Why are 1024 bit keys the limit right now?

[paul at fatmans.demon.co.uk]

> I am just starting at this. I know that part of RSA/PGP's strength comes from
> the size key you choose. What prevents someone from writting a 2048 bit key?
> Is it because computers can't handle it? Is 1024 top of  the prime number
> size right now? Am I way off track? 

2048 bit keys are quite commonly used but the reason that arbitrarily 
large keys are not good is because of the amount of time taken to 
generate the keys then encrypt and decrypt messages with them, PGP 
uses a hybrid system whereby the rsa algorithm encrypts a one time 
session IDEA key, a longer RSA key would result in unacceptably long 
waits for most users when encrypting and decrypting messages.

In the end it comes down to a trade off between speed and security 
and 1024 bits is a sensible compromise for most uses.

 

  Datacomms Technologies web authoring and data security
       Paul Bradley, Paul at fatmans.demon.co.uk
  Paul at crypto.uk.eu.org, Paul at cryptography.uk.eu.org    
       Http://www.cryptography.home.ml.org/
      Email for PGP public key, ID: 5BBFAEB1
     "Don`t forget to mount a scratch monkey"