A few days ago, TNOC was updated again on TI-BANK . Not only it can be used to reduce the size of your OS file, increasing your calc user memory in the process, but more importantly TNOC allows you to break the anti-downgrade protection in OS 3.0. To remove that protection, you have to use the software to remove Boot2 3.0 from the OS file before installation on the calculator.

The current version of TNOC can be downloaded here.

However, if you already installed OS 3.0 without removing the included Boot2 from it, then you're stuck with no way to downgrade, as Nleash will not work on OS 3.0, since the exploit used to run Ndless-type files was fixed in OS 3.0. Basically, the only way to downgrade then is using 3 wires connected to the TI-Nspire dock connector (at the bottom of the calculator) and connected to a RS232/TTL converter. In other words, you need extra hardware.

Critor has published a tutorial on how to achieve this, including pictures, on TI-BANK. For those who don't speak French there is a post by him in English and some pictures on Omnimaga forums too.

TI's anti-downgrade protection was broken in 6 hours, compared to 2 weeks with OS 2.1. Unfortunately it depends of if you removed Boot2 3.0 from the OS prior installing it, though, and a solution to downgrade from an unmodified OS file without acquiring extra hardware nor sending your calculator to somebody who has it might take longer, now that TI fixed the exploit Nleash used to remove the previous anti-downgrade protection...

Quote

TI's anti-downgrade protection was broken in 6 hours, compared to 2 weeks with OS 2.1.

* TI Community  wins

I'm really happy, this is a great achievement!
This works both for the CX and non-CX, right?

We don't know.
We need a CX to check if the modified TCC/TCO file is accepted.

I'm really happy, this is a great achievement!
This works both for the CX and non-CX, right?

For the CX, there are no older OSes to go back to.

Note that the reason boot2 3.0 doesn't load older OSes isn't exactly "anti-downgrade protection". boot2 3.0 requires that the OS have 2048-bit RSA signatures. Older OSes had only 1024-bit RSA signatures, OS 3.0 for the non-CX has both 1024-bit and 2048-bit, and OS 3.0 for the CX has only 2048-bit.

WHAT? 2048 BIT RSA KEYS?

They really don't want us to create third-party OSes, don't they?

Looks like it's time to try all the harder.
Maybe not crack the key, but it might be possible to modify the OS for programming ability.

Which made the NFS factorization maybe ten orders of magnitude beyond the state of the art.

this isnt quantum computing now, this requires quantum servers!

It is impossible with any modern algorithm(isn't 2^2048 more thn the number of atoms in the universe?). We need a new way or extremely good luck now(maybe its an even number key). Maybe the Lua in the calc will help us get around this.

   Actually, we need to stop thinking about factoring the RSA keys. As Goplat said, it's gone from impossible to impossible. As in, it will rain pink flying unicorns before we can factor it. Hoping to get lucky finding it is statistically foolish.

We should just enjoy the new scripting and use RunOS/OSLauncher for what it can't do if we really need OS3 (right now, we don't), though that would require some modifications to the OS which could not be distributed.