iOS 10.3.1 Firmware

Apple signs firmware on a per‑device basis. A version may remain signed for newer devices while being unsigned for older ones, especially after a device reaches end‑of‑life or if a security patch only applies to certain chips.

The table above shows the build ID for each device. You can also look up build IDs on sites like ipsw.me or check your device’s "About" screen after installing (Settings → General → About → Version → tap the version number to reveal the build).

Not through normal means. Apple’s TSS server must sign the restore, and it will reject unsigned versions. However, if you have saved SHSH2 blobs and your device is compatible with a bootrom exploit (like checkm8 on A5–A11), you may be able to restore with tools like futurerestore.

These are cryptographic hashes that let you verify the integrity of your downloaded IPSW. After downloading, compare the file’s hash with the one shown in the details modal. If they match, the file is complete and untampered.