Thanks for your thoughtful comments, Robert. Replies are inline below...
-----Original Message-----
From: Robert Sparks [mailto:rjsparks(_at_)nostrum(_dot_)com]
Sent: Monday, December 14, 2015 5:12 PM
To: Mike Jones <Michael(_dot_)Jones(_at_)microsoft(_dot_)com>; General Area
Review Team
<gen-art(_at_)ietf(_dot_)org>; ietf(_at_)ietf(_dot_)org;
jose(_at_)ietf(_dot_)org; draft-ietf-jose-jws-signing-
input-options(_at_)ietf(_dot_)org
Subject: Re: Gen-Art LC review: draft-ietf-jose-jws-signing-input-options-06
Mike -
No, this still doesn't explain why crit is not sufficient.
I'll plan on adding something along these lines to the draft to explain this:
"Implementations receiving JWSs using "b64" with a value of "false" will not be
able to successful use those JWSs unless they support this extension, since
they will be unable to obtain the payload value. If the JWS includes the
"crit" Header Parameter with "b64" in the set of values, this will ensure that
implementations not supporting this extension will reject the JWS, but
including "crit" is insufficient to enable the receiving implementation to use
the JWS; that requires supporting this extension."
You are making a bare assertion that using crit doesn't achieve a). I think it
does. Please explain (in the draft) why it doesn't.
You are making me guess, but I think you are only trying to avoid having to
include the few extra bits in the message. If you've _done_ the work of
ensuring all the applications understand using b64 through some out-of-
band magic, then including crit will just work. Are you pushing back on
anything _but_ the packet-bloat in this case?
If you _haven't_ done this out-of-band work, and you send to a receiver that
understands the extension, then a) is achieved. If you send to a receiver that
doesn't understand, things _should_ fail - arguably this also achieving a),
though I suspect you are wincing at perhaps not having a clear path to
recovery in this case?
I really think this boils down to you not wanting to pay the extra few bits in
the packet to say "crit".
if that's not the case, please explain (and again, this needs to be in the
draft,
not just an email thread).
Yes, size matters, but that's not the primary thing that's in play here. For
the extension to be useful, all parties using the JWS must implement the
extension, as explained in the new proposed text above. And once the JWT with
the extension is understood, "crit" adds nothing, because it's redundant.
That's why the draft doesn't require it.
But based on your comments and those of other reviewers, since there seems to
be demand for it, I plan to add the following text, which I think gets at the
heart of the issue you're discussing:
"Using "crit" with "b64"
If a JWS using "b64" with a value of "false" might be processed by
implementations not implementing this extension, then the "crit" Header
Parameter MUST be included with "b64" in its set of values to cause such
implementations to reject the JWS. Conversely, if used in environments in
which all participants implement this extension, then "crit" need not be
included, since its inclusion would have no effect, other than increasing the
JWS size and processing costs."
RjS
Thanks again, Robert,
-- Mike
On 12/13/15 10:04 PM, Mike Jones wrote:
Hi Robert,
You asked "_WHY_ is crit not sufficient? I think that's the thing that's
missing as motivation."
There are two goals we're discussing, which are related:
(a) Having an application that uses "b64":false work.
(b) Having an application that receives a JWT with "b64":false not
misinterpret the payload content.
Including "crit":["b64"] would be sufficient to achieve (b), as it would
cause
the JWS to be rejected by implementations not supporting "b64". But it does
not achieve (a), since the JWS would be rejected.
In contrast, using an implementation that understands "b64" achieves both
(a) and (b) without needing to include "crit". That's why it's not required.
Does that make sense now?
Best wishes,
-- Mike
-----Original Message-----
From: Robert Sparks [mailto:rjsparks(_at_)nostrum(_dot_)com]
Sent: Sunday, December 13, 2015 1:11 PM
To: Mike Jones <Michael(_dot_)Jones(_at_)microsoft(_dot_)com>; General Area
Review
Team
<gen-art(_at_)ietf(_dot_)org>; ietf(_at_)ietf(_dot_)org;
jose(_at_)ietf(_dot_)org;
draft-ietf-jose-jws-signing-input-options(_at_)ietf(_dot_)org
Subject: Re: Gen-Art LC review:
draft-ietf-jose-jws-signing-input-options-06
Cutting away a bit to focus on the question:
On 12/12/15 8:32 PM, Mike Jones wrote:
Hi Robert. Thanks for the useful review. Replies are inline below...
-----Original Message-----
<snip/>
I would have been much more comfortable with a consensus to require
'crit'.
(Count me in the rough if this proceeds with crit being optional).
I assume there is a strong reason to allow for option 1. Please add
the motivation for it to the draft, and consider adding a SHOULD use
'crit'
requirement if option 1 remains.
It's a reasonable request to have the draft say why "crit" isn't required.
My working draft adds the following new paragraph at the end of the
security considerations section to do this. Unless I hear objections, I'll
plan
on publishing an updated draft with the paragraph shortly.
"Note that methods 2 and 3 are sufficient to cause JWSs using this
extension to be rejected by implementations not supporting this extension
but they are not sufficient to enable JWSs using this extension to be
successfully used by applications.
The conclusion you draw here is not at all obvious.
_WHY_ is crit not sufficient? I think that's the thing that's missing as
motivation.
Thus, method 1 - requiring support for this extension - is the preferred
approach and the only means for this extension to be practically useful to
applications. Method 2 - requiring the use of <spanx
style="verb">crit</spanx> - while theoretically useful to ensure that
confusion between encoded and unencoded payloads cannot occur, is not
particularly useful in practice, since method 1 is still required for the
extension to be usable. When method 1 is employed, method 2 doesn't add
any value and since it increases the size of the JWS, its use is not required
by
this specification."
Nits/editorial comments:
In the security considerations, the last sentence of the first
paragraph needs to be simplified. I suggest replacing it with:
"It then becomes the responsibility of the application to ensure
that payloads only contain characters that will not cause parsing
problems for the serialization used, as described in Section 5. The
application also incurs the responsibility to ensure that the
payload will not be modified during retransmission.
I have simplified this in the manner that you suggested.
Thanks again,
-- Mike