Hex Editing Tutorial (by Foxbat)

Hex Editing Tutorial (by Foxbat)

Description: Guide to explain the basics of code editing.

Categories: Tutorials (1.1x) - Code Editing


[color=yellow:f56389e5be][i:f56389e5be]NOTE (by Alkalund) - code offsets in this tutorial are for D2: LoD 1.09b.[/i:f56389e5be][/color:f56389e5be]



In Diablo II, there are many things that can't be modified via the text
files. If you'd like to give your monsters a new coat of paint, if you
want your paladin to throw blizzards, if you would like to gamble a
unique in your lifetime, then you will need to delve into modifying
binary files via hex editing.

There are some freeware and shareware hex editors out there, I use XVI32 at http://wielandbelka.hypermart.net/opera/tools/xvi32.htm . Hex workshop is shareware but is popular, which you can find at http://www.bpsoft.com/.
One handy utility is a hex calculator, which you already have. Just
open up the windows calculator, go to scientific mode, then select hex
from the view menu.

You may be able to
open a file in a hex editor , but when you see 0A 3F 44 F6 it all looks
like greek (geek?) to you. But the greek is simple to read once you
understand it.

All data on a computer
is stored as a series of on/off states, represented by a 0 or a 1.
Everything on your hard drive, from your Windows operating system to
microsoft word to even the D2 text files, is stored as an ordered
series of 0s and 1s. A specifc instance of 0 or 1 is called a bit. A
byte is a series of 8 bits, and is an important unit as we will see.

A byte can be represented as a whole number between 0 and 255, like so:

0 0 0 0 0 0 0 0 = 0
0 0 0 0 0 0 0 1 = 1
0 0 0 0 0 0 1 0 = 2
0 0 0 0 0 0 1 1 = 3
0 0 0 0 0 1 0 0 = 4
0 0 0 0 0 1 0 1 = 5
0 0 0 0 0 1 1 0 = 6
0 0 0 0 0 1 1 1 = 7
0 0 0 0 1 0 0 0 = 8

and so on. This continues all the way up to 11111111, which is 255.

We
can use Hex instead to represent a byte. A byte is made up of two
alpha-numeric hex digits (meaning it is represented by both numbers and
letters) Below is a table with numbers on the left and hex on the right.

0 = 00
1 = 01
2 = 02
3 = 03
4 = 04
5 = 05
6 = 06
7 = 07
8 = 08
9 = 09
10 = 0A
11 = 0B
12 = 0C
13 = 0D
14 = 0E
15 = 0F
16 = 10
17 = 11
18 = 12

...

25 = 19
26 = 1A
27 = 1B
28 = 1C
29 = 1D
30 = 1E
31 = 1F
32 = 20
33 = 21

...

This
goes all the way up to 255, represented as FF. If you want to find the
whole number value for a hex number like B7, we should

1) convert each digit to whole number

B = 11, 7 = 7

2) use the following formula

1st number * (16^0) + 2nd no. * (16^1) + 3rd no. * (16^2) ... + Nth no. * (16^[n-1])

for n digits, with the digits being numbered from right to left.

In this case we have two digits, so n = 2

7 * (16^0) + 11 * (16^1)
7 * 1 + 11 * 16
7 + 176
183

therefore B7 = 183.

Most
hex editors usually offer some way to do the conversion for you. Hex
Workshop has a specific option for it, XVI32 you can do the conversion
by selecting 'goto' from the menu, select the 'hex' option, put in your
hex value, then click on 'decimal' and it's converted to whole number.

So
great, now we know how to convert hex to whole number(usually referred
to as decimal) or to 0s and 1s. What can we do with this?

Well,
say you want to change how much hit points a light healing potion gives
you. Someone has found a place in the 1.09 file d2game.dll that
controls this. They tell you to go to address B2B50.

What's
an address you say? It's a way of keeping track of where we are in a
file. They are also called offsets sometimes. A hex editor will number
every byte, usually in hex. So the first byte in a file is adress 0.
The second byte in a file is adress 1. The sixteenth byte is at adress
F. The seventeenth is at adress 10. And so on. Usually hex editors have
a 'go to' feature, you just need to put the hex value into the editor
and it will take you there. So go to address B2B50. Once you're there,
a hex editor should let you know where you are. You should be at adress
B2B50. move to the right, and it will tell you that you are at B2B51.
To the left, and you'd instead go to B2B4F.

Anyways,
at B2B50 you will find the value of that byte is x32 (hex 32), or dec
(decimal) 50. So the light healing potion will give
sorceress/necro/druid 50 HP. Pal/Zon/Asn get 1.5 times this value,
barbs 2 times this value. Say you want to double it to 100 HP. Convert
100 dec to hex with long division by sixteen and hold onto the
remainder. That gives us 6 R 4, so in hex 64. Now you want to replace
that 32 at B2B50 with 64. Be careful that you are not in INSERT mode,
we want to over-write what is already there not add new stuff (adding
new will change the location of all the bytes following and will crash
Diablo II) Once that is done, save the file (hopefully you made a
backup first though) and now your light healing potions will be twice
as good.

What if we want our healing
potion to be rediculously good? Say we want it to be 300, well we can
do that too. First convert 300 to hex, which can be a little tricky
since we need to represent it with two hex bytes.

We want to convert from dec to hex, so we should use this general formula

1) Divide the number by 16 with long divison and remainder.

300/16 = 18 R 12

2) If the whole number result is 16 or larger, then divide that whole number by 16 and keep the remainder.

