Re: [Anima-bootstrap] Detailed BRSKI review, part 1

"Max Pritikin (pritikin)" <pritikin@cisco.com> Thu, 20 October 2016 20:11 UTC

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From: "Max Pritikin (pritikin)" <pritikin@cisco.com>
To: "Michael Behringer (mbehring)" <mbehring@cisco.com>
Thread-Topic: [Anima-bootstrap] Detailed BRSKI review, part 1
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Date: Thu, 20 Oct 2016 20:11:44 +0000
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Cc: Michael Richardson <mcr+ietf@sandelman.ca>, "anima-bootstrap@ietf.org" <anima-bootstrap@ietf.org>
Subject: Re: [Anima-bootstrap] Detailed BRSKI review, part 1
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I’ve been working through these comments. Below are my working notes and responses but any of you all can also look to the github repository to see how the text looks ‘in place’ within the current document. 

Search the following notes for “CONCERN” to quickly find comments I had trouble integrating or was worried about. (M. Richardson, some of the comments references you for more input). 

> On Oct 17, 2016, at 9:38 AM, Michael Behringer (mbehring) <mbehring@cisco.com> wrote:
> 
> Looking at version -03. There is a lot of detail in this document, and overall I think it's very good! Tons of work went into this doc, and it's pretty apparent! 
> 
> The biggest question to me is the one from my email from Friday: In the original document we assumed the audit method, and wrote the entire document around it. And while I was originally in favour of writing the doc for a single method, and afterwards explaining exceptions, but I now think reality is that we'll see the three methods I mentioned in my mail in parallel: 
> 
> 1) join any domain (first come first join)  
>   --> No MASA required
> 2) require audit token 
>   --> MASA required, audit mode
> 3) require authentication token 
>   --> MASA required, ownership tracking mode
> 
> My main comment, thus, for discussion is: Given that we're likely to see the three variants in parallel in real life, we should probably explain in each step how the different variants affect this particular step. This would require quite some work, but my feeling is it's needed for clarity. 
> 
> The other think I would like to discuss: We now kept ANIMA pretty much outside scope. This seems wrong to me. Yes, we should not REQUIRE ANIMA, but we should still explain how BRSKI works in an ANIMA context. This would add some small notes in various places (see detailed comments). For example, we don't explain that proxy to Registrar connection is through the ACP, and that Registrar is found through GRASP. That feels wrong. 

CONCERN: Not addressing this yet. 

> 
> Detailed review comments, mostly editorial, but sometimes important (I think :-) are below. 
> 
> Michael
> 
> --
> 
> - section 1: " A complexity that
>   this protocol deals with are dealing with devices from a variety of
>   vendors, and a network infrastructure (the domain) that is operated
>   by parties that do not have any priviledged relationship with the
>   device vendors."
> 
> I don't understand "priviledged relationship". I guess we want to say that any domain can claim a device, and that domain doesn't have to be authenticated by the vendor, right? It might be clearer to say "prior relationship". The work "priviledged" is not entirely clear, I find. 

This paragraph was needlessly complex. It has been simplified to map to the questions that directly proceed it:

"A precise answer to [the prior] questions can not be obtained without leveraging an established key infrastructure(s). The New entity's decisions are made according to verified communication with a trusted third-party. The domain's decisions are made by comparing the New entity's authenticated identity against domain information such as a configured list of purchased devices supplimented by information provided by a trusted third-party. The third-party is not required to provide sales channel ownership tracking nor is it required to authenticate the domain."

> - if we use "pledge", we should use it throughout. I suggest to do a global search/replace. Like, the intro uses "new entity" many times. 

Done. 

> 
> - definition of "pledge": I don't think we should link to "definition 6" on a web page, since that could well change. 

Agreed. I removed the reference when I did the substitution above.

