How to explain crypto?

Brock, the crypto-challenged, humbly apologizes for his gaffe. He was
looking for a way to draw an understandable comparison of how much harder a
1024-bit implementation of RSA is to break than what current export
controls allow.

He's asking for suggestions on how in future articles he could word this so
a layman could understand it... Preferably something that could be said in
a few sentences. (Brock cops to the fact that it does an incredible
disservice to a complex topic. Remember, tho, he writes for a broad
audience with a way diverse range of understanding -- or misunderstanding,
as the case may be!)

For example, someone sent me this explanation:

  "The 1024 bit key is likely an RSA key, and is not comperable to a 40 bit
  symetric key.  From memory, 1024 bit RSA is about as hard to crack as 90
  bit symetric."

Is this a reasonable comparison?

-Declan

Im quoting directly from the PGP manual from pgp2.6.2:

"People who work in factoring research say that the workload to
exhaust all the possible 128-bit keys in the IDEA cipher would
roughly equal the factoring workload to crack a 3100-bit RSA key,
which is quite a bit bigger than the 1024-bit RSA key size that most
people use for high security applications..."

If we take phil at his word, I would say that comparing 90bit symetric to
1024bit RSA would be a bit generous to RSA. 

On Tue, 4 Jun 1996, Declan McCullagh wrote:

>   "The 1024 bit key is likely an RSA key, and is not comperable to a 40 bit
>   symetric key.  From memory, 1024 bit RSA is about as hard to crack as 90
>   bit symetric."
> 
> Is this a reasonable comparison?
> 
> -Declan
> 
>

Ben Holiday writes:
> Im quoting directly from the PGP manual from pgp2.6.2:
> 
> "People who work in factoring research say that the workload to
> exhaust all the possible 128-bit keys in the IDEA cipher would
> roughly equal the factoring workload to crack a 3100-bit RSA key,
> which is quite a bit bigger than the 1024-bit RSA key size that most
> people use for high security applications..."
> 
> If we take phil at his word, I would say that comparing 90bit symetric to
> 1024bit RSA would be a bit generous to RSA. 

It is very far from clear that Phil was right.

As I said, these comparisons are all based on insufficient data. I
don't think they are a great idea.

Perry