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..= Cracking Tuto : Disk Based Protection =..
by Heavy aka VrS!-Cybfree

Z-Out/Rainbow Arts - Advantec (1990)

 Amiga Tutos

- I used original disk from the IPF file #609 EU Retail
- AR and/or a disassembler/debugger (not specific tuto)
- an assembler (AsmOne/DevPac/Barfly...) if you want to rewrite the boot.

Try the IPF disks. Non-Dos game, No passwords required.

Do a quick scan of the disk with X-Copy : something is wrong at the first track. Seems to be a disk based protection.

Make a copy of disk. boot it : the screen stay black after reading the track 1.
From AR, disassemble where the program is stopped (F4D6) :

Compare start of sector with $4521 (MFM sync marker).
cross backward : this test routine start at F4D0 and is called from F3E2 (fa f4d0) : read sector 1 at D2F6. at F408, test if read error. jump to F434 if ok.


here is the routine called for reading sector (motor on, trackload...)

at F56E, he jumps to F4D0 : the uncode MFM routine.
It's used as the "protection".

so, reboot. stop with AR after track 49 loaded. Then, disassemble at F4D0 (d F4D0) : the code is here.
first try : put RTS at F4D2 to skip the whole routine.
restart (x)
lets loading until track 1.
...it's Ok! Intro start !

but what is this sector. Important one ? only protection ?

disassemble more :
at F4D0 he decode the data from D2F6 to D396.
at F448, he copy D2F6 to D396
at F45c, D2F6 is used with sub prog at F616 : seems to be a writing track routine!
this game save the hiscore on disk : at sector 1 !
the hiscore is used as protection.

so, for the patch, we have to nop the test of $4521 else the hiscore is not decoded. And also erase the $4521 at write sub prog (at F6Ac).
put 6x 4E71 at F4D6 and 3x 4E71 at F6AC.

(I've not tested the hiscore saving because I used winuae : unsupported format for writing)

patching:
I loaded and disassembled the starter program - 44 block loaded @ 50000 from block 22. It's the main program crunched. Starting at 50024, decrunch it to 40000, then jump to 40000, copy the main program at 0 and jump to 500 to start.
The program load some files and load Intro at B000.
the "protection" is in the Intro code.

it's possible to patch directly from boot :
after loading prog at 50000, change boot

...
move.w #$4e75,$5012a ; replace JMP $40000 by RTS
jsr $50024 ; replace JMP by JSR : decrunch to 40000 and return here
after this line, we have to install the patch of the Intro, but not yet loaded at this moment...patch copied at free space $b8.
lea $b8.w,a0
move.l a0,$40100+$5DA ; replace JSR $B000 by JSR $B8

I use $40100 as base, because it's the part of the prog copied at 0. and I copy the patch at $40100+$b8...the patch will be at $b8!

lea patchintro(pc),a1 ; copy patch to $b8 (unused address)
lea $40100+$b8,a0
moveq #sizepatch-1,d7
.cpy
move.b (a1)+,(a0)+
dbf d7,.cpy

jmp $40000 ; copy prog to $500 and start

here is the patch:

patchintro:
; skip test $4521
move.l #$4e714e71,$f4d6
move.l #$4e714e71,$f4da
move.l #$4e714e71,$f4de
; skip $4521 in write score
move.l #$4e714e71,$f6ac
move.w #$4e71,$f6b0

jmp $B000 ; start Intro
sizepatch=*-patchintro

write new boot and restart : the loading is ok!


Start game, play. Quit game (Esc) : program jump to Intro (read hiscore - track 1)
that works.
You can test the whole game by using builtin trainer : J+1 to 6 for level, J+K for invulnerability.

to fix the hiscore save, try to replace sync word $4521 with standard one : $4489
new patch:

...
move.w #$4e71,$f4da
move.w #$4e71,$f4e0
move.l #$44894489,$f6ae
jmp $B000

(not tested on real amiga. doesnt work on winuae)


Original game have some bugs. why not fix them now ?
- first bug : the Intro logo is not centered ! incredible!
lets go with AR:
take a look at the copperlist intro : c1
the logo is at the bottom of screen/copperlist.
found at BD40 : $e0,$2,$e2,$3e84,... bitplan pointer for logo.

a shift of 128 pixels (16 bytes - $10) :
add $10 to values of bplxpt : 3e84 -> 3e94 ...
try : it's ok!