> That definition sounds very weird to me. "Neither the device nor the network knows if the
>      device yet knows if this device belongs with this network." (he?)  Surely, the device knows if it knows the domain?!?! 
>   Do we need this sentence !?!?
> Here we say the identity is coming from a "factory". Above it was "third party". We should use the same term, consistently.
> 
> What about: 
> Pledge: the new device seeking to join a domain, with an identity provided by a third party (e.g., vendor, integrator). 

I’ve included ‘manufacturer’ in this list as this is a term we used above. 

> 
> - I don't understand capitalization of the definitions. When uppercase, when lowercase? Should probably be uppercase for all?

CONCERN: Currently the capitalization is when we’ve defined a “thing” (DomainID, Pledge, Audit Token, Ownership) vs a process (drop ship, enrollment). I’m leaving this for now if only to focus on other points. I’m sure we’ll have to clean this up though.  

> 
> - "Optimal security is achieved with IEEE 802.1AR certificates on each
>   new entity, accompanied by a third-party Internet based service for
>   verification."
> 
> I suggest to add after "third party" something like "(e.g., manufacturer, integrator) (that's what we mean, right?)

Yes, kinda. There is a subtle distinction possible being the third-party that installed the credential and the third-party that provides the MASA service but I don’t think thats worth exploring at this time. I’ve added as you suggest. 

> 
> - should we not define MASA? I think we need to. (I see it's defined later on page 7, but it should be defined up front.)

I’ve moved all the definitions up into the terminology section. This has the advantage of reducing duplication (pledge was being defined multiple times). 

> 
> - Page 5: "imprint:  the process where a device obtains the cryptographic key
>      material to identity and trust future interactions with a network."
> s/identity/identify/

Fixed.

> 
> - Page 5: definition of "DomainID": I suggest to add "see section 4.2.1.2 of RFC5280" (I found it, but would have found it faster with this ref ;-) 

Fixed.

> - reference I-D.irtf-nmrg-autonomic-network-definitions should be replaced with RFC7575. (globally)

Fixed.

> 
> - Page 5: audit token / authorization token / ownership voucher: I think we really have TWO things only, the audit token and the ownership voucher. 
>  Are we still using "authorization token" at all? If not, let's take it out. In any case, I don't think we ever used "authorization token" equal to "audit toke", which this section implies. 
>  If we use "third party" elsewhere, we should also use it here. 
>  Both get issued by the same entity, but are used for different things. This should be reflected here. 
>  Right now, one is from a "manufacturer" the other from a "vendor", etc. All inconsistent. I suggest let's define "third party" above (see comments above) and then only use that term. 
> 
> What about: 
> - Audit Token: A signed token from the MASA of a third party (e.g., manufacturer, integrator) indicating that the bootstrapping has been successfully logged, including historic logging information from this device. 
> 
> - Ownership Voucher: A signed token from the MASA of a third party (e.g., manufacturer, integrator) indicating that a specific domain "owns" the pledge as defined in [netconf draft]

I think I’ve got this cleaned up. 

> 
> Page 6
> 
> Section 1.2: IOT suitability: "In general the answer is no" - I would prefer to rephrase to: "This depends on the capabilities of the devices in question. The terminology of ..."
>  (because capabilities may well change in the next years, potentially making the general answer a "yes”)

This is a good point. I’ve made the change. 

> - "delays for privacy reasons" - can you expand?

I believe this substitution is accurate and clarifies:
"The network communication itself is not optimized for speed; the discovery process allows for the Pledge to avoid broadcasting for privacy reasons."

> Section 1.3: " between the domain Registrar and the new device". Replace "the" with "a" - there can be more than one Registrar. Alternatively, "between domain trust anchor and new device". (do a global search and replace "the Registrar" with "a Registrar”)

I’ve attempted this change. Grammatically there are still a number of “the Registrar” is still more appropriate though; such as when a Registrar has been contacted and it performs an action. There is a chance I messed that up in the text at some point. I regret accepting this change. 

> 
> We have comments about constrained devices a bit all over the intro. I suggest we collect them under a separate heading. 

