See comments inline
From: Ace [mailto:[email protected]] On Behalf Of Somaraju Abhinav Sent: 02 February 2017 03:48 To: Jim Schaad <[email protected]>; [email protected] Cc: 'ace' <[email protected]> Subject: Re: [Ace] draft-somaraju-ace-multicast Hi Jim, thank you for the review and I apologise for the delayed response - I was on sick leave due to a surgery. Please see comments inline from the authors. Why restriction on reading messages? It is not like an external observer is not going to be able to see the lights go on or off. [AS] There are several situations where lights are not visible but (multicast) network data is accessible. Moreover, sensors (e.g. presence detectors) are continuously talking to actuators and controllers without necessarily having a visible effect on the lights. For several customers privacy is a very important concern and is almost a given. The statement "anybody can listen to the traffic and tell when sensors detect presence in a building without even being in the building" is a very difficult sell. Having said that, it is true that simply encrypting the multicast traffic at the application layer is only a prerequisite to provide the privacy needed and additional work is required (e.g. generating random messages at different times). In that sense the symmetric solution is probably not much better than the asymmetric solution. But the demand for privacy from customers is very clear and the perception among them is that unencrypted data implies poor security. [JLS] I am sensing a problem here. You have stated that there is a requirement that encryption is a requirement that people are going to say must be me. However, below you have stated that if authentication is a requirement then encryption suddenly becomes a non-requirement? You appear to be stating that there are circumstances where it is fine not to have the data encrypted if one needs to know where it came from. Consider the following case I have a sensor in a room. When the sensor sees movement, it broadcasts a lights one command. The command is picked up by both the lightbulbs and by the security system. The security system must know which sensor provided the command and therefore no encryption is going be needed here? That just seems wrong. Additionally, the situation where things are "continuously" talking would seem to be a good place where one would want to install a controller and not have the sensor directly talking to the actuator. You don't want to flood the actuators with trying to constantly turn on the lights. Also the use of actuators in this sense makes one think that this is a solution for things other than lighting systems which is what people are complaining about. The solution in section 4 does not seem to meet the following requirement "Only authorized members of the application group must be able to read and process messages." [AS] You are right, we cannot satisfy the privacy requirement in Section 4. We could extend the current solution to include a group wide encryption key to meet this requirement. However, this will add additional latency to the asymmetric solution. This document needs to have a solution for dealing with nonce space allocation for the cases where more than one sender is going be able to use the same key. This is going to be part of the problems with replay detection as well as security considerations. [AS] Okay. Will add some text in the next version of the draft for better clarification. The idea as written in 4.3 (Nonce value) is to use the Client ID along with the sender's sequence number to create the complete nonce for replay and CCM processing. Should the algorithms be using high water detection of sequence numbers rather than the case of not yet used? Or is that an application specific type thing? [SK] This is tricky since it can create all kind of new issues. One way to handle if the sequence number of a sender is about to roll over is that the sender requests a new key issued for the group by the KDC. Tricky part is if there are multiple senders who are not reaching the roll over of their sequence number then have to be forced to use a new key or there needs to be some overlap between the old key and new key before every sender in the group starts using the new key. [JLS] Lots of spinning in graves from the idea of having a sequence number roll over given the harsh requirements that a nonce (built from the sequence number) must never be re-used twice for many of the algorithms that are going to be used here. I do not think that the current security requirements is sufficiently strident to reflect both the threat of breakage, cross-breakage and restrictions on where it should be used to pass muster. [AS] I thing this will be the main discussion item in the webex. We will make a proposal for the security guidelines section after the interim webex. [JLS] A proposal before the call is better because then we have a starting point for discussions as well as allowing people who will not make the call be able to have some initial input on where discussions points should be directed. _______________________________________________ Ace mailing list [email protected] <mailto:[email protected]> <https://www.ietf.org/mailman/listinfo/ace> https://www.ietf.org/mailman/listinfo/ace ________________________________________________________ The contents of this e-mail and any attachments are confidential to the intended recipient. 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