Changes to Apple’s TSS servers currently render Prometheus non functional


Update: tihmstar has stated that the tool is working perfectly, and that he has used it successfully multiple times today. However, some users have been encountering a TSS server error when using the tool nonetheless.

Hot on the heels of Prometheus’ release at the 33c3 convention two days ago, tihmstar’s tool for upgrading and downgrading to unsigned iOS firmwares seems already to have hit a snag. Following some changes to Apple’s TSS servers today, the nature of which are yet to be investigated, the tool has been rendered non-functional at the present time.

The first misconception to clear up, which has been repeated in many places, is that Apple has completely taken its TSS servers offline. That is not the case; the servers are clearly still up, as can be proven by attempting to restore or upgrade a device through iTunes. If the TSS servers truly were down, no iTunes restores would be able to complete.

Having said that, some changes to the servers do seem to have been made, as attempting to connect to them returns an error, and Prometheus is unable to proceed at the present time. This is due to the fact that it relies on currently signed SEP and baseband sections during its restore process. Even though it circumvents signing for the rest of the process by using your saved blobs, an inability to get the TSS server to approve the SEP and baseband signing will cause the tool to fail.

A second rumour which has been perpetrated by some is that Apple will temporarily sign all firmwares when the servers come back online. Whilst this is not literally impossible, it is almost certainly false. Firstly, because as already discussed the servers are not totally down, and secondly, because there is no reason to think they would be forced to do so even if they were. This idea seems to be driven more by hope than anything else, and I would not place any amount of reliance in it, especially not in making decisions about upgrading or downgrading your devices.


Tihmstar has not yet commented on what changes have been made by Apple, only stating that they have not shut down the servers. As he is currently attending the 33c3 convention in Hamburg he may not be able to look into the issue for a few days, but I am cautiously optimistic that the issue will be able to be worked around.

At the moment all that can be said is that something has changed server-side which is preventing Prometheus from working as it did before, but whether it is improved verification of signing requests in response to his tool’s release or just coincidental maintenance, can not be known for sure. If some patches have been applied, only tihmstar will be able to clarify if they can be worked around, or if they have rendered his methods fundamentally impossible going forward.

For now, the following common sense practices should apply:

  • Do not try to use Prometheus to restore your device. It will fail and, although unlikely, may force you to upgrade to iOS 10.2.
  • Do not try to restore to any other unsigned firmware based on word-of-mouth promises that they will be signed again; this is foolish.
  • Do not angrily delete your saved blobs in the belief that Prometheus will never work again, or do anything else rash like upgrade to iOS 10.2. Be patient and see if the tool can be made to work again.

One final piece of Prometheus news, which is not related to the TSS server trouble but is still relevant, is that tihmstar has identified a problem with iPhone 7(+) .shsh2 blobs saved with TSSChecker. Again, do not panic and do not delete the blobs if you have them saved. Whilst he claims the blobs will not be able to be used with his Prometheus tool, he says they may still be usable with a different technique. He has also mentioned that he can fix TSSChecker so that it saves iPhone 7(+) blobs correctly from now on, so look out for that update.

Have you personally encountered a failed Prometheus restore due to the TSS servers refusing requests? Did you have iPhone 7(+) blobs saved? Say your piece below, and in the meantime, be patient and wait for developments from tihmstar.