[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: Poll: use of TLS channel bindings in SCRAM
Nicolas Williams <Nicolas.Williams@xxxxxxx> writes:
> Huh, I think we can do something far simpler still: just add enough ABNF
> to define non-critical GS2 header extensions. (That's what I get for
> posting late at night instead of sleeping on the idea.)
> ;; Non-critical GS2 extension headers; servers MUST ignore if they don't
> ;; understand them
> gs2-ext-attr = "gs2-" 1*ALPHA
> gs2-ext-attr-val = gs2-ext-attr "=" value
> gs2-ext-attrs = gs2-ext-attr-val *("," gs2-ext-attr-val)
> ;; GS2 header
> gs2-cbind-flag = "n" / "y" / "p"
> gs2-header = gs2-cbind-flag [ authzid ] "," [ gs2-ext-attrs "," ]
> Or something like that. (One might prefer something slightly different
> that makes it easier to find the end of the GS2 header.)
Right, you need a reliable way to identify the end of the gs2-header. I
also dislike the complexity in a parser that always will have to ignore
any number of gs2-* parameters, so how about this instead:
string = 1*(UTF8-char-safe / "=2C" / "=3D")
gs2-authzid = "a=" string
gs2-cbind-flag = "n" / "y" / "p"
gs2-nonstd-flag = "F"
gs2-header = [gs2-nonstd-flag "," ] gs2-cbind-flag "," [ gs2-authzid ] "," [ "gs2-ext" "=" string ] ","
Servers that doesn't understand a gs2-ext token MUST fail
Having thought about this proposal (briefly), I don't think an extension
idea is a good idea. What you propose is an extension mechanism inside
a SASL mechanism. I have a fairly strong general preference against
that -- SASL is an extensible protocol, and the way to negotiate
extensions is to specify a new SASL mechanism name and have clients
prefer that mechanism. The new mechanism can be a cut'n'paste of the
old mechanism, plus some new wording. I don't see a need for an
extension mechanism inside GS2 here?
So, my preferences are:
1) GS2 -13 but remove tls-server-end-point and only support tls-unique.
2) GS2 -13 plus the changes I proposed earlier to send a list of channel
binding types. This allows tls-server-end-point to work if there is
someone that is willing to do the work (specify an outer negotiation
protocol) for that.
3/4) GS2 -13.
3/4) GS2 plus your Y/P proposal.
Not sure how to rate these two against each other. The Y/P scheme is
close to an extension scheme.
5) GS2 plus the above extension scheme.