Re: [OAUTH-WG] JWT: add "iss" and "aud" to Reserved Header Parameter Names in JWE

Thanks for writing this, Dick.  I think I understand your requirements and why they exist.

One question you didn't answer that will come up is whether these fields must also be present in the JWT claims set if they're present in the JWE header.  The logical answer to me seems to be something like "All claims MUST be present in the JWT Claims Set; specified claims MAY also be duplicated in the JWE header, and if present there, must have exactly the same values as in the JWT Claims Set."

Is that the way that you imagined this working?

				-- Mike

-----Original Message-----
From: oauth-bounces@ietf.org [mailto:oauth-bounces@ietf.org] On Behalf Of Dick Hardt
Sent: Wednesday, May 01, 2013 2:12 PM
To: O Auth WG
Subject: [OAUTH-WG] JWT: add "iss" and "aud" to Reserved Header Parameter Names in JWE

"iss" and "aud" would be optional parameters in a JWE. These parameters are in the payload, but since it is encrypted, the payload must be decrypted before they can be read. Some times knowing these parameters is required to be able to decrypt the payload ...

These would be additions to 9.3.1 in the JWT specification.

Why "iss" is needed:

Bob and Charlie each gave Alice a KID and a symmetric key to use to verify and decrypt tokens from them. 

The App and Alice share keys so Alice knows it is the App.

The User authorizes Bob to give the App a token (which authorizes the App to do something)

The App gives the token to Alice.

Since Alice indirectly received the token,  the only way for Alice to know who sent the token, is to look at the KID as the "iss" claim is encrypted. If the "kid" values are GUIDs, then Alice can just look up the "kid" and retrieve the associated symmetric key, and then decrypt and verify the token and THEN see who sent it. If there is a collision in KID values (Bon and Charlie gave the same KID for different keys), then Alice will not know which symmetric key to use.

Why "aud" is needed:

Dave gives a KID and symmetric key to Ellen, and Frank gives a KID and symmetric key to Gwen. 

Ellen and Gwen trust each other and know how to talk to each other. Gwen does not know Dave. Ellen does not know Frank

The App and Gwen share keys so Gwen knows it is the App.

The User authorizes Dave to give the App a token

Dave gives the token to Gwen (Dave does not have a relationship with Ellen)

Gwen now has a token that Ellen can decrypt and verify, but has no method for knowing that Ellen can do that. The "aud" property would allow Gwen to give the token to Ellen to decrypt and verify.
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