modified on 15 September 2012 at 22:42 ••• 7,771 views

Talk:CXI

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How 3DS system judge encryption type? --Matyapiro

Sorry the question is not understood. What do you mean? --Neimod
I think that he means "How does the 3DS decide what encryption method must be used" --Quincy 23:47, 29 May 2011 (CEST)
That question does not make sense. There are no decisions. It is always AES CTR. --Neimod

Sorry,how does the 3DS decide what key to use for encryption? --Matyapiro

If you figure that out, let us know, thanks. --Neimod 02:45, 1 June 2011 (CEST)

There's a common key used to generate output at compile time, when the cci/ctx files are made. Why do you say 128 bit AES CTR though? --Jl12

Because 128-bit AES CTR is used to encrypt those formats. --Neimod 15:40, 18 June 2011 (CEST)

AES CTR is more difficult to attack via DPA or EM-DPA

I know *something* is used to encrypt but do we know it is 128 bit AES CTR? --Jl12 do you know that the cipher text is xored at the end but not the exact algo or are you sure about AES also

Frankly I don't think it was AES. I think it's using RSA for encryption. Besides it already used it once for the 2048-bit signature as you said. Wouldn't it make way more sense to also use it for the encryption scheme. --Jl12

Lol. --Neimod 16:06, 20 June 2011 (CEST)

agree the (LOL) RSA would not be of use to slow for an real time decryption or load of a game at runtime also the block size would not match and there would be no advantage using RSA as when console talks to the cartridge both keys are exposed to the end user and therefore could be potentially broken. RSA would only make sense if they can keep a secret key at their place. which is the case for DSA to sight the firmware for example preventing anybody to load unauthorized firmware into the device. and nobody could fake the signature as he does not have the private key. (fairly standard methods today for all sorts of consumer electronics).

What's funny? So I guess it's just based purely on speculation? You should say so. That way nobody believes something that isn't right. --Jl12 22:28, 20 June 2011 (CEST)

RSA is only used for the signature. After that a symmetric block cipher called AES is used in CTR mode. --Neimod 23:32, 20 June 2011 (CEST)

i guess if Neimod has the RAM simulator he could dump the firmware if not fire walled by a MMU. the PROC is ARM and there are nice IDA modules for it plus the Hexrays decompiler. Don't forget the RAM is executable and i don't think that neimod just read from it !

How did you get this data? Did you find some way to dump 3DS cartridges? --Popoffka 09:15, 1 June 2011 (CEST)

Yes, someone found a way to dump the data on 3DS cards. Unfortunately the method cannot be disclosed, and at this point dumping is not really useful since most of the information is encrypted. --Neimod 10:03, 1 June 2011 (CEST)

Do you have any method to run a Dump? and did you find the key for the ctrtool? --Stevechou

Nope on both questions. --Neimod 17:33, 25 June 2011 (CEST)

There's code in ctrtool that takes the AES counter value from some partition ID and type. I can't help but wonder, how do you know that the counter value is generated this way? And if we know that, isn't it a start to finding out the key? --Luigi2us 20:17, 25 June 2011 (CEST)

Sorry this information cannot be disclosed. --Neimod 05:17, 27 June 2011 (CEST)

Anyway, can you read the encrypt datas?


Hi! Do we already know where the offset of the ARM11 code is? And that I got correctly, that the hole 3DS ROM encrypted by AES? --Lazymarek9614 21:10, 1 August 2011 (CEST)

Yes, see ctrtool for more exact details. --Neimod 17:44, 6 September 2011 (CEST)
I mean the offset of the ARM11 code not the exefs. Exefs contains not only the code, right?
Would CXI be the homebrew application file format, what do you think? If so, then I think we can modify it a bit for homebrew,
because some parts doesn't make sense.--Lazymarek9614 19:18, 6 September 2011 (CEST)
The ExeFS contains only the ARM11 code and the banner. To know the offset of the ARM11 code you would need to scan the ExeFS for the file ".code".
As for the homebrew file format, I think it's a little too early for that. Whatever happens, happens. --Neimod 23:12, 6 September 2011 (CEST)
Thanks, but please can you give me the parameters for your tool to decrypt the ExeFS and save it? The usage for that is a bit ununderstandable.--Lazymarek9614 20:01, 7 September 2011 (CEST)
One of the parameters to use this tool is the master decryption key, which is currently not known. So at this point, nobody can use this tool to decrypt the ExeFS. --Neimod 03:12, 8 September 2011 (CEST)
This master decryption key, is it used for every game? For the 3ds homebrew format I will create a tool which includes a 3d model, an icon and the machine code in the file. However, before we should think about the structure for it. I know that's a bit early, but later (when we can run homebrew) we will be glad if we have it.--Lazymarek9614 20:14, 9 September 2011 (CEST)
We can also use the elf Format for homebrew--ichfly
Yes, but it has not a banner.--Lazymarek9614 16:54, 10 September 2011 (CEST)
Shall I create a new talk about the homebrew format? We should discuss and plan it a bit.--Lazymarek9614 11:08, 11 September 2011 (CEST)
Yes, you shall.. --Elisherer 11:55, 11 September 2011 (CEST)

Hi Neimod, love your work! my question is: The extended header suppose to start right after the NCCH header so why there is twice the space? (extended header size is usually 1024 and plain region offset is usually 5*512 = 2560 -> 2048 after the end of the ncch) thanks. --Elisherer 11:46, 6 September 2011 (CEST)

