Downgrade 5.1.1 to 5.0.1 5.1

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You can downgrade the firmware on your iPhone 4 after upgrading to iOS 5.1 till Apple is signing the older firmware for your phone .

ios 5 downgrade ios 4.3.3

Note : iPhone 4S , iPad 2 and iPad 3 cannot be downgraded following this method . Works only to downgrade iPhone 4, iPhone 3GS, iPad 1st generation , iPod Touch 4 and iPod Touch 3G .

Requirements :

Redsnow Latest Version
APTicket + saved SHSH blobs for the iOS 5.1 , 5.0.1 or iOS 5.0 firmware
A Computer running MAC or Widows
iOS 5.0.1 ipsw (as required for downgrading your device)
iOS 5.1 ipsw ( ” )
iOS 5.0 ipsw ( ” )

Redsnow Downgrade Method :

Download latest version of Redsnow for your computer running Mac or Windows OS
Use iTunes and backup all your device content in case you have some important data ( iTunes > Select device on left panel > Summary > Backup)
After the backup is complete launch Redsnow and go to Extras > SHSH blobs > Stitch (as shown in the image below)
click on the IPSW button and browse to the .ipsw file to which you want to downgrade your device . All download Links for iOS firmware above under Requirements header .
Now click on “Local” button point Redsn0w to the .plist file containing the SHSH blobs and APTicket, if stored locally on your computer . If these files are stored in Cydia , the option will be greyed out but will become available when the device is in DFU mode.
Put your device in DFU Mode (explained)
Use Redsnow to further put your device on Pwned DFU Mode. On Redsn0w main screen click on Extras > Pwned DFU and follow the on screen instructions.
Edits hosts file to change the address of Apple servers . For that head over to Windows > System 32 > drivers > etc . Mac OSX users go to etc. Use a text editor to add the following line at the end of the hostsfile : 74.208.105.171 gs.apple.com as shown in the image below
Now launch iTunes and hold down the SHIFT key (on Windows) or the ALT key (if you’re on Mac) and click on the Restore button on iTunes . Select the stitched IPSW file and restore .