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How to fix some mysterious problems.

I wonder how Apple prevent me from downgrading my iPhone 6 (iOS 9.2 to iOS 9.0.2), If I am offline and have older iTunes (which of course supports iOS 9.0.2). Thank you in advance!

asked 16 Jan '16, 04:21

i3udypt's gravatar image

i3udypt
86316


Apple stops signing older versions of iOS once newer ones have been released.

You can start the installation, iTunes will attempt to restore to 9.0.2. But iTunes is built so that it asks Apple for SHSH and keys for the firmware you are trying to restore to. Once iTunes finds out that there are none for 9.0.2, it will deny the restore.

You can save both SHSH and keys when the firmware is being signed and use them to restore after the signing window has been closed. Though it is a pretty tedious procedure: iTunes will cross-check the key with Apple. Since Apple never sends down the same one (they are randomly generated) iTunes will deny the restore. So you need to trick iTunes into thinking it is asking Apple for the key, while it is actually asking a proxy. Similar to Tiny Umbrella.

link

answered 16 Jan '16, 13:04

King%20Shoot's gravatar image

King Shoot
11.3k78891

edited 16 Jan '16, 13:09

Because any iOS version needs to be signed by Apple, which means connecting with Apple's servers, and 9.02 is no longer being signed.

link

answered 16 Jan '16, 05:43

Fishy2's gravatar image

Fishy2
4.3k251336

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Asked: 16 Jan '16, 04:21

Seen: 3,957 times

Last updated: 16 Jan '16, 13:09

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