Re: [manet] Message integrity and message mutability (was RE: draft-ietf-manet-aodvv2-13 review - a couple of big ticket Items)

[Victoria Mercieca <[e-mail]>]

Hi Chris,


On Mon, Apr 25, 2016 at 3:51 PM, Dearlove, Christopher (UK) <
[e-mail]> wrote:

> I has to go back to Victoria’s summary here. It says:
>
>
>
> 2) C creates the RREP. Since it doesnt know if the link to B is
> bidirectional, it includes the AckReq (an address to indicate that it
> expects to receive a RREP_Ack from B).
>
>
>
> That doesn’t actually indicate if that’s C’s address or B’s address being
> included. I’d assumed it was C’s address. Your comment makes sense if it’s
> B’s address. Reading again, I think you’re probably right. But only
> probably. Can we confirm that.
>
>
>

C creates the RREP. The included AckReq address is B's address. The RREP
then gets multicast.
B receives it, sees that it own address is marked as the AckReq address,
and sends an ack unicast back to C.
Anyone else who receives the multicast RREP from C does not send the Ack,
since the AckReq address does not match any of their interface addresses.


> I assume you meant that the RREP (not RREP_Ack) is multicast. There’s a
> bit of a chicken and egg problem here. We do know how we want to unicast.
>

The RREP is multicast (when we dont know if the link is bidirectional), the
RREP_Ack is always unicast.

Kind regards,
Vicky.


>
> *-- *
>
>
>
>
> *Christopher Dearlove Senior Principal Engineer BAE Systems Applied
> Intelligence Laboratories *
> *__________________________________________________________________________
> *
> *T*:  [phone]  |  *E: *[e-mail]
>
> BAE Systems Applied Intelligence, Chelmsford Technology Park, Great
> Baddow, Chelmsford, Essex CM2 8HN.
> www.baesystems.com/ai
>
> BAE Systems Applied Intelligence Limited
> Registered in England & Wales No: 01337451
>
> Registered Office: Surrey Research Park, Guildford, Surrey, GU2 7YP
>
>
>
> *From:* Justin Dean [mailto:[e-mail]]
> *Sent:* 25 April 2016 15:26
> *To:* Thomas Heide Clausen
> *Cc:* Dearlove, Christopher (UK); Christopher Dearlove; Mobile Ad Hoc
> Networks mailing list; Victoria Mercieca
> *Subject:* Re: [manet] Message integrity and message mutability (was RE:
> draft-ietf-manet-aodvv2-13 review - a couple of big ticket Items)
>
>
>
>
>
> **** WARNING ****
>
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>
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>
> The address in the RREP_Ack may be required due to the RREP_Ack being
> multicast as there is not yet a verified unicast route installed yet.
> Going to double check if I'm remembering correctly.
>
> Justin
>
>
>
> On Mon, Apr 25, 2016 at 10:18 AM, <[e-mail]> wrote:
>
> Hi,
>
>
>
> I must admit that while I have reviewed the protocol several times, I’ve
> not been digging that deep into the protocol functioning to catch this
> issue of how invasive the protocol operations are when forwarding a
> message: there were other “major” issues to address (and which obscured the
> details), so as a first order: thank you Victoria, for having called
> attention to this.
>
>
>
> To the substance of these emails.
>
>
>
> I am afraid that I do not understand the use of inserting validity TLVs
> while in-flight, into a message. Actually, I am dubious for both the
> originator inserting this (how can the originator of a message know how
> “latter parts of the path” will be have”) except if we are talking
> duty-cycling of devices and inserting “the remaining time that I am going
> to be up before I suspend”. Intuitively, that would also assume fairly long
> duty cycles “I am up for tens of seconds”, which I am not sure are actually
> realistic. And, as Chris says in another email, this is trading off “the
> ability to do security” for an unknown/untested feature — which I think is
> the wrong trade-off.
>
>
>
> On he topic of “needing to put an address in” for RREP-ACK, I must admit
> that this seems roundabout. I can see three issues here:
>
>
>
> o I am not sure that adding an address vs. a flag may not have to do with
> the “multiple interfaces/
>
> multiple addresses” discrimination mechanics of the protocol? I haven’t
> worked it through, though,
>
> but that would be a guess.
>
>
>
> o The end-to-end topology diffusion mechanism should not need to be
> concerned with the
>
> “bidirectionally check” of a local link (in part, as it encumbers
> security, but not only).  In short, a
>
> flag or an address, both are (equally) bad.
>
>
>
> o A cleaner mechanism would be a “hello mechanism”, not necessarily as
> NHDP, but a “when
>
> forwarding a RREQ/RREP, trigger a 3-way hello exchange, if the link is
> estimated to be of a
>
> type which potentially can be unidirectional”. There is another benefit to
> doing that, see the end
>
> of this email.
>
>
>
> Either way, I do not like the notion of fusing
> metrics-and-link-bidirectionality-detection any more than I like fusing
> global-topology-diffusion-and-link-bidirectionality-detection.
