Re: [Ace] Artart last call review of draft-ietf-ace-mqtt-tls-profile-14

[Cigdem Sengul <[e-mail]>]

Dear Jean,
Thank you for your review.
I implemented changes and prepared a pull request at:
https://github.com/ace-wg/mqtt-tls-profile/pull/102

Below is a summary of how I revised the text according to your
suggestions, and corrected references for this document (removing unused
references due to changes of text etc.) I have still kept MQTT as
normative, as the document is about MQTT, but is it expected to be
informative when the reference is a non-RFC?

Kind regards,
--Cigdem

On Fri, 4 Mar 2022 at 21:40, Jean Mahoney via Datatracker <[e-mail]>
wrote:

> Reviewer: Jean Mahoney
> Review result: Ready with Issues
>
> This document is ready but has minor issues with wording and references.
>
> Minor issues:
>
> Section 1: The subject seems to be missing in the following sentence.
> Should "recommended" be normative?
>
> Current:
>    The Client-AS and RS-AS MAY also use protocols other
>    than HTTP, e.g.  Constrained Application Protocol (CoAP) [RFC7252] or
>    MQTT; it is recommended that TLS is used to secure these
>    communication channels between Client-AS and RS-AS.
>
> Perhaps (add "exchanges", split into two sentences):
>    The Client-AS and RS-AS exchanges MAY also use protocols other
>    than HTTP, e.g., Constrained Application Protocol (CoAP) [RFC7252] or
>    MQTT. It is recommended that TLS is used to secure these
>    communication channels between Client-AS and RS-AS.
>

[CS: Done.]


>
> Section 2.2.4.2.2: I'm having difficulty parsing the following normative
> statements. Does "MUST" also cover the Authentication Data (i.e., MUST be
> set
> to "ace" and MUST contain Authentication Data)? If the Authentication Data
> MUST
> NOT be empty, MUST it contain the 8-byte RS nonce or could it contain
> something
> else?
>
> Current:
>    The AUTH packet to continue authentication includes the
>    Authentication Method, which MUST be set to "ace" and Authentication
>    Data.  The Authentication Data MUST NOT be empty and contains an
>    8-byte RS nonce as a challenge for the Client (Figure 6).
>

[CS: Revised as:
The Broker continues authentication using an AUTH packet that contains the
Authentication Method
and the Authentication Data. The Authentication Method MUST be set to
"ace", and the Authentication Data MUST NOT be empty and contain
an 8-byte RS nonce as a challenge for the Client.
]


> Section 4: I'm having difficulty parsing the following. Is it talking about
> using a challenge from the current TLS session?
>
> Current:
>    To re-authenticate, the
>    Client MUST NOT use Proof-of-Possession using a challenge from the
>    TLS session during the same TLS session to avoid re-using the same
>    challenge value from the TLS-Exporter.
>

[CS: Revised:
If re-authenticating during the current TLS session, the Client MUST NOT
use the method
   described in Section 2.2.4.2.1, Proof-of-Possession using a challenge
   from the TLS session, to avoid re-using the same challenge value from
   the TLS-Exporter.
]

>
> Section 6.1: Could more guidance or examples of necessary policies be
> provided
> here?
>
> Current:
>    However, stored Session state can be discarded as a
>    result of administrator policies, and Brokers SHOULD implement the
>    necessary policies to limit misuse.
>

[CS: Revised as:
"However, stored Session state can be discarded as a result
of administrator action or policies (e.g. defining an automated
response based on storage capabilities), and Brokers SHOULD implement the
necessary policies to limit
misuse."

Would this work?
]

>
> References: idnits identifies the following issues. The three informative
> RFCs
> are already listed in the downrefs registry, though
> (https://datatracker.ietf.org/doc/downref).
>
>   == Unused Reference: 'I-D.ietf-ace-oauth-params' is defined on line 1499,
>      but no explicit reference was found in the text
>

[CS: This is fixed based on the revision for genart review, and the ID is
referenced.]


>
>   == Unused Reference: 'RFC7251' is defined on line 1563, but no explicit
>      reference was found in the text

[CS: Reference removed; added RFC 8442 for the PSK cipher reference]

>
>   == Unused Reference: 'RFC8422' is defined on line 1609, but no explicit
>      reference was found in the text
>

[CS: Now cited]

>
>   == Unused Reference: 'RFC8705' is defined on line 1625, but no explicit
>      reference was found in the text
>
[CS: Removed as does not apply to the current text]

>
>   -- Possible downref: Non-RFC (?) normative reference: ref.
>      'MQTT-OASIS-Standard'
>
>   -- Possible downref: Non-RFC (?) normative reference: ref.
>      'MQTT-OASIS-Standard-v5'
>

[CS: OK for these two, I feel on the fence as the document is about MQTT.
Is the downref suggested because this is a Non-RFC and a standard coming
from OASIS]


>
>   ** Downref: Normative reference to an Informational RFC: RFC 6234
>

[CS: Moved to Informative references]

>
>   ** Downref: Normative reference to an Informational RFC: RFC 7251
>

[CS: Reference removed]

>
>   ** Downref: Normative reference to an Informational RFC: RFC 8032
>

 [CS: Moved to informative]

>
>   == Outdated reference: A later version (-04) exists of
>      draft-ietf-ace-pubsub-profile-01
>

[CS: Fixed.]

