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Author Topic: Hacking into the .g3p/b format [HALTED]  (Read 29751 times)

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Offline fxdev

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Hacking into the .g3p/b format [HALTED]
« on: March 03, 2012, 01:12:08 pm »
All hacking has been stopped because of recent concerns expressed by the community.

KermMartian writes:

Quote
I am one of the Prizm hackers who had been expressing concerns on #cemetech. I've been in various contact with Casio marketing and engineering personnel over the past year or so, and they have made it clear that they're currently turning a blind eye to mature, responsible third-party hacking. Officially, they're supposed to both not support it and potentially disallow it, but that hinges on how we behave. [...]

We do not want to drive Casio into the same cat-and-mouse game the Nspire developers have to work around.


General header format:

Code: [Select]
AAACBDAF90889A8D _xFF_yFF_yFF..FE
_a_a_a_a.._b_c_c 00000000_._._d_d

_x : file type
- .g3a=0xD3; .g3e=0xB6; .g3p/b=0x82; .g3m=0x8A

_y : unknown
- if (.g3a) then 0xFE else 0xEF

.. : check bytes
- upper=LSB_of_a+0xBF
- lower=LSB_of_a+0x48

_. : CP check bytes
- rightmost=if (Casio Provided) then LSB_of_a+0x85 else LSB_of_a+0x17
- leftmost=(checksum of LSW_of_a) + ...
-- if (Casio Provided) then (.g3p/b=0x9B; .g3e=0xCF) ...
-- else (.g3p/b=0x09; .g3e=0x3D; .g3m=0x11)

_a : inverted file size

_b : unknown
- if (.g3m) then 0x01 else 0x00
- could be related to _d

_c : unknown
- if (!.g3a) then 0x0000
- seems to be unrelated to _a

_d : inverted element count
- if (!.g3m) then 0x0000

The .G3P format:

A 32-bit ckecksum seems to be stored at the end of the image data block (starts at 0xD0), but before any footer. The procedure to calculate this checksum is not known. Without disassembling the Prizm's CAPTURE routine, further analysis appears to be a waste of time.

References to zlib inside the OS imply they are using this for data compression. Also, it is not known if the type ID at _o (see below) is required for the decompression part.

Code: [Select]
AAACBDAF90889A8D 82FFEFFFEFFF..FE
_a_a_a_a..000000 00000000_._.0000
4350_b_b_b_b_c_c _c_c_c0000000000
_d_d_d_d0000_e_e _f_f_f_f00000000
00000000000000_g 0000000000000000
0000000000000000 00000000000000_h
00000000000000_i 0000000000000000
0000000000000000 0000000000000000
0000000000000000 0000000000000000
0000000000000000 0000000000000000
0000000000000000 0000000000000000
0000000000000000 _b_b_b_b_j_j_j_j
??_k_l_l_m_m???? ????????_n_n_n_n
_o_o???????????? ????????????????

Main header:
.. : check bytes (see 'General header format')
_. : CP check bytes (see 'General header format')
_a : inverted file size

Sub header:
_b : if "CP" then 0x00010000 else 0x30313030
_c : if "CP" then 0x00 else 0x4C79373535
_d : file_size - 0x20
_e : if "CP" then (0x0001 or 0x0009) else (0x0A09 or 0x0009)
_f : file_size - (0xB8 + _g + _i + _h)
_g : if _e=0x0001 then 0x00 else 0x8C // length footer 1
_h : if _e=0x0A09 then 0x2C else 0x00 // length footer 3
_i : if _e=0x0A09 then 0x?? else 0x00 // length footer 2
_j : file_size - (0xCC + _g + _i + _h)
_k : if CAPTURE then 0x01 else 0x00
_l : image_width
_m : image_heigth
_n : file_size - (0xD0 + _g + _i + _h)
_o : type ID (see 'Sub formats' below)

Sub formats:

"CP" format with _e=0x0001 and _g=0x00
- no footer; Casio Provided (ID: 0x3C1B)

"CP" format with _e=0x0009 and _g=0x8C
- one footer; Casio Provided (ID: 0x3C1B)

"CP0100" format with _e=0x0001 and _g=0x00
- no footer; CAPTURE Format (ID: 0x388D)

"CP0100" format with _e=0x0009 and _g=0x8C
- one footer; Converter Format (ID: 0x789C)

"CP0100" format with _e=0x0A09 and _g=0x8C; _i=0x??; _h=0x2C
- three footers; Casio Provided (ID: 0x3E93)

The .G3B format:

A 32-bit ckecksum should be stored at the end of the image data block (starts at 0xD0), but before any footer.

Code: [Select]
AAACBDAF90889A8D 82FFEFFFEFFF..FE
_a_a_a_a..000000 00000000_._.0000
4350_b_b_b_b_c_c _c_c_c0000000000
_d_d_d_d0000_e_e 00000000_f_f_f_f
0000000000000000 0000008C00000000
000000000000002C 0000000000000000
000000_z00000000 0000000000000000
0000000000000000 0000000000000000
0000000000000000 0000000000000000
0000000000000000 0000000000000000
0000000000000000 0000000000000000
0000000000000000 _b_b_b_b_j_j_j_j
_l_l_m_m???????? ????????_n_n_n_n
_o_o???????????? ????????????????

