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The Amatuer Crackist Tutorial

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     VOL 1                                                   NUM 1

                     The Amatuer Crackist Tutorial
                              Version 1.3
                            Specular Vision

                          Special Thanks to:
                            Mr. Transistor
                           The Grand Elusion
                            Banzai Buckaroo

                      Another fine PTL Production
                        Call The Myth Inc. BBS
     Table of Contents:
     ------------------       (Page  Numbers will be aprox.  until
                                  final version is finished)
          i.        Table of Contents                         2

          ii.       Introduction                              3

          I.        How to Crack                              4
                      Debugging DOS                           4
                      Cracking on the IBM PC Part 1           7
                      Cracking on the IBM PC Part 2          11

          II.       Example Cracks                           14
                      Mean-18 by Accolade                    14
                      Submarine by Eypx                      18
                      Space Station Oblivion by Eypx         22

          III.      Removing Doc Check Questions             23
                      F-15 Strike Eagle by MicroProse        23
                      Battlehawks 1945 by Lucasfilms         25
                      Yeager's AFT by Electronic Arts        26

          IV.       Cracking Self Booters                    27
                      Disk Basics
                      Victory Road by Data East              27
                      MS-Flight Simulator (Ver 2.x)          30

          V.        Creating Title Screens                   33

          VI.       Appendix                                 35
                      A - Interrupt Tables                   36
                          (This will be an add-on file)


     Due to the current lack of Crackers, and also keeping in mind
     the  time it took me to learn the basics of cracking,  I  de-
     cided  to put this tutorial together.   I will  include  many
     files which I have found helpful in my many cracking  endeav-
     ors.   It also has comments that I have included to  make  it
     easier to understand.

     Comments Key:

     Comments in the following material will be made by one of the
     following  and the lines that enclose the comments  show  who
     made the comment.

     Specular Vision = -------------
     Mr. Transistor  = +++++++++++++
     Ironman         = |||||||||||||

     Special thanks to Mr.  Transistor, for coming out of "Retire-
     ment" to help compose this document.

     Chapter I                                        How to Crack

     Let's start with a simple introduction to patching a  program
     using the DOS DEBUG program.  The following article will  in-
     troduce you to the basic ideas and concepts of looking for  a
     certain area of a program and making a patch to it.

     By:            Charles Petzold / Specular Vision
     Title:         Case Study: A Colorful CLS

       This article originally appeared in the Oct.  14,1986 Issue
     of PC Magazine (Vol 15. Num 17.). Written by Charles Petzold.

       The hardest part of patching existing programs is determin-
     ing  where the patch should go.  You really have to  make  an
     intelligent guess about the functioning of the program.

       As an example,  let's attempt to modify COMMAND.COM so that
     is colors the screen on a CLS command.   As with any type  of
     patch try it out on a copy and NOT the original.

       First, think about what we should look for.  CLS is differ-
     ent from all the other DOS internal Commands,  It is the only
     internal command that does something to the screen other than
     just write to it with simple teletype output.  CLS blanks the
     screen and homes the cursor.   Since it can't do this through
     DOS Calls (unless ANSI.SYS is loaded), it is probably calling
     the BIOS Directly.   The BIOS Interrupt 10h call controls the
     video,  and so the CLS command probably uses several INT  10h
     instructions.  The machine code for INT 10h is CD 10.

       (While  this  same method will work under  any  version  of
     PC-DOS,  Version 2.0 and later, the addresses I'll  be  using
     are from PC-DOS 3.1. Other versions of PC-DOS(or MS-DOS) will
     have  different addresses;  you should be absolutely  certain
     that you're using the correct addresses.)

       Load COMMAND.COM into DEBUG:

                    DEBUG COMMAND.COM

     and do an R (Registers) command.  The size of COMMAND.COM  is
     in  register CX.   For DOS 3.1's COMMAND.COM,  this value  is

       Now do Search command to look for the CD 10 bytes:

                    S 100 L 5AAA CD 10

     You'll get a list of six addresses, all clustered close to-

     gether.  The first one is 261D. You can now pick an address a
     little before that (to see what the first call is doing)  and
     start disassembling:

                    U 261B

      The  first INT 10 has AH set to 0F which is a Current  Video
     State  call.   The code checks if the returned  value  of  AL
     (Which  is  the  video mode) is less than 3 or  equal  to  7. 
     These are the text modes.   If so,  it branches to 262C.   If
     not, it just resets the video mode with another INT 10 at ad-
     dress 2629.

       At 262C,  the code first sets the border black (the INT  10
     at  2630),  then does another Current Video  State  call  (at
     2634) to get the screen width in register AH.  It uses infor-
     mation from this call to set DX equal to the bottom right row
     and column.   It then clears the screen by scrolling the  en-
     tire screen up with another INT 10 (at 2645),  and then  sets
     the cursor to the zeroth row and zeroth column with the final
     INT 10 (at 264D).

       When it scrolls the whole screen, the zero value in AL  ac-
     tually  means blank the screen,  the value of BH is  the  at-
     tribute  to be used on the blanked area.   In  an  unmodified
     COMMAND.COM,  BH is set to 7 (Which is white on black) by the
     following statement at address 2640:

                    MOV  BX,0700

       If  you  prefer a yellow-on-blue attribute  (1E),  you  can
     change this line by going into Assemble mode by entering:


     then entering

                    MOV  BX,1E00

     and exiting Assemble mode by entering a blank line.

       Now you can save the modified file:


     and quit DEBUG:


       When  you load the new version of COMMAND.COM (and you  can
     do so without rebooting by just entering:


     on  the DOS command level),  a CLS will turn the screen  blue
     and display characters as yellow.

       If it doesn't or if anything you type shows up as white  on
     black,  that probably means you have ANSI.SYS loaded.  If you
     use ANSI.SYS,  you don't have to make this patch but can  in-
     stead use the prompt command for coloring the screen.


     That was just one section of a very large article that helped
     me  to get started.   Next we'll look at two other  articles,
     both written by Buckaroo Banzi.   These two articles  CRACK-1
     and  CRACK-2 give you an introduction to the  different  copy
     protection schemes used on IBM PC's, and how to find and  by-
     pass them.

