Re: [DNSOP] Key sizes was Re: I-D Action:draft-ietf-dnsop-rfc4641bis-01.txt

[Joe Abley <[e-mail]>]

On 24 Apr 2009, at 22:18, Paul Hoffman wrote:

>> If there is a practical limit to key size due to concerns about  
>> peoples' validators running out of steam, then I think it needs to  
>> be stated clearly. Otherwise as a zone administrator my instinct  
>> will be to use keys that are as large as possible, since the costs  
>> incurred by doing so are going to be borne by other people and all  
>> I see is benefit (in the form of increased comfort level and a  
>> better story for upper management, even if there is no practical  
>> improvement in security).
>
> That's certainly your option. Another option is to listen to  
> cryptographers about what is possible with a reasonable amount of  
> money and time, and stop there.

My point is that given the choice between "doing what is currently  
considered safe" and "exceeding what is currently considered safe by a  
factor of four with no additional cost to you" I think many otherwise  
uninformed zone administrators are conditioned to choose the latter.

>> On the flip side, how can the "real cost" for validator-operators  
>> that you assert be quantified?
>
> Exactly.

So your point is that you don't know how to quantify it?

>> I have a hand in running a couple of non-validating resolvers for a  
>> local ISP. 35,000 customers are served by two machines running BIND  
>> 9.5.x on FreeBSD 7.1, and the CPUs are 96% idle at peak load.  
>> That's a fair amount of headroom, even ignoring the fact that the  
>> ISP in question is in the process of replacing each machine with an  
>> ECMP/OSPF cluster of two machines in order to simplify ad-hoc  
>> maintenance.
>>
>> I'm not arguing about the assertion that there is a limit to what  
>> validators can tolerate. However, it seems reasonable to ask if  
>> it's the kind of limit that we need to worry about, and not, the  
>> kind of limit that is always going to fit in that headroom as  
>> validator hardware gets upgraded on a typical cycle and DNSSEC  
>> deployment proceeds over time.
>
> How will you know? Why not stop when enough is enough?

Because there's no incentive for a zone administrator to choose  
anything other than the largest key her tools let her create. So what  
is "enough"?


Joe