>
>
>
> The solution all this is, to me, threefold
>
>
>
> 1) Factor out the bidirectionally check in a (triggered) neighbour
> detection mechanism
>
> (triggered HELLO message)
>
>
>
> 2) Remove the “validity time TLVs”, since they add complexity for no
> perceivable benefits
>
>
>
> 3) Use the security model that we’ve discussed previously, where (only)
> the metrics change per hop.
>
>
>
> Since we’re discussing bi-directionality of links here, and the necessity
> of a mechanism for handling these, I want to call attention to a related
> issue, as I hinted previously.
>
>
>
> The abstract states that the protocol:
>
>
>
>    ...is intended for use by mobile routers in wireless, multihop
>
>    networks.
>
>
>
> Section 5 paragraph 4  of the document, however, reads:
>
>
>
>    Assuming link metrics are symmetric, the cost of the routes installed
>
>    in the Local Route Set at each router will be correct.  While this
>
>    assumption is not always correct, calculating incoming/outgoing
>
>    metric data is outside of scope of this document.
>
>
>
> I do not know of *any* wireless systems, where the assumption that “link
> metrics are symmetric” actually holds. Consequently, the conclusion in the
> quoted paragraph:
>
>
>
>    calculating incoming/outgoing
>
>    metric data is outside of scope of this document.
>
>
>
> Is not an acceptable design choice.
>
>
>
> While this protocol may not want to “calculate if for this link the
> metrics is 4 or 5”, the protocol must be able to convey and distinguish
> that “the metric from A to B is 4, and the metric from B to A is 19”.
>
>
>
> This is a “related issue” since the solution may (as with the
> bi-directionality check) be in the triggered neighbour detection mechanism:
> that exchange could, if designed carefully, be used to probe for and convey
> metrics information, also.
>
>
>
> Hope this helps,
>
>
>
>
>
> Thomas
>
>
>
> On 25 Apr 2016, at 15:27, Dearlove, Christopher (UK) <
> [e-mail]> wrote:
>
>
>
> Assuming for the moment that everyone will need an RREP-Ack or won’t
> (let’s come back to that) why do C and B need to put an address in as an
> RREQ-Ack request? Why not a flag, because the address will be included as
> the IP sending address - and we know 5444 is required to pass that on.
> (It’s used by NHDP as well.) Then we don’t need to change the RREP, it will
> have a flag set or not, and won’t change (in this regard).
>
>
>
> Now let’s consider do we know whether we can set a fixed flag. First I’d
> say there are two cases - you’ve got a firm control on what’s going on in
> your network, or it’s one of unknown parties and behaviour (consistent with
> specification). In the former case you only want one setting, for example
> no-Ack if running NHDP or your MAC layer tells you about bidirectionality,
> Ack otherwise. In the latter case, I think you just always want an Ack. So
> both cases get you to the same place.
>
>
>
> Should that not be an acceptable argument (though I think it’s good for
> where we are - in fact always Ack is close) then at flag is a step better,
> it’s a fixed location to change. However it would be better in that case if
> the two things to change (metric and ack flag) were together. But that has
> its own issues, so I won’t go there.
>
>
>
> *--*
>
>
>
>
> *Christopher Dearlove Senior Principal Engineer BAE Systems Applied
> Intelligence Laboratories *
> *__________________________________________________________________________
> *
> *T*:  [phone]  |  *E: *[e-mail]
>
> BAE Systems Applied Intelligence, Chelmsford Technology Park, Great
> Baddow, Chelmsford, Essex CM2 8HN.
> www.baesystems.com/ai
>
> BAE Systems Applied Intelligence Limited
> Registered in England & Wales No: 01337451
>
> Registered Office: Surrey Research Park, Guildford, Surrey, GU2 7YP
>
>
>
> *From:* Victoria Mercieca [mailto:[e-mail]
> <[e-mail]>]
> *Sent:* 25 April 2016 14:15
> *To:* Jiazi YI
> *Cc:* Dearlove, Christopher (UK); Christopher Dearlove; Mobile Ad Hoc
> Networks mailing list
> *Subject:* Re: [manet] Message integrity and message mutability (was RE:
> draft-ietf-manet-aodvv2-13 review - a couple of big ticket Items)
>
>
>
>
>
> **** WARNING ****
>
> *This message originates from outside our organisation, either from an
> external partner or the internet.*
>
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> attachments or reply. For information regarding **Red Flags** that you
> can look out for in emails you receive, click here
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>
> Hi Jiazi,
>
>
>
> On Mon, Apr 25, 2016 at 1:04 PM, Jiazi YI <[e-mail]> wrote:
>
> Hi,
>
>
>
> On Mon, Apr 25, 2016 at 11:20 AM, Dearlove, Christopher (UK) <
> [e-mail]> wrote:
>
> With regard to your validity time point, we here have a tradeoff. If you
> allow that feature, it significantly impacts on the approach that was
> coming together on as best you can end to end encryption.
