Re: [TLS] Eric Rescorla's Discuss on draft-ietf-tls-dnssec-chain-extension-06: (with DISCUSS and COMMENT)

[Viktor Dukhovni <[e-mail]>]

> On Feb 21, 2018, at 10:57 AM, Shumon Huque <[e-mail]> wrote:
> 
> On Thu, Feb 8, 2018 at 11:35 AM, Viktor Dukhovni <[e-mail]> wrote:
> 
> Summary as I see it:
> 
>   * Mandatory DANE: MUST Refuse absence of TLSA RRs or failure
>     of PKIX-TA(0) and PKIX-EE(1).  Must fail when no TLSA RRs
>     are cache and the server does not present the extension.

Just to clarify "failure of PKIX-TA(0) and PKIX-EE(1)" is intended to
consider failure to satisfy the usual PKIX verification requirements
for these certificate usages. Naturally, mandatory DANE can also be
satisfied via matching DANE-TA(2) or DANE-EE(3) or fail via broken
DANE-TA(2) or DANE-EE(3).

> 
>   * "Opportunistic DANE": MAY refuse failed PKIX-TA(0) and PKIX(1)
>     if caching replies, and SHOULD attempt to refresh cache before
>     expiration to reduce opportunity for downgrades.  Non-caching
>     clients don't really gain security by refusing valid PKIX on
>     DANE failure, and MAY choose to continue.
> 
> This seems reasonable to me too.

Here too, a client MAY choose to fail when the presented certificate
chain fails all the associated (cached or freshly obtained) DANE TLSA
records whether these are PKIX-TA/EE, DANE-TA/EE or some mixture.
The restricted focus on just PKIX-TA/PKIX-EE is not needed.

-- 
	Viktor.