     By:            Buckaroo Banzai
     Title:         Cracking On the IBM PC Part I

       For  years,  I have seen cracking tutorials for  the  APPLE
     computers,  but never have I seen one for the PC.  I have de-
     cided to try to write this series to help that pirate move up
     a level to a crackest.

       In this part, I will cover what happens with INT 13 and how
     most copy protection schemes will use it.  I strongly suggest
     a  knowledge of Assembler (M/L) and how to use  DEBUG.  These
     will be an important figure in cracking anything.

     INT-13 - An overview

       Many  copy  protection  schemes  use  the  disk   interrupt
     (INT-13).  INT-13 is often use to either try to read in a il-
     legally   formatted   track/sector  or  to   write/format   a
     track/sector that has been damaged in some way.

       INT-13 is called like any normal interrupt with the  assem-
     bler  command INT 13 (CD 13).  [AH] is used to  select  which
     command to be used, with most of the other registers used for

     INT-13 Cracking College
       Although,  INT-13 is used in almost all protection schemes,
     the easiest to crack is the DOS file.  Now the protected pro-
     gram  might use INT-13 to load some other data from a  normal
     track/sector on a disk, so it is important to determine which
     tracks/sectors  are  important to the protection  scheme.   I
     have  found  the best way to do this is to  use  LOCKSMITH/pc
     (what, you don't have LS. Contact your local pirate for it.)

       Use LS to analyze the diskette. Write down any track/sector
     that seems abnormal.  These track are must likely are part of
     the protection routine.   Now, we must enter debug. Load in

     the  file  execute a search for CD 13.   Record  any  address

       If no address are picked up,  this mean 1 or 2 things,  the
     program is not copy protected (right...) or that the check is
     in an other part of the program not yet loaded.   The  latter
     being  a real hassle to find,  so I'll cover it in  part  II. 
     There is another choice.   The CD 13 might be hidden in  self
     changing  code.   Here is what a sector of hidden code  might
     look like

     -U CS:0000
     1B00:0000 31DB     XOR    BX,BX
     1B00:0002 8EDB     MOV    DS,BX
     1B00:0004 BB0D00   MOV    BX,000D
     1B00:0007 8A07     MOV    AL,[BX]
     1B00:0009 3412     XOR    AL,12
     1B00:000B 8807     MOV    [BX],AL
     1B00:000D DF13            FIST   WORD...

       In  this  section of code,  [AL] is set to DF  at  location
     1B00:0007.   When you XOR DF and 12,  you would get a CD(hex)
     for  the  INT opcode which is placed right next to a  13  ie,
     giving you CD13 or INT-13.   This type of code can't and will
     not be found using debug's [S]earch command.

     Finding Hidden INT-13s

       The  way I find best to find hidden INT-13s,  is to  use  a
     program called PC-WATCH (TRAP13 works well also).   This pro-
     gram  traps  the interrupts and will print  where  they  were
     called  from.   Once running this,  you can just  disassemble
     around  the address until you find code that look like it  is
     setting up the disk interrupt.

       An  other way to decode the INT-13 is to use  debug's  [G]o
     command.   Just  set  a breakpoint at  the  address  give  by
     PC-WATCH  (both  programs give the return address).   Ie,  -G
     CS:000F (see code above).   When debug stops,  you will  have
     encoded  not only the INT-13 but anything else leading up  to

     What to do once you find INT-13

       Once you find the INT-13,  the hard part for the most  part
     is over.   All that is left to do is to fool the computer  in
     to thinking the protection has been found.   To find out what
     the computer is looking for, examine the code right after the
     INT-13.  Look for any branches having to do with the

       CARRYFLAG or any CMP to the AH register.  If a JNE or JC
      (etc) occurs, then [U]nassembe the address listed with the
     jump.  If it is a CMP then just read on.

       Here you must decide if the program was looking for a  pro-
     tected  track or just a normal track.   If it has a CMP  AH,0
     and it has read in a protected track,  it can be assumed that
     it  was looking to see if the program had  successfully  com-
     plete  the  READ/FORMAT of that track and that the  disk  had
     been  copied thus JMPing back to DOS (usually).   If this  is
     the case,  Just NOP the bytes for the CMP and the correspond-
     ing JMP.

       If  the program just checked for the carry flag to be  set,
     and it isn't,  then the program usually assumes that the disk
     has been copied. Examine the following code

           INT 13      <-- Read in the Sector
           JC 1B00     <-- Protection found
           INT 19      <-- Reboot
     1B00  (rest of program)

       The program carries out the INT and find an error (the  il-
     legally formatted sector) so the carry flag is set.  The com-
     puter,  at the next instruction,  see that the carry flag  is
     set  and know that the protection has not been  breached.  In
     this case, to fool the computer, just change the "JC 1B00" to
     a "JMP 1B00" thus defeating the protection scheme.

     NOTE: the PROTECTION ROUTINE might be found in more than just
           1 part of the program

     Handling EXE files

       As we all know,  Debug can read .EXE files but cannot write
     them.   To get around this,  load and go about  cracking  the
     program as usual.   When the protection scheme has been found
     and tested, record (use the debug [D]ump command) to save + &
     - 10 bytes of the code around the INT 13.    Exit back to dos
     and  rename the file to a .ZAP (any extension but  .EXE  will
     do) and reloading with debug.  Search the program for the 20+
     bytes  surrounding  the code and record  the  address  found. 
     Then  just load this section and edit it like  normal.   Save
     the  file and exit back to dos.   Rename it back to the  .EXE
     file and it should be cracked.  

     ***NOTE:  Sometimes  you have to play around with  it  for  a
               while to make it work.

     DISK I/O (INT-13)
       This interrupt uses the AH resister to select the  function
     to be used.  Here is a chart describing the interrupt.

