Subject: RE: (D)TLS considered harmful: was Re: [Isms] Coming to consensus

From: "Fleischman, Eric" <[email-masked]>
Date: Fri, 1 Jul 2005 11:56:32 -0700

Tom,

I am sorry that my lazy typing "(D)TLS" was misleading. In the future, I
could type DTLS/TLS, if that would be clearer or whatever reference
mechanism you prefer.

I have no problems with your characterizations of DTLS. I also recognize
that its lower maturity means that there are more risks for us to
leverage DTLS than there is adopting the mature TLS or SSH alternatives.
However, I can't think of a UDP variant with stronger credentials (i.e.,
it is based upon TLS) and greater promise than DTLS. If anyone can name
a better UDP candidate, please do so. 

However, if it is actually the case that DTLS is the only (or best)
alternative enabling ISMS to support SNMP over UDP transports, then the
next question for our WG is "how important is the preservation of a
transport choice for SNMP?"

My own conclusion is that it is important, because SNMP's performance
differs as a partial function of its underlying transport, such that
each alternative has differing performance behaviors more suited to
different environments/uses. I value and leverage this distinction
because I work in different environments. Individuals with a more
uniform operating environment may perhaps not value this flexibility.
That's fine, but, as I argued previously within this WG in regards to
authentication infrastructures, I believe that we should enable greater
flexibility to the fullest extent that we can because SNMP users operate
in so many diverse environments. This is why I recommend an approach
that could support both TCP and UDP.

--Eric 

-----Original Message-----
From: Tom Petch [mailto:[email-masked]] 
Sent: Friday, July 01, 2005 10:22 AM
To: Fleischman, Eric; [email-masked]
Subject: (D)TLS considered harmful: was Re: [Isms] Coming to consensus 

I think the use of the term (D)TLS somewhat misleading.

TLS, reliable transport based, a comprehensive set of I-Ds updating well
established RFC, in turn building on extensive experience of the similar
but differently named SSL, I regard as a mature standard, worthy of
serious consideration for any security issue.

DTLS is a single I-D, in the RFC editor queue (thanks for that), expects
to achieve reliable transport with 64 bits of extra header.  Its
pedigree is impeccable but it is untested. Will it fly? will it prove
vulnerable to some class of attacks, will it be widely available, will
it go on being updated in parallel with TLS?

So I see two very different protocols even if in their elements of
security they share a common set of methods.  To refer to them together
as (D)TLS as if were something like FTP which can be configured to run
over TCP or UDP I think misleading.

Tom Petch

_______________________________________________
Isms mailing list
[email-masked]
https://www1.ietf.org/mailman/listinfo/isms

---

From: "Tom Petch" <[email-masked]>
Date: Sat, 2 Jul 2005 09:37:04 +0200

No problem; yes, I would prefer DTLS/TLS as a reference to the two jointly.

I sense a disagreement with you over the UDP/TCP question (which, unfortunately
but inevitably, is bound up with the TLS, DTLS, SSH etc question).

I agree that it would be nice if there were a choice of running SNMP over TCP or
UDP but in practice, I don't see that choice in the marketplace (in the way I do
for eg ftp).  The port numbers are allocated but I don't see the products.
Hence my question to Juergen.

And I see confirmation of this in the fact that the RFC is Experimental.  I
believe it would need to be Standards Track for the work of isms to progress and
that too raises issues of its availability

Tom Petch

----- Original Message -----
From: "Fleischman, Eric" <[email-masked]>
To: "Tom Petch" <[email-masked]>; <[email-masked]>
Sent: Friday, July 01, 2005 8:56 PM
Subject: RE: (D)TLS considered harmful: was Re: [Isms] Coming to consensus

Tom,

--Eric

-----Original Message-----
From: Tom Petch [mailto:[email-masked]]
Sent: Friday, July 01, 2005 10:22 AM
To: Fleischman, Eric; [email-masked]
Subject: (D)TLS considered harmful: was Re: [Isms] Coming to consensus

Tom Petch

---

From: Juergen Schoenwaelder <[email-masked]>
Date: Sat, 2 Jul 2005 22:55:12 +0200

On Sat, Jul 02, 2005 at 09:37:04AM +0200, Tom Petch wrote:

> believe it would need to be Standards Track for the work of isms to progress 
> and that too raises issues of its availability

SNMP over TCP is SNMP over TCP. If someone specifies SNMP over SSH (or TLS)
then this is SNMP over SSH (or TLS). I don't think you need SNMP over TCP 
to specify and implement SNMP over SSH (or TLS).