>
>
>
> So the question is, is this a feature that’s really wanted? Unfortunately
> I think we know that the answer to that is, we don’t know because we don’t
> have any experience. My view would be that in the tradeoff of an untested
> feature (unless I’m wrong about that) and the security complication,
> security wins and drop the feature. If there is some real requirement, then
> there’s a discussion. (Questions like how often the intermediate routers
> actually have any knowledge - typically links break for unexpected rather
> than expected reasons. Andan intermediate router could possibly use a
> validity time to influence its behaviour.) Note that dropping the ability
> of intermediate routers to modify/set still allows validity times per route
> to be set at endpoints.
>
>
>
> I agree with Chris' concern.
>
> The ValidityTime is optional, which makes the integrity protection hard.
> Furthermore, it gives a potential attack vector: as all the routers in a
> path will take the shortest validityTime, a compromised router can set the
> the validityTime to a very short value, which will make the route installed
> along the path became invalid (very soon).
>
>
>
> On the other hand, I'm not sure this option will give us much help. Chris
> mentioned much knowledge intermediate router would have to decide this
> value (and how much sense the value would make).
>
> Another issue is, a route to a destination might be updated by different
> sources. For example, in the network below:
>
>
>
> A----B-----C
>
>
>
> A first establish a route to B with long validity time. Then A initiates a
> route discovery to C. C tends to set a short validity time, which will make
> the route between B and A expire earlier than expected.
>
> Is this a problem? Maybe yes, maybe no -- I'm not sure it's considered or
> not.
>
>
>
>
>
> Not sure I follow here.
>
> Currently, the validity time of the route between A and B would not
> affected by a short validity time of a route between A and C. Validity
> times are per-route, and the route A-B and the route A-C are separate.
>
> If we switched to a validity time per neighbor (so that we can keep
> validity time separate from route advertisements) as I mentioned in the
> email below, then the validity of a route between A and C would be affected
> if there was a short validity time between A and B. But, if B will only
> route for a certain amount of time, then the route between A and C will of
> course be affected. Is it best to know in advance that there's a time
> limit, or just deal with RERRs when they happen?
>
>
>
>
>
>
>
> With regard to the acknowledgements, the problem (with regard to security)
> comes from trying to do two jobs with the same message - end to end route
> advertisement and hop by hop acknowledgement. I understand the reasons -
> saving bytes and message types. (I would have to study the protocol really
> hard to identify if any message types can be folded together and recognised
> by content rather than type efficiently. This I do not expect to do.) Again
> a tradeoff. This one is in discussion space, though that needs people who
> understand both sides of the issue, including the details of the
> bidirectionality mechanism. Of course, as has been said, we need one of
> those.
>
>
>
> I haven't finished my review of the latest draft, and I don't get the
> necessity of AckReq and the corresponding multicast RREP yet.
>
> If possible, this "optional" field should be avoided.
>
>
>
>
> To give an overview of AckReq and RREP:
>
> Since AODVv2 requires bidirectional links, this is the way to determine if
> a link is bidirectional.
>
> A----B----C
>
>
> 1) A sends RREQ, B forwards it, C receives the RREQ. B and C both install
> a route to OrigAddr but they dont yet know if it's valid because they dont
> know if the link to their next hop is available in the reverse direction.
>
> 2) C creates the RREP. Since it doesnt know if the link to B is
> bidirectional, it includes the AckReq (an address to indicate that it
> expects to receive a RREP_Ack from B).
>
> 3) B receives the RREP, installs a route to TargAddr and marks it as
> valid, since it knows the link to C is bidirectional, because the RREQ went
> in one direction and the RREP came in the other. B also sends the RREP_Ack
> to C and forwards the RREP to A (and might change the message to indicate
> its own AckReq - ie that it requires an ack from A).
>
> 4) C receives the RREP_Ack from B, and therefore knows that B received the
> RREP, therefore the link is bidirectional. C can then mark its route to
> OrigAddr as valid.
>
> 5) Similarly, A receives the RREP, installs the route to TargAddr and
> sends an RREP_Ack to B.
>
> 6) B receives the RREP_Ack and marks its route to OrigAddr as valid.
>
>
>
> Alternatively, in step 2, if C knows the link to B is bidirectional
> (perhaps from some earlier route discovery), it doesnt need to put the
> AckReq in the RREP. Then in step 3, since B doesnt know if the link to A is
> bidirectional, it changes the message to add the AckReq address, in order
> to get an RREP_Ack from A.
>
> If we want to avoid changing the message, we'll need to look at forwarding
> the RREP as-is, and creating a second message to solicit an RREP_Ack, in
> order to verify that the link is bidirectional before marking the route to
> OrigAddr as valid.
>
> Kind regards,
>
> Victoria.
>
>
>
>
>
> regards
>
>
>
> Jiazi
>
>
>
>
>
> *--*
>
>
>
>
> *Christopher Dearlove Senior Principal Engineer BAE Systems Applied
> Intelligence Laboratories *
> *__________________________________________________________________________
> *
> *T*:  [phone] <%2B44%20%280%291245%20242194>  |  *E: *
> [e-mail]
>
> BAE Systems Applied Intelligence, Chelmsford Technology Park, Great
> Baddow, Chelmsford, Essex CM2 8HN.
