Re: Update of GS2

[Nicolas Williams <[e-mail]>]

On Thu, Jun 29, 2006 at 12:32:35PM +0200, Simon Josefsson wrote:
> 5.  Channel Bindings
> 
>    [[This section is tentative further discussion on the topic.  This
>    was written to provide an example of how the details of how one
>    approach to this concept could look like.  There are other approaches
>    that may be preferable.]]
> 
>    The GS2 mechanism provide its own token field for channel bindings,
>    in addition to the "chan_binding" parameter in the GSS-API context
>    functions.  The reason for this is that the GS2 mechanism wish to
>    provide an option to proceed even if the channel bindings does not
>    match.  The GSS-API framework specifies that authentication cannot
>    proceed if channel bindings does not match.  The GSS-API framework
>    also does not specify the kind of privacy layer the channel binding
>    should be transferred under, thus making it possible for attackers to
>    modify it to always make channel binding negotiation succeed.

Strike the last sentence.  It's not useful -- we only need integrity
protection for channel binding data, and GSS-API mechanisms that support
channel binding do provide that.

>    The client can select, using the "Native Channel Bindings" bit,
>    whether it wishes to use the "chan_bindings" parameter in the GSS-API
>    layer or not.  If it wishes to use this, it is not possible to
>    continue after a failed channel binding negotiation.

I don't understand why we should use the GSS-API channel binding
facility at all given that we need to build a SASL-specific channel
binding facility to support the semantics we want.

I think this text would be simplified if it required that
GSS_C_NO_CHANNEL_BINDINGS be used for channel bindings in the GSS_Init/
Accept_sec_context() calls.

>    For TLS, the channel binding data is specified in the next section.
>    For other security layers, channel binding data will have to
>    specified elsewhere, and this specification will have to be updated
>    with explicit considerations.
> 
>    [[All channel bindings should go into a separate document.]]

I've resubmitted draft-ietf-nfsv4-channel-bindings-04.txt, it doesn't
have quite the txt below, but we can modify it.

> 5.1.  Name Of Tls Channel For Use As Channel Binding

...

Nico
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