Subject: new milestones for charter update

From: Tom Yu <[email-masked]>
Date: Tue, 18 Dec 2007 13:10:48 -0500

These are milestones from the proposed charter update, modified to be
about four months later.  In about a week, if there are no objections,
I will submit the proposed charter to the IESG.

Done	initial I-D for DIGEST-MD5 to Historic
Done	WGLC I-D for DIGEST-MD5 to Historic
Feb 08	initial impl. report questionnaire
Feb 08	initial RFC4422bis
Feb 08	initial I-D for DIGEST-MD5 successor
Feb 08	DIGEST-MD5 to Historic I-D to IESG
Mar 08	send impl. report questionnaire
Apr 08	compile impl. questionnaire responses
Jun 08	WGLC RFC4422bis
Jun 08	WGLC DIGEST-MD5 successor
Jul 08	discuss impl. questionnaire responses
Aug 08	final impl. report
Aug 08	RFC4422bis to IESG
Aug 08	DIGEST-MD5 successor to IESG

---

From: Alexey Melnikov <[email-masked]>
Date: Thu, 20 Dec 2007 20:43:33 +0000

>Feb 08	DIGEST-MD5 to Historic I-D to IESG
This is Ok with me considering Sam's paternity leave and my business in 
the Lemonade WG.
But I would really like to have more or less solid SCRAM document before 
we obsolete DIGEST-MD5.

>Aug 08	DIGEST-MD5 successor to IESG

Date: Thu, 20 Dec 2007 20:43:33 +0000
From: Alexey Melnikov <[email-masked]>
To: Tom Yu <[email-masked]>
CC: [email-masked]
Subject: Re: new milestones for charter update
Sender: [email-masked]

>Feb 08	DIGEST-MD5 to Historic I-D to IESG
This is Ok with me considering Sam's paternity leave and my business in 
the Lemonade WG.
But I would really like to have more or less solid SCRAM document before 
we obsolete DIGEST-MD5.

>Aug 08	DIGEST-MD5 successor to IESG

Date: Thu, 20 Dec 2007 10:55:03 -0600
From: Nicolas Williams <[email-masked]>
To: Sam Hartman <[email-masked]>, Simon Josefsson <[email-masked]>, [email-masked]
Subject: Re: What am I waiting on for gs2?
Mail-Followup-To: Sam Hartman <[email-masked]>, Simon Josefsson <[email-masked]>, [email-masked]
Sender: [email-masked]

On Thu, Dec 20, 2007 at 09:59:35AM -0600, Nicolas Williams wrote:
> I'd rather see that bit in the client/server's second wrap token, yes.

We almost already have it.  Since the last wrap token carries the
selected security layer, and that selection is derived from channel
binding success/failure.  Of course, if a given mechanism does not
support confidentiality protection but the underlying channel does and
channel binding failes then we need a way to signal this.  So, yes, I
think we need one more bit in the client/server's last wrap token for
this.

From: Simon Josefsson <[email-masked]>
To: Sam Hartman <[email-masked]>
Cc: [email-masked]
Subject: Re: What am I waiting on for gs2?
OpenPGP: id=B565716F; url=http://josefsson.org/key.txt
Date: Thu, 20 Dec 2007 17:52:18 +0100
Sender: [email-masked]

Sam Hartman <[email-masked]> writes:

>>>>>> "Simon" == Simon Josefsson <[email-masked]> writes:
>
>     >> The channel binding spec requires applications know about
>     >> channel binding failure.  You added text passing this
>     >> requirement along, but I don't see how your protocol allows the
>     >> client to detect channel binding failure.
>     >> 
>     >> We have c->m->s where m is a passive man in the middle that
>     >> joins the TLS stream.  So, the channel bindings are different.
>     >> C sends the gss_wrap to s using the same qop for channel
>     >> binding and non-channel binding.  How does s indicate to c that
>     >> the channel binding from s's standpoint is not the same as what
>     >> it received from c?
>     >> 
>     >> I think you need a bit (possibly as a flag bit xored in with
>     >> the qop) to indicate this.
>
>     Simon> FYI, I had interpreted the requirement in RFC 5056:
>
>     Simon>    o Authentication frameworks and mechanisms that support
>     Simon> channel binding MUST communicate channel binding failure to
>     Simon> applications.
>
>     Simon> to mean that implementations must let the local
>     Simon> applications know about the situation.  That allows them to
>     Simon> abort the connection depending on local policy.  I didn't
>     Simon> read that to mean that protocols are required to notify the
>     Simon> other side of the situation.  The latter requirement is
>     Simon> stronger than the former.  I must admit that I don't see
>     Simon> why the stronger requirement is a useful one.
>
> Hmm.  You may be right that I was reading more into RFC 5056 than is
> actually there.  In GS2 I'd prefer that we do indicate channel binding
> failure back because we don't generally want people to abort at least
> if they are willing to use a security layer instead.

Right.  I think that was already possible, given:

   Note that "client_qop" and "server_qop" MAY indicate a quality of
   protection that was not offered by the server and client,
   respectively.  This SHOULD only be used when the server or client
   (respectively) would otherwise fail the entire authentication
   exchange.  The server/client that receives a "client_qop"/
   "server_qop" MUST verify that it corresponds to an acceptable
   security level.

When deciding whether to permit this or not, it can be useful to know
whether the other side made this choice because of a failed QOP or not.
That isn't possible with -09, and your suggestion fixes it.

It is not possible to verify the chosen QOP against *_qops and *_cbqops
unless you know whether channel binding negotiation was successful or
not.  In -09, you could only verify the chosen QOP against the logical
OR between *_qops and *_cbqops, which is sub-optimal.  Your suggestion
fixes this.

> However if the WG doesn't have consensus behind this change then it
> should be backed out.

I support the change below.  Others?

/Simon

--- 1/draft-ietf-sasl-gs2-09.txt	2007-12-20 16:30:00.000000000 +0100
+++ 2/draft-ietf-sasl-gs2.txt	2007-12-20 16:30:00.000000000 +0100
@@ -564,25 +564,25 @@
    channel bindings do not match.
 
    Client and servers MUST set the "chan_binding" parameter in the calls
    to GSS_Init_sec_context and GSS_Accept_sec_context, respectively, to
    NULL.
 
    Implementations SHOULD set the "client_cbqops" and "server_cbqops" to
    no security layer and instead depend on the session security afforded
    by the bound-in channel.
 
-   In order to accomodate the requirement in [16] "Authentication
+   In order to accomodate the requirement in [8] "Authentication
    frameworks and mechanisms that support channel binding MUST
    communicate channel binding failure to applications" implementations
-   MUST provide a way to communicate channel binding failures to
-   applications.
+   assert a bit in the security layer bitmask (see Section 9) on
+   negotiation failures.
 
    Use of no SASL security layers in combination with channel binding
    should provide better performance than using SASL security layers
    over secure channels, and better security characteristics than using
    no SASL security layers over secure channels without channel binding.
 
    For more discussions of channel bindings, and the syntax of the
    channel binding data for various security protocols, see [8].  For
    easy reference, the channel binding format used for The Transport
    Layer Security (TLS) Protocol [14] is specified in [16].
@@ -749,21 +749,22 @@
 
    o  GSS_Unwrap() returns anything other than GSS_S_COMPLETE.  (There
       can't be supplementary status codes in GS2 at this point, so any
       indications of out of order processing or replays is fatal.)
 
    o  The token returned from GSS_Unwrap fail to parse correctly (e.g.,
       too short, invalid maximum buffer size) as the expected Wrap
       token.
 
    o  Local policy reject the attempt.  For example, client and server
-      can't agree on qop proposal.
+      can't agree on qop proposal, or channel binding negotiation
+      failed.
 
    o  (server-side) Authorization of client principal (i.e., src_name in
       GSS_Acecpt_sec_context) to requested authzid failed.
 
 8.  GSS-API Parameters
 
    The implementation MAY set any GSSAPI flags or arguments not
    mentioned in this specification as is necessary for the
    implementation to enforce its security policy.
 
@@ -778,63 +779,80 @@
    layer.
 
    Note that "client_qop" and "server_qop" MAY indicate a quality of
    protection that was not offered by the server and client,
    respectively.  This SHOULD only be used when the server or client
    (respectively) would otherwise fail the entire authentication
    exchange.  The server/client that receives a "client_qop"/
    "server_qop" MUST verify that it corresponds to an acceptable
    security level.
 
+   Whether the channel binding negotiation is successful or not may
+   influence the security layer selection.  The most significant bit is
+   used to signal failed channel binding negotiation.  Implementations
+   MUST set the bit if channel bindings were provided from the other end
+   and a local channel binding is absent or not equal.  Implementation
+   MUST clear the bit otherwise.
+
    The security layers and their corresponding bit-masks are as follows:
 
-     1 No security layer
+     1    No security layer.
      2 Integrity protection.
-       Sender calls GSS_Wrap with conf_flag set to FALSE
+           Sender calls GSS_Wrap with conf_flag set to FALSE.
      4 Confidentiality protection.
-       Sender calls GSS_Wrap with conf_flag set to TRUE
+           Sender calls GSS_Wrap with conf_flag set to TRUE.
+     8-64 Reserved.
+     128  Channel binding negotiation failed.
 
-   Other bit-masks may be defined in the future; bits which are not
-   understood MUST be negotiated off.
+   The bit-masks 8-64 are reserved and may be defined in the future;
+   bits which are not understood MUST be negotiated off.
 
    When decoding any received data with GSS_Unwrap the major_status
    other than the GSS_S_COMPLETE MUST be treated as a fatal error.
 
    For integrity and confidentiality protection, GS2 negotiates the
    maximum size of the output_message to send.  Implementations can use
    the GSS_Wrap_size_limit call to determine the corresponding maximum
    size input_message.
 
 9.1.  Examples
 
    When no security layer is negotiated the octet will encode an integer
    1 as follows.
 
