The two devices that qualify are the iPhone 4S and the iPad (2nd generation). It is in fact possible to install iOS versions that Apple isn't singing anymore on devices newer than pre-A5 devices in very specific circumstances. Models manufactured in early 2010 or earlier (old bootrom) have a bootrom exploit that allows for downgrading without SHSH blobs, while newer models (new bootrom) have a separate exploit that allows for downgrading with SHSH blobs. ![]() Not all instances of the iPhone 3GS are the same. If you do happen to fall into the small group of users that have all of these pieces, consider yourself lucky, as you can use iFaith by iH8sn0w to stitch your SHSH blobs into the firmware to create a custom IPSW that you can use with iTunes after you put your device into Pwned DFU using iREB inside iFaith. iTunes ( version 11.0.5 or earlier for the iPhone 4).ipsw for your device for that version of iOS A valid APTicket (for iOS 5 and above) for your device for that version of iOS.SHSH blobs (if required) for your device for the particular version of iOS that you wish to install.Installing iOS on any device using a bootrom exploit requires you to put your device into a state known as Pwned DFU, which allows you to install custom firmware. The following devices have a different bootrom exploit known as limera1n, which allows installation of any version of iOS as long as valid SHSH blobs are provided: The following devices can utilize a special bootrom exploit that allows for installing any version of iOS without SHSH blobs: It is important to note that while all devices listed in the first section do have working bootrom exploits, there are different types of bootrom exploits, and each allow for different levels of boot manipulation. The following subset of devices do not utilize SHSH blobs, and can therefore install any version of iOS at-will: In short, unless you have one of the following devices (devices with A4 processors or earlier, hereafter referred to as "pre-A5 devices"), you cannot install anything except for the iOS versions that Apple currently signs: My answer is still up-to-date (other than anything having to do with these notes). When I find some time, I will add these to the answer below. It can allow you to install any IPSW as long as valid SHSH blobs are provided (it is unclear if you need a valid APTicket as well, as it's been demonstrated it isn't necessary in some cases). Other Other Other Note: There is an new bootrom exploit for A5 to A11 devices called checkm8. Other Other Note: There is an even newer method of downgrading/upgrading that will allow almost all 32-bit devices (doesn't include the 32-bit devices that can install iOS 10) to go from iOS 9.3.5 firmware to any other iOS 9.X firmware. Other Note: I am missing information about the original Odysseus which allows a few 32-bit iOS devices to downgrade in the iOS 6 and 7 range. Right now, the best tutorial for Prometheus is by and is endorsed by the author of Prometheus, I will be updating this answer later to explain more about it, but I wanted to get this information posted here sooner rather than later. The biggest caveat to this tool is that you must be jailbroken in most cases before initiating the restore (and you only have one shot, so a failed restore will force you to install a signed firmware) (if that signed firmware is also jailbreakable, then technically you get second chances, but it's rare for that to be the case unless there's a bootrom exploit for your device). The tool for it is called futurerestore (codenamed Prometheus). Note: There is a new method of downgrading/upgrading that doesn't require Apple to be currently signing, and it works on newer devices that aren't present in the first list of my answer below. This wikipedia page contains a list of iOS devices & the latest iOS they can support. ![]() See this article for some general information around this topic. ![]() ![]() If you had previously Jailbroken your device on iOS 6, it may be possible, providing you have saved your 'SHSH blobs' which can 'sign' the install instead of Apple. Once a new version comes out, Apple stops signing previous releases to keep everyone running the same iOS version and to prevent you from jailbraking your device again after restoring by forcing you to do an update. Putting a newer iOS on older hardware that never even supported that OS is near impossible.Īs part of the iOS restore process, iTunes has to check with Apple's servers to 'sign' each install of iOS just like App Store apps must be signed to run. This signing window typically is closed within days of a new version shipping. Downgrading or upgrading to a no longer current version of iOS is generally not possible once Apple stops signing the old software, as is needed when iTunes is preparing to install or restore an iOS.
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