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I don't know if it is a good idea, but James has already given you a simple way of tagging fields that cannot be ignored - just append a '!' character. I guess you could just as easily append a '?' to those that could be ignored. That being said, I don't know that having optional mandatoriness is a good or a bad thing. Jim From: [email protected] [mailto:[email protected]] On Behalf Of Mike Jones Sent: Thursday, July 26, 2012 10:39 AM To: Breno de Medeiros; Manger, James H Cc: [email protected] Subject: Re: [jose] MUST understand ALL header fields I agree with this analysis. If there's an explicit way defined to indicate which additional header parameters may be ignored, that would be OK. Allowing ignore-by-default would be a recipe for disaster. -- Mike From: [email protected] [mailto:[email protected]] On Behalf Of Breno de Medeiros Sent: Thursday, July 26, 2012 10:35 AM To: Manger, James H Cc: [email protected] Subject: Re: [jose] MUST understand ALL header fields 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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