CONCERN: not addressed yet.

> Section 2
> 
> Under Figure 1 we define terms, and in the intro we did as well. There are overlapping ones (pledge and new entity), similar ones (domain and domainID), it's confusing.  I suggest we take all the definitions into the intro section. Figure 1 doesn't actually introduce new terms. 

Fixed.

> 
> MASA versus Ownership tracker: The document makes it sound like two different entities ("MASA or Ownership Tracker") In my mind, there is a single entity which I thought we called MASA. It has two functions, one is auditing, the other is issuing ownership vouchers. In the discussion from last week this seemed to be the consensus as well. In that case, we need to adapt the drawing and the explanations. "MASA service" provides two services "ownership attestation" and "audit logging".  
> 
> (This is a bit of a repeat of my last email:  I think we should define the three general models up front (ownership validation, audit log, and no MASA), explain the terms of the tokens up front, and what goes where.)

This was started by the new definitions and I’ve made minor cleanups. The diagrams do indicate the ownership voucher is from the same vendor service.

I’m starting to wonder if “Audit Token” and “Ownership Voucher” is too much. What about:
	Audit Voucher and Ownership Voucher? 
so we can say:
	Audit or Ownership voucher? 

> 
> 3.1: " A New Entity MUST NOT automatically initiate bootstrapping if it has already been configured." Add: "or is in the process of being configured. 

Done. 

> Figure 3: 
> Bullet 1: I would remove "closest" Registrar. I think there will be many criteria. Say here "to a Registrar". (And, we should capitalise "Registrar" consistently)

Done.

> Bullet 2: replace " (Although the Registrar is also authenticated these credentials are only provisionally accepted at this time)" (confusing) with " (The Registrar credentials are only provisionally accepted at this time)”

Done.

> I think bullet 2 and 3 are actually the same operation. By presenting itself, it implicitly requests to join. We should not make it sound like these are two distinct operations. Make it one box and call it "Request join (presenting ID)". If we do this, then we should also merge 3.1.2 and 3.1.3.

CONCERN: There are actually two steps here. The device establishes the connection (the Identity is presented in the TLS connection) and then requests join (via a REST interface call). So this more accurately represents the protocol exchange. I have not made a change to the text. 

> 
> Bullet 4 / Imprint operation: 
> 
> A specific device may require a MASA token to bootstrap, another one may NOT. This is really a feature of the pledge. And this behaviour MUST NOT be changeable (ie it's hard coded). (somewhere we should state that, I think we don't so far). 

CONCERN: I think section 6 about reduced security modes directly addresses this; by specifically allowing this to be changed (e.g. allow a reduced security mode).
What we don’t talk about is how a device might indicate it wants one type of token from the MASA or the other. I’m comfortable mandating that a Pledge is required to support either format; since my concerns about the ownership voucher are around how the sales channel integration work. The client side implementation is pretty trivial. 

> In the "Imprint" step three errors can happen: 1) The device receives a bad MASA token, or doesn't receive one; and 2) the domain Registrar receives a bad or no MASA token or 3) the audit log makes the Registrar reject the device. For trouble shooting, I think it is imperative that in 1) the pledge informs the Registrar of the error,

CONCERN: So I think you recommend either expanding s5.7.4 “status telemetry” to explicitly cover this case or add another telemetry option? 

> and in 2) and 3) the Registrar informs the pledge (e.g., to turn on a red LED, such that the installer knows that an error condition has arisen. I think we don't cover those cases yet? 

CONCERN: This is an interesting idea but w/o a valid MASA response the domain has no secure way to drive behavior on the Pledge. What do you think about the Pledge being required to indicate something about failed attempts when it moves on to future discovery? (via timeout etc). 

> 3.1.1
> " The result of discovery is logically (should be "logical") communication with a Proxy instead ... " I would have said it the other way round, and reduced that paragraph to: " The result of discovery is a logical communication with a Registrar, through a Proxy.” 

