Genuine Crypto!

[John Brazier]

Ian stated:

> If you had 1024 or so bits available to store `something' that would be
useful for a rainy day, what would you store?

> But if I've only got 1024 bits, is that enough?   And is RSA viable  
> using a small PowerPC embedded processor?

> Any suggestions?  In the absence of anything better, I'm going to put
> 1024 bit RSA keys on the boards and record the public keys locally.

1024 bits would usually be regarded as short for RSA now, though I believe
it would be appropriate for an elliptic curve system (which should also be
more appropriate for a light processor). Of course - it depends on what the
value is of the information you're protecting!

If it's ID you are worried about, how about using 160 or 256 bits for a hash
of the serial number (plus a salt, and perhaps other parameters such as a
second hash of the memory contents)? You could then use the rest for, say,
an AES key and a base/modulus for Diffie-Hellman (giving yourself all sorts
of possibilities!).

ATB

JB