Main header:
.. : check bytes (see 'General header format')
_. : CP check bytes (see 'General header format')
_a : inverted file size

Sub header:
_b : if "CP" then 0x00010000 else 0x30313030
_c : if "CP" then 0x00 else 0x4C79373535
_d : file_size - 0x20
_e : if "CP" then 0x0492 else 0x0092
_f : file_size - (0xB8 + 0x8C + _z + 0x2C)
_z : if "CP" then 0x10 else 0x00 // length footer 2
_j : file_size - (0xCC + 0x8C + _z + 0x2C)
_l : image_width
_m : image_heigth
_n : unknown length
_o : type ID (see 'Sub formats' below)

Sub formats:

"CP" format with _e=0x0492 and _z=0x10
- three footers; Casio Provided (ID: 0x3C1B)

"CP0100" format with _e=0x0092 and _z=0x00
- two footers; Casio Provided (ID: 0x3C1B)
- two footers; Converter Format (ID: 0x789C)
« Last Edit: April 08, 2012, 08:24:14 pm by cfxm »
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Offline sammyMaX

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Re: Hacking into the .g3p/b format
« Reply #1 on: March 03, 2012, 01:13:46 pm »
Why does Casio have two formats? Do they serve different purposes?
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Offline fxdev

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Re: Hacking into the .g3p/b format
« Reply #2 on: March 03, 2012, 01:24:37 pm »
The "CP" format seems to be older. All later tools and files use "CP0100". I did not focus on what is stored inside these footers. If it contains extra security against modifications, then we can just modify the _e flag to ignore this (at least for .g3p files).
« Last Edit: March 03, 2012, 01:25:42 pm by cfxm »
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Offline sammyMaX

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Re: Hacking into the .g3p/b format
« Reply #3 on: March 03, 2012, 01:38:46 pm »
I meant, what's the difference between .g3b and g3p files?
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Offline fxdev

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Re: Hacking into the .g3p/b format
« Reply #4 on: March 03, 2012, 01:47:00 pm »
Quote from: sammyMaX on March 03, 2012, 01:38:46 pm
I meant, what's the difference between .g3b and g3p files?

Sorry, I did not expect such a basic question. ;)

.g3p is the Prizm's image format
.g3b is the Prizm's animation format
The latter is only used along with the Picture Plot add-in.
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Offline sammyMaX

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Re: Hacking into the .g3p/b format
« Reply #5 on: March 03, 2012, 02:01:09 pm »
Cool, thanks for the info :)
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Offline bynary_man

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Re: Hacking into the .g3p/b format
« Reply #6 on: March 06, 2012, 11:54:01 am »
This is very interesting :)
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Offline krazylegodrummer56

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Re: Hacking into the .g3p/b format
« Reply #7 on: March 06, 2012, 05:06:19 pm »
And how does this help?

Will you now be able to put modified pics onto the prizm?
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Offline fxdev

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Re: Hacking into the .g3p/b format
« Reply #8 on: March 07, 2012, 04:24:21 am »
Quote
And how does this help?

Will you now be able to put modified pics onto the prizm?

The missing part is the checksum calculation. When we know it, we can (hopefully) create Casio provided images. ;)
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Offline calc84maniac

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Re: Hacking into the .g3p/b format
« Reply #9 on: March 07, 2012, 05:58:42 am »
Won't that completely nullify the point of them making the CG-10?
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Re: Hacking into the .g3p/b format
« Reply #10 on: March 07, 2012, 07:25:48 am »
So this will allow us to change the Prizm Startup screen and system screens?
That sounds really cool, we could completely change what it says, or 'rearrange' pixels for efficiency.
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Offline fxdev

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Re: Hacking into the .g3p/b format
« Reply #11 on: March 07, 2012, 11:08:22 am »
Quote
Won't that completely nullify the point of them making the CG-10?
Yep. :)

Quote
So this will allow us to change the Prizm Startup screen and system screens?
As far as I know, these are simple bitmaps inside the OS. On legacy models, OS patching is not too complicated from within an add-in as you can use flash writing syscalls. But I don't know if the Prizm adds extra security against modifications. Well, the OS checksum is already known.
« Last Edit: March 07, 2012, 11:13:05 am by cfxm »
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Offline JosJuice

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Re: Hacking into the .g3p/b format
« Reply #12 on: March 07, 2012, 12:21:07 pm »
Quote from: calc84maniac on March 07, 2012, 05:58:42 am
Won't that completely nullify the point of them making the CG-10?
Yes.
Quote from: Jonius7 on March 07, 2012, 07:25:48 am
So this will allow us to change the Prizm Startup screen and system screens?
That sounds really cool, we could completely change what it says, or 'rearrange' pixels for efficiency.
No. What this will allow us to do is to create our own images to use as backgrounds for graphs and other math purposes that already support the images that are supplied by Casio.

EDIT: Ninja'd by more that an hour. I should use F5 more. :P
« Last Edit: March 07, 2012, 12:21:43 pm by JosJuice »
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Offline DJ Omnimaga

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Re: Hacking into the .g3p/b format
« Reply #13 on: March 07, 2012, 02:53:24 pm »
I would definitively like if it was made possible to create CG10 custom images or port CG20 ones to the CG10.

A lot of PRIZM BASIC games do not run on the CG10 because of the different format.
« Last Edit: March 07, 2012, 02:53:32 pm by DJ_O »
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Offline fxdev

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Re: Hacking into the .g3p/b format
« Reply #14 on: March 07, 2012, 04:26:33 pm »
Anyone skilled in disassembling PC programs like the Casio image converter? Because I'm not... :P
And Simon doesn't seem to be interested in reverse-engineering the CAPTURE routine.

In the worst case, this could take us another year.
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