Re: [dnsext] about ECDSA

On 11/04/2012 06:57, Francis Dupont wrote:
>   In your previous mail you wrote:
>
>>   On 04/06/2012 08:23 PM, Francis Dupont wrote:
>>   >>>  - I still have a question about the 256/384 pair: are they
>>   >>>  supposed to be handled as two different algos (as RSASHA1 and
>>   >>>  RSASHA256, or RSASHA256 and RSASHA512) or as the same algo with
>>   >>>  two different "strengths"? Note at the beginning (i.e., when I
>>   >>>  asked this many months ago) it was only a concern for the
>>   >>>  signer but according to a recent discussion it is concern for
>>   >>>  resolvers too.
>>
>>   The first not the latter, like RSASHA1 and RSASHA256, they are
>>   different algorithms.  Use the same algorithm for your ZSK and KSK
>>   (but apply different policy).
>
> =>  note my question is really about the application of the word
> "same" to ECDSAP256SHA256 / ECDSAP384SHA384 (a priori if they
> have different code points and names they are not the "same",
> now RSA has a degree of freedom which is not present in ECDSA).
>
>>   >>  They are different algorithms with different strengths, so your
>>   >>  either/or question doesn't make sense. Similarly, each of the
>>   >>  defined SHA-2 variants are also different algorithms and each has
>>   >>  a different strength.
>>   >
>>   >  =>  I'll rephrase the question: does it make sense to use
>>   >  ECDSAP256SHA256 for ZSKs and ECDSAP384SHA384 for the KSK?
>>
>>   No, that is dnssec-bogus.  The ECDSAP384SHA384 for KSK but does not
>>   sign the zone is a signing-error.  You must sign the entire zone with
>>   that algorithm, if you use it.  The algorithm-support is signalled
>>   per-algorithm in DS and DNSKEY records, not for a range or suite of
>>   algorithms.
>
> =>  I agree but I want to be sure it is the intented thing.
> If there is no opposed opinion in the list I follow you.
>

Think of the two ECDSA allocations as two DIFFERENT algorithms,
if you elect to use KSK and ZSK split (which I do not think not always 
needed) ECDSA does not allow you the flexibility to pick strength for 
the various roles.
Thus you pick the ECDSA algorithm that your KSK role needs/demands.

	Olafur

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