-       0 1 2 3 4 5 6 7
+       7 6 5 4 3 2 1 0
       +-+-+-+-+-+-+-+-+
       |0|0|0|0|0|0|0|1|
       +-+-+-+-+-+-+-+-+
 
    When integrity is negotiated the octet will encode an integer 2 as
    follows.
 
-       0 1 2 3 4 5 6 7
+       7 6 5 4 3 2 1 0
       +-+-+-+-+-+-+-+-+
       |0|0|0|0|0|0|1|0|
       +-+-+-+-+-+-+-+-+
 
-   When confidentiality is negotiated the octet will encode an integer 4
-   as follows.
+   When confidentiality is negotiated, and channel binding negotiation
+   failed, the octet will encode an integer 128+4=132 as follows.
 
-       0 1 2 3 4 5 6 7
+       7 6 5 4 3 2 1 0
       +-+-+-+-+-+-+-+-+
-      |0|0|0|0|0|1|0|0|
+      |1|0|0|0|0|1|0|0|
+      +-+-+-+-+-+-+-+-+
+
+   When a bitmask that indicates that all security layers are
+   acceptable, the octet will encode an integer 1+2+4=7 as follows.
+
+       7 6 5 4 3 2 1 0
+      +-+-+-+-+-+-+-+-+
+      |0|0|0|0|0|1|1|1|
       +-+-+-+-+-+-+-+-+
 
 10.  Non-integrity capable GSS-API mechanisms
 
    Mechanisms that do not support integrity can be used with GS2, but
    some security features cannot be provided, in particular including
    channel bindings, security layers, and integrity protection of the
    authorization identity.
 
    Channel bindings and security layers MUST NOT be negotiated when the
@@ -955,20 +973,23 @@
    GSS-API mechanism widely on the Internet that do not support
    integrity.
 
    Because the negotiation of a particular GSS-API mechanism may be done
    in the clear, it is important for the GSS-API mechanisms to be
    designed such that an active attacker cannot obtain an authentication
    with weaker security properties by modifying the challenges and
    responses.  This is a generic design critera for the GSS-API
    mechanisms used under GS2.
 
+   GS2 permits channel binding negotiation to fail.  Implementation may
+   have a local policy to reject authentication attempts in this case.
+
    When a server or client supports multiple GSS-API mechanisms, each of
    which has a different security strength, it is possible for an active
    attacker to cause a party to use the least secure mechanism
    supported.  This problem and a solution is discussed in section 6.1.2
    of [2], but some additional methods to mitigate the problem include:
 
    1.  Use of an integrity protected transport, such as TLS [14].  To
        protect against certain tunnel attacks [18], channel bindings
        need to be used.

Date: Thu, 20 Dec 2007 10:13:10 -0600
From: Nicolas Williams <[email-masked]>
To: Sam Hartman <[email-masked]>
Cc: [email-masked]
Subject: Re: SASL mechanisms via GSS-API and round trips
Mail-Followup-To: Sam Hartman <[email-masked]>, [email-masked]
Sender: [email-masked]

On Thu, Dec 20, 2007 at 10:40:01AM -0500, Sam Hartman wrote:
> Note, I'm only saying we should require prot_ready for new mechanisms
> that people are going to want to implement as sasl native, not for all
> new mechanisms.

Ah, I must have misread -- I thought you wanted to make this requirement
for all GSS mechanisms.  I think I'm OK with making that requirement
only of all SASL/GS2 mechanisms.

Date: Thu, 20 Dec 2007 09:59:35 -0600
From: Nicolas Williams <[email-masked]>
To: Sam Hartman <[email-masked]>
Cc: Simon Josefsson <[email-masked]>, [email-masked]
Subject: Re: What am I waiting on for gs2?
Mail-Followup-To: Sam Hartman <[email-masked]>, Simon Josefsson <[email-masked]>, [email-masked]
Sender: [email-masked]

On Thu, Dec 20, 2007 at 10:09:47AM -0500, Sam Hartman wrote:
> 
> >>>>> "Simon" == Simon Josefsson <[email-masked]> writes:
> 
>     >> The channel binding spec requires applications know about
>     >> channel binding failure.  You added text passing this
>     >> requirement along, but I don't see how your protocol allows the
>     >> client to detect channel binding failure.
>     >> 
>     >> We have c->m->s where m is a passive man in the middle that
>     >> joins the TLS stream.  So, the channel bindings are different.
>     >> C sends the gss_wrap to s using the same qop for channel
>     >> binding and non-channel binding.  How does s indicate to c that
>     >> the channel binding from s's standpoint is not the same as what
>     >> it received from c?
>     >> 
>     >> I think you need a bit (possibly as a flag bit xored in with
>     >> the qop) to indicate this.
> 
>     Simon> FYI, I had interpreted the requirement in RFC 5056:
> 
>     Simon>    o Authentication frameworks and mechanisms that support
>     Simon> channel binding MUST communicate channel binding failure to
>     Simon> applications.
> 
>     Simon> to mean that implementations must let the local
>     Simon> applications know about the situation.  That allows them to
>     Simon> abort the connection depending on local policy.  I didn't
>     Simon> read that to mean that protocols are required to notify the
>     Simon> other side of the situation.  The latter requirement is
>     Simon> stronger than the former.  I must admit that I don't see
>     Simon> why the stronger requirement is a useful one.
> 
> Hmm.  You may be right that I was reading more into RFC 5056 than is
> actually there.  In GS2 I'd prefer that we do indicate channel binding
> failure back because we don't generally want people to abort at least
> if they are willing to use a security layer instead.
> 
> However if the WG doesn't have consensus behind this change then it
> should be backed out.

I'd rather see that bit in the client/server's second wrap token, yes.

Date: Thu, 20 Dec 2007 09:48:56 -0600
From: Nicolas Williams <[email-masked]>
To: Simon Josefsson <[email-masked]>
Cc: Sam Hartman <[email-masked]>, [email-masked]
Subject: Re: What am I waiting on for gs2?
Mail-Followup-To: Simon Josefsson <[email-masked]>, Sam Hartman <[email-masked]>, [email-masked]
Sender: [email-masked]

On Thu, Dec 20, 2007 at 03:09:14PM +0100, Simon Josefsson wrote:
> FYI, I had interpreted the requirement in RFC 5056:
> 
>    o  Authentication frameworks and mechanisms that support channel
>       binding MUST communicate channel binding failure to applications.
> 
> to mean that implementations must let the local applications know about
> the situation.  That allows them to abort the connection depending on
> local policy.  I didn't read that to mean that protocols are required to
> notify the other side of the situation.  The latter requirement is
> stronger than the former.  I must admit that I don't see why the
> stronger requirement is a useful one.

Your interpretation of that requirement is correct.  The stronger
requirement perhaps should have been included.  I think Sam and I never
settled the issue of the Kerberos V GSS mechanism's initiator not having
any idea of whether the server checked or ignore channel bindings when
the server returns and AP-REP token.  Sam?

From: Sam Hartman <[email-masked]>
To: [email-masked]
Subject: Re: SASL mechanisms via GSS-API and round trips
Date: Thu, 20 Dec 2007 10:40:01 -0500
Sender: [email-masked]

>>>>> "Nicolas" == Nicolas Williams <[email-masked]> writes:

    Nicolas> Sam, GS2 takes adavantage of PROT_READY where available.

No, GS2 implementations may take advantage of prot_ready where available but are not required to do so.

    Nicolas> 
    Nicolas> I think that's enough.  I don't think there's any need to
    Nicolas> require PROT_READY support of new mechanisms, though I
    Nicolas> would strongly recommend PROT_READY support where it is
    Nicolas> actually feasible (I can imagine mechanisms where
    Nicolas> PROT_READY couldn't be signalled before GSS_S_COMPLETE).

I explained why I don't think this is enough.  I'd appreciate an explanation of why I'm wrong.

Note, I'm only saying we should require prot_ready for new mechanisms
that people are going to want to implement as sasl native, not for all
new mechanisms.

Date: Thu, 20 Dec 2007 09:26:50 -0600
From: Nicolas Williams <[email-masked]>
To: Sam Hartman <[email-masked]>
Cc: [email-masked]
Subject: Re: SASL mechanisms via GSS-API and round trips
Mail-Followup-To: Sam Hartman <[email-masked]>, [email-masked]
Sender: [email-masked]

Sam,

GS2 takes adavantage of PROT_READY where available.  I think that's
enough.  I don't think there's any need to require PROT_READY support of
new mechanisms, though I would strongly recommend PROT_READY support
where it is actually feasible (I can imagine mechanisms where PROT_READY
couldn't be signalled before GSS_S_COMPLETE).

Nico
-- 

Date: Thu, 20 Dec 2007 09:24:03 -0600
From: Nicolas Williams <[email-masked]>
To: Sam Hartman <[email-masked]>
Cc: [email-masked]
Subject: Re: Channel Binding and GSS-API mechanisms
Mail-Followup-To: Sam Hartman <[email-masked]>, [email-masked]
Sender: [email-masked]

On Thu, Dec 20, 2007 at 09:37:55AM -0500, Sam Hartman wrote:
Sam> First, if you have a channel binding that requires
Sam> confidentiality for a channel that does not provide
Sam> confidentiality you cannot use it with GS2.  Honestly I don't
Sam> consider this a big deal because I cannot think of any reason
Sam> you'd define such a channel binding.  It seems like such a bad
Sam> idea I'd hope that the expert would decline the registration.  If
Sam> we do find a channel where this is the right solutionwe'll have
Sam> some work to do.

Correct.  It's because such a thing would be so silly that this doesn't
bother me in the least.

Sam> The second problem is more concerning.  The way GS2 handles
Sam> channel bindings makes it a bit tricky for things that want to be
Sam> both a SASL mechanism and a GSS-API mechanism.  GS2 does not use
Sam> the GSS-API binding facility.  It instead uses a wrap token.  So,
Sam> you'll need to define a wrap token for your mechanism.

Sam> However if your mechanism is going to support channel binding
Sam> when it is used as a GSS-API mechanism, then it needs to also
Sam> support channel bindings in the GSS-API token.