     AH=0    Reset Disk
     AH=1    Read the Status of the Disk
             system in to AL

         AL          Error
         00   - Successful
         01   - Bad command given to INT
        *02   - Address mark not found
         03   - write attempted on write protected disk
        *04   - request sector not found
         08   - DMA overrun
         09   - attempt to cross DMA boundary
        *10   - bad CRC on disk read
         20   - controller has failed
         40   - seek operation failed
         80   - attachment failed
     (* denotes most used in copy protection)
     AH=2    Read Sectors

          DL = Drive number (0-3)
          DH = Head number (0or1)
          CH = Track number
          CL = Sector number
          AL = # of sectors to read
       ES:BX = load address
           AH =error number (see above)
               [Carry Flag Set]
           AL = # of sectors read

     AH=3 Write (params. as above)
     AH=4 Verify (params. as above -ES:BX)
     AH=5 Format (params. as above -CL,AL
                  ES:BX points to format

       For more information on INT-13 refer to appendix A.


     In part II,  Buck cover's Calls to INT-13 and INT-13 that are
     located  in  different overlays of the program.   This  is  a
     method that is used often.

     Cracking Tutorial II.

     By:            Buckaroo Banzai
     Title:         Cracking On the IBM PC Part II


       OK guys,  you now passed out of Copy Class 101 (dos  files)
     and have this great new game with overlays.   How do I  crack
     this one.  You scanned the entire .EXE file for the CD 13 and
     it's nowhere.  Where can it be you ask yourself.

       In  part II,  I'll cover cracking Overlays and the  use  of
     locksmith in cracking.   If you haven't read part I,  then  I
     suggest you do so.  The 2 files go together.

     Looking for Overlays
       So, you cant find CD 13 in the .EXE file, well, it can mean
     4 things. 

          1:  The .EXE (though it is mostly .COM) file is  just  a
              loader for the main file. 

          2:  The .EXE file loads in an overlay.  

          3:  The CD 13 is encrypted &/or hidden in the .EXE file. 

          4:  Your looking at the WRONG file.

       I  won't  discuss case 1 (or at least no here)  because  so
     many UNP files are devoted to PROLOCK and SOFTGUARD,  if  you
     can't figure it out with them, your stupid.

       If you have case 3, use the technique in part I and restart
     from the beginning. And if you have case 4, shoot your self.

       You  know  the program uses overlays but don't see  and  on
     disk?   Try looking at the disk with good old Norton's.   Any
     hidden files are probably the overlays.   These are the  ones
     we  are after.   If you still can't find them,  use  PC-WATCH
     (this program is a must!!! For all crackists.   Traps ALL in-


     Using PC-Watch to Find Overlays
       Start up PC-Watch and EXCLUDE everything in the left  Col.. 
     Search  the  right Col.  until you find DOS21 -  OpnFile  and
     select it.  

          Now run the program to be cracked.  
          Play the game until the protection is checked.  
          Examine  you PCWatch output to see what file was  loaded
           right before it.  
          This probably is the one holding the check.  
          If not, go through all the files.

     You Have Found the Overlays
       Great,  now just crack the overlay as if it was a DOS file. 
     You don't need to worry about .EXE file,  debug can write  an
     overlay  file.   Part I explains the basics of  cracking.   I
     suggest that you keep a backup copy of the overlay so if  you
     mess up,  and you will, you can recover quickly. Ah,  and you
     thought cracking with overlays was going to be hard.

     Locksmith and Cracking

      The  copy/disk utility program Locksmith by AlphaLogic is  a
     great tool in cracking.   It's analyzing ability is great for
     determining what and where the protection is.

      I find it useful,  before I even start cracking,  to analyze
     the  protected  disk to find and id  it's  protection.   This
     helps in 2 ways.   First,  it helps you to know what to do in
     order to fake out the protection.   Second,  it helps you  to
     find what the program is looking for.

      I  suggest that you get locksmith if you don't already  have
     it.   Check your local pirate board for the program.   I also
     suggest  getting PC-Watch and Norton Utilities 3.1.(Now  4.1)
     All of these program have many uses in the cracking world.


     Chapter II                                     Example Cracks

     OK,  now let's put some of this information into practice  by
     examining a few cracks of some common programs.   First we'll
     look at a Crack for Mean-18 Golf by Accolade.   Accolade  has
     been one of those companies that has a fervent belief in Copy

     Title:         MEAN-18 UnProtect For CGA/EGA Version

     This crack works by eliminating the code that tests for known
     bad  sectors  on the original diskette to see if  it  is  the
     genuine article or an illegal copy.   The code begins with an
     INT 13 (CD 13 HEX),  a DOS BIOS disk service routine followed
     a few bytes later by another INT 13 instruction.  The program
     then checks the returned value for the bit configuration that
     signifies the bad sectors and, if all is as expected, contin-
     ues on with program execution.

     The code that needs to be patched is in the GOLF.EXE file and
     in the ARCH.EXE file.  It is identical in both files and lies
     near the end of each file.

     In the following steps,  you'll locate the start of the  test
     code and patch it by replacing it with NOP instructions  (HEX
     90).   The  method described uses the DOS DEBUG  utility  but
     Norton's Utility (NU) works too.

     Copy  all  of the files from the MEAN-18 disk  onto  a  fresh
     floppy  using  the DOS COPY command and place  your  original
     diskette out of harm's way.

     Assuming DEBUG is in the A:  drive and the floppy  containing
     the files to be unlocked is in the B: drive , proceed as fol-

     First  REName  the  GOLF.EXE  file  so  it  has  a  different
     EXTension other than .EXE.

                    REN GOLF.EXE GOLF.DEB

     Next  load the file GOLF.DEB into DEBUG and displays the  "-"
     DEBUG prompt.  

                    A:> DEBUG B:GOLF.EXE

     Search for the beginning of the code to be patched by typing:

                    - S CS:100 FFFF CD 13

     Searches  the file for the two byte INT 13  instruction.   If
     all goes well, two addresses should appear on the screen.


     XXXX indicates that the numbers preceeding the ":"  vary from
     system  to system but the numbers following the ":"  are  the
     same on all systems.  

