The Hacker's Encyclopedia 1998

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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 Protection. ------------------------------------------------------------- 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- lows: 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 13 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:019C XXXX:01A8 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> 14 XXXX:01B0 NOP <enter> XXXX:01B1 <enter> This just wipes out the section of code containing the INT 13 check. 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 drive) 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. END. 15 ------------------------------------------------------------ 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 world. ------------------------------------------------------------ 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 "-" prompt: RCS<cr> 16 Debug will prompt you for the new value of CS with: CS:27FC: 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 "-" prompt: 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: 12CE:4307 12CE:431F 12CE:4335 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 17 another tricky part. Just type in "U<cr>" after the "-" prompt. 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- lows: 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: A4307<cr> 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: 12CE:4307 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- 18 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 FOUR BYTES DOWN AND MAKE SURE THEY ARE CORRECT. 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 19 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 search. ------------------------------------------------------------- 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. END. 20 ------------------------------------------------------------- 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- bug. 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 from. 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 you. 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 21 INT 21. Then I run the program, and yes immediately after the red light comes on the drive, the program will terminate nor- mally. 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. END. Which G-file (Q=Quit) ? 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