>
> Appendix A: Perhaps add a reference to [I-D.ietf-ace-oauth-authz] for the
> origin of the checklist.
>

[CS: Added:
"Based on the requirements on profiles for the ACE framework
   [I-D.ietf-ace-oauth-authz], this document fulfills the following: "

>
> Nits:
>
> Section 1: The following list is somewhat hard to read.
>
> Current:
>    Implementations
>    MAY also use "application/ace+cbor" content type, and CBOR encoding
>    [RFC8949], and CBOR Web Token (CWT) [RFC8392] and associated PoP
>    semantics to reduce the protocol memory and bandwidth requirements.
>
> Perhaps:
>    To reduce protocol memory and bandwidth requirements, implementations
>    MAY also use 'application/ace+cbor' content type, CBOR encoding
>    [RFC8949], and CBOR Web Token (CWT) [RFC8392] with its associated PoP
>    semantics.
>

[CS: Fixed]

>
> Section 2.2.3.2: Would it clarify the normative text to split this
> sentence
> into two?
>
> Current:
>    ...a client MAY omit support for the cipher suites
>   TLS_PSK_WITH_AES_128_CCM_8 and TLS_ECDHE_ECDSA_WITH_AES_128_CCM_8,
>    but for TLS 1.2, MUST support TLS_ECDHE_PSK_WITH_AES_128_GCM_SHA256
>    for PSK and TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256 for RPK, as
>    recommended in [RFC7525] (and adjusted to be a PSK cipher suite as
>    appropriate).
>
> Perhaps:
>    ...a client MAY omit support for the cipher suites
>    TLS_PSK_WITH_AES_128_CCM_8 and TLS_ECDHE_ECDSA_WITH_AES_128_CCM_8.
>    For TLS 1.2, however, a client MUST support ...
>

[CS: Fixed]

>
> Section 2.3: "an an exact" / "an exact"
>

[CS: Fixed]

>
> Section 2.4.1: Does the authentication check fail for any of these cases?
>
> Current:
>    If the Client does not provide a valid token or omits the
>    Authentication Data field and the Broker has no token stored for the
>    Client or the token or Authentication data are malformed, or if the
>    Will flag is set, the authorization checks for the Will topic fails,
>    authentication fails.
>
> Perhaps:
>    Authentication can fail for the following reasons:
>
>    * the Client does not provide a valid token or omits the Authentication
>      Data field,
>
>    * the Broker has no token stored for the Client,
>
>    * the token or Authentication data are malformed, or
>
>    * if the Will flag is set, the authorization check for the Will topic
> fails.
>

[CS: the conditions are separated at each "or", so revised as:
"Authentication can fail for the following reasons:

   o  If the Client does not provide a valid token,

   o  the Client omits the Authentication Data field and the Broker has
      no token stored for the Client,

   o  the token or Authentication data are malformed, or

   o  if the Will flag is set, the authorization checks for the Will
      topic fails."



>
> Section 3.3: "has a token token permits" / "has a token that permits"
>
[CS: Fixed]

>
> Section 5: Would the following be clearer as a list?
>
> Current:
>    The MQTT session state is
>    identified by the Client Identifier and includes state on client
>    subscriptions; messages with QoS levels 1 and 2, and which have not
>    been completely acknowledged or are pending transmission to the
>    Client; and if the Session is currently not connected, the time at
>    which the Session will end and Session State will be discarded.
>
> Perhaps:
>    The MQTT session state is identified by the Client Identifier and
>    includes the following:
>
>    * Client subscription state,
>
>    * messages with QoS levels 1 and 2 that either have not been
>      completely acknowledged or are pending transmission to the
>      Client, and
>
>    * if the Session is currently not connected, the time at which the
>      Session will end and Session State will be discarded.
>

[CS: Done]

>
> Section 6: Perhaps switching the order here would improve readability:
>
> Current:
>    ... MQTT v5.0 clients are NOT
>    RECOMMENDED to use the flows described in this section.
>
> Perhaps:
>    ... the flows described in this section are NOT RECOMMENDED for
>    use by MQTT v5.0 clients.
>
[CS: Done]


>
> Figure 11: endoded / encoded
>

[CS: Fixed]

>
> Section 6.2:  "and not attempt" / "and do not attempt"
>

[CS: Fixed]

>
>               "no more authorized" / "no longer authorized"
>
[CS: Fixed]

>
> Section 7.2: The spacing after the colons is inconsistent.
>

[CS: Fixed to have all with a single space after the colon.]

>
> Formatting and terminology:
>
> According to Wikipedia, MQTT is no longer considered an acronym (i.e., it
> no
> longer needs to be expanded).
>
[CS: Is it OK that we leave things as they are, as this will affect title
etc.]

>
> Could the terms "RS" and "Broker" be consistently scoped? That is, "RS" is
> used
> when talking about OAuth interactions, and "Broker" is used when talking
> about
> MQTT interactions? (From Section 1: "In the rest of the document, the terms
> "RS", "MQTT Server" and "Broker" are used interchangeably.)
>

[CS: Revised as much as possible so that Broker is used when we refer to
the entity defined in this profile,
and RS is used more for generic OAuth interactions]

>
> Check the use of single and double quotation marks, for instance:
>
>    'application/ace+json' vs "application/ace+cbor"
>    '0x18 (Cont. Authentication)' vs "0x18 (Continue Authentication)"
>

[CS: Switched to double quotes, but removed quotation marks around reason
codes as in the MQTT standard.]


>
> Because the acronym for "proof-of-possession" was given in the
> introduction,
> the rest of the instances can be replaced with "PoP". Same with other
> acronyms
> used, like PSK. Just expand on first use and use the acronym thereafter.
>
> [CS: Done for PoP, was done for PSK/RPK for genart review.]