I agree with Steve's and Paul's analyses.
In addition, it's not clear to me how this SHOULD-level requirement
squares with the IANA registration of this algorithm as OPTIONAL (in
Section 8), since in RFC 2119 OPTIONAL == MAY. The document that
defines that registry (draft-ietf-dnsext-dnssec-registry-fixes) does
not allow algorithms to be RECOMMENDED, so it seems like the
requirement for support has to be either a MUST or a MAY to be
consistent with the registry.
--Richard
On Feb 11, 2010, at 4:24 PM, Paul Hoffman wrote:
At 4:04 PM -0500 2/11/10, Andrew Sullivan wrote:
So the question here is not what algorithms get "first class" status
in general, but whether we want to have different classes of support
for DNSSEC, given the current conditions.
First off, thank you for better stating the question.
There are a plethora of signing algorithms. Note that a signing
algorithm consists of a public key algorithm *and* a hash algorithm.
The question here is whether they also have SHOULD-level
requirements to process every signing algorithm that is in the IANA
registry. Having such a requirement gives attackers a much wider
target: in order to spoof a signature, they can pick the weakest of
a large collection of algorithms.
For example, there is already a published attack on the GOST hash
function that does not exist in SHA-256 and SHA-512. The GOST
algorithms have had much less cryptographic review than other
algorithms. If that attack becomes practical, an attacker can create
signatures using GOST that he/she could not create in RSA/SHA-256 or
RSA/SHA-512.
Given this, the answer to the question should be "no, not all
algorithms automatically get SHOULD-level requirements". The IETF
can, on a case-by-case basis, decide if they want to update the base
DNSSEC spec to include a SHOULD-level or MUST-level requirement for
a new signature algorithm.
--Paul Hoffman, Director
--VPN Consortium
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