     The  next  step is to use the "U"  command  as  indicated  to
     un-assemble  a few bytes in order to verify your position  in
     the file)

                    - U CS:019C

     (Un-assembles  32 bytes of code.   Verify the  following  se-
     quence of instructions:

                    INT       13
                    JB        01E9
                    MOV       AL,[BX+01FF]
                    PUSH      AX
                    MOV       AX,0201
                    INT       13
                    POP       AX
                    JB        01E9
                    CMP       AL,F7
                    JNZ       01B5

     These are the instructions you'll be patching out in the fol-
     lowing step)

                    - A CS:019C

     This command assembles the new instructions you enter at  the
     keyboard into the addresses shown.  Beginning at CS:019C, and
     for the next 21 bytes, ending with and including CS:01B0, en-
     ter  the no op command "NOP" (90h) followed by a <return>  or
     <enter>.   Just hit <enter> at address XXXX:01B1 to  end  the
     assemble command.)

                    XXXX:019C  NOP <enter>
                    XXXX:019D  NOP <enter>
                    XXXX:01AE  NOP <enter>
                    XXXX:01AF  NOP <enter>

                    XXXX:01B0  NOP <enter>
                    XXXX:01B1 <enter>

     This just wipes out the section of code containing the INT 13

     Now  do  a HEX dump and verify that bytes 019C  through  01B0
     have been set to 90 HEX.

                    - D CS:019C

     If they have, write the patched file to the disk as follows)

                    - W

     This    writes    the    patched    file    back    to    the                        
     disk where it can be run by typing    GOLF just as before but
     now,  it  can be run from any drive,  including  the     hard

     Now just [Q]uit or exit back to DOS.  This command can be ex-
     ecuted at any "-" DEBUG prompt if you get lost.  No modifica-
     tion will be made to the file on the disk until you issue the
     "W" command.

                    - Q

     The process is the same for the ARCH.EXE file but because  it
     is a different length, the segment address, (XXXX part of the
     address),  will be different.   You should find the first INT
     13  instruction  at address XXXX:019C and the second  one  at
     XXXX:01A8 as before. 

     You  will again be patching 21 bytes and you will start  with
     019C and end with 01B0 as before.   After doing the HEX  dump
     starting  at address 019C,  you again write the file back  to
     the disk with a "W" command then "Q" uit.

     Norton's utilities can also be used to make this patch.   Be-
     gin  by searcing the GOLF.EXE or ARCH.EXE files for  the  two
     byte  combination  CD  13 (remember to  enter  these  as  HEX
     bytes).  Once located, change the 21 bytes, starting with the
     first "CD"  byte, to 90 (a NOP instruction).  As a check that
     you  are in the right place, the byte sequence in both  files
     is  CD 13 72 49 8A 87 FF 01 50 B8 01 02 CD 13 58 72 3C 3C  F7
     75 04.   After modifying the bytes,  write the modified  file
     back to the disk.  It can then be run from any drive.


     That was the first the tutorial cracks,  here's another crack
     based on the same ideas but using Norton's Utilities instead. 
     The  following  is an unprotect method  for  Eypx  Submarine. 
     Eypx is another one of those companies bent on protecting the

     By:            Assembler Magic
     Title:         EPYX Submarine Unprotect

       You  will  only need to make one modification to  the  main         
     executable program of Submarine, SUB.EXE.  I will assume that         
     your  computer  has a hard disk and that you have a  path  to
     DOS. It's time to fire up DEBUG as follows:

                    DEBUG SUB.EXE<cr>

       The computer should respond with a "-" prompt.  Now look at
     the  registers,  just to make sure everything came  up  okay. 
     Type the letter "R"  immediately after the prompt.   The com-
     puter should respond with a few lines of info as follows:
     AX=0000  BX=0001  CX=6103  DX=0000  SP=0080  BP=0000  SI=0000
     DI=0000  DS=12CE ES=12CE SS=37B2 CS=27FC IP=0010 NV UP EI  PL
     NZ NA PO NC
          27FC:0010 8CC0       MOV     AX,ES

       Note  the value of CS is "27FC".   That is the  hexadecimal
     segment address for the beginning of the program code in your
     computer's memory.   It is highly probable that the value you
     see for CS will differ from mine.   Whatever it is,  write it
     down.  Also, the values you see for DS, ES and SS will almost
     certainly differ from mine and should not cause you  concern. 
     The other registers should show the same values mine do,  and
     the flags should start with the same values. 

       Next,  we will do a search for Interrupt 13's.   These  are
     BIOS  (not DOS) Interrupts built into the program  which  are
     used  to ensure that the original disk is being used  to  run
     the program. The whole key to this unprotect scheme is to by-
     pass these Interrupts in the program code.   The tricky  part
     of this unprotect is to find them!   They are not in the seg-
     ment  of  program code starting at the value of CS  equal  to
     "27FC".   They are closer to the beginning of the program  in
     memory.   Easy enough!   Reset the value of CS to  equal  the
     value  of DS as follows; type immediately after  Debug's  "-"


     Debug will prompt you for the new value of CS with:


       You  respond  by typing the value of DS you  saw  when  you
     dumped the registers the first time.   For example,  I  typed
     "12CE<cr>".   The  value you type will be  different.   Debug
     will  again respond with the "-"  prompt which means  we  are
     ready to do our search.   Type in the following after the "-"

                    S CS:0 FFFF CD 13<cr>

       The computer should respond with three lines of information
     which are the addresses of the three Interrupt 13 calls built
     into the program.   The first four digits are the segment ad-
     dress  and will equal to the value of CS you have  just  set. 
     The second four digits following the colon are the offset ad-
     dresses which are of primary interest to us.   On my  machine
     they came back as follows:


       The segment addresses will be identical and the three  off-
     set  addresses should all be relatively close together.   Now
     look at the first offset address.  (As you can see,  mine was
     "4307".) Write it down.  Now we do a bit of Unassembly.