Fixed. "The result of discovery is a logical communication with a Registrar, through a Proxy. The Proxy is transparent to the Pledge but  is always assumed to exist."

> " To discover the Domain Bootstrap Server" you mean " To discover a Registrar" - right? I suggest to remove the term "bootstrap server" completely (globally) to avoid confusion. 

Fixed. 

> a): We exclude a case with normal DHCP for IPv4. Do we really want to do this? Also, if option d) is the only one working, we require DNS to work. So a) should probably be expanded to include these options?

Good point. I’ve added a reference to DHCP [RFC2131] as follows:

The Plege MAY obtain an IP address via DHCP [RFC2131]. The DHCP provided parameters for the Domain Name System can be used to perform step (d) DNS operations if all local discovery attempts fail (see below). 

CONCERN: how to balance this MAY with the MUST concerning RFC3927 and RFC4862 (dynamic IP address for v4 or v6)? 

> b): Do we need an IANA registration for the "_bootstrapks._tcp.local" service? We have no IANA considerations section!! 

CONCERN: great point. I’ve added the section but left the content as a [[EDNOTE:]]

> c) We're using both "example.com" and "example.net". Only use .com (http://www.iana.org/domains/reserved)

Fixed.
CONCERN: the next example is “vendor-example.com” to distinguish it. Perhaps this should be example.com as well? 

> d) "Vendors that leverage this method SHOULD provision appropriately." Explain? I don't understand what that means? 

If they sell devices that search for this address they should build out their infrastructure sufficiently to handle the load of whatever devices they ship. I’ve changed the text to read: "Vendors that leverage this method on the Pledge are responsible for providing the bootstrapks service”.

> Not sure, just verifying: Our proxy methods would work if the pledge is IPv4 and the Registrar IPv6? 

CONCERN: I believe so but MCR’s input would be helpful. 

> "to avoid overloading that discovery methods network infrastructure." Does that make sense? I think "to avoid overloading the network infrastructure with discovery”. 

Fixed. 

> In the reference model we state that if a pledge has been rejected by a domain, it should preferably use other domains that are seen. We may want to add something at the end of 3.1.1. This is also the reason why the pledge needs to know if the Registrar has rejected it based on MASA input. 

CONCERN: Discovery doesn’t include a secure statement of the domain identity. So this behavior would imply something like “if the TLS authentication results in a domain that has explicitely rejected the Pledge previously then the attempt immediately fails and no request is initiated” in section 5? 

> s/Therefore or clarity/Therefore for clarity/

Fixed with an above comment. 

> 3.1.2 suggest to merge with 3.1.3. The "request join" includes the "identity", really. These are NOT two separate steps. 
> s/ bootstrapping protocol server/Registrar/g
> s/bootstrapping server/Registrar/g
> s/Bootstrapping server/Registrar/g

CONCERN: as noted above these are two distinct protocol steps. Leaving this for now. 

> 3.1.4
> The non-autonomic methods are confusing here. I wonder whether we should exclude them? Are they really in scope? 

CONCERN: I’d like to leave these for now. I receive a lot of questions about how this is different than the non-autonomic methods in EST and around how TOFU etc relates. I think it seems extraneous to us to discuss these (again) for but newer readers it helps. 

> The pledge must support three modes: 
> 1 - (no MASA): doesn't require an ownership voucher or audit token

CONCERN: I emphatically don’t see this as a requirement on the Pledge. Section 6 allows this case only because we’re not yet serious about security. 

> 2 - (MASA with audit only): requires an audit token
> 3 - (MASA with ownership tracking): requires an ownership voucher. 

