Shsh: Blobs

You can always move to the latest version.

An SHSH blob (Signature HaSH blobs) is a digital signature that Apple uses to verify the firmware version you are trying to install on your device. shsh blobs

It sounds like you're referring to (a common typo: "shsh" instead of "SHSH"). You can always move to the latest version

When you restore or update an iPhone via iTunes or Finder, the software sends a request to Apple's servers. This request includes your device's unique (Exclusive Chip ID) and the version of iOS you want to install. If Apple is currently "signing" that version, their servers send back a unique SHSH blob. Without this signed response, your device’s hardware will refuse to boot the operating system. The "Signing Window" Problem When you restore or update an iPhone via

Starting with iOS 5, Apple introduced a nonce —a random string of numbers generated for every single restore attempt. This means a saved blob will only work if your device generates the exact same nonce that was used when the blob was originally saved.

A popular web-based tool where you simply enter your device details, and it saves your blobs to a public server for later retrieval.