I'd guess that it's an asymmetric algorithm that uses some kind of public-key signing of the code: http://en.wikipedia.org/wiki/Public-key_cryptography http://

I'd guess that it's an asymmetric algorithm that uses some kind of public-key signing of the code: http://en.wikipedia.org/wiki/Public-key_cryptography http://en.wikipedia.org/wiki/Public-key_cryptography The 'input' (the public key) of the problem can probably be found in the firmware of the device (it's probably too large to have been bruteforced). To be able to sign code so that the device will run it, you need the private key, which is one of the factors of the public key. So the guy used a program to factor the public key to get the private key so that he could sign the code (whatever code he wants) with it and get the calculator to run it.