Subject: [xmpp] SCRAM as MTI?

From: Peter Saint-Andre <[email-masked]>
Date: Mon, 14 Sep 2009 10:04:20 -0600

The SASL SCRAM mechanism is currently in IETF Last Call:

http://www.ietf.org/internet-drafts/draft-ietf-sasl-scram-07.txt

This mechanism is intended to replace DIGEST-MD5. Does it make sense for
the XMPP WG to specify SCRAM as mandatory-to-implement?

Peter

- --
Peter Saint-Andre
https://stpeter.im/

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From: Simon Josefsson <[email-masked]>
Date: Tue, 15 Sep 2009 13:21:54 +0200

> the XMPP WG to specify SCRAM as mandatory-to-implement?

Yes. (although I'm not a XMPP implementer)

Did XMPP make use of DIGEST-MD5 security layers, in theory
(specification) and in practice (implementations)?

/Simon

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From: Fabio Forno <[email-masked]>
Date: Tue, 15 Sep 2009 14:15:39 +0200

2009/9/14 Peter Saint-Andre <[email-masked]>:
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
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Does SCRAM support a digest based auth like DIGEST-MD5 or, better,
does it allow secure authentication over an unsecure channel? In that
case definitively yes, since there many case in which I don't need
TLS, but at least i want to protect my credentials.

-- 
Fabio Forno, Ph.D.
Bluendo srl http://www.bluendo.com
jabber id: [email-masked]

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From: Simon Josefsson <[email-masked]>
Date: Tue, 15 Sep 2009 14:20:17 +0200

Fabio Forno <[email-masked]> writes:

> does it allow secure authentication over an unsecure channel?

Yes.  (Of course it depend on your definition of "secure"..)

> In that case definitively yes, since there many case in which I don't
> need TLS, but at least i want to protect my credentials.

You are still vulnerable to active attackers that hijack the connection
after you have authenticated yourself.  But I agree in some situations
that is an acceptable risk.

To use SCRAM (or CRAM-MD5 or DIGEST-MD5) you need a secure channel.  If
you used DIGEST-MD5 with security layers you will need SCRAM+TLS
instead.  SCRAM does not provide any SASL security layers.  I hope you
weren't using DIGEST-MD5 security layers, because they weren't that
good...

/Simon

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From: Fabio Forno <[email-masked]>
Date: Tue, 15 Sep 2009 14:33:13 +0200

> that is an acceptable risk.

Sure, the rationale is minimizing damage: most the times I can survive
an hijacked session, while a stolen password could make me cry.

> weren't using DIGEST-MD5 security layers, because they weren't that

Well indeed that's the only option offered by most servers if you
can't run TLS on the client (for some mobiles it's too heavy), and
since users can choose any server..

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From: Peter Saint-Andre <[email-masked]>
Date: Tue, 15 Sep 2009 07:54:36 -0600

On 9/15/09 5:21 AM, Simon Josefsson wrote:
> (specification) 

In theory, yes (by inheritance from RFC 2831).

> and in practice (implementations)?

Not in practice as far as I know.

Peter

- --
Peter Saint-Andre
https://stpeter.im/

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From: Peter Saint-Andre <[email-masked]>
Date: Tue, 15 Sep 2009 14:33:08 -0600

> weren't using DIGEST-MD5 security layers, because they weren't that

As mentioned, I don't think that anyone was using DIGEST-MD5 security
layers in XMPP. If I'm wrong about that I'd love to be corrected.

Peter

- --
Peter Saint-Andre
https://stpeter.im/

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From: Justin Karneges <[email-masked]>
Date: Tue, 15 Sep 2009 14:37:28 -0700

> layers in XMPP. If I'm wrong about that I'd love to be corrected.

Psi supports this feature but nobody knows it.  You have to pair the client 
with cyrus-sasl, which is not how we ship by default.

I'm not aware of anyone using DIGEST-MD5 security layers in practice.  That's 
a shame, because I do think it's a useful feature.  Even if the security 
isn't that good, it's certainly better than unchecked TLS (something people 
still do today).

-Justin

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From: Kurt Zeilenga <[email-masked]>
Date: Tue, 15 Sep 2009 23:58:57 +0100

> the XMPP WG to specify SCRAM as mandatory-to-implement?

Yes.

-- Kurt