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Comment by reedlaw | Hacker News Reader

What could TI's motivation possibly be? How could they lose any business by hackers modifying firmware? Instead, it seems it would be more likely to increase hardware sales.

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I think this is down to the educational market. For many exams you can only used an approved make/model calculator.

If you can hack the OS you can use it to store answers, notes or similar aids in cheating for an exam. If the platform isn't locked down they'll lose their exam board approval which would have a big impact on that models sales.

I don't think TI is still selling the 83; they've moved on to promoting the supposedly new and improved N-Spire.

The 83 is still listed on their product website -

http://education.ti.com/educationportal/sites/US/productCate...

http://education.ti.com/educationportal/sites/US/productDeta...

Notice on the page it also says - "Count on TI calculators at exam time. You can use this TI graphing calculator on the PSAT, SAT, and ACT college entrance exams, IB, and AP tests."

The TI-83/84 is still used in a lot of textbooks, and teachers are loathe (sometimes) to learn something new. It's entrenched.

2008-09 list of approved calculators:

http://www.collegeboard.com/student/testing/ap/calculus_ab/c...

It's one of the most common calculators in high schools still

I'm thinking it goes something like this. The TI calculators have something called "press-to-test", where a teacher can hit a combination of keys to disable functionality on the calculator. When in this mode, a LED flashes on the calculator so a teacher can tell at a glance that the student isn't "cheating".

Now imagine a homebrew OS where you hit the "press-to-test" keys, and the light blinks, but all the calculator's functionality is still there. If this became prevalent, then schools could outright ban the calculators on tests, so students would be less likely to buy them. Lost sales from this would dwarf any pickup from home hobbyists.

Bah; they should all just use slide rules anyways. /sarcasm

We weren't allowed calculators on most tests. (And when we were, most of the time I forgot to bring one. I've never been so fast with mental and written arithmetic since.)

That doesn't sound like something that couldn't be bypassed already with just a tiny bit of hardware hacking.

I'm not sure about the details, but perhaps they're afraid that if the ROM key is broken, people can more easily read out the ROM code, and use it in a cheap clone of the hardware?

There might be a larger monetary value associated with the actual OS code, than with the hardware design itself.

As I said though, I'm not sure about the details here; you'd of course expect the CPU on the calculator to be able to access the ROM code in order to run it, but perhaps it's somehow obfuscated when that happens.

My understanding (which is incomplete) is that this is only a signing key.

Even if they are somehow relying on this key to prevent cloning, are they seriously under the impression that a 512-bit key is sufficient to keep a bunch of guys in Shenzhen from making a firmware-compatible device? Any effort to clone has long since come to fruition, and it's extremely likely they know this.

My guess: lawyers justifying their existence by picking fights with people they expect can't fight back. I'm glad the EFF has stepped in.

It's not even keeping anyone from cloning, because a Chinese manufacturer could just copy the ROM wholesale, signing key and all. Or patch out the signing key checks, or replace the key with one of their own... quite literally, the only thing this key is doing is keeping device owners from installing unauthorized applications and replacement OSes.

This is purely a signing key. It's not used for any sort of copy protection but solely to prevent unauthorized code from running.

Didn't this hacker make a replacement OS better than TI's? I don't think TI will face serious competition from clones, except possibly in Asia and third-world countries. This hack doesn't even help in making clones, except maybe by giving engineers a chance to practice programming calculator OS's.

Are they trying to get away with selling cheap low-features versions that aren't different except in software?

This would be plausible except AFAIK all of their models have different hardware capabilities. The 83 and 84 even un the same exact software; they just have different specs.

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