is this address directly in copperlist or from a pointer?
searching BD40 : nothing. searching BD42 : found at C492.(or searching $23e84 - fa 23e84 : found at bd83). The logo pointer is at BD80

so, add the fix to the patchintro:

...
move.l #$23e94,$bd80 ; $23e84 -> $23e94
...

reboot, and enjoy.


others bugs are found by crackers or whdload patchers: fixes for the main program ($40000)
- problem with weapons in 2 players mode : fixed by Angels/Defjam

move.b #$14,$40100+$3E5A ; clr.w $12(a3) -> clr.w $14(a3)
move.b #$14,$40100+$3E60 ; addq.w #1,$12(a3) -> addq.w #1,$14(a3)

- gfx bug in level 5 : fixed by Harry/WHDteam

move.b #$20,$40100+$7C34 ; copperlist wait $4000 -> $2000

- trainer keys J+K replaced by J+I (pb with a2000/4000 keyboard): by WHD patchers (Jotd/Harry)

move.b #$17,$40100+$1A9B ; replace keycode "K" by "I"


final boot code :
dc.b 'DOS',0
dc.l 0
dc.l $370
; original code
Start
move.w #$180,$DFF096
clr.w $DFF180
move.l a1,-(sp)
lea loc_0_400AA(pc),a5
movea.l 4.w,a6
move.l #$20004,d1
jsr -$D8(a6) ; availmem(req)(d1)
move.l d0,4(a5)
move.l #4,d1
jsr -$C6(a6) ; allocmem(size,req)(d0,d1)
add.l d0,4(a5)
clr.w d0
move.l d0,(a5)
movea.l (sp)+,a1
move.w #2,$1C(a1)
move.l #$50000,$28(a1) ; load crunched main program
move.l #44*512,$24(a1) ; len: 44*512
move.l #22*512,$2C(a1) ; offset: 22*512
jsr -$1C8(a6)
move.w #9,$1C(a1)
clr.l $24(a1)
jsr -$1C8(a6)
move.w #$7FFF,$DFF09A
move.w #$7FFF,$DFF096
movem.l d0-a6,-(sp)
nop
nop
nop
movem.l (sp)+,d0-a6
move.l 0(a5),d0 ; ptAllocMem C00000
move.l 4(a5),d1 ; ptAvailMem+ptAllocMem C7E800
; patch
move.w #$4e75,$5012a ; replace JMP $40000 by RTS
jsr $50024 ; decrunch to 40000 and return here

; patch 40000 main prog
; trainer key j+k replaced by j+i (pb with a2000/4000 keyboard)
move.b #$17,$40100+$1A9B ; replace keycode "K" by "I"
; fix weapons in 2 players mode (by Angels/Defjam)
move.b #$14,$40100+$3E5A ; clr.w $12(a3) -> clr.w $14(a3)
move.b #$14,$40100+$3E60 ; addq.w #1,$12(a3) -> addq.w #1,$14(a3)
; gfx bug in level 5
move.b #$20,$40100+$7C34 ; copperlist wait $4000 -> $2000
; install patch Intro
movem.l d7/a0-a1,-(sp)
lea $b8.w,a0
move.l a0,$40100+$5DA ; replace JSR $B000.L by JSR $B8.w
lea patchintro(pc),a1 ; copy patch to $b8 (unused address)
lea $40100+$b8,a0
moveq #sizep-1,d7
.cpy
move.b (a1)+,(a0)+
dbf d7,.cpy
movem.l (sp)+,d7/a0-a1

jmp $40000 ; copy prog to $500 and start

patchintro:
; correct centering of Advantec logo
move.l #$23e94,$bd80 ; $23e84 -> $23e94

; skip test sync word
move.l #$4e714e71,$f4d6
move.l #$4e714e71,$f4da
move.l #$4e714e71,$f4de
; or skip only bne/beq
; move.w #$4e71,$f4da
; move.w #$4e71,$f4e0

; skip write score sync word
move.l #$4e714e71,$f6ac
move.w #$4e71,$f6b0
; or put standard sync word
; move.l #$44894489,$f6ae

jmp $B000
sizep=*-patchintro

loc_0_400AA:
ds.l 2


that's all
for saving hiscore, the final 100% crack will be to recreate a DOS disk...in another tuto ^^

2008 (c) Heavy/VrS!/Cyb

Download :
- Cracked disk 1 (use built-in trainer)
- sources of the original boot and patched boot