Re: [Suit] draft-housley-suit-cose-hash-sig

[Jim Schaad <[e-mail]>]

> -----Original Message-----
> From: Suit <[e-mail]> On Behalf Of Michael Richardson
> Sent: Wednesday, June 13, 2018 11:09 AM
> To: suit <[e-mail]>
> Subject: [Suit] draft-housley-suit-cose-hash-sig
> 
> 
> I have read the -01 draft today.
> I have not read [HASHSIG] yet.
> I thought I'd try reading this first, to see what questions I had.
> 
> I have implemented COSE Sign1 with ECDSA in Ruby, so I have a grasp of
> what we are trying to plug hash-sig *into*.
> 
> 
> Suggestions:
> 1) would the structure show in section 3 be easier if it was described by
>    CDDL?  I'm rather unclear about this.

No - this are not CBOR structures they are pure binary strings

> 
> 2) I din't understand section 4, where it says:
>       o  If the 'key_ops' field is present, it MUST include 'sign' when
>                  creating a hash-based signature.
> 
>       o  If the 'key_ops' field is present, it MUST include 'verify'
>                  when verifying a hash-based signature.
> 
> Clearly this is not something that travels over the network.  Is this
somehow
> indicating how to understand if one is dealing a public (verify) key or a
private
> (sign) key?

The key_ops field can be considered to potentially be transported over a
network.  It is part of the COSE_Key object rather than part of the
COSE_Sign1 object.

> 
> 3) the variations: LMS_SHA256_M32_H20, and LMOTS_SHA256_N32_W2,
> etc. are
>    listed, but I don't know if they need to be carried in the signature
>    structure somehow.

See the [HASHSIG] draft.  It is encoded into the signature structure and the
key type is in the public key structure.

> 
> 4) I thought that perhaps we'd need CBOR or COSE specific way to transport
>    the signatures.  I guess I shall read HASHSIG to find out what the
>    signatures look like.

We have that.  This is looking at a signature just like ECDSA would produce.
This is a different "ECDSA" replacement.

> 
> I understand draft-mcgrew-hash-sigs-11 is being advanced by CFRG.
> I believe that SUIT should adopt this document, and should do so in the
> current state.
> 
> I would like to have some examples in CBOR/COSE worked out with private
> keys available in the appendices.

Always a good thing to have.

Jim

> 
> --
> ]               Never tell me the odds!                 | ipv6 mesh
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> ]   Michael Richardson, Sandelman Software Works        | network
architect  [
> ]     [e-mail]  http://www.sandelman.ca/        |   ruby on rails
[
> 
> --
> Michael Richardson <[e-mail]>, Sandelman Software Works
> -= IPv6 IoT consulting =-
> 
>