It dawned on me a few months back when the SSL Cert on my Bluesocket Wireless Controller expired. I started by generating a new CSR on my Bluesocket, I then logged onto GoDaddy to purchase a new cert and low and behold, GoDaddy wouldn't accept my 1024-bit CSR. No big deal, I thought, I'll just open the Bluesocket and generate a 2048-bit CSR. Unfortunately, I couldn't do it without a code upgrade. The key takeaway is to keep an eye out for any SSL-enabled devices in your environment that might require updates in order to support the new key length standard.
In special advisory (800-57), NIST advises that 1024-bit RSA keys will no longer be viable after 2010. The recommendation, which has been broadly adopted, is to move to 2048-bit keys, which should be viable until 2030, according to NIST. This change has prompted a number of vendors to bolster their SSL acceleration offerings. A recent Citrix Netscaler PR release points out that that the doubling of the key size from 1024-bit to 2048-bit increases CPU computational requirements from 4x to 8x. As a result, if you're managing any externally facing services, or commerce related services that are highly SSL dependent and already have high concurrent connect counts, it makes sense to assess the performance implications of jumping to 2048-bit keys before you make the leap, if you haven't already.
Jordan Sissel from semicomplete.com recently did some interesting performance testing on the CPU and network impact of running SSL at various key lengths. His analysis offers a valuable lesson as you plan for the performance impact of 2048 and 4096 bit keys. To summarize, while offloading SSL to a hardware appliance can be valuable computationally, the network latency impact of processing a large number of SSL handshakes can often introduce the bulk of any perceived delays on the front end. There's not a whole lot you can do about latency, aside from strategically locating services and load balancing appropriately.
The upshot is that if you're moving to 2048-bit keys or higher anytime soon, make sure you assess the performance implications of that move.