       Type "U4307<cr>"  which is the letter "U", followed immedi-
     ately  (with no blank spaces) by whatever your  first  offset
     address turned out to be, followed by a carriage return.   If
     you are not familiar with unassembled machine code,  it  will
     look like lines of gibberish as follows:

                    12CE:4307 CD13        INT      13
                    12CE:4309 4F          DEC      DI
                    12CE:430A 744C        JZ       4358
                    12CE:431F CD13        INT      13
                    12CE:4321 4F          DEC      DI
                    12CE:4324 BF0400      MOV      DI,0004
                    12CE:4326 B80102      MOV      AX,0201
       In  my computer,  Unassemble will automatically  output  16
     lines of code to the screen.  Yours may differ.  Note, in the
     abbreviated list I have shown above, the addresses at the be-
     ginning  of  the two lines which contain the  Interrupt  13's
     (INT  13) correspond to the first two addresses we  found  in
     our search.  Now we continue the unassemble, and here comes

     another  tricky part.   Just type in "U<cr>"  after  the  "-"

       You'll get sixteen more lines of code with the third Inter-
     rupt 13 on a line which begins with the address (CS):4335  if
     you  have  the same version of Submarine as I do.   It's  not
     terribly  important  to  this  exercise,   but  it  will   at         
     least show you that things are proceeding okay.   Now type in         
     "U<cr>"  again  after the prompt.  You are  now  looking  for
     three key lines of code.   On my program they appear as  fol-

                    12CE:4335 07          POP      ES
                    12CE:4356 5D          POP      BP
                    12CE:4357 CB          RETF

     The true key is the instruction "POP ES".   This  instruction
     begins  the normal return sequence after the program has  ex-
     ecuted its Interrupt 13 instructions and accompanying checks. 
     If  Debug on your machine prints fewer than 16 lines of  code
     at a shot, you may have to type in "U" more than twice at the
     "-" to find these instructions.  (If you haven't found any of
     this stuff, either get help on the use of Debug or go back to
     using your diskette version!)  Write down the offset  address
     of  the "POP ES"  instruction; the four digits following  the
     colon,  which in my example is "4354".   You're well on  your
     way now, so please persevere.

       The  next step is to modify the program to JUMP around  the
     code which executes the Interrupt 13's and go immediately  to
     the  instruction  which  begins the  normal  return  sequence
     (again,  it's the "POP ES".  Type in the  following  instruc-
     tions carefully:


       This first bit tells Debug that new Assembler code will  be
     inserted at the address of the first Interrupt 13.   If  your
     first  Interrupt 13 is at an address other that  "4307",  use
     the correct address,  not mine.  The computer will prompt you              
     with the address:


     After which you will immediately type:

                    JMP 4354<cr>

     This instruction jumps the program immediately to the  normal
     return code instructions.  Again, at the risk of being redun-
     dant, if your "POP ES" instruction is at a different address,
     use that address, not "4354"!

     The computer will prompt you with the address of the next in-

     struction  if  all went well.   MAKE SURE you  just  hit  the
     carriage  return at this point.  Debug will then  return  the
     familiar "-" prompt.

     Now  it's  time  to examine your  handiwork.   Let's  do  the
     unassemble again starting at the address of what had been the
     first Interrupt 13 instruction, but which is now the Jump in-
     struction.  Type in "U4307<cr>" or "U" followed by the appro-
     priate address and a carriage return.   The first line begin-
     ning with the address should appear as follows:

                    12CE:4307 EB4B        JMP      4354

     The key here is the four bytes immediately following the  ad-
     dress.   In my example they are "EB4B".   Yours may  not  be. 
     But,  they are VERY IMPORTANT because they represent the  ac-
     tual machine code which is the Jump instruction.  WRITE THESE

       Now  if  you want to have some fun before we go  on,  reset
     register  CS to its original value by first typing  "RCS<cr>"
     at  the "-"  prompt.   Then type in the original value of  CS
     that I asked you to write down.   Using my example,  I  typed
     "27FC<cr>".  Next, you will type "G<cr>" after the "-" prompt
     which  means GO!   If all went well,  SUB should run at  this
     point.   At  least it will if you put all  of  the  Submarine
     files  onto the diskette or into the hard  disk  subdirectory
     where youre working.   If it didn't run, you may have made an
     error. Check through what you have done.  

     Don't give up at this point if it does not run.  Your version
     of Debug may simply have not tolerated our shenanigans.  When
     you are done playing, quit Submarine ("Alt-Q<cr>") and type a
     "Q<cr>" after the Debug prompt "-" appears.

     Now  comes  the tough part.   I can't walk you  through  this
     phase  in complete detail,  because you may be using  one  of
     several programs available to modify the contents of SUB.EXE. 
     Debug is not the way to go,  because it can't write out  .EXE
     files, only .COM files.

     Note:  Another method of doing this is to REName the  SUB.EXE
     file  so it has a different extension other than .EXE  before
     you enter DEBUG.   That way after you've made the change  you
     can then [W]rite then changes out to the file right in DEBUG. 
     Then one drawback is that you can't run the program in  DEBUG
     once you've changed the name.

     You have to get into your sector modification package (NORTON
     works good) and work on the SUB.EXE file on your new diskette
     or your hard disk.  Remember, I warned you that doing this on
     your hard disk is dangerous if you are not fully aware of

     what you are doing.  So, IF YOU MESS UP, it's YOUR OWN FAULT!

     You  are looking for the first occurrence of an Interrupt  13
     (the "CD 13") using the search facility in your program.   If
     you  don't have the ability to search for the two-byte  hexa-
     decimal code "CD 13" directly, then you will have to manually

     Note:  Norton 4.x now has a search utility.   When you get to
     the  point of typing in the search text,  just press the  TAB
     key, and you can type in the actual hexadecimal code "CD 13".

     Start  at the beginning of SUB.EXE and proceed.   Again,  you
     want to find the first of the three (first from the beginning
     of the program).  

     I  will give you a hint.   I found it in NORTON  at  location
     4407  hexadecimal  which is location 17,415  decimal  in  the
     SUB.EXE program file.   DOS standard sectors are 512  decimal
     bytes.  Replace  the two bytes "CD 13"  with the "EB  4B"  or
     whatever  your Jump instruction turned out to be.   Write  or
     save the modified file.

