Re: [jose] Should we delete the "typ" header field

>From what I understand, both typ and cty are something to be consumed by
the application and not JOSE processor. From the point of view of the JOSE
processor, they should be ignored.

We could drop both fields from JOSE specs, but that is going to cause each
and every application that uses JOSE to define their own field, which is a
waste. That is why we are defining them here.

I would rather drop them than define JOSE processing semantics to these
fields.

2013/5/31 Mike Jones <Michael.Jones@microsoft.com>

>  No, “cty” is used by the derived class to determine the type of the
> encapsulated field.  But that’s not a complete description of the **entire
> object** - especially not the additional meaning imbued by the additional
> parameters the derived type may add to the JOSE header.  “typ” is there to
> provide the type of the entire object, including what you’re calling the
> wrapper parts.****
>
> ** **
>
>                                                             -- Mike****
>
> ** **
>
> *From:* Richard Barnes [mailto:rlb@ipv.sx]
> *Sent:* Thursday, May 30, 2013 7:58 AM
>
> *To:* Mike Jones
> *Cc:* Jim Schaad; jose@ietf.org; Dick Hardt
> *Subject:* Re: [jose] Should we delete the "typ" header field****
>
> ** **
>
> Isn't that requirement met by "cty"?  The only thing JOSE adds is a crypto
> wrapper around the real application content.  If you're an application, you
> know a JOSE object is the thing you want because it contains the content
> you want -- it's a JWT because it contains JWT claims.****
>
> ** **
>
> Inheritance is the wrong metaphor.  This is encapsulation of application
> data:****
>
> if (jws.valid && jws.cty == "application/jwt_claims") {****
>
>     jwtClaims = jws.content;****
>
> }****
>
> ** **
>
> --Richard****
>
> ** **
>
> On Thu, May 30, 2013 at 10:43 AM, Mike Jones <Michael.Jones@microsoft.com>
> wrote:****
>
> Thanks for sharing the S/MIME details.  Although I was actually making the
> analogy to MIME – not S/MIME.  Like many analogies, it’s imperfect, but I
> believe still illustrative.****
>
>  ****
>
> The reason that the analogy isn’t perfect is that the JOSE data structures
> are used to build application-specific data structures that are legal JOSE
> data structures but also have additional properties – including additional
> header fields with specific semantics.  (When we agreed to ignore
> not-understood header fields we let that horse out of the barn.)  For
> instance, Dick Hardt uses JWEs with issuer and audience fields in the
> headers, so they can be used by routing software.****
>
>  ****
>
> Think of JOSE as the base class and the application types built using it
> as derived classes.  JWT is a derived class.  Dick’s structures are a
> derived class.  These derived classes sometimes need names.  That’s what
> “typ” is for.****
>
>  ****
>
>                                                             -- Mike****
>
>  ****
>
> *From:* Richard Barnes [mailto:rlb@ipv.sx]
> *Sent:* Thursday, May 30, 2013 7:34 AM****
>
>
> *To:* Mike Jones
> *Cc:* Jim Schaad; jose@ietf.org; Dick Hardt
> *Subject:* Re: [jose] Should we delete the "typ" header field****
>
>  ****
>
> You're mixing up "typ" and "cty".  If you want to make the analogy to
> S/MIME, "cty" is the equivalent to Content-Type inside the protected MIME
> body; "typ" is the content-type on the outer MIME header.  Pasting in an
> example:****
>
>  ****
>
> -----BEGIN-----****
>
> Content-Type: application/pkcs7-mime; smime-type=signed-data;****
>
>      name=smime.p7m****
>
> Content-Transfer-Encoding: base64****
>
> Content-Disposition: attachment; filename=smime.p7m****
>
>  ****
>
> 567GhIGfHfYT6ghyHhHUujpfyF4f8HHGTrfvhJhjH776tbB9HG4VQbnj7****
