Subject: [MSEC] Re: I-D ACTION : Simple Multicast Receiver Access Control

From: Ghassan Chaddoud <[email-masked]>
Date: Fri, 23 Nov 2001 15:07:24 +0100

Hi,
I have two comments on this draft:

1) in 4.2. 

The host IP address is used, in the access token,to prevent another host
outside the same network to use the same access token. Why you don't
replace the IP address by  the network ID ( a prefixe), such that the
host can use dynamic configuration (ie DHCP).

2) in 2.2.
... End-to-end data encryption ensures data integrity, source
authentication, and data confidentiality: 
I am not sure that in the case of multicast (n-to-n), end-to-end data
encryption can ensure source authentication!

Regards

-- 
Ghassan CHADDOUD

LORIA/INRIA

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From: Thomas Hardjono <[email-masked]>
Date: Mon, 26 Nov 2001 16:57:57 -0500

>host can use dynamic configuration (ie DHCP).

Actually, the aim is to prevent another host *inside* the same network
to initiate a join to a group that previously did not have any
membership in that (non-member) host's subnet.

Thus, the two problems are:

   - preventing illegal "First Joins", which pulls the multicast distribution
     tree to a subnet that has no members.

   - preventing illegal "Last prunes", which prunes the multicast
     distribution tree from a subnet that still has members.

>encryption can ensure source authentication!

Correct.  End-to-End encryption with a symmetric key will not
provide source-authentication.  However, the aim of the draft is
provide member access control at the routing level, above which
(or on which) encrypted data flows.

This draft is only one part of 3-part solution that is needed to
provide security for IP multicast:

    1. Sender and Receiver access control (from the edge of the network
       to the distribution tree).

    2. Multicast routing protection (to ensure multicast control packets
       are authentic and thus preserves the correct routing behavior)

    3. Data/content protection (in the form of encryption, accompanied
       by the group key management protocol, etc.).

cheers,

thomas
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From: "Haixiang He" <[email-masked]>
Date: Tue, 27 Nov 2001 10:52:31 -0500

> host can use dynamic configuration (ie DHCP).

What do you gain by using prefix? Do you mean after the host get the Access
Token, the host may change its IP address?

> encryption can ensure source authentication!

I mean group authentication here. My mistake!

Haixiang

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From: Ghassan Chaddoud <[email-masked]>
Date: Wed, 28 Nov 2001 10:06:20 +0100

> Token, the host may change its IP address?

I mean if the host obtains an access token for an IP address A1, then if
this host reboots and uses DHCP,  its new address, A2, would be
different from A1. Consequently it will not be capable to join another
groups. And, since the access token, is used to prevent another host
*outside* the same network to use the same access token. You do't care
about hosts *inside* the network. For this reason, the use of prefix ( a
prefix could represent the set of addresses used by DHCP, if it is used)
can resolve the problem of dynamic configuration of hosts. 

Ghassan

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From: "Haixiang He" <[email-masked]>
Date: Wed, 28 Nov 2001 10:37:49 -0500

> can resolve the problem of dynamic configuration of hosts.

I did not think about this scenario in greater details. The problem with using
prefix is that it does not work well with switch network such as switch ethernet.
In switch network, two hosts connecting two different ports may have the same
prefix.

And also we did not try to apply this solution for mobile node at this time.

Haixiang