Shsh — Blobs

: When you try to restore or update an iPhone using iTunes, your computer sends a request to Apple's signing server. This request includes your device's ECID (Exclusive Chip ID), a unique serial number burned into its processor, and the iOS version you are trying to install.

| Factor | Impact | |--------|--------| | | On cellular iPads and iPhones, the baseband firmware must also be signed. Blobs cannot bypass baseband signing, preventing downgrades to very old iOS versions. | | SEP (Secure Enclave) compatibility | SEP firmware must be compatible with the target iOS version. Older iOS SEP is not signed, so downgrades must use a still-signed SEP (usually from a recent iOS). | | Nonce entanglement (A12+) | Without a bootrom exploit, setting the nonce requires a jailbreak. Nonce generation uses hardware random numbers, making brute-force impractical. | | Apple’s countermeasures | In 2019, Apple introduced nonce entropy on A12+, greatly reducing replay utility. In 2021, they tied APNonce to bootrom state. |

SHSH blobs are the digital locks that prevent unauthorized downgrades on iOS devices. For users, saving them is a crucial preemptive action to maintain freedom over their device’s software. Whether you're waiting for a new jailbreak or simply want the security of being able to return to a stable iOS version, taking a few minutes to save your blobs is highly recommended. shsh blobs

It is best practice to save blobs for every iOS version Apple releases while the signing window is open, even if you are not currently interested in jailbreaking. Tools for Saving Blobs

The Ultimate Guide to SHSH Blobs: Understanding iOS Digital Signatures and Downgrading : When you try to restore or update

Technically called , an SHSH blob is a unique digital signature generated by Apple's servers.

Many jailbreaks are only compatible with specific, often older, versions of iOS. Saving blobs allows you to "hop" to those versions later, even after Apple has closed the signing window. How the Process Works | | Nonce entanglement (A12+) | Without a

: Each blob is tied to a specific iOS version and build ID.

Keeping everyone on the latest software ensures app developers only have to optimize for recent iOS builds.