Re: Proposal and intent to implement "dsa-sha2-256" SSH key algorithm

[Jeffrey Hutzelman <jhutz%cmu.edu@localhost>]

On Tue, 2015-10-27 at 22:50 +0000, denis bider wrote:
> I choose the name "dsa-sha2-256", rather than a suffixed name
> ("...@bitvise.com") for the following reasons:

Please don't do that, unless you are going to write and publish an IETF
consensus RFC and register the name properly.  Just making up names
leads to collisions and resulting interop problems, which is a very real
possibility if someone else is thinking the same as you but isn't active
on this list.

Also, with no registration, someone seeing this and wanting to
interoperate has no idea where to look for a specification.


> - Suffixed names are overly long and clumsy. If I were to choose a
> suffixed name instead, I would go with just "...@bv".

Please don't do that either.  Besides being non-compliant, it again
leaves anyone wanting to interoperate with no idea how to find a spec.



> - Suffixed names complicate standardization. If a suffixed algorithm is
> commonly implemented, there's pressure to have a version with a
> non-suffixed name, and now we have multiple names for the same thing.

Yes, that's an issue, if the thing actually gets standardized.  The
right answer is to keep using the original name, rather than inventing a
new one, unless the algorithm has actually changed during the
standardization process.



> - I don't see many ways for "dsa-sha2-256" to be implemented
> incorrectly or incompatibly by a reasonable implementor. There's really
> only one DSA, the one specified in FIPS 186. This has four variants.
> The suffix -sha2-256 explicitly specifies which hash function to use,
> and strongly suggests use of the 256-bit subgroup sizes.

Well, someone could decide to implement only one of the two modulus
sizes available with 256-bit subgroups.  Or, they could decide that all
four options are permissible, as long as the hash is SHA-256.  I think
it would be desirable to publish an RFC to nail these sorts of things
down.

-- Jeff