> www.baesystems.com/ai
>
> BAE Systems Applied Intelligence Limited
> Registered in England & Wales No: 01337451
>
> Registered Office: Surrey Research Park, Guildford, Surrey, GU2 7YP
>
>
>
> *From:* Victoria Mercieca [mailto:[e-mail]]
> *Sent:* 23 April 2016 10:55
> *To:* Christopher Dearlove
> *Cc:* [e-mail]; Dearlove, Christopher (UK); Mobile Ad Hoc
> Networks mailing list
>
>
> *Subject:* Re: [manet] Message integrity and message mutability (was RE:
> draft-ietf-manet-aodvv2-13 review - a couple of big ticket Items)
>
>
>
>
>
> **** WARNING ****
>
>
>
> *This message originates from outside our organisation, either from an
> external partner or the internet. Consider carefully whether you should
> click on any links, open any attachments or reply. For information
> regarding **Red Flags*
> * that you can look out for in emails you receive, click here
> <http://intranet.ent.baesystems.com/howwework/security/spotlights/Documents/Red%20Flags.pdf>.
> If you feel the email is suspicious, please follow this process
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>
> Hi Chris,
>
>
>
> These have both been in the draft in some form since before I got
> involved... but I'll do my best to explain.
>
>
>
> - For Validity Time, its a way to advertise that you would only support
> the route contained in the message for a certain period of time. The
> originator might use this, but the draft was written to allow any
> intermediate node to be able to add it or update it too. The route created
> in the Local Route Set has an expiration time associated with it, based on
> the received validity time.
>
> - For the AckReq address, its so that you can add into a RREP a request
> for an acknowledgement, so that you don't have to have a different message
> type altogether for working out whether links to neighbors are
> bidirectional, and also, since you only care about bidirectionality on
> routes that are being set up, you dont need to constantly monitor all
> neighbors.
>
>
>
>
>
> In order to avoid the potential AckReq-related changes to each message,
> maybe we do need to introduce a different message specifically for this. We
> could maybe use RREP_Ack to both request and acknowledge? It means an extra
> message of control traffic that needs to be sent, maybe one extra message
> per hop on the path of a RREP, but it could still be limited to neighbors
> which have participated in the route discovery rather than monitoring all
> neighbors at all times.
>
>
>
> This message could maybe also include "I'm happy to route anywhere for a
> certain amount of time", sort of like willingness in OLSR/OLSRv2. So
> instead of having a validity time per route, its a validity time per
> neighbor. Then, for RREQ and RREP, only the metric value would change in
> transit, as discussed. However, that leads to some issues with deciding
> what a route's expiration time is. You might know how long the next hop
> router is valid for, but what if a router beyond that, which was also part
> of the route, had a lower validity time? You couldn't determine the real
> validity time. Do we remove the route expiration time altogether to avoid
> this issue? In which case, we would have to rely on RERR messages being
> sent for routes which become invalid when the neighbor's validity time has
> expired? So neighbor validity time expiration is treated the same as a link
> break.
>
>
>
> What do you think?
>
>
>
> Kind regards,
>
> Victoria.
>
>
>
>
>
>
>
>
>
>
>
>
>
> On Sat, Apr 23, 2016 at 1:09 AM, Christopher Dearlove <
> [e-mail]> wrote:
>
> Pretty much all of the discussion has been assuming only a metric value
> change. With multiple things changing many of the ideas go out of the
> window. That reinforces the point about not making specifications now that
> might turn out to be wrong for ICVs.
>
>
>
> Ignoring how this misunderstanding happened, I'll start by asking why.
> Metric changing I understand. Why the other two? (there's a partial
> explanation of one). What alternatives have people implemented in
> comparable protocols?
>
> --
>
> Christopher Dearlove
>
> [e-mail] (iPhone)
>
> [e-mail] (home)
>
>
> On 23 Apr 2016, at 00:26, Victoria Mercieca <[e-mail]> wrote:
>
> Hi all,
>
>
>
> Continued in this thread because the other one seems to be more about TLV
> types and metric type numbers, whereas this is about
> regeneration/forwarding.
>
>
>
> To recap, in the current draft, there are 3 things that might change at
> each hop:
> - the metric value (happens in RREQ and RREP),
> - adding/changing Validity Time using the Validity Time TLV (can happen in
> RREQ and RREP),
> - adding an address (and corresponding value in the AddressType TLV to
> indicate how to interpret the address) to indicate the address from which
> an RREP_Ack is expected, to accomplish the bidirectionality check (can
> happen in RREP).
>
> If we define a certain portion of the message as immutable and include the
> ICV to verify that part, end to end:
> - The metric value would be excluded from the ICV since it needs changing
> at each hop.
> - Would adding a Validity Time TLV at an intermediate hop be acceptable?
> The whole TLV could be removed in order to calculate the ICV?
>
> - Would adding an address cause issues for the ICV, because it's in the
> address block? Could the rule be "if it contains an AckReq address, remove
> it (and the corresponding value in the AddressType TLV), before checking
> the ICV", is that OK? Or would we need to avoid touching the ICV'ed part of
> the message altogether, maybe put the AckReq address in a separate Address
> Block, with an extra AddressType TLV following that address block? Is there
> a way to accomplish this?
