Put it another way: If we want the JWT security header to be extensible we need to define an explicit extension mechanism. It is NOT sufficient to say MUST ignore non-understood fields in the header. This will make it impossible to write secure implementations of validation libraries in practice.
An extension mechanism would define: - How to bundle fields of an extension as a single object. - How to indicate that this object is an extension, and whether the extension is critical (can't be safely ignored) or not. You can't get extensibility cheaply in a security spec. A choice is needed whether to support extensibility explicitly (at the expense of significant increase of spec complexity, since a lot will have to be spelled out right now) or not. Giving up clear security semantics to get cheap extensibility is not an acceptable 3rd option. On Thu, Jul 26, 2012 at 9:16 AM, Breno de Medeiros <[email protected]> wrote: > > > > On Wed, Jul 25, 2012 at 10:28 PM, Manger, James H < > [email protected]> wrote: > >> Breno,**** >> >> ** ** >> >> >> How about stapling an OCSP response to a JOSE message?**** >> >> > That's a more compelling use case -- it's security-specific but only >> adds to the security validation context.**** >> >> ** ** >> >> ** ** >> >> How about the signing time?**** >> >> ** ** >> >> How about some DNS records with DANE and DNSSEC info giving evidence that >> the public key is associated with a domain?**** >> >> ** ** >> >> How about a blob of data related to Sovereign Keys, or Perspectives, or >> Convergence, or some other proposal to bolster PKI?**** >> >> ** ** >> >> How about a domain_parameter_seed so you can verify that the common >> domain parameters (eg p & q in DSA) were not chosen to have special >> properties?**** >> >> ** ** >> >> How about data to allow you to validate a public key (eg co-factor for >> EC? Something complicated for RSA?)?**** >> >> ** ** >> >> How about a timestamp from a timestamp service?**** >> >> ** ** >> >> ** ** >> >> I’m not sure which, where, or when an item like the ones mentioned above >> will be needed. I am confident that someone will need some items like >> these. When that happens they should have a choice about whether including >> the item needs to break interop with all existing receivers. A mode field >> that MUST be understood (eg “t”:”sig”) coupled with MUST ignored any >> unrecognized parameters keeps our future choices open. >> > > That's not good enough for a security spec. If fields are added and not > all MUST be understood, then we need explicit syntax about what fields are > to be ignored when not understood. E.g., in X509 certificates, extensions > (while optional) have the ability to declare themselves critical, so that > implementations that don't understand that extension MUST reject the > certificate as invalid. > > >> **** >> >> ** ** >> >> ** ** >> >> > However declaring that any header you don't understand could be >> optional is a far worse balance on the extensibility versus simplicity >> spectrum (where simplicity here is a stand-in for security, >> interoperability, etc.)**** >> >> ** ** >> >> I’m not sure I understand this “simplicity” argument. Ignoring >> unrecognized fields is the simplest implementation choice. Is your idea >> that if you tightly constrain extensibility (by making them MUST >> understand) then messages will not accumulate as many “enhancements” of >> dubious value. That is, over time a MUST ignore rule allows messages to get >> more complex (and hence less secure/interoperable). Do you want “MUST >> understand” to strongly discourage people misusing the header to carry >> content metadata, for instance? >> > > Inevitably, a field will be added that shouldn't be ignored because it > modifies the meaning of some other widely understood header entry, followed > by usual antics and general perplexity. > > >> **** >> >> ** ** >> >> ** ** >> >> --**** >> >> James Manger**** >> >> ** ** >> >> *From:* Breno de Medeiros [mailto:[email protected]] >> *Sent:* Thursday, 26 July 2012 1:12 PM >> *To:* Manger, James H >> *Cc:* [email protected] >> >> *Subject:* Re: [jose] MUST understand ALL header fields**** >> >> ** ** >> >> That's a more compelling use case -- it's security-specific but only adds >> to the security validation context.**** >> >> ** ** >> >> There may be a case to define optional entries in the JWT header. However >> declaring that any header you don't understand could be optional is a far >> worse balance on the extensibility versus simplicity spectrum (where >> simplicity here is a stand-in for security, interoperability, etc.) So I am >> not convinced that losing the ability to declare OCSP bindings in JWTs >> justifies dropping the MUST language. If there is rough consensus that >> defining optional security fields in the header is prudent from the >> viewpoint of future spec extensibility then we should devise some simple >> way to declare a JWT header field optional and exempt _only_those_ from the >> MUST fail when not understanding clause. Changing the default behavior even >> to SHOULD appears to me to sacrifice too much on the altar of >> extensibility. **** >> >> ** ** >> >> On Wed, Jul 25, 2012 at 7:38 PM, Manger, James H < >> [email protected]> wrote:**** >> >> How about stapling an OCSP response to a JOSE message? >> >> Why should that be "MUST understand"? >> >> -- >> James Manger**** >> >> >> >> **** >> >> ** ** >> >> -- >> --Breno**** >> > > > > -- > --Breno > -- --Breno
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