RSA Weak?

[Sven Radde]

Hi!

Alexander W. Janssen schrieb:

> How do you come to that figure? A keyspace of 1024 is the double
> amount of 1023 bit, so I'm curious how you come to that figures.

While this is true for symmetric ciphers, there are far more efficient
attack methods on asymmetric ciphers (factoring - instead of brute-forcing).

> It's one thing to brute-force 256-bit RSA in, let's say, a couple of
> months, but a totally different to break 1024 bits.

The current public record is a 663-bit RSA-key ("RSA-200" as it has 200
digits) AFAIK:
http://www.rsa.com/rsalabs/node.asp?id=2879

More recent is the factorization of a 640-bit RSA-key:
http://www.rsa.com/rsalabs/node.asp?id=2964

As mentioned above, the difficulty does not scale exponentially: The
663-bit number took 55 CPU-years on a 2,2GHz Opteron, the 640-bit number
 30 CPU-years. The actual computations were apparrently carried out by a
cluster with 80 machines.

In fact, some mathematician has proven that factoring is a polynomial
problem, IIRC.

cu, Sven