Subject: [MSEC] Multisender environment

From: "Alan Tamer Vasques" <[email-masked]>
Date: Thu, 2 Jun 2005 01:12:00 -0300

Hi, all,

I'm studying multicast security in multisender scenarios but I'm not understanding some topics, mainly in the anti-replay protection.

Well, GSAKMP supports this kind of scenario without trouble, because each sender has its own SA (i.e. Data Security SA), right?

On the other hand, the newer IPSec drafts (AH, ESP, IKE) say that the SA is shared among the senders and, like that, the sequence number replay protection doesn't work accordingly in multisender environment.

My questions are:

- If GSAKMP has the solution to multisender environment, why doesn't IPSec WG adopts it in the official implementation?
- Will the MSEC protocols be aggregated with IPSec?
- If not, why IPSec is trying to support multicast?

Thanks in advance.

Regards,

Alan Tamer Vasques
www.alan.pro.br
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From: Brian Weis <[email-masked]>
Date: Wed, 01 Jun 2005 22:16:48 -0700

Hi Alan,

Alan Tamer Vasques wrote:
> Hi, all,
>  
> I'm studying multicast security in multisender scenarios but I'm not 
> understanding some topics, mainly in the anti-replay protection.
>  
> Well, GSAKMP supports this kind of scenario without trouble, because 
> each sender has its own SA (i.e. Data Security SA), right?
>  
> On the other hand, the newer IPSec drafts (AH, ESP, IKE) say that the SA 
> is shared among the senders and, like that, the sequence number replay 
> protection doesn't work accordingly in multisender environment.

These documents should say that the SA *could* be shared among the 
senders. It would still be possible to define an individual IPsec SA for 
each sender, just as you describe above.

> My questions are:
>  
> - If GSAKMP has the solution to multisender environment, why doesn't 
> IPSec WG adopts it in the official implementation?

Yes. You're right that anti-replay protection is an open topic. We may 
address this in an upcoming MSEC draft document that clarifies some of 
the issues with using IPsec to protect IP multicast packets.

Thanks,
Brian

> www.alan.pro.br <http://www.alan.pro.br>
> 
> 
> ------------------------------------------------------------------------
> 

-- 
Brian Weis
Advanced Security Development, Security Technology Group, Cisco Systems
Telephone: +1 408 526 4796
Email: [email-masked]
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---

From: Lakshminath Dondeti <[email-masked]>
Date: Thu, 02 Jun 2005 08:19:50 -0400

Hi Alan,

Those are excellent questions and I think Brian addresses them to an 
extent in his email.  But since multisender replay protection might be 
one of the topics that might be under discussion for some new work we 
are pursuing,  I encourage you to open a discussion thread so Brian and 
others can share their thoughts too and we can work toward consensus on 
what's doable. 

best,
Lakshminath

Alan Tamer Vasques wrote:

> On the other hand, the newer IPSec drafts (AH, ESP, IKE) say that the 
> SA is shared among the senders and, like that, the sequence number 
> replay protection doesn't work accordingly in multisender environment.
>  
> My questions are:
>

---

From: "Alan Tamer Vasques" <[email-masked]>
Date: Thu, 2 Jun 2005 12:24:38 -0300 (BRT)

Hi Brian,

Actually, the ESPv3 draft (
http://www.ietf.org/internet-drafts/draft-ietf-ipsec-esp-v3-10.txt ) says:

"Sharing an SA among multiple senders is permitted, though generally not
recommended. ESP provides no means of synchronizing packet counters among
multiple senders or meaningfully managing a receiver packet counter and
window in the context of multiple senders. Thus, for a multi-sender SA,
the anti-replay features of ESP are not available."

AH draft has the same text.

You said that it's possible to define an individual IPsec SA for each
sender, but imagine this scenario: I have two GCKS that manage a
multi-sender group (where each GCKS is responsible for one or more
senders) and a receiver that listens to all senders. If the group
controllers attribute the same SPI (it can happen) to two different
senders, how the receiver can identify the correct one? Replay protection
will not function correctly, right?

Regards,

Alan Tamer Vasques
www.alan.pro.br

---

From: Brian Weis <[email-masked]>
Date: Thu, 02 Jun 2005 09:34:46 -0700

Hi Alan,

> AH draft has the same text.

Right, now anti-replay is currently "not available" for a multi-sender 
SA because how to do it has not been agreed upon and specified. We're 
hoping to fix that.

> will not function correctly, right?

Actually, this is a matter of making sure the SA lookup finds the 
correct SA. You're correct that in RFC 2401 this is a problem because 
the three-tuples of {protocol, destination, SPI} of the two SAs would be 
identical. This was corrected in RFC2401bis. Section 4.1 of 
http://www.ietf.org/internet-drafts/draft-ietf-ipsec-rfc2401bis-06.txt 
describes when the source address is used in the SA lookup. This was 
added for the exact case you mention. Once the correct SA is found, 
replay protection should function correctly.

Thanks,
Brian