Re: [trill] TRILL IPsec encapsulation

Stephen Farrell <stephen.farrell@cs.tcd.ie> Thu, 23 July 2015 07:19 UTC

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Date: Thu, 23 Jul 2015 08:15:12 +0100
From: Stephen Farrell <stephen.farrell@cs.tcd.ie>
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To: Yaron Sheffer <yaronf.ietf@gmail.com>, trill@ietf.org
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Cc: kathleen.moriarty.ietf@gmail.com
Subject: Re: [trill] TRILL IPsec encapsulation
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Thanks Yaron, that's useful.

S

On 22/07/15 18:48, Yaron Sheffer wrote:
> I have read the TRILL-over-IP draft (draft-ietf-trill-over-ip-03) as a kind of 
> early SecDir review, focusing on its use of IPsec. Thanks to Donald Eastlake who 
> graciously provided me with a crash course on TRILL. He's not responsible for 
> any stupidity on my part, of course.
> 
> So here are some comments:
> 
> - The draft currently uses IPsec but not IKE or any kind of key management. The 
> end result is that data is being encrypted by very long-lived keys, not enjoying 
> the benefit of forward secrecy etc. Please use IKEv2 and do NOT use IPsec 
> directly.RFC 4107 explains why.
> - There is in fact IPsec-with-multicast, but it's not widely deployed and is 
> based on the obsolete IKEv1. Instead, I suggest to use unicast encapsulation 
> with IKEv2. I suppose this means that you'd want to only encapsulate data but 
> not IS-IS frames.
> - The draft currently derives encryption keys from IS-IS keys. This is 
> problematic at several levels:
>    * The IS-IS key is common to a large group of devices (a.k.a. "a group key") 
> and so is likely to be compromised.
>    * The key is used directly for encryption, as noted.
>    * The key is derived using HMAC, which is specified incorrectly in the draft 
> (one parameter instead of two).
>    * The derived key is identical for all routers/links.
> - I would suggest to use a derived key for authentication only, and to derive it 
> differently for each link - although I realize that this does not raise the 
> security level significantly. Something like: link-psk = HMAC(IS-IS-key, 
> 6-byte-system-id-1 | 6-byte-system-id-2).
> - Note that IKE generates a different encryption key for each link even if 
> everybody is using the same authentication key (pre-shared secret). But it's 
> still a bad practice for all principals to have the same key...
> - Longer term it would improve security hugely if each router had an 
> authenticated identity of its own. In other words, its own certificate and 
> private key.
> - Please don't define your own MTI algorithms. Just use RFC 7321.
> 
> Thanks,
>      Yaron
>