Why is downgrading baseband impossiable?

Discussion in 'Jailbreaks and iOS Hacks' started by Hf44, Oct 30, 2011.

  1. Hf44 macrumors member

    Joined:
    Sep 17, 2011
    #1
    Wirelessly posted (Mozilla/5.0 (iPhone; CPU iPhone OS 5_0 like Mac OS X) AppleWebKit/534.46 (KHTML, like Gecko) Version/5.1 Mobile/9A334 Safari/7534.48.3)

    Hi, just a quick question that keeps bothering me. Why is downgrading basebands impossiable? Downgrading firmware is possiable of course, through tinyumbrella. But why is it not possiable for BB? Thanks for the information :)
     
  2. Applejuiced macrumors Westmere

    Applejuiced

    Joined:
    Apr 16, 2008
    Location:
    At the iPhone hacks section.
    #2
    Basebands are different.
    Once updated they're not meant to be downgraded again.
    Unless there's a nice exploit that can be used but those are rare.
     
  3. Charadis macrumors 6502a

    Joined:
    Jul 3, 2010
    #3
    Someone correct me if I'm wrong, but I think it possibly has something to do with it being that the baseband, or modem firmware, is installed on the memory chip integrated on the communications radio? Whereas the operating system, iOS, is installed in the system memory "hard drive?"

    Not sure myself, but I'm curious for other explanations, too.

    -C

    Sent from my MacBook Pro
     
  4. anthdci macrumors 6502

    Joined:
    Jun 8, 2009
    #4
    the reason is due to apples signing. When you request to do a firmware install, it gets a signature for the firmware, and another for the baseband. If you do repeated installs on the same device, the signature for the iOS is exactly the same, (hence it can be saved for later use) but the baseband is different every time.

    If you update your phone to say 5.0 it will get the relevant baseband. But apple usually keeps the previous version window open for a day or two. So you could install 4.3.5 and because apple are still signing it, it will install the 4.3.5 baseband. (that window is long closed now though)

    Apple has changed iOS to be the same as the baseband from 5.0 onwards.
     
  5. maturola macrumors 68040

    maturola

    Joined:
    Oct 29, 2007
    Location:
    Atlanta, GA
    #5
    The SHSHs required to downgrade the BB are encrypted and change on the fly every time they are requeste from Apple server, unless someone get access to the engine it cannot be done. Same way they new SHSHs work on iOS5.
     

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