Yes, this has bothered me before too, but I came to accept it as a
result of the difference in channel binding failure semantics that we
want for SASL vs. the GSS-API's.  I suppose we could work on a GSS-API
extension to make channel binding failure result in an output ret_flag
rather than plain failure, then we could use GSS channel binding in GS2,
say, but it turns out that there are lots of complexities there as well.

The biggest problem with the GS2 approach is that we lose the
opportunity to work the channel bindings into the mechanism's context
tokens, where it makes the most sense.  There was a discussion about
this after most of you left the SASL jabber room.

Sam> This complexity isn't a over-the wire complexity issue.  It does
Sam> not effect round trips.  If you are only implementing the SASL
Sam> mechanism there is not more work to do.

Sam> However it makes the spec kind of complicated.

I know.  I wish it weren't so.  I'll think a bit more about alternatives
that don't merely shift the complexity elsewhere.

Nico
-- 

From: Sam Hartman <[email-masked]>
To: Simon Josefsson <[email-masked]>
Cc: [email-masked]
Subject: Re: What am I waiting on for gs2?
Date: Thu, 20 Dec 2007 10:09:47 -0500
Sender: [email-masked]

>>>>> "Simon" == Simon Josefsson <[email-masked]> writes:

    >> The channel binding spec requires applications know about
    >> channel binding failure.  You added text passing this
    >> requirement along, but I don't see how your protocol allows the
    >> client to detect channel binding failure.
    >> 
    >> We have c->m->s where m is a passive man in the middle that
    >> joins the TLS stream.  So, the channel bindings are different.
    >> C sends the gss_wrap to s using the same qop for channel
    >> binding and non-channel binding.  How does s indicate to c that
    >> the channel binding from s's standpoint is not the same as what
    >> it received from c?
    >> 
    >> I think you need a bit (possibly as a flag bit xored in with
    >> the qop) to indicate this.

    Simon> FYI, I had interpreted the requirement in RFC 5056:

    Simon>    o Authentication frameworks and mechanisms that support
    Simon> channel binding MUST communicate channel binding failure to
    Simon> applications.

    Simon> to mean that implementations must let the local
    Simon> applications know about the situation.  That allows them to
    Simon> abort the connection depending on local policy.  I didn't
    Simon> read that to mean that protocols are required to notify the
    Simon> other side of the situation.  The latter requirement is
    Simon> stronger than the former.  I must admit that I don't see
    Simon> why the stronger requirement is a useful one.

Hmm.  You may be right that I was reading more into RFC 5056 than is
actually there.  In GS2 I'd prefer that we do indicate channel binding
failure back because we don't generally want people to abort at least
if they are willing to use a security layer instead.

However if the WG doesn't have consensus behind this change then it
should be backed out.

From: Sam Hartman <[email-masked]>
To: Simon Josefsson <[email-masked]>
Cc: [email-masked]
Subject: Re: Channel Binding and GSS-API mechanisms
Date: Thu, 20 Dec 2007 10:04:58 -0500
Sender: [email-masked]

>>>>> "Simon" == Simon Josefsson <[email-masked]> writes:

    Simon> Sam Hartman <[email-masked]> writes:
    >> Folks, a couple of odd consequences of how GS2 and channel
    >> binding interact came to me during the meeting and I want to
    >> make sure we're aware of them and agree they are OK.
    >> 
    >> First, if you have a channel binding that requires
    >> confidentiality for a channel that does not provide
    >> confidentiality you cannot use it with GS2.  Honestly I don't
    >> consider this a big deal because I cannot think of any reason
    >> you'd define such a channel binding.  It seems like such a bad
    >> idea I'd hope that the expert would decline the registration.
    >> If we do find a channel where this is the right solutionwe'll
    >> have some work to do.

    Simon> There is a security consideration in GS2 about this:

    Simon>    The channel binding is sent without privacy protection
    Simon> and knowledge of it is assumed to provide no advantage to
    Simon> an attacker.  This is a property that has to be considered
    Simon> when specifying channel bindings for a security protocol
    Simon> that will be used with GS2.

    Simon> Is there anything else the document could say, or is this
    Simon> sufficient?

No, I think the doc is fine.
The question is whether the WG is OK with that consequence.
My personal recommendation is no change in this area.

    >> The second problem is more concerning.  The way GS2 handles
    >> channel bindings makes it a bit tricky for things that want to
    >> be both a SASL mechanism and a GSS-API mechanism.  GS2 does not
    >> use the GSS-API binding facility.  It instead uses a wrap
    >> token.  So, you'll need to define a wrap token for your
    >> mechanism.

    Simon> I don't think that is required, see section 4.3.1 of GS2:

    Simon> 4.3.1.  The GS2_Wrap function

    Simon>    The GS2_Wrap function have two implementations, and
    Simon> which one is used depends on whether the negotiated GSS-API
    Simon> context supports per- message protection.  When a context
    Simon> is successfully negotiated (i.e., when GSS_S_COMPLETE is
    Simon> returned from, for clients, GSS_Init_sec_context, or, for
    Simon> servers, GSS_Accept_sec_context) and the output variable
    Simon> integ_avail is FALSE, then GSS_Wrap cannot be used and
    Simon> instead we define GS2_Wrap to be the identity function.
    Simon> When integ_avail is negotiated TRUE, the GS2_Wrap is
    Simon> identical to calling the GSS_Wrap function with conf_flag
    Simon> set to FALSE and using the generated output_message as the
    Simon> output data.

    Simon> The rest of the document uses GS2_Wrap, not GSS_Wrap.

You cannot use channel binding with contexts that do not have
integ_avail.

So, if you are going to design a SASL mechanism as a GSS-API mechanism
and want channel binding to work, you must provide gss_wrap with
integrity tokens.

The GS2 document explains why we made that design decision.  I
understand and agree with that explanation.  I just want to make sure
the WG is aware of the consequences.

From: Sam Hartman <[email-masked]>
To: [email-masked]
Subject: SASL mechanisms via GSS-API and round trips
Date: Thu, 20 Dec 2007 09:55:44 -0500
Sender: [email-masked]

One of the things I think we're going to need to do to make specifying
mechanisms as GSS-API mechanisms acceptable to the apps community is
to reduce options and implementation complexity.

Unless we've screwed something up, I think we have the normal case of
a client-first mechanism via GS2 working so that it will be the same
number of packets without significant extra bytes as the same
mechanism as a native SASL mechanism.

However GS2 does not require prot_ready support and does not require
optimal number of round trips.

Let's take a simple challenge response mechanism

c->s: {client_name , null}
s->c: {server_nonce,null}
c->s: {f(key,client_nonce,server_nonce), wrap(authz_id,cbdata)}
s->c: {g(server_nonce, client_nonce), wrap(flags)}

I'm talking about an idealized gs2 here; there's also goop to say that
neither side wants a security layer in some of those packets.

That's roughly what gs2 of a sasl mechanism would look like assuming
that people are being optimal.  I don't think doing a native
non-gss-implementation that is wire compatible with that is hard.
However if that native implementation talks to a real gss
implementation you may get something like

c->s: {client_name , null}
s->c: {server_nonce,null}
c->s: {f(key,client_nonce,server_nonce), null}
s->c: {g(server_nonce, client_nonce), wrap(flags, cbdata)
c->s: {null, wrap(flags,authzid)}

I'd need to go back and look at the spec.  IT may turn out that it can
take an extra round trip if the wrap token from the server to the
client is null and the client has to send first after all the context
tokens are done.  I don't think that is permitted though.

It seems like supporting that interaction would significantly increase
the control loop complexity of the native SASL mechanism.  I bet that will be unacceptable to a lot of people.

So, I think we're going to have to require that you use the optimal
number of round trips.  That's kind of complicated to do.  Not all
mechanisms specify whether they support prot_ready.

I'm sort of imagining a requirement in GS2 that for GSS-API mechanisms
that mandate prot_ready support,GS2 must take advantage of it.  Then
in anything we design expecting that it will be both a SASL mechanism
without GSS code and is using the GS2 wire protocol we require
prot_ready support in the mechanism.

Put another way, we thread a requirement through a couple abstraction
layers to say that you shouldn't be stupid.

This does increase the minimum complexity of a generic GS2 mechanism.
However I think it significantly saves on the complexity of
wire-compatible native SASL mechanisms.

From: Simon Josefsson <[email-masked]>
To: Sam Hartman <[email-masked]>
Cc: [email-masked]
Subject: Re: Channel Binding and GSS-API mechanisms
OpenPGP: id=B565716F; url=http://josefsson.org/key.txt
Date: Thu, 20 Dec 2007 15:52:57 +0100
Sender: [email-masked]

Sam Hartman <[email-masked]> writes:

> Folks, a couple of odd consequences of how GS2 and channel binding
> interact came to me during the meeting and I want to make sure we're
> aware of them and agree they are OK.
>
> First, if you have a channel binding that requires confidentiality for
> a channel that does not provide confidentiality you cannot use it with
> GS2.  Honestly I don't consider this a big deal because I cannot think
> of any reason you'd define such a channel binding.  It seems like such
> a bad idea I'd hope that the expert would decline the registration.
> If we do find a channel where this is the right solutionwe'll have
> some work to do.

There is a security consideration in GS2 about this:

   The channel binding is sent without privacy protection and knowledge
   of it is assumed to provide no advantage to an attacker.  This is a
   property that has to be considered when specifying channel bindings
   for a security protocol that will be used with GS2.

Is there anything else the document could say, or is this sufficient?

> The second problem is more concerning.  The way GS2 handles channel
> bindings makes it a bit tricky for things that want to be both a SASL
> mechanism and a GSS-API mechanism.  GS2 does not use the GSS-API
> binding facility.  It instead uses a wrap token.  So, you'll need to
> define a wrap token for your mechanism.