     That's ALL there is to modifying SUB.EXE.   You can go  ahead
     and execute your program.   If you have followed my  instruc-
     tions, it should run fine.  Get help if it doesn't.  Now, you
     should be all set.  You can load onto your hard disk,  if you
     haven't already.  You can run it from a RAM disk using a  BAT
     file if you really want it to hum.   Or,  if you have the fa-
     cilities,  you can copy it from 5-1/4" floppy to 3-1/2"  dis-
     kette and run it on machines which accept that medium if  you
     upgrade to a new computer.


     Now let's take a look at a newer crack on the program,  Space
     Station Oblivion by Eypx.  At a first [S]earch with Debug and
     Norton's  Utility no CD 13's could be found,  and yet it  was
     using them... So a different approach had to be taken...

     By:            PTL
     Title:         Space Station Oblivion Crack

     First of all,  you must determine which file the INT 13's are
     in,  in this case it had to be the file OBLIVION.EXE since it
     was the main program and probably contained the INT 13's.  So
     then rename it to a different EXTension and load it into  De-

     Then do a [S]earch for INT 13's.

                    -S 100 FFFF CD 13

     Which will promptly turned up nothing.  Hmmm...

     Next you might decide that, maybe, the code was modifying it-
     self.   So quit from Debug and load up PC-Watch,  include all
     the  INT  13  Calls.   For those of  you  not  familiar  with
     PC-Watch,  it is a memory resident program that can be set to
     look  for  any type of BIOS call.   When that  call  is  made
     PC-Watch prints to the screen the contents of all the  regis-
     ters  and the current memory location that the call was  made

     After PC-Watch is initialized, then run the OBLIVION.EXE file
     from the hard disk,  leaving the floppy drive door open,  and
     sure  enough,  when the red light comes on in   the  diskette
     drive,  PC-Watch  will report the address's of  some  INT  13
     calls.  Which you should then write down.

     From  there,  quit the game, reboot,  (To dump PC-Watch  from
     memory) and load the OBLIVION.EXE into Debug and issue a [G]o
     command with a breakpoint.  What address should you use for a
     breakpoint?   You guessed it, the same address PC-Watch gives

     Well,  it locked up did'nt it?  Which is quite common in this
     line of work so don't let that discourage you.   So next  re-
     loaded  it into debug and this time [U]nassemble the  address
     that you got from PC-Watch.   But instead of finding the  INT
     13's you'll find harmless INT 21's.

     Hmm...  could  it be that the program was converting  the  CD
     21's to CD 13's during the run?   Well,  to test the idea as-
     semble an INT 20 (Program Terminate) right after the first 

     INT 21. Then I run the program, and yes immediately after the
     red light comes on the drive, the program will terminate nor-

     Then [U]nassemble that same area of memory,  and low and  be-
     hold,  some  of the INT 21's have magically turned  into  INT
     13's.  How clever...

     So,  then it is just a matter of locating the address of  the
     routine that it jumped (JMP) to if the correct disk was found
     in  drive A:.   Once you have that address,  just go  to  the
     start of all this nonsense and [A]ssemble a JMP XXXX command. 
     Where  XXXX was the address to jump to if the  original  disk
     was in drive A:.

     Then  just [W]rite the file back out to the disk  and  [Q]uit
     debug,   and  then  REName  the  file  back  to  OBLIVION.EXE
     afterwhich it should work fine.


     Chapter III                      Removing Doc Check Questions

     A  new fad has recently started up with software vendors,  it
     involves  the use of "Passwords" which are either  stored  in
     the  documentation or are actually the documentation  itself. 
     Then  when you reach a certain part of the  program  (Usually
     the beginning) the program will ask for the password and  you
     have  to look it up in the Docs before being allowed to  con-
     tinue.   If the wrong password is entered,  it  will  usually
     drop you to DOS or take you to a Demo version of the program.

     This  new form of copy protection is very annoying,  but  can
     usually  be cracked without too much effort,   and the  files
     and the disk are usually in the standard DOS format.   So now
     we'll take a look at cracking the Doc check questions.

     First  of  all  we'll crack the startup  questions  in   F-15
     Strike Eagle by MicroProse.

     By:            JP ASP
     Title:         F-15 Unprotect

     Make a copy of the original disk using the DOS DISKCOPY  pro-

                    >DISKCOPY A: B:

     Then  insert the copy disk in the A drive and invoke DOS  DE-


     Now we'll [F]ill an area of memory with nothing (00).

                    -F CS:100 L FEFF 0

     Next we will [L]oad into address CS:0100 the data that is  on
     the A: disk (0) from sector 0 to sector 80.

                    -l cs:100 0 0 80

     Now  lets [S]earch the data we loaded for the area where  the
     copy protection routine is.

                    -s cs:100 l feff FA EB FD

     Then for each of the occurences listed, use the address DEBUG
     returned in the [E]nter command below.


                    -e xxxx 90 90 90

     Here's the part we are interested in,  it's where you  change
     all  the autorization codes to a space.   Notice how you  can
     use the [S]earch command to look for ASCII text.

                    -s cs:100 l feff "CHIP"

     Then for each occurance of "CHIP"  use the address DEBUG  re-
     turned in the [F]ill command below.

                    -F XXXX L F 20

     Write out the modified data

                    -W CS:100 1 0 80

     Quit DEBUG


       You should now be able to DISKCOPY and boot from all copies
     also  just press the space bar when it ask for ANY  authority
     code and then press "ENTER". Now there is no need to remember
     (or look up) any codes that are so finely tucked away in  the 


     Here is a similar method that was used break the passwords in
     the  program BATTLEHAWKS 1945 by Lucasfilms.  However  Norton
     Utilities  is  used to search for the  passwords  and  change

     By:            PTL
     Title:         BATTLEHAWKS-1945 Doc Check Crack

     In  keeping in line with their previous programs,  Lucasfilms
     has  released yet another program which uses Doc  Checks  for
     its means of copy protection, Battlehawks 1942.

