# Re: 64bit or 1024bit - will it make a difference? (fwd)

**Jeff Simmons** (*jsimmons@goblin.punk.net*)

*Mon, 12 May 1997 10:58:16 -0700 (PDT)*

*> *

*> Remember also, that when we talk about 1024-bit RSA keys, we are trying*

*> to find the two prime factors of a very large number. To brute force an*

*> RSA key, you actually only have to examine the PRIMES between 0 and the*

*> key length. It's been estimated (see Schneier) that a 2304-bit RSA key has*

*> roughly the resistance to a brute force attack that a 128-bit symetric*

*> key has.*

*> *

*> It's still computationally infeasable. In "Applied Cryptography", *

*> Schneier estimates that for $10,000,000,000,000, you could build a*

*> special purpose key cracker that could brute force a 128 bit key in *

*> only 100,000,000,000 years. Note that the same machine could crack*

*> a 56 bit DES key in approximately 1 millisecond.*

*> *

*> > *

*> > I'm curious about something - and I will grant that I am not technically*

*> > knoweldgable about the subject as I should be. If it takes us using spare*

*> > cycles a few months to crack a 64 (56 really) bit by brute force, why in 10*

*> > years couldn't the same exact thing be done to a 1024 bit key? We've all*

*> > seen the amazing leaps and bounds by which processors (not to mention RAM,*

*> > etc) have come in the last 5 or 6 years. Somehow I think there must be a*

*> > better way than just making the key longer. Because as the keys get*

*> > longer, the computers will get better. And even now, its possible to crack*

*> > a 1024 bit code. Yeah, it'd take a heck of lot longer - but for*

*> > $120,000,000 worth of equipment - it could probably be done in a decent*

*> > amount of time.*

--
Jeff Simmons jsimmons@goblin.punk.net
Hey, man, got any spare CPU cycles? Help crack DES.
http://www.frii.com/~rcv/deschall.htm