>
> 77n8HHGT9HG4VQpfyF467GhIGfHfYT6rfvbnj756tbBghyHhHUujhJhjH****
>
> HUujhJh4VQpfyF467GhIGfHfYGTrfvbnjT6jH7756tbB9H7n8HHGghyHh****
>
> 6YT64V0GhIGfHfQbnj75****
>
> -----END-----****
>
> <http://tools.ietf.org/html/rfc3851#section-3.4.2>****
>
>  ****
>
> The outer Content-Type, which is analogous to "typ", MUST be
> application/pkcs7-mime, with a parameter indicating the type of CMS object.
>  This is the same as requiring "typ" to be JWE or JWS.  The inner
> Content-Type (ASN.1/base64 encoded in the example) can be anything, just
> like "cty".****
>
>  ****
>
> --Richard****
>
>  ****
>
>  ****
>
>  ****
>
>  ****
>
> On Thu, May 30, 2013 at 12:53 AM, Mike Jones <Michael.Jones@microsoft.com>
> wrote:****
>
> Requiring that the “typ” value be only “JWS” or “JWE” would be analogous
> to the MIME spec requiring that the Content-Type: field be only
> “text/plain” or “message/external-body”.  It would render it useless.****
>
>  ****
>
>                                                             -- Mike****
>
>  ****
>
> *From:* jose-bounces@ietf.org [mailto:jose-bounces@ietf.org] *On Behalf
> Of *Richard Barnes
> *Sent:* Wednesday, May 29, 2013 8:03 PM
> *To:* Mike Jones
> *Cc:* Jim Schaad; jose@ietf.org; Dick Hardt****
>
>
> *Subject:* Re: [jose] Should we delete the "typ" header field****
>
>  ****
>
> If this is the level of "type" you're referring to, I think we should drop
> it from the spec.  It's an application-layer thing that the app can add or
> not according to its wishes.****
>
>  ****
>
> I'm with Dick on this.  I think we should either have a mandatory
> indicator of what type of JOSE object this, or nothing at all.   If the
> former, the allowable values are "JWE" and "JWS".  The "+JSON" options are
> non-sensical -- the app needs to know what it's parsing before it gets this
> header.  While I have a preference for the former (for clarity), the latter
> approach is also OK with me, since the MIME types are specific to JWE/JWS.
> ****
>
>  ****
>
> Another approach here would be to address the JSON and compact forms
> separately.  The JSON form has no need of "typ" at all, since the type of
> the object is completely clear from what fields are there, e.g.,
> "recipients" vs. "signatures".  For the compact form, we could do something
> like James's "E."/"S." prefix idea, which you need because the
> dot-separated components have different meanings and no field names to
> indicate this.****
>
>  ****
>
> --Richard****
>
>  ****
>
> On Wed, May 29, 2013 at 8:30 PM, Mike Jones <Michael.Jones@microsoft.com>
> wrote:****
>
> A standard library is unlikely to know the meanings of all possible “typ”
> values – and more to the point, *it doesn’t have to*.  It’s the
> application’s job to determine that “this blob is a JOSE object” and then
> pass it to a standard library, which will then ignore the “typ” value.****
>
>  ****
>
> A standard JOSE library won’t know what “typ”: “JWT” means.  It won’t know
> what “typ”: “BCGovToken” is, should the BC Government want to declare that
> it’s using a token with particular characteristics.  It won’t know what
> “typ”: “XMPP” is, should XMPP want to declare that it’s using a JOSE data
> structure with particular characteristics.  Etc.****
>
>  ****
>
> All these values can be registered in the registry and used by
> applications that understand them.  That’s the application’s job – not the
> library’s job.  The “typ” field is just there so that applications have a
> standard place to make any such declarations that they may need.****
>
>  ****
>
>                                                                 -- Mike***
> *
>
>  ****
>
> *From:* Dick Hardt [mailto:dick.hardt@gmail.com]
> *Sent:* Wednesday, May 29, 2013 5:18 PM