I’ve updated the statement before the list to read:
"This document describes autonomic methods that MUST be supported by the Pledge:"

> 
> 3.1.5
> "   o  In accordance with IEEE 802.1AR and RFC5280 all manufacturing
>      installed certificates and trust anchors are assumed to have
>      infinite lifetimes.  All such certificates "SHOULD be assigned the
>      GeneralizedTime value of 99991231235959Z" [RFC5280].  The New
>      Entity, Registrar and MASA server MUST ignore any other validity
>      period information in these credentials and treat the effective
>      lifetime as 99991231235959Z.  This ensures that client
>      authentication (see Section 3.3.1) and the audit token signature
>      (see Section 5.3) can always be verified during RFC5280 path
>      validation."
> 
> The MUST statement implies that a MASA etc actually knows whether a certificate is 8201.AR or another type of cert, right? Is that true? When I look at a device certificate, how do I know it's an IDevID? 
> 
> Assuming you *can* distinguish IDevID from a "normal" cert, we may run into cases where "normal" certs are used in the function of an IDevID, right? I.e. a device type doesn't really support IDevID, but a manufacturer has pre-loaded certs at manufacturing time. 
> 
> This "All such certificates "SHOULD be assigned the GeneralizedTime value of 99991231235959Z" [RFC5280]. " in combination with "MUST ignore" makes me nervous…

I’ve updated this bullet as:

During Pledge authentiation by the Registrar a realtime clock can be used by the Registrar. This bullet expands on a closely related issue regarding Pledge lifetimes. RFC5280 indicates that long lived Pledge certifiates "SHOULD be assigned the GeneralizedTime value of 99991231235959Z" [RFC5280] so the Registrar MUST support such lifetimes and SHOULD support ignoring Pledge lifetimes if they did not follow the RFC5280 recommendations. 

Arguably this bullet could be moved to a different section. 

> 
> We're referring to an audit token in this section, but not to the other 2 methods  (Onwership voucher and no MASA). This isn't complete… 

I’ve moved the nonce discussion to the end of this section and added a comment about Ownership vouchers:

The nonce included in join attempts provides an alternate mechanism for the Pledge to ensure Audit Token responses are associated with a particular bootstrapping attempt. Nonceless Audit Tokens from the MASA server are always valid and thus time is not needed.

Ownership Vouchers include time information and MUST be validated a realtime clock.

> 
> Specifically, in a case without MASA, I think we need to simply state that we cannot validate time during enrolment. I think this is what the statement "When accepting an enrollment certificate the validity period
>      within the new end entity certificate is assumed to be valid by
>      the New Entity." wants to say? 

CONCERN: I don’t see how “without MASA” enters into this so I’ve probably not addressed something here. 

> Actually, we only look at the domain validating time from the pledge, shouldn't we also describe the other direction? --> 
> Wouldn't it be correct to say "A pledge without real-time clock cannot securely bootstrap time. During the bootstrap process it accepts all certificates without validating time. Once bootstrapped such devices MUST be provided with the current correct time for other PKI operations to succeed."
> 
> This whole section 3.1.5 makes me a bit nervous… 

Good. :/ Its a scary concept and I’m happy to have folks comment. Do the above cleanups help?

> 
> 3.1.6 
> "The New Entity contacts the Registrar" add "via a proxy". We always assume a proxy. 

Fixed.

> 
> In this section we don't foresee a case without MASA sever. (Bullet list)
> 
> "   o  The EST server is authenticated by using the Ownership Voucher
>      indicated fully qualified domain name to build the EST URI such
>      that EST section 4.1.1 bootstrapping using the New Entity implicit
>      Trust Anchor database can be used."
> 
> Read this several times, still don't parse it. Can we make this sentence simpler? Not even sure this is grammatically correct?!? 
> 
> Also this section, I think we should distinguish the three cases of MASA. Last paragraph starts with "once the audit token is received". What if there is none or an ownership voucher? 

Fixed. 

"Ownership Vouchers are obtained by a Registrar from the MASA service and explicitly indicate the owner of the Pledge.”

"The Ownership Voucher contains the Owner Certificate which the Pledge uses to authenticate the TLS connection."