>
>
>
> Also, to be thorough, do we need to consider RERR messages while we
> discuss regeneration vs forwarding?
>
> - RERR (sent when a link breaks) is a way of saying "I've lost my route so
> I'm telling others" and "you were my next hop, so now I've also lost my
> route, I'll tell others", etc. It's going to be tailored at each step to
> include the relevant routes that got deleted, it's not one message being
> sent end-to-end like RREQ and RREP are.
>
> - However, RERR (sent when a source of traffic is sending data on a route
> which comes through you, and you want to tell the Packet Source's router to
> delete the route) could be seen as an end-to-end message which all
> intermediate routers learn from, similar to RREQ and RREP. It reports one
> route, and doesn't need changing at intermediate hops, so could be
> protected with ICV.
>
> - Would it be OK to only require a message ICV if a PktSource address was
> included, i.e. when the message needs to go via a number of intermediate
> hops to PktSource's router? All other RERRs are intended to be one-hop
> messages, which may in turn prompt other one-hop messages, etc..., and a
> packet ICV might be more appropriate?
>
>
>
> Kind regards,
>
> Victoria.
>
>
>
> On Thu, Mar 17, 2016 at 5:26 PM, <[e-mail]> wrote:
>
>
>
> On 17 Mar 2016, at 18:17, Dearlove, Christopher (UK) <
> [e-mail]> wrote:
>
>
>
> Yes, I meant AODVv2, thanks for the catch.
>
>
>
> So is your (Thomas) proposed base specification a hop count only metric?
>
>
>
> No, the would be silly as base specification, given that hop count mostly
> is useless.
>
>
>
> As base specification I would simply say “Include a Metric Type Message
> TLV with a value field, and a 7182 Message TLV & Timestamp” as we do in
> OLSRv2 (with the appropriate verbiage as to generation and processing).
>
>
>
> With the message generated by the originator of the RREQ/RREP and *not*
> deconstructed/reconstructed/reordered (as is the risk with “regeneration)
> allows knowing that it would be *only* that metric field being modified
> (other than hop count/limit) for when eventually writing up the extension.
>
>
>
> (Actually doesn’t the current specification only define hop count, or has
> that changed in latest draft?)
>
>
>
> No. That is one of the issues I raise in my original. For some reason, it
> cites RFC6551, which is a ROLL document and which has in its abstract that:
>
>
>
>    Low-Power and Lossy Networks (LLNs) have unique characteristics
>
>    compared with traditional wired and ad hoc networks that require the
>
>    specification of new routing metrics and constraints.
>
>
>
> I.e. this document cites a metric document which clearly claims to be
> inapplicable in ad hoc networks. I note that this is another thing I’ve
> raised for years without seeing it attempted resolved.
>
>
>
> Best,
>
>
>
> Thomas
>
>
>
>
>
>
>
> *--*
>
>
>
>
> *Christopher Dearlove Senior Principal Engineer BAE Systems Applied
> Intelligence Laboratories *
> *__________________________________________________________________________
> *
> *T*:  [phone] <%2B44%20%280%291245%20242194>  |  *E: *
> [e-mail]
>
> BAE Systems Applied Intelligence, Chelmsford Technology Park, Great
> Baddow, Chelmsford, Essex CM2 8HN.
> www.baesystems.com/ai
>
> BAE Systems Applied Intelligence Limited
> Registered in England & Wales No: 01337451
>
> Registered Office: Surrey Research Park, Guildford, Surrey, GU2 7YP
>
>
>
> *From:* [e-mail] [mailto:[e-mail]
> <[e-mail]>]
> *Sent:* 17 March 2016 17:10
> *To:* Dearlove, Christopher (UK)
> *Cc:* Lotte Steenbrink; Mobile Ad Hoc Networks mailing list
> *Subject:* Re: [manet] Message integrity and message mutability (was RE:
> draft-ietf-manet-aodvv2-13 review - a couple of big ticket Items)
>
>
>
>
>
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>
>
> On 17 Mar 2016, at 18:04, Dearlove, Christopher (UK) <
> [e-mail]> wrote:
>
>
>
> OK, so we have a message that mutates by:
>
> - Modifying hop count/limit.
>
> - Modifying a metric value.
>
> Anything else?
>
>
>
> As mutating (other than hop count/limit) messages aren’t covered by 5444
> or any derivative document (but only recommended against, not banned) that
> you may need to make the message otherwise immutable (no deconstruction and
> rebuilding, other than guaranteed unchanging) that would have to be
> specified by AODVv2. (Easy to say, but needs saying.)
>
>
>
> With you so far.
>
>
>
> Then that information is not in a guaranteed fixed location given by a
> simple offset. So any signature algorithm that finds it and ignores it or
> aggregates on it is specific to OLSRv2.
>
>
>
> Surely you mean AODVv2
>
>
>
> So standard 7182 ICVs don’t do the job, you would need an AODVv2
> specialised variant. Which is the sort of thing that the message specific
> TLV space is there for, I’d be strongly against a “but ignore the value of
> this specific TLV should it occur” being in the general space. However it
> can easily be defined by reference to 7182 (“this TLV is like that TLV,
> except if an X TLV is present, set its value field to zero”).
