Re: [secdir] secdir review of draft-ietf-karp-bfd-analysis-06

Manav Bhatia <manav@ionosnetworks.com> Mon, 24 November 2014 05:15 UTC

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References: <alpine.BSF.2.11.1408181618010.1960@fledge.watson.org> <CAGS6MpC4XC8A0vaHGPUmFSGNF=_5+KUeZgkmQHbVkT_m3HckGQ@mail.gmail.com> <alpine.BSF.2.11.1411021334220.21474@fledge.watson.org>
Date: Mon, 24 Nov 2014 10:45:11 +0530
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From: Manav Bhatia <manav@ionosnetworks.com>
To: Samuel Weiler <weiler@watson.org>
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Cc: draft-ietf-karp-bfd-analysis.all@tools.ietf.org, The IESG <iesg@ietf.org>, secdir@ietf.org
Subject: Re: [secdir] secdir review of draft-ietf-karp-bfd-analysis-06
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Hi Sam,

I work for a fledgling startup and am able to spare very few cycles to IETF
and hence the delay. Please accept my apologies for that.


> In the other other two cases, I am not satisfied with the discussion to
> date.
>
>  Theoretically the two should use algorithms of similar strength.
>>
>
> Why?  (Explain your theory...)


 The attack vector for the BFD and the routing protocols would be similar.
There is no evidence (empirical or otherwise) till date that proves that
attacking one is more complex than the other.


>
>  In fact one could argue that BFD needs stronger algorithm since an attack
>> on BFD can bring down all your control protocols.
>>
>
> Has the WG had that discussion?


I thought this was common wisdom. If i were an attacker then i would aim at
bringing down BFD since it brings down the entire network along with it.
Given that its usually run in plaintext i would think that its the weakest
link.


>
>
>        Lastly, RFC5880 (the BFD spec) says:
>>          An attacker who is in complete control of the link between
>>       the
>>          systems can easily drop all BFD packets but forward
>>       everything else
>>          (causing the link to be falsely declared down), or forward
>>       only the
>>          BFD packets but nothing else (causing the link to be falsely
>>          declared up).  This attack cannot be prevented by BFD.
>>
>>       Given that, does it make sense to go to this pain to replace MD5
>>       and SHA1?
>>
>>
>> Sure, but such attacks are outside the scope of routing protocol security.
>>
>
> Do we have a solid definition of that scope?  (Where?)
>
> And how vulnerable would BFD be to off-link attackers anyway?  Are we
> doing all of this work solely to defend against on-link attackers who have
> only _incomplete_ control of the link?  (It may well be a stupid question,
> but, if it is stupid, then it should at least have an easy answer, right?)
>

Such attacks are out of scope. You can look at RFC 6862, section 3.3

Cheers, Manav

>
> -- Sam