For those of you not on the NZISIG list, the following messages were posted there by Peter Guttmann on the subject of key sizes, which he has agreed I can repost to this list:
For the key size, see e.g. "The Curse of Cryptographic Numerology", http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=5772965&tag=1 (you may need to be an IEEE member to get access to this, unfortunately).
OTOH if it's only for KSKs and not any other, frequently-used keys then it's not so bad, just use 1024 or 1280 bits for other keys. You're also fighting against organisations who've chosen their key sizes based on numerology rather than any real risk assessment, so you may have to bite the bullet even though it doesn't make any sense to use a longer key, and (as the Numerology article points out), is in fact a net detriment to security.
and
During DNSSEC's lifetime, there will inevitably be security breaches and compromises. The one thing that will never happen is that an attacker will factor the RSA key ("break" it), no matter what key size is used. Therefore any effort spent in debating key sizes is totally wasted, and should be expended on examining real weak points that attackers will actually exploit, and how to mitigate against attacks at those points.
The only reason for choosing a key size of 2048 bits rather than 1280 is through a conscious choice to make the same fashion statement that other countries are making. Since this is purely a fashion statement, it should be documented as such, i.e. "We use a key size of 2048 bits not because it provides any extra security but because other countries use it, and if we didn't then the vast majority of users who don't understand cryptography might incorrectly perceive us as being less secure. This key size has a negative impact due to extra processing overhead and message sizes, but this is deemed justifiable because <something about the cost of bad publicity being even worse>".
FWIW, I'd support staying with 1280 bits, if only so you/we (NZ) can point out how pointless other countries' using 2048 bits is. Then in ten years time we can all do a collective "I todja so!" when nothing happens.
This may be politically unacceptable though.
In the event that this changes anyone's views then please let me know before we settle on switching to 2048 bits. cheers Jay -- Jay Daley Chief Executive .nz Registry Services (New Zealand Domain Name Registry Limited) desk: +64 4 931 6977 mobile: +64 21 678840