Re: [Suit] Fwd: New Version Notification for draft-housley-suit-cose-hash-sig-03.txt

Sounds good to me. The "and" after the first comma seems odd to me, but that's an editorial nit.
-- Tony

-----Original Message-----
From: Suit [mailto:suit-bounces@ietf.org] On Behalf Of Russ Housley
Sent: 02 July 2018 17:15
To: Tony Putman
Cc: suit
Subject: Re: [Suit] Fwd: New Version Notification for draft-housley-suit-cose-hash-sig-03.txt

I think I understand now.

How about:

      o  If the 'kid' field is present, and it MAY be used to identify
           the top of the HSS tree.  In [HASHSIG], this identifier is
           called 'I', and it is the 16-byte identifier of the LMS
           public key for the tree.

Russ

> On Jul 2, 2018, at 11:59 AM, Tony Putman <Tony.Putman@dyson.com> wrote:
> 
> Russ,
> 
> You say:
>> I think the kid would identify a tree, not a node in the tree.  The signature value itself contains the information necessary to locate the node within the tree.
> 
> Which I fully agree with, so I guess my text was off. How about:
>  "If the 'kid' field is present, then it MAY contain the identity of the top-level HSS tree. This is called 'I' in [HASHSIG] and is contained in the public key which corresponds to this tree."
> 
> Without this hint, the verifier would potentially have to try the verification step for each of the trust anchors that it knows of (though only as far as verifying the next public key in the chain); there is no direct way to obtain 'I' from the signature and it is a parameter in the verification process. 'I' is present in the public key, but you're right that it's not the identity of the key, but rather the identity of the tree as a whole. 
> 
> Tony
> 
> Dyson Technology Limited, company number 01959090, Tetbury Hill, Malmesbury, SN16 0RP, UK.
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