> 
> 3.1.7
> As mentioned in my other mail, I would prefer to call the final state here "enrolled". We could explain here that in the case of ANIMA, the next step is the establishment of the ACP, see draft ...  and in the non-ANIMA case we expect normal management to take place, ex via NETCONF, ... But I suggest to have a reference to the ACP draft. 

CONCERN: I like switching this to ‘enrolled’. Not sure what the rest of the suggestion is. 

> 
> 3.2
> We should re-state here that architecturally, a Pledge ALWAYS interfaces a Proxy; if the directly adjacent device happens to be a Registrar, it has to present itself to the pledge in the same way a normal Proxy would. 

Fixed. 
"A Proxy is always assumed even if directly integrated into a Registrar”. 

> 
> "the chosen mechanism SHOULD... " - This is the mechanism we specify later in the doc, right? (Sounds like this is a requirement outside this doc). Then I would re-phrase "the chosen mechanism was designed to …" 
> 
> I disagree with the *general* goal "SHOULD use the minimum amount of state on the proxy device." This is a good goal for constrained devices, but in a normal network we always try to handle DoS for example as far "out" as possible. (We had that discussion a while back).
> 
> What are we planning to do with draft-richardson-anima-state-for-joinrouter? It contains valuable background. Wouldn't it be nice to have that as an appendix in brski? (However, then the naming would need to be adapted to the brski terminology). 
> 
> Add: "If this bootstrap mechanism is used in an ANIMA context, the proxy device will discover Registrar(s) through GRASP based discovery, inside the ACP. The connection from the Pledge will also be forwarded inside the ACP." A proxy will only be enabled when a device sees a Registrar; if it loses connections to all Registrars, it withdraws the proxy service announcements. 
> Or did we decide to leave ANIMA completely out of the draft? (I thought we wanted it independent, but ANIMA is still the main use case for now). 

CONCERN: I’d like to hear MCR’s thoughts about this proxy discussion. 

> 
> 3.3
> I think we need to take a step back here. First, explain that the registrar is typically configured. Then, we need to give a bit more context: On one side, it expects connections from pledges, on the other we have a CA connection and (optionally) a MASA. 

Fixed. 

"A Registrar listens for Pledges and determines if they can join the domain. A Registrar obtains either Audit Tokens or Ownership Vouchers from the MASA service and delivers them to the Pledge as well as facilitating enrollment with the domain PKI. A Registrar is typically configured manually."

> Then, in an ANIMA context, the Registrar(s) announce their service inside the ACP, and they expect to be contacted by proxies through the ACP. 

CONCERN: I agree with the announce point as per the continued GRASP discussions (over the ACP). I don’t know that the proxy communications is necessarily through the ACP. Holding off on changes to this section until we hear from MCR on that. 

> 
> 3.3.2
> The whole document is focused on the audit method; If this is the main method, then we MUST explain the white list here, because neither of the 3 bullets in this section is sufficient for authorizing exactly "my" devices. (I realise white lists appear later on). 

Fixed. 

> 
> Paragraph "In order to validate the IEEE 802.1AR device identity..." belongs into 3.3.1. 

Fixed.

> 
> s/it is expected request/it is expected to request/

Fixed. 

> 
> "these certificates can subsequently be used to determine the boundaries of the homenet..." - remove the homenet references here. I suggest to re-phase: "These certificates can be used for other methods, for example boundary detection, auto-securing protocols, etc.”. 

Fixed.

> 
> "The authorization performed during this phase MAY be
>   cached for the TLS session and applied to subsequent EST enrollment
>   requests so long as the session lasts." - not clear?!? Each request is for a single device. Why cache? 

Fixed. 
I’ve changed it to “is used for”. The point is, and maybe this isn’t clear, that the same TLS session is maintained using session resumption so don’t think you’re gonna do some other authorization about the certificate issuance. 

> 
> I stop the detailed review here for a moment, since my comments would depend too much on how we resolve the question asked above about the 3 methods. Will resume here once we settled on this... 
> 
> 
> 
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