I don't think that is required, see section 4.3.1 of GS2:

4.3.1.  The GS2_Wrap function

   The GS2_Wrap function have two implementations, and which one is used
   depends on whether the negotiated GSS-API context supports per-
   message protection.  When a context is successfully negotiated (i.e.,
   when GSS_S_COMPLETE is returned from, for clients,
   GSS_Init_sec_context, or, for servers, GSS_Accept_sec_context) and
   the output variable integ_avail is FALSE, then GSS_Wrap cannot be
   used and instead we define GS2_Wrap to be the identity function.
   When integ_avail is negotiated TRUE, the GS2_Wrap is identical to
   calling the GSS_Wrap function with conf_flag set to FALSE and using
   the generated output_message as the output data.

The rest of the document uses GS2_Wrap, not GSS_Wrap.

> However if your mechanism is going to support channel binding when it
> is used as a GSS-API mechanism, then it needs to also support channel
> bindings in the GSS-API token.
>
> This complexity isn't a over-the wire complexity issue.  It does not
> effect round trips.  If you are only implementing the SASL mechanism
> there is not more work to do.
>
> However it makes the spec kind of complicated.

That may still be the case, though.

/Simon

From: Simon Josefsson <[email-masked]>
To: Sam Hartman <[email-masked]>
Cc: [email-masked]
Subject: Re: What am I waiting on for gs2?
OpenPGP: id=B565716F; url=http://josefsson.org/key.txt
Date: Thu, 20 Dec 2007 15:42:56 +0100
Sender: [email-masked]

Simon Josefsson <[email-masked]> writes:

> +     7 Channel binding negotiation failed.

That was incorrect.  I've fixed this (same URL as before), and also
fixed the bitmask examples to have the bit numbers in the reverse order.

http://josefsson.org/sasl-gs2/draft-ietf-sasl-gs2.txt

/Simon

   The security layers and their corresponding bit-masks are as follows:

     1    No security layer.
     2    Integrity protection.
           Sender calls GSS_Wrap with conf_flag set to FALSE.
     4    Confidentiality protection.
           Sender calls GSS_Wrap with conf_flag set to TRUE.
     8-64 Reserved.
     128  Channel binding negotiation failed.
...
   When confidentiality is negotiated, and channel binding negotiation
   failed, the octet will encode an integer 128+4=132 as follows.

       7 6 5 4 3 2 1 0
      +-+-+-+-+-+-+-+-+
      |1|0|0|0|0|1|0|0|
      +-+-+-+-+-+-+-+-+

From: Sam Hartman <[email-masked]>
To: [email-masked]
Subject: Channel Binding and GSS-API mechanisms
Date: Thu, 20 Dec 2007 09:37:55 -0500
Sender: [email-masked]

Folks, a couple of odd consequences of how GS2 and channel binding
interact came to me during the meeting and I want to make sure we're
aware of them and agree they are OK.

First, if you have a channel binding that requires confidentiality for
a channel that does not provide confidentiality you cannot use it with
GS2.  Honestly I don't consider this a big deal because I cannot think
of any reason you'd define such a channel binding.  It seems like such
a bad idea I'd hope that the expert would decline the registration.
If we do find a channel where this is the right solutionwe'll have
some work to do.

The second problem is more concerning.  The way GS2 handles channel
bindings makes it a bit tricky for things that want to be both a SASL
mechanism and a GSS-API mechanism.  GS2 does not use the GSS-API
binding facility.  It instead uses a wrap token.  So, you'll need to
define a wrap token for your mechanism.

However if your mechanism is going to support channel binding when it
is used as a GSS-API mechanism, then it needs to also support channel
bindings in the GSS-API token.

This complexity isn't a over-the wire complexity issue.  It does not
effect round trips.  If you are only implementing the SASL mechanism
there is not more work to do.

However it makes the spec kind of complicated.

From: Simon Josefsson <[email-masked]>
To: Sam Hartman <[email-masked]>
Cc: [email-masked]
Subject: Re: What am I waiting on for gs2?
OpenPGP: id=B565716F; url=http://josefsson.org/key.txt
Date: Thu, 20 Dec 2007 15:09:14 +0100
Sender: [email-masked]

Sam Hartman <[email-masked]> writes:

>>>>>> "Sam" == Sam Hartman <[email-masked]> writes:
>
>>>>>> "Simon" == Simon Josefsson <[email-masked]> writes:
>
>     Simon> Sam Hartman <[email-masked]> writes:
>     >>> I seem to have dropped the ball on gs2.  What if anything am I
>     >>> waiting on to align with RFC 5056?
>     >>> 
>     >>> Were the other issues all resolved?
>
>     Simon> As far as I understood, the concern you raised was that GS2
>     Simon> had to supply two fields for the channel binding prefix and
>     Simon> the channel binding data, which was not how I had
>     Simon> understood the channel-binding document.  The
>     Simon> channel-binding document was changed to prefix all data
>     Simon> with the unique prefix, I think.  Thus no change would be
>     Simon> needed for GS2.
>
> Simon, I reviewed the changes and I believe that there is one open
> issue.
>
> The channel binding spec requires applications know about channel
> binding failure.  You added text passing this requirement along, but I
> don't see how your protocol allows the client to detect channel
> binding failure.
>
> We have c->m->s where m is a passive man in the middle that joins the
> TLS stream.  So, the channel bindings are different.  C sends the
> gss_wrap to s using the same qop for channel binding and non-channel
> binding.
> How does s indicate to c that the channel binding from s's standpoint is not the same as what it received from c?
>
> I think you need a bit (possibly as a flag bit xored in with the qop)
> to indicate this.

FYI, I had interpreted the requirement in RFC 5056:

   o  Authentication frameworks and mechanisms that support channel
      binding MUST communicate channel binding failure to applications.

to mean that implementations must let the local applications know about
the situation.  That allows them to abort the connection depending on
local policy.  I didn't read that to mean that protocols are required to
notify the other side of the situation.  The latter requirement is
stronger than the former.  I must admit that I don't see why the
stronger requirement is a useful one.

I have applied the patch below to address your concern.  Updated
document:

http://josefsson.org/sasl-gs2/draft-ietf-sasl-gs2.txt

Changes since the last version:

http://josefsson.org/sasl-gs2/draft-ietf-sasl-gs2-from--09.diff.html

As always, general information available from:

http://josefsson.org/sasl-gs2/

I'll submit this to the IETF in a few days unless there are comments.

/Simon

@@ -802,11 +802,11 @@
    no security layer and instead depend on the session security afforded
    by the bound-in channel.
 
-   In order to accomodate the requirement in [16] "Authentication
+   In order to accomodate the requirement in [8] "Authentication
    frameworks and mechanisms that support channel binding MUST
    communicate channel binding failure to applications" implementations
-   MUST provide a way to communicate channel binding failures to
-   applications.
+   assert bit 7 in the security layer bitmask (see Section 9) on
+   negotiation failures.
 
    Use of no SASL security layers in combination with channel binding
    should provide better performance than using SASL security layers
@@ -1087,7 +1087,8 @@
       token.
 
    o  Local policy reject the attempt.  For example, client and server
-      can't agree on qop proposal.
+      can't agree on qop proposal, or channel binding negotiation
+      failed.
 
    o  (server-side) Authorization of client principal (i.e., src_name in
       GSS_Acecpt_sec_context) to requested authzid failed.
@@ -1195,6 +1195,13 @@
    "server_qop" MUST verify that it corresponds to an acceptable
    security level.
 
+   Whether the channel binding negotiation is successful or not may
+   influence the security layer selection.  Bit 7 is used to signal
+   failed channel binding negotiation.  Implementations MUST set the bit
+   if channel bindings were provided from the other end and a local
+   channel binding is absent or not equal.  Implementation MUST clear
+   the bit otherwise.
+
    The security layers and their corresponding bit-masks are as follows:
 
      1 No security layer
@@ -1202,6 +1209,7 @@
        Sender calls GSS_Wrap with conf_flag set to FALSE
      4 Confidentiality protection.
        Sender calls GSS_Wrap with conf_flag set to TRUE
+     7 Channel binding negotiation failed.
 
    Other bit-masks may be defined in the future; bits which are not
    understood MUST be negotiated off.
@@ -1530,6 +1530,9 @@
    responses.  This is a generic design critera for the GSS-API
    mechanisms used under GS2.
 
+   GS2 permits channel binding negotiation to fail.  Implementation may
+   have a local policy to reject authentication attempts in this case.
+
    When a server or client supports multiple GSS-API mechanisms, each of
    which has a different security strength, it is possible for an active
    attacker to cause a party to use the least secure mechanism

To: [email-masked]
Subject: new milestones for charter update
From: Tom Yu <[email-masked]>
Date: Tue, 18 Dec 2007 13:10:48 -0500
Lines: 18
Sender: [email-masked]

From: Simon Josefsson <[email-masked]>
To: Paul Leach <[email-masked]>
Cc: Alexey Melnikov <[email-masked]>, "ietf-sasl\@imc.org" <[email-masked]>
Subject: Re: Working Group Last Call: draft-melnikov-digest-to-historic-00.txt
OpenPGP: id=B565716F; url=http://josefsson.org/key.txt
Date: Mon, 10 Dec 2007 15:14:01 +0100
Sender: [email-masked]

Paul Leach <[email-masked]> writes:

>>1) One of the main disadvantages with DIGEST-MD5 for me is that its
>>   cryptographic primitives are sub-standard by today's standard.  The
>>   text in 7.B touches on this, but seems misplaced as 7 is about
>>   missing features.  I suggest adding to section 1:
>>
>>   8. The cryptographic primitives in DIGEST-MD5 are not up to today's
>>   standards, in particular:
>>
>>      A. The MD5 hash is sufficiently weak to make a brute force attack
>>      on DIGEST-MD5 easy with common hardware.
>>
>>      B. Using the RC4 algorithm for the security layer without
>>      discarding the initial key stream output is prone to attack.
>>
>>
>
> [Paul Leach] While I certainly agree that MD5 is suspect, I'm not
> aware that there are any known attacks on the usage in DIGEST. The bad
> usage is: given a hash and a known input, it is possible to find other
> inputs that yield the same hash. However, given an input part of which
> is unknown (secret) and a hash, I wasn't aware that it is
> computationally feasible to do better than to try to test all possible
> secrets. Have I missed the relevant paper?

