Re: [CHANNEL-BINDING] Re: draft-ietf-sasl-gs2 AD review comments

On Wed, Oct 10, 2007 at 11:51:03AM -0400, Jeffrey Hutzelman wrote:
> On Wed, 10 Oct 2007, Nicolas Williams wrote:
> > I don't agree.  The I-D is clear on channel bindings being a single
> > octet string.  The prefix is a US-ASCII string prefixed to the raw
> > channel binding octet string.  After the prefix is added you still have
> > a single octet string.
> 
> Ah, but the spec doesn't actually _say_ that.  It doesn't actually say
> anywhere that the prefix is prepended to the channel-specific binding
> data, resulting in a single octet string for the application to transport.
> On the other hand, it _does_ say that the application needs to distinguish
> channel types based on the prefix, which suggests (but only suggests) that
> they are treated as separate items.

Well, OK, we can clarify that.

> If it's a single string, then you need a separator, for two reasons:
> 
> - Without it, it's not good enough for prefixes to be unique; it must be
>   the case that no prefix is an initial substring of another.
> 
> - Without a separator, it is difficult for the application (or library)
>   to separate the prefix from the data, which it must do in order to
>   determine the channel type, which affects interpretation of the data.
> 
> Of course, one could use another approach, like a counted string, or a
> fixed-width field, or a fixed-size integer.  I don't care much.

Sure.

I'll send text this afternoon.

Nico
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