Re: A89: U.S. Encryption Laws
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Re: A89: U.S. Encryption Laws
On Fri, Dec 03, 1999 at 09:21:02 +0200, Risto Järvinen wrote:
>
> Hm. Are the apps actually encrypted?
No, only the signatures are.
> Instead RSA could be used to make a digital signature on programs and the
> calc would refuse to run them. This wouldn't protect the programs from
> being pirated (you can copy them but they won't run on another calc) but
> it'd let the calculator be exported.
The MD5 algorithm is used to make a digital signature and this signature is
encrypted (by TI) using RSA. The calculator decrypts this and verifies the
checksum, if it doesn't match the app is deleted.
> Plus if calculator actually decrypts something using RSA, it means that it
> has the 'private key', so you could just disassemble the ROM to find it
> out. Authenticating digital signature needs only the 'public key' while
> signing requires the 'private'.
Right and wrong. It's true that authenticating requires the public key, and
that's why you will *not* find the private key in the ROM. Only TI knows the
private key, and only TI can sign apps/ROMs.
//Johan
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