BootMii's dumps getting smaller?

Discussion in 'Wii - Hacking' started by Det1re, Jul 18, 2009.

Jul 18, 2009
  1. Det1re
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    Member Det1re det1re.de

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    I noticed something odd:

    I've got four NAND dumps of my second Wii. So here's a table:

    Code:
     # | Date/TimeÂÂ|ÂÂDescriptionÂÂ| NAND usage | RAR size
    --+------------+---------------+------------+----------
    1 | 2009/07/02 | 3.1E ONLYÂÂÂÂ |ÂÂ 29.7%ÂÂÂÂ|ÂÂ324MB
    ÂÂ|ÂÂ 14:00ÂÂÂÂ| BootMiiÂÂÂÂÂÂ |ÂÂÂÂÂÂÂÂÂÂÂÂ|
    --+------------+---------------+------------+----------
    2 | 2009/07/02 | 4.0E HBCÂÂÂÂÂÂ|ÂÂ 32.4%ÂÂÂÂ|ÂÂ347MB
    ÂÂ|ÂÂ 15:00ÂÂÂÂ| cIOS, BootMii |ÂÂÂÂÂÂÂÂÂÂÂÂ|
    --+------------+---------------+------------+----------
    3 | 2009/07/10 | 4.0E SV,ÂÂÂÂÂÂ|ÂÂ 41.7%ÂÂÂÂ|ÂÂ307MB
    ÂÂ|ÂÂ 02:30ÂÂÂÂ| FW channelsÂÂ |ÂÂÂÂÂÂÂÂÂÂÂÂ|
    --+------------+---------------+------------+----------
    4 | 2009/07/18 | 4.0E more SVÂÂ|ÂÂ 42.0%ÂÂÂÂ|ÂÂ262MB
    ÂÂ|ÂÂ 20:15ÂÂÂÂ|ÂÂÂÂÂÂÂÂÂÂÂÂÂÂ |ÂÂÂÂÂÂÂÂÂÂÂÂ|
    
    
    SV = various Savegames
    FW = USB Forwarder
    Anyone else notices the RAR sizes? The difference between dump #1 and #2 is the only one I understand. The others are odd. Also compare the "NAND usage" between those.
    I used the same compression mode for all of them. Any explanation for this?
     
  2. wrettcaughn

    Member wrettcaughn Misunderstood Moral Elitist

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    That's crazy. I've never compressed them before. Do you always let BootMii verify the dumps?
     
  3. Maikel Steneker

    Member Maikel Steneker M3 Fanboy

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    Could it be that the dumps are encrypted? In that case, compression ratio is pretty much random.
     
  4. s3phir0th115

    Member s3phir0th115 GBAtemp Advanced Fan

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    That may be part of it, that's for sure. I'm not sure what the dumps look like in a hex editor to be certain though.

    Although I'd have to say that getting a compression of 3xx MB for a ~512 MB file is pretty good, and I don't think you'd get that much of it was all just random encrypted trash. (Look at Wii ISO's being compressed without being scrubbed if you don't know what I mean.)
     
  5. Det1re
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    Member Det1re det1re.de

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    They are. However this is a giant size difference for my understanding.
     
  6. Helsionium

    Member Helsionium Alpha and Omega

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    The dumps are supposed to be encrypted, because they're raw dumps of the NAND, which is encrypted, so they shouldn't be compressible at all. An encrypted 528 MB file should never compress to less than 500 MB.
     
  7. s3phir0th115

    Member s3phir0th115 GBAtemp Advanced Fan

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    Hmm. That's why I didn't think they were encrypted.

    My nand dump, compressed with 7z on Ultra settings, comes out to be:
    330 MB (346,598,036 bytes)

    That's damn good compression for something that's encrypted I must say.
     
  8. Helsionium

    Member Helsionium Alpha and Omega

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    Well, then it's obviously not encrypted. That's strange, because I thought all NAND dumpers simply extract the NAND, which would be encrypted. BootMii apparently decrypts it as well, though I don't know for what purpose.
     
  9. Det1re
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    Member Det1re det1re.de

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    They must be encrypted, else we wouldn't need zestig to unpack them. However the encryption then might be the solution.
     
  10. Dteyn

    Member Dteyn GBAtemp Fan

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    I've done 4 backups with BootMii so far, here are the file sizes:

    Code:
    # | Date/TimeÂÂ|ÂÂDescriptionÂÂ| 7z Ultra size
    --+------------+---------------+--------------
    1 | 2009/06/14 | 3.2U SV, HBCÂÂ|ÂÂÂÂ 369MB
    ÂÂ|ÂÂ 02:00ÂÂÂÂ| cIOS, BootMii |
    --+------------+---------------+--------------
    2 | 2009/06/14 | 4.0U SV, HBCÂÂ|ÂÂÂÂ 305MB
    ÂÂ|ÂÂ 04:45ÂÂÂÂ| cIOS, BootMii |
    --+------------+---------------+--------------
    3 | 2009/07/16 | 4.0U SV, HBCÂÂ|ÂÂÂÂ 384MB
    ÂÂ|ÂÂ 23:00ÂÂÂÂ| cIOS, BootMii |
    --+------------+---------------+--------------
    4 | 2009/07/18 | 4.1U SV, HBCÂÂ|ÂÂÂÂ 400MB
    ÂÂ|ÂÂ 15:00ÂÂÂÂ| cIOS, BootMii |
    Before I did the latest backup today, I removed a couple WiiWare and VC games. But yet the dump compresses larger? Installing more stuff on the Wii seems to result in a smaller compressed NAND dump... whereas removing stuff from the Wii results in a larger NAND dump.

    I think we're in the Twilight Zone... lol [​IMG]
     
  11. arctic_flame

    Member arctic_flame GBAtemp ATMEGA8 Fan

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    Simple, The encryption method is not a stream cipher.

    Who said encrypting a file results in the result being pseudorandom?
     
  12. caitsith2

    Member caitsith2 GBAtemp Regular

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    Encryption is actually a 128 bit block cipher, AES, in CBC mode. What is compressing is repeats of completely erased blocks, which are NOT encrypted, as well as repeats of file data. (A new cluster is assigned to the file, if the file is in any way modified, as a wear leveling mechanism. Also, the AES CBC encryption, is done on a cluster at a time. So, if there are repeats of the same data, like ALL 0x00 through out 20 clusters, then the compression will be those 20 clusters compressed to the size of 1 cluster.

    The size of 1 cluster on the NAND is 16KiB. There are 32768 clusters in total. The first 64 clusters make up boot 1 and boot 2. The last 256 clusters makes up your filing system table. In general, a 16KiB cluster is often encrypted, and it is only repeats of the same encrypted cluster data that actually compresses.
     
  13. OncleJulien

    Member OncleJulien tool of peers

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    maybe its simply cutting back on its fiber?
     
  14. Pip_X

    Member Pip_X GBAtemp Regular

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    Deleteing data in the nand. is not actually deleting it. It simply mark it to be usable, ur data is still there eventhough u deleted it and it wont show up in the system. Hence ur backup size.
     

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