1. Background: What Are IPSW and Signing?

• IPSW – iOS/iPadOS firmware file used to restore or update Apple devices (iPhone, iPad, iPod touch, Apple TV).
• Signing – Apple cryptographically signs each IPSW release for a limited time after a new iOS version is released. Once a newer version is out, Apple stops signing the older one within 1–2 weeks (sometimes less).

Your device usually needs to be in a jailbroken state to set a "nonce generator" that matches your saved blobs. What it is: A popular all-in-one free management tool for Windows. How it works:

Turdus Merula (Free/Open Source): Specialized for older A9 and A10 devices (like iPhone 6S and 7). It is unique because it can sometimes bypass SEP checks for these specific chips, allowing for "tethered" (temporary boot) or "untethered" (permanent) restores.

Free Availability: Official leetdown domain (open source on GitHub).

A. futurerestore (The Industry Standard)

• Type: Command Line Interface (CLI) / Open Source.
• Cost: Free.
• Functionality: This is the core engine behind almost all downgrade attempts. It allows users to "stitch" saved SHSH blobs into the restore process, essentially tricking the Apple verification server (TSS) into validating an older firmware.
• Pros:

  3uTools: A popular third-party suite that offers a "Flash & JB" section. While it primarily facilitates restores of signed versions, it can sometimes import and flash firmware in specific jailbreak contexts, though success is limited for newer devices.

  Key Features: