Re: [COSE] Review draft-ietf-cose-webauthn-algorithms-02.txt

[Jim Schaad <[e-mail]>]

 

 

From: Mike Jones <[e-mail]> 
Sent: Tuesday, October 29, 2019 4:20 PM
To: Jim Schaad <[e-mail]>; [e-mail]
Subject: RE: [COSE] Review draft-ietf-cose-webauthn-algorithms-02.txt

 

Replies are inline, prefixed by “Mike>”.

 

-----Original Message-----
From: COSE <[e-mail] <mailto:[e-mail]> > On Behalf
Of Jim Schaad
Sent: Tuesday, October 29, 2019 12:39 PM
To: [e-mail] <mailto:[e-mail]> 
Subject: [COSE] Review draft-ietf-cose-webauthn-algorithms-02.txt

 

 

5.  I have problems with the following text: "Implementation of this
algorithm is RECOMMENDED because of its widespread use in decentralized
systems and those that chose it over the NIST curves."  Firstly, this is an
incorrect use of the RFC 2119 language, this is not a protocol statement.

 

Mike> I’ve lowercased “recommended”.

 

Secondly, this is not what the recommended column in table 2 means and thus
is trying to overload that column with something that is not real.  Third,
the fact that people chose this over the NIST curves is not necessarily a
reason for the IETF to recommended its implementation.

 

Mike> Recall that the JOSE algorithms come with Implementation Requirements
(see https://tools.ietf.org/html/rfc7518#section-7.1.1), whose values are
one of Required, Recommended, Optional, Deprecated, or Prohibited.  It’s in
that sense that the word “Recommended” is being used – more than Optional
but less than Required.  The COSE registry value that seems to most closely
correspond with this is “Recommended: True”.  (As I see it, it’s unfortunate
that COSE compressed these five values down to two, but I realize that
that’s water under the bridge, unless we want to reconsider this choice in
the BIS COSE registry instructions.)

[JLS] What COSE does is aligned with what the TLS working group does with
this.  We do not specify implementation requirements which is what JOSE did.

 

6.  I still want to see in the text the reasoning behind not just using the
current ECDSA algorithm in COSE.  

 

Mike> I provided the reasoning in my response to your previous review.
Having a curve-specific algorithm identifier lets implementations do what
you asked about – ensuring that the curve associated with a key cannot be
changed and the modified key still be used.

 

[JLS] I want to see this in the text itself.  Given that this is not the
same way that one would expect it to be done in COSE from history that needs
to be placed in the document.  I would completely disagree with your second
statement. 

 

7.  Add text on checking point is on the curve to section 5.4

 

Mike> I assume you’re talking about adding text like that in
https://tools.ietf.org/html/draft-ietf-oauth-jwt-bcp-07#section-3.4.  I’ll
admit that I’m not enough of an expert on secp256k1 usage to know whether an
on-curve check is what is called for or a different validation procedure.  A
definitive reference would be highly appreciated.  In particular, I don’t
know whether the Galois y² = x³ + 7 finite field form used with secp256k1 is
amenable to a check that the (x, y) pair are on the curve or whether a
different check is needed.

 

[JLS] section 3.2.2 of  SEC 1.

 

Thanks again for your detailed reviews, Jim.  I’ll plan to publish a new
draft incorporating these issue resolutions before Monday’s submission
cutoff.

 

                                                                -- Mike 

 

-----Original Message-----

From: COSE < <mailto:[e-mail]> [e-mail]> On Behalf
Of  <mailto:[e-mail]> [e-mail]

Sent: Thursday, October 24, 2019 2:35 PM

To:  <mailto:[e-mail]> [e-mail]

Cc:  <mailto:[e-mail]> [e-mail]

Subject: [COSE] I-D Action: draft-ietf-cose-webauthn-algorithms-02.txt

 

 

A New Internet-Draft is available from the on-line Internet-Drafts
directories.

This draft is a work item of the CBOR Object Signing and Encryption WG of
the IETF.

 

        Title           : COSE and JOSE Registrations for WebAuthn

Algorithms

        Author          : Michael B. Jones

                Filename        : draft-ietf-cose-webauthn-algorithms-02.txt

                Pages           : 13

                Date            : 2019-10-24

 

Abstract:

   The W3C Web Authentication (WebAuthn) specification and the FIDO

   Alliance FIDO2 Client to Authenticator Protocol (CTAP) specification

   use CBOR Object Signing and Encryption (COSE) algorithm identifiers.

   This specification registers the following algorithms in the IANA

   "COSE Algorithms" registry, which are used by WebAuthn and CTAP

   implementations: RSASSA-PKCS1-v1_5 using SHA-256, SHA-384, SHA-512,

   and SHA-1, and ECDSA using the secp256k1 curve and SHA-256.  It

   registers the secp256k1 elliptic curve in the IANA "COSE Elliptic

   Curves" registry.  Also, for use with JSON Object Signing and

   Encryption (JOSE), it registers the algorithm ECDSA using the

   secp256k1 curve and SHA-256 in the IANA "JSON Web Signature and

   Encryption Algorithms" registry and the secp256k1 elliptic curve in

   the IANA "JSON Web Key Elliptic Curve" registry.

 

 

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