>
>
>
> Messy, but could work.
>
>
>
> Not that messy, actually, although clearly not as nice as “fixed offset”.
>
>
>
> That said, I am arguing for the base spec being:
>
>
>
>             “make the message otherwise immutable (no deconstruction and
> rebuilding, other
>
>              than guaranteed unchanging)” which is afforded by forwarding
>
>
>
>                                     +
>
>
>
>             RFC7182 Timestamps and ICVs.
>
>
>
>                                     +
>
>
>
>             RFC7183 style text bringing it all together.
>
>
>
> The “aggregated signatures around mutable field” would very be an
> experimental extension.
>
>
>
> What I object to is, if the base spec specifically renders such extensions
> impossible
>
>
>
>
>
>
>
> *--*
>
>
>
>
> *Christopher Dearlove Senior Principal Engineer BAE Systems Applied
> Intelligence Laboratories *
> *__________________________________________________________________________
> *
> *T*:  [phone] <%2B44%20%280%291245%20242194>  |  *E: *
> [e-mail]
>
> BAE Systems Applied Intelligence, Chelmsford Technology Park, Great
> Baddow, Chelmsford, Essex CM2 8HN.
> www.baesystems.com/ai
>
> BAE Systems Applied Intelligence Limited
> Registered in England & Wales No: 01337451
>
> Registered Office: Surrey Research Park, Guildford, Surrey, GU2 7YP
>
>
>
> *From:* Lotte Steenbrink [mailto:[e-mail]
> <[e-mail]>]
> *Sent:* 17 March 2016 16:48
> *To:* Dearlove, Christopher (UK)
> *Cc:* [e-mail]; Mobile Ad Hoc Networks mailing list
> *Subject:* Re: [manet] Message integrity and message mutability (was RE:
> draft-ietf-manet-aodvv2-13 review - a couple of big ticket Items)
>
>
>
>
>
> **** WARNING ****
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>
> Hi all,
>
>
>
> Am 17.03.2016 um 17:44 schrieb Dearlove, Christopher (UK) <
> [e-mail]>:
>
>
>
> Good point about whether you just pass on one cost or a set of costs. As I
> said, not looked at details - I will, when time permits. One cost is much
> easier, and yes, it reduces the fixed size aggregated signatures problem to
> “just” one of computational load.
>
>
>
> For the record, Thomas’ understanding is correct; the cost is one
> aggregated value.
>
>
>
> Best regards,
>
> Lotte Steenrbink
>
>
>
>
>
> *--*
>
>
>
>
> *Christopher Dearlove Senior Principal Engineer BAE Systems Applied
> Intelligence Laboratories *
> *__________________________________________________________________________
> *
> *T*:  [phone] <%2B44%20%280%291245%20242194>  |  *E: *
> [e-mail]
>
> BAE Systems Applied Intelligence, Chelmsford Technology Park, Great
> Baddow, Chelmsford, Essex CM2 8HN.
> www.baesystems.com/ai
>
> BAE Systems Applied Intelligence Limited
> Registered in England & Wales No: 01337451
>
> Registered Office: Surrey Research Park, Guildford, Surrey, GU2 7YP
>
>
>
> *From:* [e-mail] [mailto:[e-mail]
> <[e-mail]>]
> *Sent:* 17 March 2016 16:38
> *To:* Dearlove, Christopher (UK)
> *Cc:* Mobile Ad Hoc Networks mailing list
> *Subject:* Re: Message integrity and message mutability (was RE: [manet]
> draft-ietf-manet-aodvv2-13 review - a couple of big ticket Items)
>
>
>
>
>
> **** WARNING ****
>
>
>
> *This message originates from outside our organisation, either from an
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> click on any links, open any attachments or reply. For information
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>
>
>
> On 17 Mar 2016, at 17:30, Dearlove, Christopher (UK) <
> [e-mail]> wrote:
>
>
>
> I appreciate Thomas’s comments about the limitations of message
> regeneration, but I would be a bit less absolute.
>
>
>
> The issues over end to end authentication and more advanced signatures are
> valid. I need to read the given reference on aggregate signatures to
> increase my knowledge (thanks for it), but my understanding of the
> possibilities in this field may offer a solution to the problem, but with
> some other issues (possibly including a new type of TLV).
>
>
>
> But the hop count/limit point I don’t fully agree with, you can regenerate
> with an incremented/decremented count/limit, which leaves the ability to
> prevent messages propagating indefinitely, including expanding ring
> searches, and retains the ability to use RFC 5497 interval and validity
> times that might be useful with an expanding ring search (or might not).
>
>
>
> But the key issue is that AODVv2 wants to accumulate metrics. I still
> haven’t got to the bottom of many details here, but let’s for the moment
> just consider that conceptually.
>
>
>
> It’s hard to handle end to end. Charlie’s draft attempts to do an end to
> end of some information, not this information. I’m not sure if that’s
> useful (and the specialised format is better avoided if possible). Other
> approaches are hop by hop (might as well use packet signatures) and shared
> key (might as well go hop by hop). Pairwise signatures for each pair of
> routers I’m discounting as scaling terribly. In the interests of
> completeness let’s mention not accumulating metrics, which puts us back to
> hop count and that’s not ideal either.
