Re: [jose] How would x5u really be used with JWE?

Richard Barnes <rbarnes@bbn.com> Fri, 25 January 2013 18:02 UTC

Return-Path: <rbarnes@bbn.com>
X-Original-To: jose@ietfa.amsl.com
Delivered-To: jose@ietfa.amsl.com
Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id CBBEF21F87FA for <jose@ietfa.amsl.com>; Fri, 25 Jan 2013 10:02:59 -0800 (PST)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -106.599
X-Spam-Level:
X-Spam-Status: No, score=-106.599 tagged_above=-999 required=5 tests=[BAYES_00=-2.599, RCVD_IN_DNSWL_MED=-4, USER_IN_WHITELIST=-100]
Received: from mail.ietf.org ([64.170.98.30]) by localhost (ietfa.amsl.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id WTG5KlB2MZ3v for <jose@ietfa.amsl.com>; Fri, 25 Jan 2013 10:02:59 -0800 (PST)
Received: from smtp.bbn.com (smtp.bbn.com [128.33.0.80]) by ietfa.amsl.com (Postfix) with ESMTP id 42F3921F873E for <jose@ietf.org>; Fri, 25 Jan 2013 10:02:59 -0800 (PST)
Received: from dhcp89-089-050.bbn.com ([128.89.89.50]:60055) by smtp.bbn.com with esmtps (TLSv1:AES128-SHA:128) (Exim 4.77 (FreeBSD)) (envelope-from <rbarnes@bbn.com>) id 1Tync7-0007Sd-9P; Fri, 25 Jan 2013 13:02:55 -0500
Content-Type: text/plain; charset=us-ascii
Mime-Version: 1.0 (Mac OS X Mail 6.2 \(1499\))
From: Richard Barnes <rbarnes@bbn.com>
In-Reply-To: <4E1F6AAD24975D4BA5B168042967394366A89CD9@TK5EX14MBXC285.redmond.corp.microsoft.com>
Date: Fri, 25 Jan 2013 13:02:54 -0500
Content-Transfer-Encoding: quoted-printable
Message-Id: <D994E08C-6C84-471C-B0D4-225E0199011A@bbn.com>
References: <CA+k3eCRyew6xdKGQVOf27MK9AqOJ1A2jmhVYF+u=3Q3TMBtEng@mail.gmail.com> <42D3BCD6-D450-4A77-ABF5-87A5ABA874DE@bbn.com> <4E1F6AAD24975D4BA5B168042967394366A89CD9@TK5EX14MBXC285.redmond.corp.microsoft.com>
To: Mike Jones <Michael.Jones@microsoft.com>
X-Mailer: Apple Mail (2.1499)
Cc: Brian Campbell <bcampbell@pingidentity.com>, "jose@ietf.org" <jose@ietf.org>
Subject: Re: [jose] How would x5u really be used with JWE?
X-BeenThere: jose@ietf.org
X-Mailman-Version: 2.1.12
Precedence: list
List-Id: Javascript Object Signing and Encryption <jose.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/jose>, <mailto:jose-request@ietf.org?subject=unsubscribe>
List-Archive: <http://www.ietf.org/mail-archive/web/jose>
List-Post: <mailto:jose@ietf.org>
List-Help: <mailto:jose-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/jose>, <mailto:jose-request@ietf.org?subject=subscribe>
X-List-Received-Date: Fri, 25 Jan 2013 18:02:59 -0000

Ok, that sort of makes sense.  

Note that in that case, there's no point to sending a cert chain ('x5c'), since it's the recipient's cert you're talking about.  Even 'x5u' is kind of overkill; all you really need is 'x5t'.




On Jan 25, 2013, at 12:43 PM, Mike Jones <Michael.Jones@microsoft.com> wrote:

> They're there exactly to let the recipient known which private key to use for decryption.  Hardly useless...
> 
> 				-- Mike
> 
> -----Original Message-----
> From: jose-bounces@ietf.org [mailto:jose-bounces@ietf.org] On Behalf Of Richard Barnes
> Sent: Friday, January 25, 2013 8:36 AM
> To: Brian Campbell
> Cc: jose@ietf.org
> Subject: Re: [jose] How would x5u really be used with JWE?
> 
> AFAICT, the X.509 fields in JWE are pretty useless.
> 
> If you're using key transport (i.e., wrapping the symmetric key in a public key), then you would use the "jwk" or "jku" fields to reference the key pair you used to do the wrapping.  The only function of the public key crypto fields in a JWE is to let the recipient know which private key to use for decryption.  The recipient already needs to have the private key, since it obviously won't be in the message.
> 
> The question of how the encrypting party figures out which public key to use for a given recipient (and in particular, roll-over), is an application-layer question, not something that JWE would address.  See the XMPP end-to-end security doc for an example; they use a separate exchange to associate a JWK with an XMPP ID.
> <http://tools.ietf.org/html/draft-miller-xmpp-e2e>
> 
> --Richard
> 
> 
> 
> 
> On Jan 22, 2013, at 1:10 PM, Brian Campbell <bcampbell@pingidentity.com> wrote:
> 
>> Is there a concrete use case for this that someone could explain to me?
>> 
>> How does an encrypting party know what URL to use to get the key to encrypt? I assume some out-of-band exchange. How would key rolling work then? An an encrypting party would need to a priori know all potential x5u's of the decrypting party? Which seems dubious. And how would the decrypting party signal a desired change of keys?  
>> 
>> Am I missing something obvious here?  
>> 
>> 
>> 
>> 
>> 
>> 
>> _______________________________________________
>> jose mailing list
>> jose@ietf.org
>> https://www.ietf.org/mailman/listinfo/jose
> 
> _______________________________________________
> jose mailing list
> jose@ietf.org
> https://www.ietf.org/mailman/listinfo/jose
> _______________________________________________
> jose mailing list
> jose@ietf.org
> https://www.ietf.org/mailman/listinfo/jose