Hello Christer,
Thank you for this thorough review and for waiting so long for my reply. My responses to your comments are inline below and a PR is included here:
Nick
On Sun, Jul 7, 2019 at 3:58 AM Christer Holmberg via Datatracker <noreply@xxxxxxxx> wrote:
Reviewer: Christer Holmberg
Review result: Ready with Issues
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Document: draft-ietf-tls-exported-authenticator-09
Reviewer: Christer Holmberg
Review Date: 2019-07-07
IETF LC End Date: 2019-07-16
IESG Telechat date: Not scheduled for a telechat
Summary: The document is well written. However, I have found some issues that
the author may want to consider clarifying in the document.
Major issues: N/A
Minor issues:
MIN_1:
The last sentence of Section 1 says that the mechanism requires TLS version 1.2
or later. Would it be useful to state that in a dedicated Applicability section?
I'm disinclined to include an applicability section considering how short it would be. I'm open to being convinced otherwise with examples.
MIN_2:
Can the mechanism be used also for DTLS?
I think the answer is yes. I don't see any reason to disallow the use of Exported Authenticators in DTLS.
MIN_3:
The documents talk about additional certificates. If I only have one additional
certificate, can I use that for multiple authenticators throughout the TLS
session?
Yes, there is nothing disallowing the creation of multiple exported authenticators with the same certificate.
MIN_4:
Section 3 and 4 say that the authenticator request and authenticator SHOULD be
sent using TLS, and Section 1 says that the proof of authentication can be sent
out-of-band. I think it would be useful to clarify whether both the
authenticator request and authenticator can be sent out-of-band ( i.e., not
using the TLS connection that the additional authentication is associated
with), and also to state whether it IS allowed to send the authenticator
request and authenticator on the TLS connection they are associated with.
Good point. I can clarify this a bit. Both the authenticator and authenticator request can be sent through either the TLS connection they were derived from or another TLS connection altogether. The important part is that they are sent over an encrypted and authenticated connection.
MIN_5:
Section 5 talks about an endpoint sending an empty authenticator. But, what if
the sender of the authenticator request does not receive anything? Does it
simply move on? Does it terminate the TLS session? Is the action based on local
policy?
The TLS layer is stateless. The decision to time out or fail the connection if an authenticator request is not responded to is left to higher-level protocols that leverage EAs.
MIN_6:
Related to MIN_5, I can't find text about how endpoints inform each other about
the support of the mechanism, so maybe a few words about that would be useful.
And some words about backward compatibility with endpoints that don't support
the mechanism.
Adding an extension to signal support for exported authenticators was discussed at some point, but it was decided that the higher-layer application should handle the signaling.
MIN_7:
What happens if the validation of an authenticator fails? Does the requester
simply move on? Does it terminate the TLS session? Is the action based on local
policy?
This is also up to the application-layer protocol. I'll add text covering MIN_5, MIN_6 and MIN_7.
Nits/editorial comments:
ED_1:
The document uses "session", "TLS connection" and "TLS communication"
terminology. Is that intentional, or wouuld it be possible to use consistent
terminology?
Good note. I'll standardize on "connection".
ED_2:
Section 3 says: "The authenticator request is a structured message that can be
created..." Section 4 says: "The authenticator is a structured message that can
be exported..."
In the 2nd paragraph of Section 4 it is stated that "authenticator" is sent
based on an "authenticator request". I wonder if that could be stated already
in the beginning of Section 4, to further clarify the difference between them.
E.g.,
"The authenticator is a structured message, triggered by an authenticator
request, that can be exported from either party of a TLS connection."
The issue is that servers can generate spontaneous exported authenticators without an authenticator request. Given this, the updated sentence would be:
"The authenticator is a structured message, sometimes triggered by an authenticator
request, that can be exported from either party of a TLS connection."
request, that can be exported from either party of a TLS connection."
Which I'm not sure is an improvement to readability.
