Because you cannot sign the firmware with Apple’s private keys, you must use a tool like or create a "Custom IPSW" via command line tools. These tools exploit vulnerabilities (like limera1n or checkm8) to bypass the signature verification during the restore process.
The most common modification is replacing the stock RestoreRamdisk with a custom one. This allows you to: modify ipsw file
To successfully edit and restore a modified IPSW, you typically need tools that can bypass Apple's signature checks: Because you cannot sign the firmware with Apple’s