Bluefreeze

Bluefreeze is a tethered downgrade solution by a group called the Private Dev Team. It claims to allow the downgrade of a device to iOS 4.3, 4.3.5, or 5.0 from 5.0.1 without SHSH blobs saved via TinyUmbrella or iFaith. iDevices that are supported are iPhone 3GS, iPod touch 3G, and all A4 devices.

Download

 * Windows

Usage
5.0.1 (9A405) -> 5.0 (9A433) c13c14abcde18bbdb7d70c8563f56ac1 -> 989b8327acab76e7632443a0e179250c
 * Step 1: Use iFaith to get an iOS 5.0.1 SHSH blob
 * Step 2: Open the iFaith SHSH file. Bluefreeze will change md5 and iOS version. For example, if downgrading to iOS 5.0 on an iPod touch 3G from iOS 5.0.1:
 * Step 3: Save the modified file, and use it to build an iOS 5.0 custom firmware. Even though the firmware has fake shsh blobs on it, iTunes will still accept it. (iREB will be used to bypass error 16XX)
 * Step 4: Since there are no shsh blobs present the device will boot up into DFU mode. A bootrom exploit, known as Limera1n, will be used to bypass Apple's blob checker per se. (Tool used: redsn0w)
 * Step 5: Device will boot up, and one will have a tethered downgrade.