your
suggestions and critics on the whole crap I wrote are also

E-mail +ORC