Re: [secdir] SHA512 in draft-dnsext-dnssec-rsa-sha2

[Jelte Jansen <[e-mail]>]

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Paul Hoffman wrote:
> At 1:02 PM -0400 6/18/09, Andrew Sullivan wrote:
> 
> "We're defining RSA/SHA-512 but we really don't think that there is any good use for it at this time. If we feel that there is a good reason for it, we will publish another RFC that explains why."
> 
> Again, by the mere act of defining the code point, you will cause a huge waste of resources. Developers will code it prematurely. Naive sysadmins will sign their zones with it. The signatures will traverse the Internet.

Just for a bit of recent history; originally the draft only defined 256. There
were some people who wanted to do all SHA2 algorithms 'while we're at it' (the
reasoning being, even if there is no known attack on 256 right now, it wouldn't
hurt to have stronger algorithms in there to be ready for the future, not so
much for the IETF overhead, but for deployment times). Because we didn't want to
waste code points, we decided on selecting two. Conforming key sizes weren't
taken into account here.

Since most implementations use crypto libraries that either don't support SHA2
at all or support both 256 and 512, it doesn't seem like a waste of resources
from an implementation point of view (of course I could be wrong here).

I don't want to define something and essentially tell people not to use it until
another RFC comes along; the definition could also go in there then. If it's
defined I expect people to use it (in fact, partly due to some overeager
developers and some misconceptions about the time this all would take, there
happens to be one implementation in the wild that actually uses them right now,
which isn't a problem, but will be if the code point that was chosen gets
assigned to another algorithm).

So, if it's up to me, SHA512 is going to be either in there 'fully' (albeit with
keys that are way to small) or not at all.

Jelte
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