18/16 = 1 R 2

3) Repeat step 2 until we have a number smaller than 16

1 < 16 so we are done

4) Convert number and remainders to hex

1 2 12
1 2 C

5) Put it together

12C

in two bytes, this is represented as 01 2C.

So now we will replace 32 with 012C. But wait, that is two bytes replacing one, how would that work?

Fortunately
for us, healing potions are stored in unsigned DWORDs. These range in
dec from 0 to 4,294,967,295 (more than enough) A DWORD is made of four
bytes, so we can represent a DWORD with four hex bytes. Thus the
original would be

00 00 00 32

and our modification

00 00 01 2C

but wait, that's not what is there. At B2B50, you see a 32, at B2B51, a 00, and so on. What you are seeing is

32 00 00 00

That's because DWORDS are stored with the bytes in REVERSE order. So we would write our new value of 300 as

2C 01 00 00

That replaces the 4 bytes from B2B50 to B2B53.

OK,
thats great, but what if we wanted to give our barbarian ice bolt
instead of taunt? Well it can be done by swapping pointers.

Locations
in the computer's memory can also be stored in hex, like in a file. So
we can have memory addresses. A pointer is an address of memory. It can
'point' to all sorts of things: it can point to a piece of code within
the dll file, it can point to code outside the dll file, it can point
to other data loaded in memory. Pointers are usually stored in DWORDS.

To
swap skills, what we will do is change the pointers to the skill code.
We will go to the pointers to the barbarian's taunt skill, and change
those pointers so that they instead point at the sorceresses' icebolt.
When D2 loads up, it will look in the same pointer for the location of
taunt, but now that it is pointing to icebolt it will use icebolt
instead.

First open up D2Game.dll. The
sorceress' table is at adress EF518. Like I said this is a table of all
the sorceress' skills, with an entry for each skill. An entry consists
of 3 dwords in this particular table.

First
we must figure out the number of the ice bolt skill. Open up skills.txt
with excel and notice the order of the sorceress skills there, it
appears in the same order in the dll files. To figure out the skill
number, look at the ID column. Subtract the ID of the ice bolt skill
from the ID of the first sorceress skill (fire bolt), that will give us
3. So ice bolt is skill 3. Thus we must go to entry 3 in this table.
The first entry starting at EF518 is entry 0. It is 12 bytes long. If
your hex editor has a 'jump' function like XVI32, you can set it to
jump each entry. Set your jump width to 12 dec, or C hex. then you jump
3 times, and you will arrive at entry 3. Or you can multiply by 3 and
just jump once. Or, if you don't have a jump function, just add the
amount you want to jump to your present location. (Windows calculator
is very handy for this!)

So once we
arrive there (EF53C hopefully) we now need to copy 12 bytes from there,
which would include bytes EF53C through EF547. Use the copy command.
Then we need to go to our barbarian table at ED618. Repeat the same
procedure for finding the skill like with the sorc. We should be
looking at taunt, skill 11, at ED69C. Now, we want to replace the 12
bytes from ED69C to ED6A7. Make sure you replace and NOT just insert.
On some hex editors, you may have to first delete this place and then
paste the sorceress data, others will let your paste 'overwrite' what
is already there. Save your work.

You
should now be able to load the game if everything went well. Make a new
barbarian, get him to level 2, and put a point into taunt. Try it out.

Not
what you expected eh? What you should have seen is the barb still
making his taunt sounds, but if you found some monsters, you would
notice they were being frozen too. Well that's because we've only gone
and changed the 'effect' of the ice bolt. D2game.dll covers many of the
server calculations, for example, do you hit an enemy, how much damage
do you do, etc. To change the apperance of skills, you must edit
D2client.dll.

The Sorceress table in
D2client.dll is at CF210, the Barbarian at CDEC8. Each entry in the
table is 5 dwords rather than three, and is thus 20 dec bytes (hex 14)
long rather than the 12 (hex C) in d2game.dll. The skills here are
numbered in the same fashion as in d2game. Copy the ice bolt entry over
the taunt entry. You should now know enough to make this change in
d2client, and see some ice bolt graphics when you are done.

Now
you know alot about hex editing, but if you want to follow code gurus
like Jarulf, you may need to know just a little more. These guys work
with Disassemblers that generate 'assembly language' based on the
binary of the file. You will see things like this

:6FABD15D E8B4370A00 Call 6FB60916

The
first value is usually the adress, that's where it is in the file. But
this is the address of the file when it is loaded into memory, not the
address when it's just sitting on the hard drive. To get that, you will
need to subtract a 'memory offset' from the given value. This
particular instruction is from D2Client.dll, and the memory offset for
that file is 6FAA0000. So the hex adress in the file for this code is
1D15D.

The second value you see is a
series of bytes. This is the hex data starting at the given adress. If
you jump to the 'corrected' adress (1D15D) you will find this data
there.

What follows is the assembly
commands which you don't have to understand. Usually, when someone has
a modification they will tell you the new hex to replace the old hex.
Just correct the address and drop the new hex in.

If you would like some idea as to what is going on with the assembly, then take a look at the assembly FAQ at http://www2.dgsys.com/~raymoon/x86faqs.html.

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[url=https://d2mods.info/forum/kb/viewarticle?a=156&sid=c3ee59faeec08c6390e7d860f0518e58]Knowledge Base - Hex Editing Tutorial (by Foxbat)[/url]