That text is already in the document, so they aren't my words.

However, I recall that there were a presentation at an appsarea meeting
a few IETF meetings ago, where CRAM-MD5 (dictionary?) attacks were
discussed and the practical consequences weren't pretty.  I wasn't there
and don't recall more details though, maybe someone else know of a
better reference.

/Simon

Date: Mon, 10 Dec 2007 09:10:33 +0530
From: Abhijit Menon-Sen <[email-masked]>
To: Paul Leach <[email-masked]>
Cc: [email-masked]
Subject: Re: Working Group Last Call: draft-melnikov-digest-to-historic-00.txt
Sender: [email-masked]

At 2007-12-09 19:00:55 -0800, [email-masked] wrote:
>
> The bad usage is: given a hash and a known input, it is possible to
> find other inputs that yield the same hash.

As far as I know, even that is not possible.

For a given input, you can construct a pair of messages that hash to the
same value and have the input text as a prefix, but you cannot target a
specific hash value, and neither colliding message is identical to the
input (i.e. no preimage attacks are possible).

-- ams

From: Paul Leach <[email-masked]>
To: Alexey Melnikov <[email-masked]>, Simon Josefsson <[email-masked]>
CC: "[email-masked]" <[email-masked]>
Date: Sun, 9 Dec 2007 19:00:55 -0800
Subject: RE: Working Group Last Call: draft-melnikov-digest-to-historic-00.txt
Accept-Language: en-US
acceptlanguage: en-US
Sender: [email-masked]

While I ver

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] On Behalf Of Alexey Melnikov
Sent: Saturday, December 08, 2007 11:42 AM
To: Simon Josefsson
Cc: [email-masked]
Subject: Re: Working Group Last Call: draft-melnikov-digest-to-historic-00.txt

>1) One of the main disadvantages with DIGEST-MD5 for me is that its
>   cryptographic primitives are sub-standard by today's standard.  The
>   text in 7.B touches on this, but seems misplaced as 7 is about
>   missing features.  I suggest adding to section 1:
>
>   8. The cryptographic primitives in DIGEST-MD5 are not up to today's
>   standards, in particular:
>
>      A. The MD5 hash is sufficiently weak to make a brute force attack
>      on DIGEST-MD5 easy with common hardware.
>
>      B. Using the RC4 algorithm for the security layer without
>      discarding the initial key stream output is prone to attack.
>
>

[Paul Leach] While I certainly agree that MD5 is suspect, I'm not aware that there are any known attacks on the usage in DIGEST. The bad usage is: given a hash and a known input, it is possible to find other inputs that yield the same hash. However, given an input part of which is unknown (secret) and a hash, I wasn't aware that it is computationally feasible to do better than to try to test all possible secrets. Have I missed the relevant paper?

(The above is just in the interest of accuracy -- I have no objection to moving DIGEST to historic.)

Date: Sat, 08 Dec 2007 19:41:38 +0000
From: Alexey Melnikov <[email-masked]>
To: Simon Josefsson <[email-masked]>
CC: [email-masked]
Subject: Re: Working Group Last Call: draft-melnikov-digest-to-historic-00.txt
Sender: [email-masked]

Simon Josefsson wrote:

>Tom Yu <[email-masked]> writes:
>  
>
>>A URL for this Internet-Draft is:
>>http://www.ietf.org/internet-drafts/draft-melnikov-digest-to-historic-00.txt
>>    
>>
>I have read the document and support it.  Two concerns though:
>  
>
Simon, thank you for your comments.

>1) One of the main disadvantages with DIGEST-MD5 for me is that its
>   cryptographic primitives are sub-standard by today's standard.  The
>   text in 7.B touches on this, but seems misplaced as 7 is about
>   missing features.  I suggest adding to section 1:
>
>   8. The cryptographic primitives in DIGEST-MD5 are not up to today's
>   standards, in particular:
>
>      A. The MD5 hash is sufficiently weak to make a brute force attack
>      on DIGEST-MD5 easy with common hardware.
>
>      B. Using the RC4 algorithm for the security layer without
>      discarding the initial key stream output is prone to attack.
>  
>
I've added this.

>   And consequently removing the text in 7.B (which is the same as 8.A),
>   except that it fixes a typo and adds a leading 'The'.
>  
>
I retained "Lack of hash agility" in 7, but removed text about MD5 
(which is now in 8)

From: Simon Josefsson <[email-masked]>
To: Tom Yu <[email-masked]>
Cc: [email-masked]
Subject: Re: IETF70 SASL summary
OpenPGP: id=B565716F; url=http://josefsson.org/key.txt
Date: Fri, 07 Dec 2007 12:52:07 +0100
Sender: [email-masked]

Tom Yu <[email-masked]> writes:

> Simon Josefsson has indicated he is not interested in purusing his
> password-based mech draft at this time

Just to clarify: I will pursue the draft (implementing it now, the draft
will change a lot), but due to lack of interest (I haven't seen any
feedback), it won't include the SASL/GS2 mappings.  The document will be
a strict password-based GSS-API mechanism.

/Simon

From: Simon Josefsson <[email-masked]>
To: "Frank Ellermann" <[email-masked]>
Cc: [email-masked]
Subject: Re: Working Group Last Call: draft-melnikov-digest-to-historic-00.txt
OpenPGP: id=B565716F; url=http://josefsson.org/key.txt
Date: Fri, 07 Dec 2007 12:29:51 +0100
Sender: [email-masked]

"Frank Ellermann" <[email-masked]> writes:

> Simon Josefsson wrote:
>  
>> A. The MD5 hash is sufficiently weak to make a brute force attack
>> on DIGEST-MD5 easy with common hardware.
>
> If "can identify the first three or four characters of the secret"
> is still state of the art (and IFF I recall that correctly), then
> "easy" might be slightly exaggerated.  From my POV various _other_
> issues with DIGEST-MD5 are predominant, not its weakness.

That text is already in the document.  I agree it isn't the major
concern, that's why I listed it last. ;)

/Simon

Date: Fri, 7 Dec 2007 10:27:30 +0530
From: Abhijit Menon-Sen <[email-masked]>
To: Chris Newman <[email-masked]>
Cc: Simon Josefsson <[email-masked]>, Tom Yu <[email-masked]>, [email-masked]
Subject: Re: Working Group Last Call: draft-melnikov-digest-to-historic-00.txt
Sender: [email-masked]

At 2007-12-06 17:31:54 -0800, [email-masked] wrote:
>
> I have read this document and would support publication of version
> -00.

I have also reviewed the document, and sent Alexey a number of minor
editorial comments in private mail. I agree with the substance of the
document, however, and support its publication (with or without the
addition of a qualified suggestion to use TLS+PLAIN instead).

-- ams

Date: Fri, 07 Dec 2007 02:29:21 +0000
From: Alexey Melnikov <[email-masked]>
To: Chris Newman <[email-masked]>
CC: Simon Josefsson <[email-masked]>, [email-masked]
Subject: Re: Working Group Last Call: draft-melnikov-digest-to-historic-00.txt
Sender: [email-masked]

Chris Newman wrote:

> I have read this document and would support publication of version -00.
>
> The suggestions Simon Josefsson made are reasonable and I would also 
> support publication of a document including those suggestions.

Agreed.

> The issue of PLAIN + TLS as mandatory-to-implement does have the 
> subtlety that it's not appropriate as mandatory-to-implement mechanism 
> for all protocols although it has been used by several standards track 
> protocols for that purpose.

Indeed. It has different properties, so I would rather not actively 
recommend it as a replacement.

> It may make it easier to get the document published if such text is 
> omitted or conservative.

Date: Thu, 06 Dec 2007 17:31:54 -0800
From: Chris Newman <[email-masked]>
Subject: Re: Working Group Last Call: draft-melnikov-digest-to-historic-00.txt
To: Simon Josefsson <[email-masked]>, Tom Yu <[email-masked]>
Cc: [email-masked]
Sender: [email-masked]

I have read this document and would support publication of version -00.

The suggestions Simon Josefsson made are reasonable and I would also support 
publication of a document including those suggestions.  The issue of PLAIN + 
TLS as mandatory-to-implement does have the subtlety that it's not appropriate 
as mandatory-to-implement mechanism for all protocols although it has been used 
by several standards track protocols for that purpose.  It may make it easier 
to get the document published if such text is omitted or conservative.

                - Chris

Simon Josefsson wrote on 12/6/07 9:25 +0100:
> Tom Yu <[email-masked]> writes:
>
>> A URL for this Internet-Draft is:
>> http://www.ietf.org/internet-drafts/draft-melnikov-digest-to-historic-00.txt
>
> I have read the document and support it.  Two concerns though:
>
> 1) One of the main disadvantages with DIGEST-MD5 for me is that its
>    cryptographic primitives are sub-standard by today's standard.  The
>    text in 7.B touches on this, but seems misplaced as 7 is about
>    missing features.  I suggest adding to section 1:
>
>    8. The cryptographic primitives in DIGEST-MD5 are not up to today's
>    standards, in particular:
>
>       A. The MD5 hash is sufficiently weak to make a brute force attack
>       on DIGEST-MD5 easy with common hardware.
>
>       B. Using the RC4 algorithm for the security layer without
>       discarding the initial key stream output is prone to attack.
>
>    And consequently removing the text in 7.B (which is the same as 8.A),
>    except that it fixes a typo and adds a leading 'The'.
>
> 2) There should be better recommendations on what users should use
>    instead.  There is the following text:
>
>      Note that despite DIGEST-MD5 seeing some deployment on the
>      Internet, this specification recommends obsoleting DIGEST-MD5
>      because DIGEST- MD5, as implemented, is not a reasonable candidate
>      for further standardization and should be deprecated in favor of
>      one or more new password-based mechanisms currently being designed.
>
>    I think there should be a reference to PLAIN+TLS here.  I think a
>    recommendation to wait for some future protocol to materialize, while
>    best from security perspective, should be amended with a practical
>    recommendation.
>
> Thanks,
> /Simon
>
>

To: [email-masked]
From: "Frank Ellermann" <[email-masked]>
Subject:  Re: Working Group Last Call: draft-melnikov-digest-to-historic-00.txt
Date:  Thu, 6 Dec 2007 22:34:27 +0100
Organization:  <http://purl.net/xyzzy>
Lines: 11
Reply-To: "Frank Ellermann" <[email-masked]>
Sender: [email-masked]

Simon Josefsson wrote:
=20
> A. The MD5 hash is sufficiently weak to make a brute force attack
> on DIGEST-MD5 easy with common hardware.

