Re: [jose] encrypting AND signing a token

Thanks Jim. An interesting historical reference. 

In my use case, who signed or who the token is for is not a secret. The payload needs to be kept a secret.

Does no one sign and encrypt SAML tokens?
Is this not a common use case?

If it does need to be solved, it would seem to me that a standards body would be the place to have lots of eyes look at how to sign and encrypt a token so that people do not do naive sign and encrypt.

Q: does anyone else need to sign and encrypt?

-- Dick

On Nov 4, 2012, at 10:24 AM, "Jim Schaad" <ietf@augustcellars.com> wrote:

> <personal>
> 
> I would note that the original PKCS#7 specifications had a mode that
> provided a similar sign and encrypt as a single operation mode.  When the
> PKCS#7 specifications where adopted by the IETF as part of the CMS work,
> this mode was discussed and very deliberately dropped because of numerous
> security problems that had been found.  These included (but are not limited
> to) the fact that it was signed or who signed it was sometimes a security
> leak.  Also there were attacks where the signed and encrypted mode could be
> converted to just an encrypted mode.
> 
> I would think that there would be a need for a very detailed security
> analysis that we are not prepared to do in order to support a signed and
> encrypted mode.
> 
> Jim
> 
> 
>> -----Original Message-----
>> From: jose-bounces@ietf.org [mailto:jose-bounces@ietf.org] On Behalf Of
>> Dick Hardt
>> Sent: Friday, November 02, 2012 12:30 PM
>> To: Mike Jones
>> Cc: jose@ietf.org
>> Subject: Re: [jose] encrypting AND signing a token
>> 
>> Not only is my original token increasing in size by 4/3, I am also adding
>> another header, payload and signature.
>> 
>> One of the objectives of JWT was to enabled compact tokens. It would seem
>> that we should be able to support both signing and encryption of the same
>> token.
>> 
>> All the encryption use cases I can think of involving asymmetric keys
> would
>> also require signing with the senders private key.
>> 
>> My suggestion is to be explicit in what the algorithm etc. is used for:
>> 
>> Rather than "alg" and "enc", we have:
>> 
>> "algs" - algorithm for token signing
>> "algk" - algorithm for content management key encryption "alge" -
> algorithm
>> for payload encryption
>> 
>> Similiarly,
>> 
>> "kids" - key id for signing
>> "kidk" - key id for content managment key encryption
>> 
>> We could probably make these three or even two letter codes if you want to
>> save a couple bytes.
>> 
>> -- Dick
>> 
>> On Nov 2, 2012, at 8:46 AM, Mike Jones <Michael.Jones@microsoft.com>
>> wrote:
>> 
>>> The way you put it brings one straightforward solution to mind.  Solve
> 1-3
>> with a JWE.  Solve 4-5 by signing the JWE as a JWS payload.  Done.
>>> 
>>> I do understand that the 4/3 space blowup-of double base64url encoding
>> the JWE motivates your earlier proposal about nested signing.  (See Dick's
>> 10/29/12 message "[jose] signing an existing JWT".)  I also understand
> that if
>> you could do integrity with the asymmetric signature then the integrity
>> provided by the JWE itself may be redundant.  I don't have a specific
> proposal
>> on how to do that.
>>> 
>>> 				-- Mike
>>> 
>>> -----Original Message-----
>>> From: jose-bounces@ietf.org [mailto:jose-bounces@ietf.org] On Behalf
>>> Of Dick Hardt
>>> Sent: Friday, November 02, 2012 8:22 AM
>>> To: jose@ietf.org
>>> Subject: [jose] encrypting AND signing a token
>>> 
>>> I am trying to figure out how to implement JWT/JWS/JWE to solve a real
>> world problem.
>>> 
>>> 1) Bob sends a token to Charlie via Alice. (Alice gets token from Bob
>>> and then Alice gives token to Charlie)
>>> 2) Alice must be prevented from reading the token. (token needs to be
>>> encrypted)
>>> 3) Bob and Charlie can share a symmetric key.
>>> 
>>> I can solve this with JWE.
>>> 
>>> Now let's add another condition.
>>> 
>>> 4) Charlie wants non-repuditation that Bob created the token.
>>> 5) Bob has a private key and a public key
>>> 
>>> I don't see how to do this using JWE. It seems I have to sign the same
> token
>> I had previously with JWS. This seems inefficient since I should be able
> to
>> replace the JWE integrity computation done with the symmetric key with the
>> private key -- but the "alg" parameter is the same in both encrypting and
>> signing.
>>> 
>>> Now let's expand this to replacing the symmetric key with a
> public/private
>> key pair for encryption. Bob encrypts with Charlies public key and signs
> with
>> Bob's private key (we also need to make sure we are not doing naive
>> encryption and signing here, would be a really useful to specify what
> needs
>> to be done there). Now we need to have parameters for both public/private
>> key pairs in the header.
>>> 
>>> Am I missing something here?
>>> 
>>> Seems like we can do this if we change the header parameters to specify
> if
>> they ("alg", "kid", et.c) are for token signing, payload encryption or
> content
>> key encryption.
>>> 
>>> -- Dick
>>> 
>>> 
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