I'm not sure I understand you. The extended header does come right exactly after the NCCH header. The only place where this does not hold is the NCCH header at offset 0x1000, but this one header should be ignored because this space does not exist on a real card. I suspect this is the plaintext header from command 0x82 that was injected into the ROM in post-processing by the dumpergroup. --Neimod 17:40, 6 September 2011 (CEST)
Thanks for the answer, what I meant is that there is a block (of 2048 bytes) between the ncch header and the plain region. this is where the extended header should be, and it supposed to be 1024 bytes. So my question was what are the extra 1024 bytes for (they are not zeros...) --Elisherer 19:07, 6 September 2011 (CEST)
Ah that, I'm not sure what that 0x400-byte region is. --Neimod 23:12, 6 September 2011 (CEST)
So... how did you get that "Example dependency list from the extended header" obviously it's encrypted...? --Elisherer 13:22, 7 September 2011 (CEST)
That was added by Jl12, maybe he can answer this for you. --Neimod 03:12, 8 September 2011 (CEST)

I have a simple question why Neimod are thinking the code is compressed? I think LZSS is not good for binary images.

Because they just are. --Neimod 17:40, 6 September 2011 (CEST)
Game editors want to fit their game in the smallest ROM chip size possible, to reduce manufacturing costs. Also, encrypting blocks of zeros/FF is bad practices, compression avoids it. --Luigi2us 18:17, 6 September 2011 (CEST)

I've found something in my Chronicles Samurai Warriors savegame:

18 A1 72 6F 6D 3A 2F 53 00 6F 75 6E 64 2F 73 74 .¡rom:/S.ound/st
72 00 65 61 6D 2F 53 54 52 4D 00 5F 53 59 53 5F MES.SAGE_GOO.D.b
63 73 74 6D F9 D7 9A 2F 95 90 8D 0A 93 00 03 B0 cstmùך/•...“..°

Looks like a path in the ROM filesystem in a LZ77 compression. Maybe it can help to find the master decryption key (if we would have a dumped Samurai Warriors).--Lazymarek9614 21:12, 16 September 2011 (CEST)

I'm by no means an expert on de/encryption, signing code and what not, but the master decryption key is probably stored in internal RAM/ROM (in other words, inside the CPU die), that way it can't be sniffed or easily obtained. I doubt Nintendo would store a key as important as that in external RAM/ROM/SRAM, or in a some form of a filesystem. If they did, their programmers are dumber than Sony's. But again, system security is not the sort of thing I am good at, so take this with a grain of salt. --CHR15x94 21:35, 16 September 2011 (CEST)

The key is stored in every 3DS and it's always the same key...! I wonder that no one sniffed the 3DS' RAM yet. This should be done now! Has anyone experience in RAM sniffing?--Lazymarek9614 22:01, 16 September 2011 (CEST)

Someone will eventually. It's not an easy thing to do, and FPGAs (the device you'd use to access RAM) are quite expensive ($500 - $700+USD for a decent one). People did it with the DSi, I'm sure it won't be _too_ long for the 3DS. Might find this interesting as well. --CHR15x94 22:55, 16 September 2011 (CEST)

FPGAs are very expensive, that is true. The cheapest one I've ever seen was about $199 (it's the Development board which was used to dump ROMs by Legacy). I know about the DSi RAM haxx, but I don't have an FPGA. If I had one, I would try it.--Lazymarek9614 10:17, 17 September 2011 (CEST)

The cheapes I saw was 52 $ but if you realy buy one get the one for 69 $ (becaus I think it is much better) http://www.altera.com/products/devkits/max-index.jsp or one with a cyclon. I recommend boards with an Embedded USB-Blaster.--ichfly

That, and the pinout of the 3DS RAM chip is completely unknown. --Luigi2us 17:52, 17 September 2011 (CEST)

"Non-Executable CXI file examples(Includes Decrypted RomFS): DLPChild" Why are you calling dlpchild non-exec NCCH when that would have an ExeFS like any other "normal" CXI?(AFAIK dlpchild is exactly the same as other exec CXIs besides being temporarily installed to NAND from wlan for running) --Yellows8 16:44, 23 June 2012 (CEST)

Bad wording, I mean DLPChild Container NCCH, the same DLPChild containers used in CCIs and installed titles, to hold the DLPChild CIA files--3dsguy 00:36, 24 June 2012 (CEST)

I've been thinking, you know how we have executable specialisations of NCCH, which are officially called .CXI (CTR Executable Image). And we also have non-executable specialisations of NCCH, which I've assumed uses the extention .CXI. But perhaps officially, non-executable specialisations of NCCH have a different file extention all together, like the case CCI and CSU (both NCSD format).--3dsguy 18:09, 7 July 2012 (CEST)

actually after looking more closely at the scarse details on the CFA (CTR File Archive), the details closely follow the non-executable specialisation of NCCH which is the dlpChild container. So are the non-executable NCCH called CFA files?--3dsguy 18:20, 7 July 2012 (CEST)

Question: from what you know today (i assume you have at lead partially disassembly) what of the mechanism is HW implemented ? and what software ? the random seeding function for example ? could you force the seeding to be constant or better at your choice ? i think if you can influence the seed and if the use AES CRT plus the cipher text cleartext info as you must have as it corresponds RAM / ROM extern intern it should be possible to launch a DPA attack on it and get the key. assuming that there are not some hidden custom functions in it.