If "can identify the first three or four characters of the secret"
is still state of the art (and IFF I recall that correctly), then
"easy" might be slightly exaggerated.  From my POV various _other_
issues with DIGEST-MD5 are predominant, not its weakness.

 Frank

Date: Thu, 06 Dec 2007 08:30:50 -0700
From: Peter Saint-Andre <[email-masked]>
To: Simon Josefsson <[email-masked]>
CC: [email-masked]
Subject: Re: Working Group Last Call: draft-melnikov-digest-to-historic-00.txt
OpenPGP: id=7BBD0573; url=http://www.saint-andre.com/me/stpeter.asc
Jabber-ID: [email-masked]
Sender: [email-masked]

This is a cryptographically signed message in MIME format.

--------------ms030203040303010208020201
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 7bit

Simon Josefsson wrote:
> Tom Yu <[email-masked]> writes:
> 
>> A URL for this Internet-Draft is:
>> http://www.ietf.org/internet-drafts/draft-melnikov-digest-to-historic-00.txt
> 
> I have read the document and support it.  Two concerns though:

<snip/>

> 2) There should be better recommendations on what users should use
>    instead.  There is the following text:
> 
>      Note that despite DIGEST-MD5 seeing some deployment on the
>      Internet, this specification recommends obsoleting DIGEST-MD5
>      because DIGEST- MD5, as implemented, is not a reasonable candidate
>      for further standardization and should be deprecated in favor of
>      one or more new password-based mechanisms currently being designed.
> 
>    I think there should be a reference to PLAIN+TLS here.  I think a
>    recommendation to wait for some future protocol to materialize, while
>    best from security perspective, should be amended with a practical
>    recommendation.

Agreed. The DIGEST-MD5 mechanism has seen wide deployment in Jabber/XMPP
systems because it is recommended in RFC 3920. In rfc3920bis we will
recommend TLS + SASL PLAIN instead.

Peter

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

--------------ms030203040303010208020201
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Content-Transfer-Encoding: base64
Content-Disposition: attachment; filename="smime.p7s"
Content-Description: S/MIME Cryptographic Signature

--------------ms030203040303010208020201--

From: Simon Josefsson <[email-masked]>
To: Tom Yu <[email-masked]>
Cc: [email-masked]
Subject: Re: Working Group Last Call: draft-melnikov-digest-to-historic-00.txt
OpenPGP: id=B565716F; url=http://josefsson.org/key.txt
Date: Thu, 06 Dec 2007 09:25:01 +0100
Sender: [email-masked]

Tom Yu <[email-masked]> writes:

> A URL for this Internet-Draft is:
> http://www.ietf.org/internet-drafts/draft-melnikov-digest-to-historic-00.txt

I have read the document and support it.  Two concerns though:

1) One of the main disadvantages with DIGEST-MD5 for me is that its
   cryptographic primitives are sub-standard by today's standard.  The
   text in 7.B touches on this, but seems misplaced as 7 is about
   missing features.  I suggest adding to section 1:

   8. The cryptographic primitives in DIGEST-MD5 are not up to today's
   standards, in particular:

      A. The MD5 hash is sufficiently weak to make a brute force attack
      on DIGEST-MD5 easy with common hardware.

      B. Using the RC4 algorithm for the security layer without
      discarding the initial key stream output is prone to attack.

   And consequently removing the text in 7.B (which is the same as 8.A),
   except that it fixes a typo and adds a leading 'The'.

2) There should be better recommendations on what users should use
   instead.  There is the following text:

     Note that despite DIGEST-MD5 seeing some deployment on the
     Internet, this specification recommends obsoleting DIGEST-MD5
     because DIGEST- MD5, as implemented, is not a reasonable candidate
     for further standardization and should be deprecated in favor of
     one or more new password-based mechanisms currently being designed.

   I think there should be a reference to PLAIN+TLS here.  I think a
   recommendation to wait for some future protocol to materialize, while
   best from security perspective, should be amended with a practical
   recommendation.

Thanks,
/Simon

To: [email-masked]
Subject: Working Group Last Call: draft-melnikov-digest-to-historic-00.txt
From: Tom Yu <[email-masked]>
Date: Wed, 05 Dec 2007 19:06:43 -0500
Lines: 18
Sender: [email-masked]

This message commences a Working Group Last Call period for the
following document:

	Title           : Moving DIGEST-MD5 to Historic
	Author(s)       : A. Melnikov
	Filename        : draft-melnikov-digest-to-historic-00.txt
	Pages           : 7
	Date            : 2007-09-08

A URL for this Internet-Draft is:
http://www.ietf.org/internet-drafts/draft-melnikov-digest-to-historic-00.txt

This Last Call will expire on Friday, December 21, 2007.  Please
review this document and address feedback to the Working Group mailing
list.

Tom Yu, SASL co-chair

To: [email-masked]
Subject: updated SCRAM document
From: Tom Yu <[email-masked]>
Date: Wed, 05 Dec 2007 13:58:33 -0500
Lines: 848
Sender: [email-masked]

--=-=-=

Abhijit submitted a new revision of SCRAM but it hasn't made it to the
I-D repository yet.  I've attached it below.  (Note that the actual
I-D revision will be -05, not -06 as in the below text.)

--=-=-=
Content-Disposition: attachment; filename=draft-newman-auth-scram-06.txt

Network Working Group                                  Abhijit Menon-Sen
Internet-Draft                                    Oryx Mail Systems GmbH
Intended Status: Proposed Standard                          Chris Newman
Expires: May 1, 2008                                    Sun Microsystems
                                                           December 2007

       Salted Challenge Response Authentication Mechanism (SCRAM)
                     draft-newman-auth-scram-06.txt

Status of this Memo

    By submitting this Internet-Draft, each author represents that any
    applicable patent or other IPR claims of which he or she is aware
    have been or will be disclosed, and any of which he or she becomes
    aware will be disclosed, in accordance with Section 6 of BCP 79.

    Internet-Drafts are working documents of the Internet Engineering
    Task Force (IETF), its areas, and its working groups. Note that
    other groups may also distribute working documents as Internet-
    Drafts.

    Internet-Drafts are draft documents valid for a maximum of six
    months and may be updated, replaced, or obsoleted by other documents
    at any time. It is inappropriate to use Internet-Drafts as reference
    material or to cite them other than as "work in progress."

    The list of current Internet-Drafts can be accessed at
    http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-
    Draft Shadow Directories can be accessed at
    http://www.ietf.org/shadow.html.

    This Internet-Draft expires in May 2008.

Copyright Notice

    Copyright (C) The IETF Trust (2007).

Abstract

    The secure authentication mechanism most widely deployed and used by
    Internet application protocols is the transmission of clear-text
    passwords over a channel protected by Transport Layer Security
    (TLS).  There are some significant security concerns with that
    mechanism, which could be addressed by the use of a challenge

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    response authentication mechanism protected by TLS. Unfortunately,
    the challenge response mechanisms presently on the standards track
    all fail to meet requirements necessary for widespread deployment,
    and have had success only in limited use.

    This specification describes the Salted Challenge Response
    Authentication Mechanism (SCRAM), which addresses the security
    concerns and meets the deployability requirements. When used in
    combination with TLS or an equivalent security layer, this mechanism
    could improve the status-quo for application protocol authentication
    and provide a suitable choice for a mandatory-to-implement mechanism
    for future application protocol standards.

1. Conventions Used in This Document

    The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
    "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
    document are to be interpreted as described in [RFC2119].

    Formal syntax is defined by [RFC4234] including the core rules
    defined in Appendix B of [RFC4234].

    Example lines prefaced by "C:" are sent by the client and ones
    prefaced by "S:" by the server. If a single "C:" or "S:" label
    applies to multiple lines, then the line breaks between those lines
    are for editorial clarity only, and are not part of the actual
    protocol exchange.

1.1. Terminology

    This document uses several terms defined in [RFC4949] ("Internet
    Security Glossary") including the following: authentication,
    authentication exchange, authentication information, brute force,
    challenge-response, cryptographic hash function, dictionary attack,
    eavesdropping, hash result, keyed hash, man-in-the-middle, nonce,
    one-way encryption function, password, replay attack and salt.
    Readers not familiar with these terms should use that glossary as a
    reference.

    Some clarifications and additional definitions follow:

    - Authentication information: Information used to verify an identity
      claimed by a SCRAM client. The authentication information for a
      SCRAM identity consists of salt and the "StoredKey" and
      "ServerKey" (as defined in the algorithm overview) for each
      supported cryptographic hash function.

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    - Authentication database: The database used to look up the
      authentication information associated with a particular identity.
      For application protocols, LDAPv3 (see [RFC4510]) is frequently
      used as the authentication database. For network-level protocols
      such as PPP or 802.11x, the use of RADIUS is more common.

    - Base64: An encoding mechanism defined in [RFC4648] which converts
      an octet string input to a textual output string which can be
      easily displayed to a human. The use of base64 in SCRAM is
      restricted to the canonical form with no whitespace.

    - Octet: An 8-bit byte.

    - Octet string: A sequence of 8-bit bytes.