     When you run this program,  it first goes through a series of
     graphic displays, then it goes through a series of questions,
     asking what type of mission you want to fly,  such as  Train-
     ing, Active Duty, or which side of the war you want to be on.

     Then right before the simulation begins,  it shows you a pic-
     ture of a Japanese Zero and ask you for a password which you

     are  then  supposed to get by looking up the picture  of  the
     Zero in the User Manual and typing the corresponding password
     in.   After which it enters the simulation,  in the event you
     enter  the wrong password,  it puts you into a training  mis-

     Removing  the  Doc Check in a program like  this  is  usually
     pretty  easy.   The ideal way to do it is to remove  the  Doc
     Check routine itself,  but if you don't have all day to debug
     and  trace  around the code this might not be the  best  way. 
     For  instance if you only have your lunch hour to work on  it
     (Like  I did),  then you need to use the standard  Q.D.C.R.S.
     (Quick Doc Check Removal System).

     How do you do a QDCRS?  Well first of all,  play around  with
     the program,  find out what it will and will NOT accept as  a
     password.   Most  programs will accept anything,  but  a  few
     (Like Battlehawks) will only accept Alpha characters.

     Once you've learned what it likes,  make an educated guess as
     to what program the Doc Check routine is in.   Then load that
     program into Norton's Utility (NU).

     At this point,  take a look at the passwords,  and write down
     the most unusual one that you can find (I'll explain  later). 
     Now  type that password in as the search string,  and let  NU
     search through the file until it finds the password.   Now  a
     couple of things can happen.

          1. It only finds one occurrence
          2. It finds more than one occurrence
          3. It doesn't find any occurrence

     In  the event of case 2 then YOU have to determine where  the
     passwords  are stored,  you can do this by opening your  eyes
     and looking.

     In the event of case 3,  go to the kitchen and start a pot of
     coffee, then tell you wife to go to bed without you,  because
     you have a "Special Project" that you have to finish tonight. 
     And by the way, Good Luck.  You'll need it.

     Hopefully case 1 will occur,  now you have to take a look  at
     the data and ask yourself 2 questions:

          1. Are all the passwords the same length?
          2. Is there a set number of spaces  between  each  pass-
          3. Does the next password always start a certain  number
             of characters from the first character of the  previ-
             ous password?

     If you can answer yes to any of the above questions,  you  in
     luck.  All you have to do is change the passwords to spaces

     (If the program allows that,  Battlehawks doesn't) or  change
     them to you favorite character. The letter X works good, it's
     easy to type and easy to remember.

     If you can't answer yes to any of the questions then you  ei-
     ther need to bypass the Doc Check routine itself or you  need
     to be adventurous and experiment. Battlehawks will not follow
     any  of the above patterns,  and your quickly running out  of
     time, so you'll have to try something, fast...

     So  just  wiped out all of the data area with  X's,  all  the
     passwords and associated "garbage" between them.   Then saved
     the changes and drop out of NU and into BH.  Then when it ask
     for the password,  just filed the area with X's.  Next  thing
     you  know,  you'll be escorting a bombing run on  a  Japanese

     So,  this one turned out to be fairly simple.   Where you may
     run into trouble is on Doc Checks that use a graphic  system,
     such as Gunship by MicroProse.  When it comes to this type of
     Doc Check, you almost have to bypass the routine itself.  And
     again, a good way to do this is with setting break points and
     using the trace option in Debug.



     That  was the easy version Doc Check crack,  however there  a
     "Better"  way to crack Doc Checks,  is to bypass the  routine
     completely  so  the user can just press enter and  not  worry
     about spaces.   Let's take a lot at this method by looking at
     a crack for the program, Yeager's Advanced Flight Trainer, by
     Electronic Arts.

     By:            PTL
     Title:         Yeager's Advanced Flight Trainer

     Chapter 5                               Cracking Self Booters

     Now we'll take a look at cracking self booters.  A few compa-
     nies  have found this to be the best copy  protection  scheme
     for them, one of which is DataEast, makers of Ikari Warriors,
     Victory Road,  Lock-On, Karnov, etc...  This posses a special
     problem  to the Amateur Cracker, since they seldom use  stan-
     dard DOS formats.  So let's jump right in!

     This  is the area where a "Higher than Normal"  knowledge  of
     Assembly  Language and DOS Diskette structures,  so first  of
     all, the Basic's.

     The Disk's Physical Structure

     Data is recorded on a disk in a series of concentric circles,
     called Tracks.   Each track if further divided into segments,
     called  Sectors.   The  standard  double-density  drives  can
     record  40 tracks of data, while the new quad-density  drives
     can record 80 tracks.

     However, the location, size, and number of the sectors within
     a  track are under software control.   This is why  the  PC's
     diskettes are known as soft-sectored.  The characteristics of
     a  diskette's sectors (Their size, and the number per  track)
     are set when each track is formatted.  Disk Formatting can be
     done either by the operating system or by the ROM-BIOS format
     service.   A lot of self booters and almost all forms of copy
     protection  create unusual formats via the ROM-BIOS  diskette

     The  5 1/4-inch diskettes supported by the standard  PC  BIOS
     may  have  sectors that are 128,256,512,  or 1,024  bytes  in
     size.   DOS, from versions 1.00 through 4.01 has consistently
     used sectors of 512 bytes, and it is quite possible that this
     will continue.  

     Here is a table displaying 6 of the most common disk formats:

     Type      Sides        Sectors       Tracks       Size(bytes)

      S-8        1             8            40            160K
      D-8        2             8            40            320K
      S-9        1             9            40            180K
      D-9        2             9            40            360K
     QD-9        2             9            80            720K
     QD-15       2            15            80          1,200K

     S  - Single Density
     D  - Double Density
     QD - Quad Density

     Of all these basic formats,  only two are in widespread  use:
     S-8  and D-9.   The newer Quad Density formats are for the  3
     1/2" and 5 1/4" high density diskettes.