>
>
>
> I don’t think there is an ideal solution. (I like ideas I’ve seen about
> aggregating, but that has some issues of its own, even apart from
> computational load.) I’d love to be proved wrong - someone with the perfect
> solution to come along.
>
>
>
> Which means that either we make an arbitrary choice - which will be
> disagreed with, but needs discussing first - or create something flexible.
> Unfortunately flexible in that regard constrains in others, e.g. some
> (many? most?) aggregating signatures need fixed data sizes (which we can do
> by defining a TLV that “fills up” with hop count, but that has a cost too).
>
>
>
> I have been told by people much more well versed in this than I in
> cryptology, that the correct answer is “some”.
>
>
>
> That said, "AODVv2 wants to accumulate metrics” — does that mean that the
> message grows as it is being forwarded, and that the recipient of a
> RREQ/RREP will know the individual costs of each path segment? My
> understanding is, that the recipient will get “the sum the costs of each
> path segment” which should be fitting within a fixed size?
>
>
>
> Thomas
>
>
>
>
>
>
>
> Sorry, no answers, just comments. And I’m not addressing Thomas’s later
> points here.
>
>
>
> *--*
>
>
>
>
> *Christopher Dearlove Senior Principal Engineer BAE Systems Applied
> Intelligence Laboratories *
> *__________________________________________________________________________
> *
> *T*:  [phone] <%2B44%20%280%291245%20242194>  |  *E: *
> [e-mail]
>
> BAE Systems Applied Intelligence, Chelmsford Technology Park, Great
> Baddow, Chelmsford, Essex CM2 8HN.
> www.baesystems.com/ai
>
> BAE Systems Applied Intelligence Limited
> Registered in England & Wales No: 01337451
>
> Registered Office: Surrey Research Park, Guildford, Surrey, GU2 7YP
>
>
>
> *From:* manet [mailto:[e-mail] <[e-mail]>] *On
> Behalf Of *[e-mail]
> *Sent:* 17 March 2016 16:00
> *To:* Mobile Ad Hoc Networks mailing list
> *Subject:* [manet] draft-ietf-manet-aodvv2-13 review - a couple of big
> ticket Items
>
>
>
>
>
> **** WARNING ****
>
>
>
> *This message originates from outside our organisation, either from an
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> click on any links, open any attachments or reply. For information
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> * that you can look out for in emails you receive, click here
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>
>
> Dear all,
>
>
>
> Apologies for not having gotten this done sooner - day-job leaving few
> spare cycles.
>
>
>
> I’ve previously offered reviews and comments, and some of those have been
> addressed in the latest I-D — others have not, but should be. I recall that
> there was some mail attempting to rebut parts of the review, and I will dig
> it out and reply to that.
>
>
>
> With that being said, I have reviewed the latest version of the document,
> and full details will be forthcoming. There’re a couple of
> big-ticket/architectural items that I want to address up front, as I
> believe that before we have those hammered out, it will be useless to go
> into details. Note, I do not claim that this is an exhaustive list of “big
> ticket items”, but that’s as far as I have gotten in thinking this through.
>
>
>
> I also bring these up as they are items that have been brought up
> repeatedly over the past years, but not resolved nor discussed.
>
>
>
> *Loops*
>
> Just to bring this out: I share Chris’ worry about conflicting and
> concurrent statements from the authors on “There are no loops possible” and
> “We need to fix two situations where loops can occur” and “we are still
> investigating some loop conditions”
>
>
>
> I particularly worry that this is not a discussion had in public, but
> apparently in some other forum…
>
>
>
>
>
> *Intermediate Route Replies, and all of section 10*
>
> Section 10 contains a set of “vaguely specified extensions”, which is
> incoherent with the intended status indicated for this document.
>
>
>
> Specifically, and this is not unrelated to the point about loops above,
> intermediate RREPs (section 10.3) are a potential source for loops.
>
>
>
> Expanding Ring Multicast (section 10.1) is not documented in a way that
> can be implemented (and also, see “Forwarding-vs-regeneration” below, it is
> in the present form of this protocol impossible), etc.
>
>
>
>
>
> *Forwarding-vs-regeneration*
>
> Recent exchanges on the list made me understand that protocol control
> messages are *not* forwarded, but are consumed at each hop, then a new
> message with (almost-but-not-quite) the same content is generated and
> transmitted.
>
>
>
> I have thought some more on this (& read some of the exchanges on the list
> on this topic by Chris, Ulrich, and others), and I am convinced that this
> is not the right way to go, *at least* for the following reasons:
>
>
>
>
>
>             o          *It renders the hop-limit/hop-count fields in the
> RFC5444 message header useless.*
>
>                         This would not be bad if the functionality offered
> by those fields was not useful
>
>                         — sadly, it is. For example, for scope limited
> flooding (expanding ring search, and
>
>                         such) which may be of interest, and which require
> hop-limit.
>
>                         A hop-count field may also provide a “cheap” (in
> terms of overhead) additional piece
>
>                         of information to use conjunctively with a “real”
> metric.