    - Salt: A random octet string that is combined with a password
      before applying a one-way encryption function. This value is used
      to protect passwords that are stored in an authentication
      database.

1.2. Notation

    The pseudocode description of the algorithm uses the following
    notations:

    - ":=": The variable on the left hand side represents the octet
      string resulting from the expression on the right hand side.

    - "+": Octet string concatenation.

    - "[ ]": A portion of an expression enclosed in "[" and "]" may not
      be included in the result under some circumstances. See the
      associated text for a description of those circumstances.

    - HMAC(key, str): Apply the HMAC keyed hash algorithm (defined in
      [RFC2104]) using the octet string represented by "key" as the key
      and the octet string "str" as the input string. The size of the
      result is the hash result size for the hash function in use. For
      example, it is 20 octets for SHA-1 (see [RFC3174]).

    - H(str): Apply the cryptographic hash function to the octet string
      "str", producing an octet string as a result. The size of the
      result depends on the hash result size for the hash function in
      use.

    - Hi(str): Apply the cryptographic hash function to the octet string
      "str", then repeat the application on the output string for a

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      number of iterations equal to the integer i minus 1.

    - XOR: Apply the exclusive-or operation to combine the octet string
      on the left of this operator with the octet string on the right of
      this operator. The length of the output and each of the two inputs
      will be the same for this use.

2. Introduction

    This specification describes the Salted Challenge Response
    Authentication Mechanism (SCRAM) which addresses the requirements
    necessary to deploy a challenge-response mechanism more widely than
    past attempts. When used in combination with Transport Layer
    Security (TLS, see [RFC4346]) or an equivalent security layer, this
    mechanism could improve the status-quo for application protocol
    authentication and provide a suitable choice for a mandatory-to-
    implement mechanism for future application protocol standards.

    For simplicity, this mechanism does not presently include
    negotiation of a security layer. It is intended to be used with an
    external security layer such as that provided by TLS or SSH.

    SCRAM provides the following protocol features:

    - The authentication information stored in the authentication
      database is not sufficient by itself to impersonate the client.
      The information is salted to prevent a pre-stored dictionary
      attack if the database is stolen.

    - The server does not gain the ability to impersonate the client to
      other servers (with an exception for server-authorized proxies).

    - The mechanism permits the use of a server-authorized proxy without
      requiring that proxy to have super-user rights with the back-end
      server.

    - A standard attribute is defined to enable storage of the
      authentication information in LDAPv3 (see [RFC4510]).

    - Bindings to several authentication frameworks are provided so the
      mechanism is not limited to a small subset of protocols.

    - Both the client and server can be authenticated by the protocol.

    - The cryptographic hash function used to authenticate can be
      upgraded gracefully without breaking backwards compatibility or
      risking downgrade attacks.

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    For an in-depth discussion of why other challenge response
    mechanisms are not considered sufficient, see appendix A. For more
    information about the motivations behind the design of this
    mechanism, see appendix B.

    Comments regarding this draft may be sent either to the ietf-
    [email-masked] mailing list or to the authors.

3. SCRAM Algorithm Overview

    To begin with, the client is in possession of a username and
    password.  It sends the username to the server, which retrieves the
    corresponding authentication information, i.e. a salt, StoredKey,
    and ServerKey. The server sends the salt and an iteration count to
    the client, which then computes the following values and sends a
    ClientProof to the server:

        SaltedPassword  := Hi(HMAC(password, salt))
        ClientKey       := H(SaltedPassword)
        StoredKey       := H(ClientKey)
        AuthMessage     := client-first-message + "," +
                           server-first-message + "," +
                           final-client-message-without-proof
        ClientSignature := HMAC(StoredKey, AuthMessage)
        ClientProof     := ClientKey XOR ClientSignature
        ServerKey       := HMAC(SaltedPassword, salt)
        ServerSignature := HMAC(ServerKey, AuthMessage)

    The server authenticates the client by computing the
    ClientSignature, exclusive-ORing that with the ClientProof to
    recover the ClientKey and verifying the correctness of the ClientKey
    by applying the hash function and comparing the result to the
    StoredKey. If the ClientKey is correct, this proves that the client
    has access to the user's password.

    Similarly, the client authenticates the server by computing the
    ServerSignature and comparing it to the value sent by the server.
    If the two are equal, it proves that the server had access to the
    user's SaltedPassword.

    The AuthMessage is computed by concatenating messages from the
    authentication exchange. The format of these messages is defined in
    the Formal Syntax section.

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4. SCRAM Authentication Exchange

    SCRAM is a text protocol where the client and server exchange
    messages containing one or more attribute-value pairs separated by
    commas. Each attribute has a one-letter name. The messages and their
    attributes are described in section 4.1, and defined in the Formal
    Syntax section.

    This is a simple example of a SCRAM authentication exchange:

        C: n=Chris Newman,h=md5,r=ClientNonce
        S: r=ClientNonceServerNonce,h=md5,s=PxR/wv+epq,i=128
        C: r=ClientNonceServerNonce,p=WxPv/siO5l+qxN4
        S: v=WxPv/siO5l+qxN4

    First, the client sends a message containing the username, a list of
    the hash functions it supports, and a random, unique nonce. In
    response, the server sends its list of supported hash functions, an
    iteration count i, the user's salt, and appends its own nonce to the
    client-specified one.  The client then responds with the same nonce
    and a ClientProof computed as explained earlier. The server verifies
    the proof and responds with a ServerSignature, concluding the
    authentication exchange.

4.1 SCRAM attributes

    This section describes the permissible attributes, their use, and
    the format of their values.

    - a: This optional attribute specifies an authorization identity. A
      client may include it in its first message to the server if it
      wants to authenticate as one user, but subsequently act as a
      different user.  This is typically used by an administrator to
      perform some management task on behalf of another user, or by a
      proxy in some situations (see appendix A for more details).

      If this attribute is omitted (as it normally would be), or
      specified with an empty value, the authorization identity is
      assumed to be the same as the username specified with the
      (required) "n" attribute.

      The server always authenticates the user specified by the "n"
      attribute.  If the "a" attribute specifies a different user, the
      server associates that identity with the connection after
      successful authentication and authorization checks.

      The syntax of this field is the same as that of the "n" field with

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      respect to quoting of '=' and ','.

    - n: This attribute specifies the name of the user whose password is
      used for authentication. A client must include it in its first
      message to the server. If the "a" attribute is not specified
      (which would normally be the case), this username is also the
      identity which will be associated with the connection subsequent
      to authentication and authorization.

      The characters ',' or '=' in usernames are sent as '=2C' and '=3D'
      respectively. If the server receives a username which contains '='
      not followed by either '2C' or '3D', then the server MUST fail the
      authentication.

    - h: This attribute is a colon-separated list of supported hash
      function names, as defined in the IANA "Hash Function Textual
      Names" registry.

    - r: This attribute specifies a sequence of random printable
      characters excluding ',' which forms the nonce used as input to
      the hash function.  No quoting is applied to this string (unless
      the binding of SCRAM to a particular protocol states otherwise).
      As described earlier, the client supplies an initial value in its
      first message, and the server augments that value with its own
      nonce in its first response. It is important that this be value
      different for each authentication. The client must verify that the
      initial part of the nonce used in subsequent messages is the same
      as the nonce it initially specified.

    - c: This optional attribute specifies base64-encoded channel-
      binding data. It may be sent by either the client or the server.
      If specified, the authentication MUST fail unless the value is
      successfully verified.  Whether this attribute is included, and
      the meaning and contents of the channel-binding data depends on
      the external security layer in use. This is necessary to detect a
      man-in-the-middle attack on the security layer.

    - s: This attribute specifies the base64-encoded salt used by the
      server for this user. It is sent by the server in its first
      message to the client.

    - i: This attribute specifies an iteration count for the selected
      hash function, and must be sent by the server along with the
      user's salt.

    - p: This attribute specifies a base64-encoded ClientProof. The
      client computes this value as described in the overview and sends
      it to the server.

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    - v: This attribute specifies a base64-encoded ServerSignature. It
      is sent by the server in its final message, and may be used by the
      client to verify that the server has access to the user's
      authentication information. This value is computed as explained in
      the overview.

5. Hash functions

    SCRAM can use hash functions defined by the IANA "Hash Function
    Textual Names" registry.

    For interoperability, all SCRAM clients and servers MUST implement
    the MD5 hash function as defined in [RFC1321].

    Servers SHOULD announce a hash iteration-count of at least 128.

6. Formal Syntax

    The following syntax specification uses the Augmented Backus-Naur
    Form (ABNF) notation as specified in [RFC4234].

      generic-message = attr-val *("," attr-val)

      attr-val        = ALPHA "=" value

      value           = *(value-char)

      value-safe-char = %20-2B / %2D-3C / %3E-7E /
                        UTF8-2 / UTF8-2 / UTF-3 / UTF8-4
                        ;; UTF8-char except CTL, "=", and ",".

      value-char      = value-safe-char / "="

      base64-char     = ALPHA / DIGIT / "/" / "+"

      base64-4        = 4*4(base64-char)

      base64-3        = 3*3(base64-char) "="

      base64-2        = 2*2(base64-char) "=="

      base64          = *(base64-4) [base64-3 / base64-2]

      saslname        = 1*(value-safe-char / "=2C" / "=3D")
                        ;; Conforms to <value>
                        ;; Usernames are prepared using SASLPrep.

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      authzid         = "a=" saslname

      username        = "n=" saslname

      channel-binding = "c=" base64

      proof           = "p=" base64

      nonce           = "r=" value [value]
                        ;; Second part provided by server.

      salt            = "s=" base64

      verifier        = "v=" base64

      hash-list       = "h=" hash-name *(":" hash-name)

      hash-name       = value
                        ;; Hash Function Textual Name, from
                        ;; http://www.iana.org/assignments/hash-
                        function-text-names

      iteration-count = "i=" 1*DIGIT

      client-first-message =
                        [authzid ","] username "," hash-list "," nonce

      server-first-message =
                        nonce "," hash-list "," salt "," iteration-count

      client-final-message-without-proof =
                        nonce "," channel-binding

      client-final-message =
                        client-final-message-without-proof "," proof

      server-final-message =
                        verifier

7. Security Considerations

    If the authentication exchange is performed without a strong
    security layer, then a passive eavesdropper can gain sufficient
    information to mount an offline dictionary or brute-force attack
    which can be used to recover the user's password. The amount of time
    necessary for this attack depends on the cryptographic hash function
    selected, the strength of the password and the iteration count

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    supplied by the server. An external security layer with strong
    encryption will prevent this attack.

