Reactions inline... On Tue, Apr 05, 2022 at 10:05:16AM +0200, Peter van der Stok wrote: > > > Hi Jurgen, > > Thanks for the review. I sympathize with your confusion issues. Many times I > shared the same confusion on other IETF documents that I thought relevant > for my work. IETF documents are not encouraged to rephrase parts of other > RFCs or provide large operational HOWTO considerations. Actually, in other > documents that I co-authored people were not happy about the large number of > examples we provided. In my view the document should state the problem that > is being solved, and the standard that proposes to remove the problem. I > tried to do that in this document. > > See below for my comments, > > much useful text is added in response. > > Greetings, > > Peter > > _____________________________________________________________________ > > Reviewer: Jürgen Schönwälder > Review result: Serious Issues > > Let me start with a disclaimer: I am not familiar with BRSKI and ANIMA > and hence I have been reading this I-D as a confused outsider and some > of my concerns may not be valid or the result of me not understanding > the relevant technologies. That said, my conclusion after reading that > document is that it is not ready. At a high level, my concerns are: > > - First, it seems to me that there are many options and there is no > clear mandatory to implement baseline. Hence, there I am concerned > that this specification will not necessarily lead to interoperable > implementations. > > Pvds ==> > > We could add normative language for one option only. We prefer that based on > use cases, an installation engineer could choose one option over the other. > The simplest option is stateful which is common in today's translation > devices, but again other use cases may not want to implement that and just > do stateless. I think it is hard for us to choose between these two options. > Not sure what an installation engineer does but if you have 5 different IoT devices that all implement different incompatible feature sets and all of them claim compliance to RFC XXXX, then clearly there is a problem. Well, the IoT space may be used to this and perhaps this is why there are 'installation engineers'. ;-) > * Join Proxy functionality > > I found the text a bit confusing. It talks about why packets to > establish a DTLS connection with a Registrar won't be delivered and > then afterwards it says that the Pledge is not even able to discover > the IP address of the Registrar. Perhaps this text can be simplified > and streamlined. It is rather obvious that if a Pledge has only a > link-local address, it won't talk with a Registrar multiple IP hops > away. > > Pvds==> > > Now I am confused. I expected you to require more text here. > > Something seems to be missing in the description of the base line scenario, > and I need more info to understand what the missing pieces are. I think it is rather obvious for people familiar with IPv6 that (i) if you don't have the Registrar's address you can't talk to it and (ii) if the Registrar is multiple hops away, you can't talk to it. Things that are less obvious are the assumptions made about how devices are connected. Apparently (if I understand your response) we are not talking about devices joining a regular wireless LAN, i.e., a shared link. This is where I got lost, i.e., in which scenario such a Join Proxy is applicable. It is not about more or less text, but text that helps me to figure out whether this is applicable to my networks or not. > ==> > > Are both modes required to be implemented? The stateless approach > seems to require support by the Registrar while the stateful > approach seems to be transparent from the Registrar's > perspective. This apparently makes a big difference for the > deployment options. To deploy the stateless Join Proxy somewhere in > a big network, you need to update the Registrar to support it, > right? > > Pvds==> > > Yes, figure 5 states the discoverable port in the Registrar So are both modes required (mandatory) to implement? > ==> > > I wondered: How does this all interact with SLAC and/or DHCP on a > shared link? You seem to assume that SLAC and/or DHCP are disabled > as long as a Pledge is not yet enrolled, right? In some networks, > you will have also 802.X for enabling layer 2 ports. How do all > these things fit operationally together? What are operationally > meaningful setups? In a shared network scenario, how do I > effectively prevent a Pledge from using router advertisements to > generate a routable address? Or is in such a deployment a Join Proxy > simply not necessary? Perhaps these questions go beyond this > document and they just show my lack of background. > > Pvds==> > > Only DTLS connections are allowed on the BRSKI mesh network. Certificates > which are signed by the Registrar are used to set up the DTLS connections. > Non protected messages may be routed but will never be accepted by the > recipient. I am still confused how this is enforced, special link-layer properties, configuration of something, ...? Which kind of mesh network is required for this to be applicable? I think this is the bit of information I am missing, to which deployments this is applicable. > ==> > > Are there any message size issues since the stateless solution > encapsulates the DTLS payload in another header? I see that this is > mentioned in the table at the end as a property of the stateless > mode, there is no discussion of any consequences this may have. > > Pvds==> > > No discussion is given, not knowing all operational conditions. > > Installation engineers are given the choice. Perhaps the goal is job security for installation engineers. ;-) > ==> > > There are three different discovery options. Are all three mandatory > to implement? Is having many options to start with desirable from an > interoperability point of view? > > Pvds==> > > Bob Wilton also commented on this aspect; that has been changed in the > latest version > > ==> > > I tried to figure out how in 6.1.1 the Registrar is found. I > followed several references, discovered several options, ended up in > GRASP as one of them. Once I have the registrar's address, I can > query the Registrar for more details. Then we have 6.1.2 which > details how GRASP can be used directly to provide all relevant > information. This section says it is "normative for uses with ANIMA > ACP". Not sure what that means, did they authors mean that it is > mandatory to implement for ANIMA ACP or that it is mandatory to use > for ANIMA ACP? Normative feels like the wrong word, or is the other > text not normative or what is conditionally normative in which > contexts? As a newcomer, I only found section 6.3.1 reasonably clear > (there is a link-local coap multicast, I can see how that works). > > Pvds==> > > Not sure about "normative for use" or "normative to implement"; Does > "normative for use" imply "normative to implement"? Normative to use? I though the installation engineer is the one to decide. In general, the IETF can be expected to define what is normative to implement (a baseline to ensure interoperability). I am not sure the IETF can be expected to define what is normative to use. Was the intention to say that one option is a normative part of an ANIMA compliant solution? Obviously, options that are not implemented are difficult to use, hence my question for a normative to implement baseline (to make the life of the installation engineer easier). > ==> > > * Security Considerations > > There may be more security relevant questions. How robust is this > design against attacks? Can this be exploited for attacks? How does > a join proxy decide which (DTLs) traffic should be forwarded and > which should not be forwarded, or is the idea that any traffic is > forwarded? Is the Join Proxy required to verify that the forwarded > traffic is actually (valid) DTLS traffic? > > pvds==> > > Good Point. In my understanding only DTLS connections are accepted by the > destination. Refusing to route non DTLS traffic may be a bit prohibitive. > The suggestions is to add the following text after the first paragraph. > > NEW > > A malicious constrained Join Proxy has a number of routing possibilities: > > * It sends the message on to a malicious Registrar. This is the same case > as the presence of a malicious Registrar discussed in RFC 8995. > * It does not send on the request or does not return the response from the > Registrar. This is the case of the not responding or crashing Registrar > discussed in RFC 8995. > * It uses the returned response of the Registrar to enroll itself in the > network. With very low probability it can decrypt the response. Successful > enrollment is deemed too unlikely. > * It uses the request from the pledge to appropriate the pledge > certificate, but then it still needs to acquire the private key of the > pledge. Also this is assumed to be highly unlikely. > > A malicious node can construct an invalid Join Proxy message. Suppose, the > destination port is the coaps port. In that case, a Join Proxy can accept > the message and add the routing addresses without checking the payload. The > Join Proxy then routes it to the Registrar. In all cases, the Registrar > needs to receive the message at the join-port, checks that the message > consists of two parts and uses the DTLS payload to start the BRSKI > procedure. It is highly unlikely that this malicious payload will lead to > node acceptance. > > A malicious node can sniff the messages routed by the constrained Join > Proxy. It is very unlikely that the malicious node can decrypt the DTLS > payload. A malicious node can read the header field of the message sent by > the stateless Join Proxy. This ability does not yield much more information > than the visible addresses transported in the network packets. > > ==> > > The stateless proxy seems to allow outside attackers to send > arbitrary packets to any link-local address inside. > > Pvds==> > > Like any node that can send link-local broadcast and unicast; I don't think > this is specific to the constrained Join Proxy. > > ==> > > This looks like > a new reflection service that must be kept operationally under > control, in particular since enrolled Pledges may later act as well > as Join Proxies. The security considerations text indicates that > future work may address this issue by encrypting the CBOR array. Is > this sufficient, do we really want to standardize a new reflection > service that we then fix in the future? I am also not sure why level > 2 protection (what is 'level 2'? layer 2? link-layer protection?) > will actually resolve the problem, once I can route IP packets to a > Join Proxy, I can let it forward traffic to arbitrary link-local > addresses, no? > > Pvds==> > > No; only DTLS packets can be sent to Registrars. The latter decides in > combination with manufacturer's MASA if a node can be accepted in the > network. What stops an attacker to send fake messages via the Join Proxy to devices on the mesh network? Are you saying that the Join Proxy has to verify that the payload is a valid DTLS message and hence the effects of this are restricted to unexpected DTLS messages? I am not sure I am convinced by that argument, there may also be simple attempts to prevent communication or to consume resources. Note, if the Join Proxy encrypts the forwarding state, then the format of the forwarding state can be entirely implementation specific. From a security and an operational perspective, it seems the stateful solution is much easier to deal with. Perhaps the security directorate reviewers will chime in on the properties of the stateless solution. /js -- Jürgen Schönwälder Jacobs University Bremen gGmbH Phone: +49 421 200 3587 Campus Ring 1 | 28759 Bremen | Germany Fax: +49 421 200 3103 <https://www.jacobs-university.de/> -- last-call mailing list last-call@xxxxxxxx https://www.ietf.org/mailman/listinfo/last-call
