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

I have whipped up a draft here:

http://www.denisbider.com/draft-dsa-sha2-256.txt

At this point, I'm most uncertain about whether we should allow the following option also:

   L = 2048, N = 224

Arguments for:

- No apparent interoperability reason to exclude it.
- Perhaps there are DSA implementations that don't easily support setting subgroup size, and can only easily generate the N=224 option? Does anyone know of one?

Arguments against:

- Slightly weaker than N = 256

Any comments? Thoughts?

 
 ----- Original Message ----- From: Jeffrey Hutzelman  Sent: Wednesday, October 28, 2015 15:31 To: denis bider  Cc: [email protected] ; [email protected]  Subject: Re: Proposal and intent to implement "dsa-sha2-256" SSH key  algorithm   On Tue, 2015-10-27 at 22:50 +0000, denis bider wrote: > I choose the name "dsa-sha2-256", rather than a suffixed name > ("[email protected]") 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