Baseband reverting - Please help me understand

Discussion in 'Jailbreaks and iOS Hacks' started by Peterg2, Nov 29, 2010.

  1. Peterg2 macrumors 6502a

    Joined:
    Jan 28, 2008
    Location:
    Montreal, Canada
    #1
    Hi,

    I have an iPhone 4 which I purchased from the Apple store a few months ago which I have not jailbroken and, at least in the short term, don't intend to.

    Here is my situation which I find odd. I am currently running the 4.2.1 firmware. Prior to the release of the 4.2.1 firmware I had tried out the 4.2.1 GM and the 4.2 GM and the 4.1 GM. All 3 of those are saved in a folder on my hard drive.

    The odd situation is that I am able to revert back to 4.1 GM very easily and by doing that my baseband is reverted back to 02.10.4 - yes I have checked. (as opposed to 03.10.01 with 4.2.1). This is not via jailbreaking, using cydia etc etc or even putting it in dfu mode. I simply hook up my phone to one of my computers here, and when itunes come up I press (using Windows 7) shift+restore and choose 4.1. Itunes then proceeds and at the end I have 4.1

    I am simply curious as to why I am able to do this so easily when supposedly I should not be able to. Something with the bootloader in my phone which is buggy? I really don't know. The only reason why I have reverted back several times to 4.1 is that I have somewhat spotting 3G connectivity with 4.2.1 which is not present in 4.1

    All comments most appreciated.
     
  2. maturola macrumors 68040

    maturola

    Joined:
    Oct 29, 2007
    Location:
    Atlanta, GA
    #2
    GM are developers releases, which are intended for Developer to update their app to the new firmware, during that period developer restore firmware often, and Apple allow this by Signing the firmware and baseband, while the GM is out, you can revert back to the "current" release not problem. Once the GM becomes Final and it is release to the general public, Apple will stop signing those baseband and firmware (there is usually a windows of a few days while Apple still sign them). After Apple stop signing those GM or anything previous to the "current" release you won't be able to revert back anymore.
     
  3. Peterg2 thread starter macrumors 6502a

    Joined:
    Jan 28, 2008
    Location:
    Montreal, Canada
    #3
    Thanks very much for the reply which clarifies the matter for me.
     
  4. bob616 macrumors 6502

    Joined:
    Jul 12, 2008
    #4
    that doesn't make sense because apple should have stopped signing the 4.1 GM back in september
     
  5. Peterg2 thread starter macrumors 6502a

    Joined:
    Jan 28, 2008
    Location:
    Montreal, Canada
    #5
    After the reply above I had a check around:

    http://modmyi.com/forums/general/737960-apple-still-signing-ios-4-1-a.html

    and this seems to confirm that they are still signing 4.1 (although, as you note, the window is a lot larger than a few days seemingly)
     
  6. maturola macrumors 68040

    maturola

    Joined:
    Oct 29, 2007
    Location:
    Atlanta, GA
    #6
    That is how usually works, all we have to go in based on previous Apple Behavior, I am not sure why Apple haven't stopped signing 4.1GM yet, I don't work for them.

    from that post, that person try the 3G , only 3GS and forward required SHSH blobs
     
  7. bob616 macrumors 6502

    Joined:
    Jul 12, 2008
    #7
    I have a question that is related to this.
    So if i have my shsh's saved for my iphone and I restore down to a lower firmware will my baseband downgrade too?

    For example I am on 4.2.1 right now. If i downgrade down to 4.0 will my baseband revert down to that version's baseband, making my phone unlockable?
     
  8. Myzhi macrumors 6502a

    Joined:
    Dec 15, 2009
    #8
    Only on IP4 does Apple have security checks for firmware and baseband. If they are still signing them, you can downgrade both. Apple no longer are signing 4.0 and 1.59 baseband so you won't be able to downgrade the baseband even if you can downgrade to 4.0 by having old saved SHSH files.
     
  9. maturola macrumors 68040

    maturola

    Joined:
    Oct 29, 2007
    Location:
    Atlanta, GA
    #9
    No you can't downgrade the baseband without apple. the SHSHs saved are used to downgrade the firmware only, the BB stay the same, however since 4.2.1 there is a BB check, meaning that if you don't have the right BB the downgrade will fail.
     

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