Why is downgrading baseband impossiable?

[Hf44]

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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

 

[Applejuiced]

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.

 

[Charadis]

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

 

[anthdci]

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.

 

[maturola]

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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

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.