     The Disk's Logical Structure

     So,  as we have already mentioned,  the 5  1/4-inch  diskette
     formats have 40 tracks,  numbered from 0 (the outside  track)
     through 39 (the inside track,  closest to the center).   On a
     double  sided diskette,  the two sides are numbered 0  and  1
     (the  two  recording heads of a double-sided disk  drive  are
     also numbered 0 and 1).

     The BIOS locates the sectors on a disk by a three-dimensional
     coordinate  composed of a track number (also referred  to  as
     the  cylinder number),  a side number (also called  the  head
     number),  and a sector number.  DOS,  on the other hand,  lo-
     cates information by sector number,  and numbers the  sectors
     sequentially from the outside to inside.

     We   can  refer  to  particular  sectors  either   by   their
     three-dimensional  coordinates or by their sequential  order. 
     All ROM-BIOS operations use the three-dimensional coordinates
     to locate a sector.  All DOS operations and tools such as DE-
     BUG use the DOS sequential notation.

     The BASIC formula that converts the three-dimensional coordi-
     nates  used by the ROM-BIOS to the sequential sector  numbers
     used by DOS is as follows:

            * SIDES.PER.DISK

     And  here are the formulas for converting  sequential  sector
     numbers to three-dimensional coordinates:

            MOD SIDE.PER.DISK
            * SIDES.PER.DISK)

          (Note:  For double-sided nine-sector diskettes, the PC's
          most  common disk format, the value of  SECTORS.PER.SIDE
          is  9 and the value of SIDES.PER.DISK is 2.   Also  note
          that  sides and tracks are numbered differently  in  the
          ROM-BIOS numbering system: The sides and tracks are num-
          bered from 0, but the sectors are numbered from 1.)

     Diskette Space Allocation

     The  formatting  process divides the sectors on a  disk  into
     four sections, for four different uses.  The sections, in the
     order they are stored, are the boot record,  the file alloca-
     tion  table (FAT),  the directory, and the data  space.   The
     size of each section varies between formats,  but the  struc-
     ture and the order of the sections don't vary.

          The Boot Record:

          This section is always a single sector located at sector
     1 of track 0, side 0.  The boot record contains,  among other
     things,  a short program to start the process of loading  the
     operating system on it.   All diskettes have the boot  record
     on them even if they don't have the operating system.  Asisde
     from  the start-up program,  the exact contents of  the  boot
     record vary from format to format.

          The File Allocation Table:

          The  FAT follows the boot record,  usually  starting  at
     sector 2 of track 0,  side 0.   The FAT contains the official
     record of the disk's format and maps out the location of  the
     sectors used by the disk files.   DOS uses the FAT to keep  a
     record of the data-space usage.  Each entry in the table con-
     tains  a specific code to indicate what space is being  used,
     what space is available,  and what space is unusable (Due  to
     defects on the disk).

          The File Directory:

          The file directory is the next item on the disk.   It is
     used  as a table of contents,  identifying each file  on  the
     disk  with a directory entry that contains several pieces  of
     information, including the file's name and size.  One part of
     the entry is a number that points to the first group of  sec-
     tors  used by the file (this number is also the  first  entry
     for this file in the FAT).

          The Data Space:

          Occupies  the bulk of the diskette (from  the  directory
     through the last sector),  is used to store data,  while  the
     other  three  sections are used to support  the  data  space. 
     Sectors  in  the  data space are allocated  to  files  on  an
     as-needed basis,  in units known as clusters.   The  clusters
     are one sector long and on double-sided diskettes, they are a
     pair of adjacent sectors.

     (From  here  on I'll continue to describe the basics  of  DOS
     disk structures, and assembly language addressing technics.

     Here  is a simple routine to just make a backup copy  of  the
     Flight Simulator Version 1.0 by Microsoft.  I know the latest
     version  is  3.x but this version will serve the  purpose  of
     demonstrating  how to access the data and program files of  a

     By:            PTL
     Title:         Microsoft Flight Simulator 1.00 Unprotect

     This procedure will NOT convert the Flight Simulator disk  to
     files  that can be loaded on a hard drive.   But...  it  will
     read  off the data from the original and put it onto  another
     floppy.  And this should give you an idea of how to read data
     directly from a disk and write it back out to another disk.

     First of all take UNFORMATTED disk and place it in drive  B:. 
     This will be the target disk.

     Now  place your DOS disk (which has Debug) into drive A:,  or
     just load Debug off you hard disk.


     Then  we  are going to enter (manually) a little  program  to
     load the FS files off the disk.

                    -E CS:0000 B9 01 00 BA 01 00 BB 00
                               01 0E 07 06 1F 88 E8 53
                               5F AA 83 C7 03 81 FF 1C
                               01 76 F6 B8 08 05 CD 13
                               73 01 90 FE C5 80 FD 0C
                               76 E1 90 CD 20

                    -E CS:0100 00 00 01 02 00 00 02 02 00 00 03 02
                               00 00 04 02 00 00 05 02 00 00 06 02
                               00 00 07 02 00 00 08 02

     Next we'll [R]eset the IP Register by typing.

                    -R IP

     And then typing four zeros after the address prefix.


     Next insert the original Flight Simulator disk into drive  A: 
     and we'll run our little loader.

                    -G =CS:0000 CS:22 CS:2A

     Now enter a new address to load from.

                    -E CS:02 0E
                    -E CS:27 19

     And run the Loader again.

                    -G =CS:0000 CS:22 CS:2A

     New address

                    -E CS:02 27
                    -E CS:27 27

     Run Loader

                    -G =CS:0000 CS:22 CS:2A

     Here  we'll  do some [L]oading directly from  the  disk  our-

                    -L DS:0000 0 0 40

     And the in turn, write it back out to the B: (1) drive

                    -W DS:0000 1 0 40


                    -L DS:0000 0 40 28
                    -W DS:0000 1 70 30
                    -L DS:0000 0 A0 30
                    -W DS:0000 1 A0 30
                    -L DS:0000 0 138 8
                    -W DS:0000 1 138 8

     When  we are all through,  [Q]uit from debug and  you  should
     have a backup copy of the Flight Simulator.


     And that's all there is to it.