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Re: [OAUTH-WG] JWE with A128CBC-HS256

John Bradley <ve7jtb@ve7jtb.com> Fri, 28 March 2014 16:10 UTC

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From: John Bradley <ve7jtb@ve7jtb.com>
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Date: Fri, 28 Mar 2014 13:09:02 -0300
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To: Antonio Sanso <asanso@adobe.com>
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Cc: "oauth@ietf.org" <oauth@ietf.org>, "jose@ietf.org" <jose@ietf.org>
Subject: Re: [OAUTH-WG] JWE with A128CBC-HS256
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This reference may be useful to you. http://tools.ietf.org/html/draft-mcgrew-aead-aes-cbc-hmac-sha2

The part of the spec you need is  http://tools.ietf.org/html/draft-ietf-jose-json-web-algorithms-24#page-23

We originally used a KDF as you mention.  In order to simplify the alg and align with draft-mcgrew-aead-aes-cbc-hmac-sha2.

K is the concatenation of the AES key and teh HMAC Key.

John B.


On Mar 28, 2014, at 11:19 AM, Antonio Sanso <asanso@adobe.com> wrote:

> hi *,
> 
> in the JWT specification [0] there is an example of a JWE that use A128CBC-HS256 for content encrpyption.
> Now I am not a cryptographer my self but IIUC the same CEK is used for encrypting with AES and authentication HMAC.
> 
> AFAIK is better to use two different keys for those 2 different primitives (this will not obviously apply to AES_GCM).
> 
> Unless I am missing something... :)
> 
> regards
> 
> antonio
> 
> [0] http://tools.ietf.org/html/draft-ietf-oauth-json-web-token-19#appendix-A.1
> [1] http://tools.ietf.org/html/draft-ietf-jose-json-web-encryption-24#appendix-A.2
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