This is an introductory article which explains how to follow our two-part guide on using the Prometheus downgrade tool.

Before attempting either Part 1 or Part 2 of the guide, everyone should read this article. It explains whether the guides apply to you, and if they do, which ones you should follow, as well as making sure that you fulfil the requirements for them to work.

Now that the Yalu jailbreak has been released and has reached a reasonably stable state, many people have been asking how they can make the jump to iOS 10.2 to use the tool, having remained on a lower firmware until now in order to keep their existing jailbreak. Of course, it is traditionally not possible to move to an unsigned firmware like iOS 10.2, but as we have reported several times recently, the release of tihmstar’s suite of tools called Prometheus has changed this.

Some users will now be able to move to iOS 10.2 even though the signing window has closed, so long as they meet certain requirements.

Before you begin, please read the list of things to bear in mind below. You must be sure that you want to do this, and that it applies to you, before you start. Not everyone can use the Prometheus tools.

If you’re looking to downgrade an older device, check out my futurerestore+libipatcher guide, which details how to use the tool on legacy 32-bit models.

Things to consider

Do you satisfy all the requirements? Look at the section Requirements below and check that you have ticked all the boxes to make this possible.

  • Do you want to upgrade to iOS 10.2? If you are already jailbroken on a lower firmware, consider whether you actually want to move. The iOS 10.2 jailbreak currently requires you to re-sign the application with your computer every seven days, unless you have a developer account. It is also semi-untethered, meaning you have to run the jailbreak app every time you reboot. If you are on an untethered jailbreak already with no certificate needed, decide whether this is worth the upgrade. In addition, not all tweaks are updated and working yet. If you are already jailbroken, you can also perform this process at a later date, there is no rush.
  • There is a small amount of risk involved. Whilst many people, including myself, have successfully used the tool, the process is fairly complicated, and if an unlikely problem occurs halfway through the restore you might be forced to upgrade to iOS 10.2.1. This would mean no iOS 10.2 jailbreak for you, and losing the jailbreak you already had to begin with. If followed carefully the instructions should not allow this to happen, but proceed at your own risk.


If you do not satisfy ALL the criteria, you cannot upgrade with Prometheus.

  • A 64-bit iOS device, excluding the iPhone 7 and iPhone 7 Plus.
  • A jailbreak on your 64-bit device with tfp0 enabled, unless you have an iPhone 5s or an iPad Air which is ALSO on a firmware which has nonce collisions. All other devices must have a jailbreak, do not ask about other devices without a jailbreak.
  • If you have an iPhone 5s or iPad Air on a firmware which has nonce collisions, for example iOS 10.3 b1, iOS 10.2, iOS 9.3.3, you must also know which nonces collide for your specific device. If you have one of these devices, and you know which nonces collide for it on your current firmware, you must also have saved blobs for those nonces for iOS 10.2, while it was still signed. As you can see, this is quite a specific set of circumstances, so if you don’t know what all of that means, assume you haven’t done it and that you just need a jailbreak.
  • Valid blobs saved for your 64-bit iOS device for the firmware you want to go to (likely iOS 10.2). The blobs must be .shsh2 files in order to use the jailbreak method, and must have been saved when the destination firmware was still signed (you can check if your blobs are valid using TSS Saver).
  • Access to a Mac or Linux computer, or a Windows computer running Mac or Linux inside a VM. This cannot be done on a normal Windows installation yet. If you only have Windows, I recommend a free trial of a VM software, and a copy of Ubuntu, also free.
  • The IPSW file for your exact device model, for a currently signed firmware. This is needed for the SEP and baseband. We will be using iOS 10.2.1 for this purpose.
  • The IPSW file for your exact device model, for the unsigned firmware you want to restore to. We will be using iOS 10.2 for this purpose.
  • The Prometheus tools, namely futurerestore and nonceEnabler. Nonce collision method users do not need nonceEnabler, most people will.
  • Time and patience.

How to use Prometheus to move to an unsigned firmware

If you fulfil the requirements and have the files ready, you can move onto the guides. There are two guides, some people must follow one, the majority must follow both:

NonceEnabler Method:

If you currently have a jailbreak and you want to move to a different firmware with Prometheus’ nonceEnabler method, you must follow Part 1 & Part 2 of the guide. This is the recommended method, and the one most people will use Prometheus for.

Nonce collision Method:

If you currently have no jailbreak, and you want to try to move to a different firmware with Prometheus’ nonce collision method, do only Part 2 of the guide, skip Part 1. Remember, this will not work except in certain cases; check the Requirements carefully before wasting your time.


Good luck, I hope your restore is successful! Please don’t ask eligibility questions unless you have read this article carefully first. If you have a question which is not answered in the article, let me know in the comments!