Saurik developed a great way to get your signature files in Cydia regardless of the firmware you are running, but it requires a jailbroken phone. Apple is almost ready to release iOS 4.01 while iOS 4.1 is distributed to developers, on the other side iPhone Dev team achieved a full jailbreak and unlock of iPhone 4 iOS 4. So it is highly recommended to save your SHSH, so you can downgrade back to iOS 4 any time. Since iOS 4 jailbreak isn’t public at the moment you can save your iOS 4 SHSH with Firmware Umbrella. Well, here is how to get them.
Why i need ECID SHSH Dump ? Apple added a new piece of security called ECID, The nature of iPad / iPhone 3GS / iPod Touch 3G / iPhone 4 hardware allows Apple to stop IPSWs from being usable unless you’ve already gotten the signed chunks they send to you based on your ECID (a unique chip ID). Actually Apple applies ECID so the iDevice will refuse to accept the ipsw file while downgrading because of a bad signature. It will treat it as a custom ipsw without having the apple server sign the ipsw specifically for your phone id before flashing.
Note : This procedure allows you to save your precious SHSH blobs on your PC/Mac so you can save them forever. You must have your SHSH saved on Saurik server by hitting the make my life easier button on home page of Cydia. If you already saved your SHSH on Saurik server you needn’t to repeat the process every time.
!! it is very important to keep doing this for every firmware version that comes out after these !!
Windows:
1. Get your ECID following this instructions: How to Grab iPad ECID on Windows and Mac
2. Download firmware umbrella thefirmwareumbrella, place on desktop.
3. Now put your iDevice in recovery mode.
4. Open umbrella.exe with administrator privileges, and it’ll automatically detect your iDevice, tick on advanced options and enter your ECID number and hit the reset button (this will request the shsh signature from APPLE and save it to your PC)
5. By doing this you will save your shsh copy in the same directory where the umbrella.exe file is, copy it and rejoice, for you have your own 64kb gold with you.
Mac:
1. Get your ECID following this instructions: How to Grab iPad ECID on Windows and Mac
2. Get firmware umbrella thefirmwareumbrella, move the Umbrella app OUT of the .dmg file preferably onto your desktop.
3. Now put your iDevice in recovery mode.
4. Launch umbrella app, and it’ll automatically detect your iDevice, tick on advanced options and enter your ECID number, select the location to Apple and hit the reset button (this will request the shsh signature from APPLE and save it to your Mac)
4. By doing this you will save your shsh copy in the same directory where the umbrella.app file is, copy it and rejoice, for you have your own 64kb gold with you.
Special thanks to FirmwareUmbrella for developing and maintaining such a wonderful application.
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Via http://www.ihackintosh.com/2010/07/how-to-backup-ios-4-shsh-blobs-for-iphone-4/