    If the external security layer used to protect the SCRAM exchange
    uses an anonymous key exchange, then the SCRAM channel binding
    mechanism can be used to detect a man-in-the-middle attack on the
    security layer and cause the authentication to fail as a result.
    However, the man-in-the-middle attacker will have gained sufficient
    information to mount an offline dictionary or brute-force attack.
    For this reason, SCRAM includes the ability to increase the
    iteration count over time.

    If the authentication information is stolen from the authentication
    database, then an offline dictionary or brute-force attack can be
    used to recover the user's password. The use of salt mitigates this
    attack somewhat by requiring a separate attack on each password.
    Authentication mechanisms which protect against this attack are
    available (e.g., the EKE class of mechanisms), but the patent
    situation is presently unclear.

    If an attacker obtains the authentication information from the
    authentication repository and either eavesdrops on one
    authentication exchange or impersonates a server, the attacker gains
    the ability to impersonate that user to all servers providing SCRAM
    access using the same password and salt. For this reason, it is
    important to use randomly-generated salt values.

    If the server detects (from the value of the client-specified "h"
    attribute) that both endpoints support a stronger hash function that
    the one the client actually chooses to use, then it SHOULD treat
    this as a downgrade attack and reject the authentication attempt.

8. IANA considerations

    (Hash function names registry, SASL mechanism registration.)

9. Acknowedgements

    The authors would like to thank Alexey Melnikov and Dave Cridland
    for their contributions to this document.

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10. Normative References

    [RFC4648]  Josefsson, "The Base16, Base32, and Base64 Data
               Encodings", RFC 4648, SJD, October 2006.

    [RFC1321]  Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321,
               April 1992.

    [RFC2104]  Krawczyk, Bellare, Canetti, "HMAC: Keyed-Hashing for
               Message Authentication", IBM, February 1997.

    [RFC2119]  Bradner, "Key words for use in RFCs to Indicate
               Requirement Levels", RFC 2119, Harvard University, March
               1997.

    [RFC3174]  Eastlake, Jones, "US Secure Hash Algorithm 1 (SHA1)", RFC
               3174, Motorola, September 2001

    [RFC4234]  Crocker, Overell, "Augmented BNF for Syntax
               Specifications: ABNF", RFC 4234, Brandenburg
               Internetworking, Demon Internet Ltd, October 2005.

    [RFC4346]  Dierks, Rescorla, "The Transport Layer Security (TLS)
               Protocol, Version 1.1", RFC 4346, Brandenburg
               Internetworking, April 2006.

    [RFC4422]  Melnikov, Zeilenga, "Simple Authentication and Security
               Layer (SASL)", RFC 4422, Isode Limited, June 2006.

11. Informative References

    [RFC1939]  Myers, Rose, "Post Office Protocol - Version 3", RFC
               1939, Carnegie Mellon, May 1996.

    [RFC2195]  Klensin, Catoe, Krumviede, "IMAP/POP AUTHorize Extension
               for Simple Challenge/Response", RFC 2195, MCI, September
               1997.

    [RFC2202]  Cheng, Glenn, "Test Cases for HMAC-MD5 and HMAC-SHA-1",
               RFC 2202, IBM, September 1997

    [RFC2289]  Haller, Metz, Nesser, Straw, "A One-Time Password
               System", RFC 2289, STD0061, February 1998.

    [RFC4949]  Shirey, "Internet Security Glossary, Version 2", RFC
               4949, FYI 0036, August 2007.

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    [RFC4086]  Eastlake, Schiller, Crocker, "Randomness Requirements for
               Security", RFC 4086, BCP 0106, Motorola Laboratories,
               June 2005.

    [RFC4120]  Neuman, Yo, Hartman, Raebun, "The Kerberos Network
               Authentication Service (V5)", RFC 4120, USC-ISI, July
               2005.

    [RFC4510]  Zeilenga, "Lightweight Directory Access Protocol (LDAP):
               Technical Specification Road Map", RFC 4510, June 2006.

    [DIGEST-MD5] Melnikov, "Using Digest Authentication as a SASL
               Mechanism", draft-ietf-sasl-rfc2831bis-12.txt, Isode
               Ltd., March 2007

12. Authors' Addresses

    Abhijit Menon-Sen
    Oryx Mail Systems GmbH

    Email: [email-masked]

    Chris Newman
    Sun Microsystems
    1050 Lakes Drive
    West Covina, CA 91790
    USA

    Email: [email-masked]

Appendix A: Other Authentication Mechanisms

    The DIGEST-MD5 mechanism has proved to be too complex to implement
    and test, and thus has poor interoperability. The security layer is
    often not implemented, and almost never used; everyone uses TLS
    instead.

    The PLAIN SASL mechanism allows a malicious server or eavesdropper
    to impersonate the authenticating user to any other server for which
    the user has the same password. It also sends the password in the
    clear over the network, unless TLS is used. Server authentication is
    not supported.

    (To be completed.)

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Appendix B: Design Motivations

    (To be written.)

Appendix C: SCRAM Examples

    (To be written.)

Appendix D: SCRAM Interoperability Testing

    (To be written.)

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Full Copyright Statement

    Copyright (C) The IETF Trust (2007). This document is subject to the
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    set forth therein, the authors retain all their rights.

    This document and the information contained herein are provided on
    an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE

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    REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE
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Acknowledgment

    Funding for the RFC Editor function is currently provided by the
    Internet Society.

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          (RFC Editor: Please delete everything after this point)

Open Issues

    - The appendices need to be written.

    - Should the server send a base64-encoded ServerSignature for the
      value of the "v" attribute, or should it compute a ServerProof the
      way the client computes a ClientProof?

    - What about this LDAP attribute to store authentication
      information?

    - It is entirely unclear to me how best to handle channel bindings.
      Should the channel binding data be sent directly at all?

    - It's not clear from the document that the hash function to use for
      a particular authentication exchange is selected by the client
      before the exchange begins.

    - Should the title include the acronym SASL to help the greppers?

Changes since -04

    - Update Base64 and Security Glossary references.

    - Add Formal Syntax section.

    - Don't bother with "v=".

    - Make MD5 mandatory to implement. Suggest i=128.

Changes since -03

    - Seven years have passed, in which it became clear that DIGEST-MD5
      suffered from unacceptably bad interoperability, so SCRAM-MD5 is
      now back from the dead.

    - Be hash agnostic, so MD5 can be replaced more easily.

    - General simplification.

Menon-Sen and Newman        Expires May 2008                   [Page 15]

--=-=-=--

Date: Wed, 05 Dec 2007 17:30:41 +0000
From: Alexey Melnikov <[email-masked]>
To: Tom Yu <[email-masked]>
CC: [email-masked]
Subject: Re: charter update: revised milestones?
Sender: [email-masked]

Tom Yu wrote:

>Milestones in my most recent charter proposal were:
>
>Done            initial document moving DIGEST-MD5 to Historic
>Sep 2007        WGLC document moving DIGEST-MD5 to Historic
>Oct 2007        initial implementation report questionnaire
>Oct 2007        initial RFC4422bis correcting references, etc.
>Oct 2007        initial document for DIGEST-MD5 successor
>Nov 2007        DIGEST-MD5 to Historic to IESG
>Jan 2008        send out implementation report questionnaire
>Feb 2008        compile implementation report questionnaire responses
>Feb 2008        WGLC RFC4422bis
>Feb 2008        WGLC DIGEST-MD5 successor
>Mar 2008        discuss implementation report questionnaire results
>Apr 2008        final implementation report
>Apr 2008        RFC4422bis to IESG
>Apr 2008        DIGEST-MD5 successor to IESG
>
>Given that we've slipped on a number of these so far, I suggest that
>we move them by three or four months.  Given the holiday season, I
>would prefer adding four months rather than three, but I am open to
>opinions either way.  Which would people prefer?
>
I think the "digest to historic" can be WGLC-ed right away.

Otherwise I don't have any preferences between 3 and 4 months.

>  Or do people think
>that adding 3 or 4 months across the board is not appropriate?  We can
>discuss this in detail during the WG session if needed.
>  
>

To: [email-masked]
Subject: charter update: revised milestones?
From: Tom Yu <[email-masked]>
Date: Wed, 05 Dec 2007 02:52:56 -0500
Lines: 25
Sender: [email-masked]

Milestones in my most recent charter proposal were:

Done            initial document moving DIGEST-MD5 to Historic
Sep 2007        WGLC document moving DIGEST-MD5 to Historic
Oct 2007        initial implementation report questionnaire
Oct 2007        initial RFC4422bis correcting references, etc.
Oct 2007        initial document for DIGEST-MD5 successor
Nov 2007        DIGEST-MD5 to Historic to IESG
Jan 2008        send out implementation report questionnaire
Feb 2008        compile implementation report questionnaire responses
Feb 2008        WGLC RFC4422bis
Feb 2008        WGLC DIGEST-MD5 successor
Mar 2008        discuss implementation report questionnaire results
Apr 2008        final implementation report
Apr 2008        RFC4422bis to IESG
Apr 2008        DIGEST-MD5 successor to IESG

Given that we've slipped on a number of these so far, I suggest that
we move them by three or four months.  Given the holiday season, I
would prefer adding four months rather than three, but I am open to
opinions either way.  Which would people prefer?  Or do people think
that adding 3 or 4 months across the board is not appropriate?  We can
discuss this in detail during the WG session if needed.

---Tom