shsh

A SHSH blob (based on the acronyms for signed hash and binary large object; also called ECID SHSH, referring to the device's ECID , a unique identification number embedded in its hardware) is an unofficial term referring to the digital signatures that Apple generates and uses to personalize IPSW (iOS firmware) files for each iOS device (iPhone, iPad, iPod touch, or Apple TV); they are part of Apple's protocol designed to ensure that trusted software is installed on the device, generally only allowing the newest iOS version to be installable. Apple's public name for this process is System Software Personalization or, as of iOS 7+, System Software Authorization.This process is controlled by the TATSU ("TSS") Signing Server (gs.apple.com) where updates and restores can only be completed by iTunes if the version of iOS is being signed. Developers interested in iOS jailbreaking have made tools for working around this signature system in order to install jailbreakable older iOS versions that are no longer being signed by Apple.

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