Subject: Re: MBone

From: "Kevin C. Almeroth" <[email-masked]>
Date: Fri, 13 Sep 2002 09:50:01 -0700 (PDT)

>>Multicast is necessarily a LOT weaker:
>>
>>      1) I can get a copy of packets by normal operation
>>      (join a group). there is no equivalent for UDP,
>>      notably for paths that aren't shared.

Again, not in all cases.  You over-simplify the effectiveness of scoping.
You can't have it both ways.  Yes, there is a situation where you can obtain
a copy of a multicast packet through standard operation.  But the fact
that scoping and addressing make it non-trivial and the fact that "normal"
operation doesn't prevent you from snooping UDP packets shrinks the
gap from a "LOT" weaker.  And as I said before, if data security is important,
effectively there is no gap. 

>>      2) UDP has application, network, and tunnel encryption that
>>      is both widely deployed and widely used. there is
>>      no equivalent for multicast.

I disagree...  a number of commercial multicast apps have encryption.
Don't try and argue now that some relative percentage of multicast apps
have less encryption than unicast apps.  You're comparing a protocol that 
has been around a lot longer than multicast and trying to make an 
apples-to-apples comparison based on less availability.

And for the record, multicast is UDP.

-Kevin

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From: Joe Touch <[email-masked]>
Date: Fri, 13 Sep 2002 10:29:09 -0700

> Again, not in all cases.  You over-simplify the effectiveness of scoping.

Unicast has TTLs too.

> that scoping and addressing make it non-trivial

Agreed - scoping sets some boundaries, but it's primitive as a
'security' mechanism, because everyone within those boundaries can very
easily get a backet.

The same is just not nearly as true for unicast.

> I disagree...  a number of commercial multicast apps have encryption.

Agreed. What I am asserting (by the above) is that security is clearly
important to the average user, and that the average user won't accept
obfuscation as a solution.

Joe

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From: Joe Touch <[email-masked]>
Date: Mon, 23 Sep 2002 15:12:19 -0700

> Again, not in all cases.  You over-simplify the effectiveness of scoping.

Scoping, like TTL, can limit the visibility of packet outside a
boundary, but cannot do much about other users inside that boundary.

PS - how can you know that the scope of ALL multicast exit paths have
been properly scoped to limit access outside of some physical locale?

> effectively there is no gap.

Users without root can run programs that listen to multicast addresses.
If that user is inside the scope boundary, game over.

As I said, weakER. IMO, still quite a lot weaker than unicast.

> apples-to-apples comparison based on less availability.

I can argue relative percentages just fine; we're talking about strength
today, not 'strength after X years of deployment'.

> And for the record, multicast is UDP.

As I was using it, agreed. (there are other protocols that use multicast
as well)

Joe