[X4U] Re: X4U Digest, Vol 15, Issue 23

[Richard Gilmore]

On 20/11/05 10:28 AM, "David Ledger" <dledger at ivdcs.demon.co.uk> wrote:

> With public/private there are two keys.......The potential weakness of
> public/private keys is that if anyone ever discoverers a way to
> generate the private key from the public one, it will be dead.

Is this likely?
 
> In practice public/private key systems do not encrypt the message
> with the public key, but they use a truly random key (or as truly
> random as the computer system doing the work can manage). This key is
> encrypted with the public key and included with the message. On
> receipt, the private key is used to retrieve the main key. This way
> less CPU time is spent doing maths. As the main key is random it
> cannot be predicted or guessed. A brute force attack is the only way
> to discover the message without the key. Bruce Schneier, in 'Secrets
> and Lies' estimates that  a 128 bit key 'will be secure for a
> millennium' as 90 billion billion key per second cracking system
> would still take a thousand million years to try all keys.
> 
> David

So this kind of encryption is for all practical reasons unbreakable? Even
though it's theoretically breakable? Do websites that you enter credit card
info use this kind of encryption? How are Visa numbers etc...protected?

Not that I'll ever need one but are there Mac/PC encryption programs out
there that encrypt this way that average people can use?

I wonder if we have something like a quantum computer if they will ever
become powerful enough to crack ciphers with brute force?

I find this subject totally fascinating.

Thanx

Richard