/js

P.S. Looking at the boxes I have access to, many do ssh. Some do TLS and 
     none of them does DTLS or BEEP. (At least not that I am aware of this.
     Perhaps I am having the wrong boxes. ;-)

-- 
Juergen Schoenwaelder		    International University Bremen
<http://www.eecs.iu-bremen.de/>	    P.O. Box 750 561, 28725 Bremen, Germany

---

From: "Tom Petch" <[email-masked]>
Date: Sun, 3 Jul 2005 09:49:47 +0200

<inline>
Tom Petch

----- Original Message -----
From: "Juergen Schoenwaelder" <[email-masked]>
To: "Tom Petch" <[email-masked]>
Cc: "Fleischman, Eric" <[email-masked]>; <[email-masked]>
Sent: Saturday, July 02, 2005 10:55 PM
Subject: Re: (D)TLS considered harmful: was Re: [Isms] Coming to consensus

> to specify and implement SNMP over SSH (or TLS).

Yeeeeees, I agree ... in protocol stack terms.  But turning to the SSH I-D I
quoted earlier, SSH needs a reliable transport.  I did not say reliable equals
TCP at that time, Eric was rather stronger in support of that.

But if I have a choice of existing transports, and the RFC allow me the choice
of
TCP, UDP, Ethernet, OSI, IPX, Appletalk
then I am likely to choose TCP for reliability.  I then believe SNMP runs over
SSH which runs over TCP which, I believe, needs a standards track document.

Or do you see an isms I-D specifying both how SNMP maps onto SSH as a subsystem
and the implications thereon of using TCP (currently only specified in your
RFC)?

Or do you see unsecured SNMP running over raw UDP while secured runs over SSH
over TCP with no need for any specification about TCP?

Or do you see UDP as reliable enough for SSH (seriously)?

I cast this in terms of SSH but the questions are much the same with  s/SSH/TLS/

>      Perhaps I am having the wrong boxes. ;-)

I find this information very helpful; it reinforces my more limited experience.

---

From: Eliot Lear <[email-masked]>
Date: Sun, 03 Jul 2005 12:39:04 +0200

>      Perhaps I am having the wrong boxes. ;-)

This is a fair point, but it is not the only consideration.  The 
flexibility we need today, pragmatically speaking, is for a way for 
either side to initiate queries through NATs, firewalls, and associated 
gook.  You *could* implement this flexibility in SSH, but nobody has, so 
far as I know.

Eliot

---

From: Juergen Schoenwaelder <[email-masked]>
Date: Sun, 3 Jul 2005 17:26:24 +0200

On Sun, Jul 03, 2005 at 09:49:47AM +0200, Tom Petch wrote:

> I then believe SNMP runs over

SNMP over SSH would need a standards-track document - SSH usually runs over
TCP - this may be mentioned in such an SNMP over SSH document but this is
not the same as SNMP over TCP.
 
> Or do you see an isms I-D specifying both how SNMP maps onto SSH as a 
> subsystem and the implications thereon of using TCP (currently only 
> specified in your RFC)?

The SNMP over TCP RFC defines things such as port numbers to use, minimum 
required max message size, how the serialization and framing is done and 
so one. Some of this might apply to SNMP over SSH while other things do 
not. 

An example: SNMP over TCP says how SNMP messages are serialized and how 
the framing on a TCP connection works. This clearly does not apply to 
SNMP over SSH since SSH does the framing in a quite different way. The
holds true if you s/SSH/TLS.

/js