>
>
>
>                         The only practical solution would be to
> re-introduce these functions by way of inserting a
>
>                         MessageTLV — which (i) is not specified in this
> document, and (ii) which would just
>
>                         serve to render messages bigger than strictly
> needed.
>
>
>
>                         Scope limited flooding  does seem to be a
> necessary requirement, if for no
>
>                         other reason than to prevent information from
> “circulating forever in the network”.
>
>
>
>             o          *It makes end-to-end authentication unnecessarily
> hard.*
>
>                         I think Chris called this out already, but it
> bears repeating: S generates a message
>
>                         (say, a RREQ), and includes an ICV calculated over
> the content of the message.
>
>                         For any recipient to be able to validate the ICV,
> the message has to be exactly
>
>                         the same — not just in content, but in structure —
> as what was generated.
>
>
>
>                         “Regenerating” rather than “forwarding” messages
> means, that the intermediate
>
>                         router “regenerating” the RREQ may chose a
> different structure (e.g., include TLVs
>
>                         in a different order).
>
>
>
>                         The proposal from
> https://tools.ietf.org/html/draft-perkins-manet-aodv-e2esec-00
>
>                         is to add constraints on (i) the set of elements
> to include in a signature and (ii) the
>
>                         order of these elements.
>
>
>
>                         One problem with that approach is (i): if an
> extension adds a message TLV, or an
>
>                         Address TLV, to a message, then that will not be
> “covered” by the proposed e2esec TLV.
>
>                         Rather for *each* extension developed, an “updates
> e2esec” clause needs to be done.
>
>
>
>                         I’d say that this approach would be prone to
> errors — and add entropy to the process
>
>                         of designing protocol extensions. The alternative,
> a message being generated by the
>
>                         source and *forwarded* (as we do in OLSRv2, for
> example) would allow ICV TLVs
>
>                         (even, allow reuse of those specified for OLSRv2)
> for covering a message and
>
>                         extensions.
>
>
>
>                         “But what about the metrics value which will
> change on each hop”, you may say?
>
>                         Fortunately, that is relatively easy to handle:
> simply zero out the value of that TLV when
>
>                         generating or verifying the ICV MessageTLV. And
> use Packet-TLVs for hop-by-hop
>
>                         authentication, if needed (but, see below).
>
>
>
>             o          *It prevents the use of more clever/advanced
> signature schemes/ICVs*
>
>                         Aggregate signature algorithms (
> https://crypto.stanford.edu/~dabo/papers/aggsurvey.pdf)
>
>                         exist, and an interesting use-case can be found in
> also reactive protocols, allowing verifying
>
>                         not “just” the end points, but also the
> intermediaries (again, with the appropriate “zero out”
>
>                         discussed above, or something smarter).
>
>                         Regeneration of messages, rather than forwarding,
> renders that impossible (or, if used,
>
>                         updating to
> https://tools.ietf.org/html/draft-perkins-manet-aodv-e2esec-00)
>
>
>
> There are other reasons, but the above are those that jump at me as
> immediate show-stoppers.
>
>
>
> I do honestly not see what possible benefit there is from “regeneration” —
> but I see very clear inconveniences, and security is not the least of
> these. Insisting on “regeneration” requires development of “non-general
> workarounds” as pointed out above.
>
>
>
> *Security Considerations*
>
> This is an always thorny subject. When OLSRv2 was going through the
> process we got a thorough education in how little we knew about security
> from the SEC-ADs, and had to spend about a year or so developing RFC7183.
> The bottom line is, that this protocol needs its “RFC7183  equivalent”,
> either as part of the main document, or as an independent document.
> currently, that is not the case.
>
>
>
> A minima, looking at BCP72 and BCP107 — taking inspiration from RFC7183
> might be aw good idea, as that was the most recent that went through the
> SEC AD. Regardless of how, however, a “mandatory to implement” security
> mechanism most be specified (I think the right term was “MUST implement,
> SHOULD use”), in sufficient detail to ensure interoperable implementations.
>
>
>
> As an example, both [RFC6130] and [RFC7181] set out that that:
>
>
>
>       On receiving a ... message, a router MUST first check if the
>
>       message is invalid for processing by this router
>
>
>
> and then proceed to give a number of conditions that, each, will lead to a
> rejection of the message as "badly formed and therefore invalid for
> processing” — a list which RFC7183 then amended. That gave a “hook” for
> RFC7183 for inserting “rejection”. Idem for message generation.
>
>
>
> If I was to do RFC7181/RFC6130 today, I would include that directly into
> the protocol specifications. It turned out to be more overhead (and slow
> down publication anyways) to do it as separate documents.
>
>
>
> Secondly, we need to be a lot more rigid in terms of what ICVs,
> Timestamps, etc. are added/removed, and what that brings.
>
>
>
> For example (with the assumption that messages are *forwarded* and *not*
> regenerated), this could be one option:
>
>
>
>                         o          When a RREQ, RREP message is generated,
> add an ICV Message TLV, which is calculated <this way>
>
>                                      …(take inspiration from RFC7183 here)
>
>
>
> ...
>
> [Message clipped]
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