Re: A89: Linux Port for 89/92


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Re: A89: Linux Port for 89/92




Adam Davis wrote:
> 
> It is a trivial matter to brute force break the code.  We just need someone
> willing to hook the calc to their computer.

While the .tib file is being downloaded, the boot loader calculates a
checksum of the code. At the end of the .tib file, there is an RSA encrypted
version of the same checksum. The boot loader decrypts the checksum and
verifies that the calculated one equals to the decrypted one and refuses to
run the code if they don't match.

The key that is required for *decrypting* is available to us, but we can't
*encrypt* our own checksum.

The RSA key that TI uses is 512 bits and the MD5 checksum is 128 bits.
Trying to adapt a ROM to get a specific checksum is would take (on average)
10^25 years if the computer can do one million tests per second. Breaking
the RSA would take 10^140 years for the same computer.

If you still think it's a "trivial matter", please tell me and the rest of
the list how you are going to deal with it!

//Johan


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