Re: [conex] Stephen Farrell's No Objection on draft-ietf-conex-destopt-09: (with COMMENT)

Suresh Krishnan <> Fri, 02 October 2015 04:08 UTC

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From: Suresh Krishnan <>
To: Bob Briscoe <>, Stephen Farrell <>
Thread-Topic: [conex] Stephen Farrell's No Objection on draft-ietf-conex-destopt-09: (with COMMENT)
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Date: Fri, 02 Oct 2015 04:08:47 +0000
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Subject: Re: [conex] Stephen Farrell's No Objection on draft-ietf-conex-destopt-09: (with COMMENT)
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Hi Bob,
   Thanks for your clarification. Since the security section seems to 
potentially have some dependence on the text needed for audit to address 
Robert's Gen-ART review, is it possible for you and Mirja to work 
offline and agree to some text before presenting it to the IESG?


On 10/01/2015 06:06 PM, Bob Briscoe wrote:
> Stephen, Suresh,
> As the person that contributed some of the text for this IPsec section,
> I can see what's happened during the evolution of the doc...
> In section 4 it says
> CDO MUST be placed as the first option in the destination option
> header before the AH and/or ESP (if present).  IPsec Authentication
> Header (AH) MAY be used to verify that the CDO has not been modified.
> We started out writing Section 7 "Compatibility with use of IPsec" to
> answering the question:
> "What if IPsec is being used; how do we ensure ConEx is still visible?"
> The answer was the above rule about placing CDO before AH and/or ESP.
> In the process, we showed how endpoints that were already authenticating
> their IP headers with IPsec would automatically get coverage for the
> ConEx header. By some perverse document evolution process, this has become:
> [Old]
> If the transport network cannot be trusted, IPsec Authentication
> should be used to ensure integrity of the ConEx information.
> So I suggest the following change:
> [Proposed]
> If the endpoints are using the IPsec Authentication Header (AH) [RFC4302] to detect alteration of
> IP headers along the path, AH will also ensure the e2e integrity of the CDO header.
> Actually, both parts of the subsequent sentence are wrong as well:
> [Old]
> If an attacker would be able to remove the ConEx marks, this could cause an
> audit device to penalize the respective connection, while the sender
> cannot easily detect that ConEx information is missing.
> a) Removing ConEx marks would make audit ignore those packets, not drop
> them.
> b) And It's not hard to design a protocol for the sender to detect
> tampering with ConEx information.
> So I suggest instead:
> [Proposed]
> A network-based attacker could alter ConEx information to fool an audit
> function in a downstream network into discarding packets. An attack on
> one network from another by changing an immutable field can be traced,
> so it would be unlikely givennetwork operators care about their
> reputation.Nonetheless, if ConEx information was being altered within a
> network, IPsec AH or other more stealthy e2e integrity checks could be
> useful tools to help pin-point the attack location.
> No need to say this, but a similar attack is already possible: decrement
> TTL in one network to cause another network to drop packets. This is
> less easy to trace too, because it uses a mutable field.
> BTW, I designed the precursor to ConEx (re-ECN) to make it possible for
> networks to identify other rogue networks mounting such attacks, without
> needing e2e authentication. But all the inter-network security only
> works with ECN, not drop. When we decided to use ConEx to expose drop as
> well as ECN, I couldn't make the drop-based aspects support these nice
> security properties. That is admitted in conex-abstract-mech. But the
> ECN side of ConEx still supports all the inter-domain security. None of
> the inter-domain security techniques are written in the ConEx drafts,
> but they're in my PhD thesis, and referenced from conex-abstract-mech
> Security Considerations.
> Bob
> On 01/10/15 09:31, Stephen Farrell wrote:
>> Hiya,
>> On 01/10/15 04:52, Suresh Krishnan wrote:
>>> Hi Stephen,
>>>      Thanks for your comments. Please find responses inline
>>> On 09/30/2015 08:06 PM, Stephen Farrell wrote:
>>>> Stephen Farrell has entered the following ballot position for
>>>> draft-ietf-conex-destopt-09: No Objection
>>>> When responding, please keep the subject line intact and reply to all
>>>> email addresses included in the To and CC lines. (Feel free to cut this
>>>> introductory paragraph, however.)
>>>> Please refer to
>>>> for more information about IESG DISCUSS and COMMENT positions.
>>>> The document, along with other ballot positions, can be found here:
>>>> ----------------------------------------------------------------------
>>>> ----------------------------------------------------------------------
>>>> - section 7: "If the transport network cannot be trusted, IPsec
>>>> Authentication should be used to ensure integrity of the ConEx
>>>> information." Hmm. Transport networks cannot be trusted so the
>>>> first condition is always met. That means you are saying IPsec
>>>> should be used. I don't see how the key management required is
>>>> going to happen and even if it did, would that affect conex
>>>> calculations? I'm ok with an experiment on that basis though,
>>>> but it'd be better if the real relationship between this and IPsec
>>>> were more fully fleshed out somewhere as part of the experiment.
>>> I am not sure if the form of key management chosen would affect the
>>> conex calculations at all.
>> My point is that the key management implied here is basically not
>> going to happen. That means IPsec will not be used and hence conex
>> calculations will need to take into account the potential for routers
>> to mess with the CDO.
>> And I think the text of this would be better if it recognised the
>> improbability of IPsec being used in the wild, or else spoke to how
>> one could arrange experiments so that use of IPsec is more likely.
>> Cheers,
>> S.
>>> I did read RFC5406 and I am still not sure
>>> what can be said here about key management. I would really appreciate
>>> some pointers/suggestions/text here.
>>>> - The secdir review [1] touches on similar issues. I'm not sure if
>>>> that got a response, but it raises a good point that seems to me to
>>>> deserve a response.
>>>>       [1]
>>> I have added the following text in the Security Considerations section
>>> of my local copy. Will submit this version after the telechat will check
>>> with Robert. There is one item pending regarding audit in the Gen-ART
>>> review and that may end up affecting this text.
>>>       This document does not define how audit mechanisms work in protocols
>>>       that use this option and how those protocols can protect themselves
>>>       from likely attacks.  This option MUST only be used alongside
>>>       protocols that define the audit mechanisms and the means for
>>>       protecting against likely attacks on such mechanisms.
>>> Thanks
>>> Suresh
>> _______________________________________________
>> conex mailing list
>> --
>> ________________________________________________________________
>> Bob Briscoe