Question about KSK

[Phil Mayers]

On 27/04/12 13:40, WBrown at e1b.org wrote:
> We are authoritative for a few dozen small zones.  Is it possible to use
> the same KSK for all of them?  I can see where if it gets compromised we
> would need to resign all zones using the KSK at once.  How much effort
> would I be saving sharing the KSK?

That depends entirely on how you are signing and managing the zones.

IMO you might be creating more work for yourself, since it's a less 
common configuration.

>
> I'm sure there are plenty of other good reasons not to do this...
> Enlighten me!
>
>

It means you can't change the ZSK independent of the KSK, so any key 
changes involve parent DS changes too.

It means you have to keep the ZSK and KSK online; if you use a separate 
KSK, you could in theory keep that stored offline and only bring it 
online when the ZSK needs re-signing.

Known plaintext attacks. ZSK signs relatively larger amounts of data. 
Hence, if you buy this argument, ZSK should be rotated more frequently 
than KSK, implying separate keys.

etc. etc.