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iPhone4S是第五代iPhone。网络制式为GSM/CDMA ，存储容量有8GB、16GB、32GB、64GB可选，机身颜色有黑色、白色可选。维修iPhone4S是容易的，需要耐心，用到的工具有螺丝刀、撬棒等。

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Why can't iPhones be downgraded?

So, here's the deal:

I love the way iphones look and feel, but why cant you downgrade them?

I would like to focus on an older one for the purposes of this article, like the iphone 4s.

Newer firmware slows it down. Apps crash. It lags.

I KNOW they use a kerberos certificate or whatnot to sign the firmware, and the iphone will only accept firmware signed by apple, but why can't you get around that?

Couldn't you just pop the sucker open and flash the darn image DIRECTLY onto the NAND?

is there some other way to FORCE the firmware onto the phone? not hook it up to itunes and stuff, but to simply copy the image onto the nand?

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It has to do with how Apple handles the SHSH blobs on the device. When the device is updated, the SHSH blobs are erased, which is one way Apple does it. They also stop signing old versions of iOS (they started to do this ~iPhone 3G because people downgraded the iPhone 2G, the Touch was later signed this way). This is their way of forcing the iOS upgrade to be the only option on these devices. Apple treats it as a numbers game so they can brag, and so developers drop old versions sooner, again to to force people who are waiting to upgrade to accept something they may not want.

At least on previous versions of iOS that predate iOS 10, you could back up the SHSH blobs and downgrade the device anyway, if there wasn't a hardware level exploit to do it. I think they have been having trouble backing these blobs up since iOS8, and it's only going to get harder with iOS 11.

Back in the day, it was easy to backup the SHSH blobs and go against what Apple wanted. Now they have made it very hard to do.

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SHSH blob is a term for a small piece of data that is part of Apple's digital signature protocol for iOS restores and updates, designed to control the iOS versions that users can install on their iOS devices (iPhones, iPads, iPod touches, and Apple TVs), generally only allowing the newest iOS version to be installable.

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I still have yet to move my iPod Touch to iOS 10, because I want the SHSH blobs in case iOS 10 proves to be as buggy as it's reported to be.

Until I know how to backup the SHSH blobs, I refuse to install it. The battery life on iOS 8 is already a joke on the Touch, to the point I have started entertaining buying the low cost iPhones to use as an iPod. I primarily want the SHSH blobs, in case iOS 10 makes the Touch battery situation worse.

Mine is the one before they put the iP6 processor in the Touch, so I also dread a performance hit.

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Because that's the way Apple wants it.

They don't want you running old versions of iOS. You can't circumvent it unless you find a vulnerability that you can exploit.

Do some research (you can start here) and stop asking for hacks and other circumvents on this forum. We are here to help individual users with fixable problems. If you want to bypass iCloud, TouchID (recommending BGA X-Rays and whatnot) and now hacking iOS, you are on the wrong forum.

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I don't want to bypass icloud! That's illegal!

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@anonymousguy Remember just who this answer came from. He's been active around here for two weeks.

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Well, I thought you had asked that in the past. Perhaps you deleted the question or asked it with one of your alternate ID's (which is odd by the way).

I'll take you at your word and stand corrected on iCloud Lock. The essence of my reply remains the same. I know you are a "kid starting out". I applaud you for trying to start something so technical. Focus on what "real customers" want and offer them great service and real solutions. Forget all this Apple lockdown BS.

If you are just curious about the security implications, that's cool too but this is not the right place for that.

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@mayer, not sure what is implied by your comment. What does how long I have been contributing have anything to do with my answer?

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@refectio You are stating what the policies are around here and wha will and won't be answered with only two weeks of being here. I don't think you really know yet.

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Wow, this got a little out of hand. I got out of the software part of the game. Conveniently, when carrier unlocking became less popular. I've been looking into getting back, and good or better at it, than I was before. Like I said earlier, it used to be easier to modify iPhones firmware. Now it's not so easy, I've heard. Also like old turkey said, we're all here to make devices and vehicles more straight forward to use. When they're obviously designed to cost you more money

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To be fair the latter iOS released for the 4S ran like molasses. I think it was so bad Apple decided at the last minute to remove 'game center' which was in the Gold Master revision of the last iOS supported, but was removed from the production version.

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bruh

DO YOU EVEN APPLE BRO?!?!?!?

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Why can't apple and samsung release all schema-- just kidding.

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@benjamen50 we can dream :)

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@benjamen50 @gigabit87898 but it is not about dreaming. It is about making it possible. We all have to continue to fight for our right (no, not to party. Wrong song) to repair our devices. We need to become more active toward that, it is not just Apple and Samsung. Try Toshiba (hate that company) John Deere, Jeep, Chevrolet and every Kitchen Appliance manufacturer. Try Keurig....There is just so much more to it. Any boardlevel repair shop is currently in an industry build around leaked copyrighted material:-)? How long would it last if Vladimir is going to tighten internet access in his country? Check on here as well. Just my 2 cents....

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Hey @benjamen50 @gigabit87898! Just to follow-up on @oldturkey03 's words of wisdom:

We helped found repair.org. We're constantly fighting for consumers' right to repair. We believe everyone should have equal access to diagnostics, schematics, and parts available to dealer facilities. If you're ever interested in learning more, you can read up on what we've been up to here: https://repair.org/news/

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I was perusing the comments all legitimate, but to downgrade to lower IOS from say 10.** is impossible. I personally tried it no way "Jose", As for the Icloud story well I bricked a iphone 5s after after I updated and the owner apparently had it removed from Icloud and I witness him doing it but when you put the previous owner's credentials on the phone "this user is not authorised to unlock" .

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Yes, you can downgrade. If you know what you are doing.

If you had SHSH blobs saved from previous iOS versions you can downgrade.

https://tinyumbrella.org/ios-10/

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If that happens to be the case for you, you've still got a window to downgrade back to iOS 9.3.5, the last version of iOS 9—but that window isn't quite known yet. It could be days or even weeks before they stop signing iOS 9.3.5, so if you want to downgrade, you've got to do it quickly.

https://smartservicingcentre.co.uk

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