> *To:* Mike Jones
> *Cc:* Jim Schaad; jose@ietf.org****
>
>
> *Subject:* Re: [jose] Should we delete the "typ" header field****
>
>  ****
>
> I'd prefer to be able to use standard libraries for creating and parsing
> tokens, and not specialized libraries dependent on the use case.****
>
>  ****
>
> I strongly think we either drop "typ" or make it required.****
>
>  ****
>
> On Wed, May 29, 2013 at 5:03 PM, Mike Jones <Michael.Jones@microsoft.com>
> wrote:****
>
> It’s fine for your application to specify that it’s required for your use
> case.  Not applications need it, so they shouldn’t be forced to pay the
> space penalty of an unnecessary field.****
>
>  ****
>
>                                                                 -- Mike***
> *
>
>  ****
>
> *From:* jose-bounces@ietf.org [mailto:jose-bounces@ietf.org] *On Behalf
> Of *Dick Hardt
> *Sent:* Wednesday, May 29, 2013 4:56 PM****
>
>
> *To:* Jim Schaad
> *Cc:* jose@ietf.org
> *Subject:* Re: [jose] Should we delete the "typ" header field****
>
>  ****
>
> I use it all the time and my code would barf if it was not there.****
>
>  ****
>
> I think it should be required rather than be a hint if it is going ot be
> there.****
>
>  ****
>
> On Wed, May 29, 2013 at 4:40 PM, Jim Schaad <ietf@augustcellars.com>
> wrote:****
>
> I think the values just changed****
>
>  ****
>
> However the way you are using it would be an argument to say that it
> should be a required field.  Are you just using it as a hint if it exists
> and then looking at the rest of the fields if it is not present?****
>
>  ****
>
> Jim****
>
>  ****
>
>  ****
>
> *From:* Dick Hardt [mailto:dick.hardt@gmail.com]
> *Sent:* Wednesday, May 29, 2013 3:49 PM
> *To:* Jim Schaad
> *Cc:* jose@ietf.org
> *Subject:* Re: [jose] Should we delete the "typ" header field****
>
>  ****
>
> Well, I have been using, but now realize the spec changed or I was
> confused.****
>
>  ****
>
> I had been setting "typ" to be either "JWE" or "JWS" depending on the type
> of token I was creating or parsing as it was easier than looking at "alg"*
> ***
>
>  ****
>
> As currently defined, I don't see value in "typ".****
>
>  ****
>
> -- Dick****
>
>  ****
>
>  ****
>
> On Wed, May 29, 2013 at 3:02 PM, Jim Schaad <ietf@augustcellars.com>
> wrote:****
>
> In reading the documents, I am trying to understand the justification for
> having the “typ” header parameter in the JOSE documents.****
>
>  ****
>
> The purpose of the field is to hold the type of the object.  In the past,
> I believe that values which should now be placed in the cty field (such as
> “JWT”) were placed in this field as well.  However the parameter is
> optional and an implementation cannot rely on its being present.  This
> means that for all practical purposes all of the code to determine the
> value of the type field from the values of the alg and enc fields.  If the
> field was mandatory then this code would disappear at a fairly small space
> cost and I can understand why the parameter would be present.****
>
>  ****
>
> Can anybody justify why this field should be present in the document – or
> should it just disappear?****
>
>  ****
>
> Jim****
>
>  ****
>
>
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>
>
>
> ****
>
>  ****
>
> --
> -- Dick ****
>
>
>
> ****
>
>  ****
>
> --
> -- Dick ****
>
>
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> https://www.ietf.org/mailman/listinfo/jose****
>
>
>
> ****
>
>  ****
>
> --
> -- Dick ****
>
>
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> https://www.ietf.org/mailman/listinfo/jose****
>
>  ****
>
>  ****
>
> ** **
>
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>
>

-- 
Nat Sakimura (=nat)
Chairman, OpenID Foundation
http://nat.sakimura.org/
@_nat_en