Re: [OAUTH-WG] Comparing the JSON Token drafts

Nat Sakimura <sakimura@gmail.com> Tue, 12 October 2010 09:20 UTC

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References: <4E1F6AAD24975D4BA5B168042967394314AA9AF0@TK5EX14MBXC207.redmond.corp.microsoft.com> <AANLkTimokq-36Xt2hjrD1+Htj74d0L9jubg_c8=4sOXk@mail.gmail.com> <1990A18DEA6E97429CFD1B4D2C5DA7E70D4009@TK5EX14MBXC101.redmond.corp.microsoft.com> <7C01E631FF4B654FA1E783F1C0265F8C635D37DB@TK5EX14MBXC113.redmond.corp.microsoft.com> <AANLkTik+StBEhK+40kqWP7qtPGHf8o0byPRdU-KLufuW@mail.gmail.com> <1990A18DEA6E97429CFD1B4D2C5DA7E70D88DA@TK5EX14MBXC101.redmond.corp.microsoft.com> <AANLkTinkQag3_xmHevY5wTNXaympZcX8W7mMFB-0ns0V@mail.gmail.com> <180155C5EA10854997314CA5E063D18F093C69@TK5EX14MBXC113.redmond.corp.microsoft.com> <AANLkTi=mkh5=GDJcbSsHnNqxLHygUF=PfOk2V07GOo6W@mail.gmail.com>
Date: Tue, 12 Oct 2010 18:21:52 +0900
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From: Nat Sakimura <sakimura@gmail.com>
To: Dirk Balfanz <balfanz@google.com>
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Subject: Re: [OAUTH-WG] Comparing the JSON Token drafts
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JWT does not state anything about how keys are expressed while JT
(JSON Tokens)  has the
discovery in it as stated by the initial mail of this thread.

In my use case, I really need X.509 certs in the conventional sense to
establish trust.
So if key discovery is to be included, finding the X.509 certs through
given URI would be good.

Please see http://jsonenc.info/jss/1.0/ for what we are doing at
Artifact Binding WG.
(Hereafter, I refer it as JSS, JSON Simple Sign).

The envelope structure used in JSS is a bit different as well.
It is closer to JWT so that we only need to base64url encode the envelope
and then apply signature, so that we do not need concatenating
operation like Dirk's proposal.
The main difference is that JSS have "name spaced" the signature
parameters and payload
so that it is easy to process, as well as to avoid name space collision.
We are currently debating if we really need to have "payload" name
space though.
We could just stick in the "sig_params" to the original JSON structure.
(Pros about having "payload" is that then it will be able to sign
practically anything, BTW.)
If we make them completely flat, without any name spacing, it will be
same as the JWT
envelope. Down side for that is it is going to be hard to have
multiple signatures, which
we have in our use cases.

=nat




On Fri, Oct 8, 2010 at 1:34 AM, Dirk Balfanz <balfanz@google.com> wrote:
> Ok, so in the spirit of convergence, I give you (optional) ECC - do you give
> me Magic Signature Compact Serialization? :-)
> Dirk.
>
> On Thu, Oct 7, 2010 at 12:18 AM, Anthony Nadalin <tonynad@microsoft.com>
> wrote:
>>
>> I think that this would be the baseline and if there is interest in some
>> sort of negotiation protocol then could take that up at  a later time, I
>> know its not the best but we need to be able to support the government
>> endorsed algorithms
>>
>>
>>
>> From: Dirk Balfanz [mailto:balfanz@google.com]
>> Sent: Wednesday, October 06, 2010 2:26 PM
>> To: Anthony Nadalin
>> Cc: Yaron Goland; Mike Jones; oauth@ietf.org
>>
>> Subject: Re: [OAUTH-WG] Comparing the JSON Token drafts
>>
>>
>>
>> So what's the proposal, then? That OAuth service providers document what
>> crypto mechanisms they support? And developers will just have to know which
>> alg to use with which service provider? I guess I could live with that...
>>
>>
>>
>> Dirk.
>>
>> On Mon, Oct 4, 2010 at 12:37 AM, Anthony Nadalin <tonynad@microsoft.com>
>> wrote:
>>
>> I don’t believe that negotiation (policy) has to be part of this proposal,
>> so in the spec if one of the claims is not supported then the token MUST not
>> be processed. We have this today in the web services security stack and
>> there are really no issues.
>>
>>
>>
>> From: Dirk Balfanz [mailto:balfanz@google.com]
>>
>> Sent: Friday, October 01, 2010 8:45 PM
>> To: Yaron Goland
>>
>> Cc: Anthony Nadalin; Mike Jones; oauth@ietf.org
>>
>> Subject: Re: [OAUTH-WG] Comparing the JSON Token drafts
>>
>>
>>
>> On Fri, Oct 1, 2010 at 3:41 PM, Yaron Goland <yarong@microsoft.com> wrote:
>>
>> No matter what algorithm or key size we pick the choice will prove
>> unsupportable for any number of implementers due to everything from security
>> issues (no matter what key size we pick, someone will have a real need for
>> something larger) to legal issues (various countries have their own opinions
>> about what to use where, a la the NSA suite list).
>>
>>
>>
>> So we are going to have to support multiple algorithms and we are going to
>> have to deal with algorithm negotiation. I literally can see no way around
>> that.
>>
>>
>>
>> I agree that over time, what will be considered secure will change. I also
>> agree that usually this means that there is some sort of negotiation
>> happening on what the two parties support. How would that happen here?
>> Remember that - as one datapoint - Google won't be able to support the ECC
>> algorithm. What happens when you can't support one of the proposed
>> algorithms, and there is no provision in the protocol to signal this to
>> other parties?
>>
>>
>>
>> Dirk.
>>
>>
>>
>>
>>
>>                                 Yaron
>>
>>
>>
>> From: oauth-bounces@ietf.org [mailto:oauth-bounces@ietf.org] On Behalf Of
>> Anthony Nadalin
>> Sent: Wednesday, September 29, 2010 8:34 AM
>> To: Dirk Balfanz; Mike Jones
>>
>> Cc: oauth@ietf.org
>> Subject: Re: [OAUTH-WG] Comparing the JSON Token drafts
>>
>>
>>
>> > So this one I do feel more strongly about: We should only include crypto
>> > mechanisms that everybody MUST support. Otherwise, we'll have to invent some
>> > sort of negotiation step in the protocol: "do you support alg XYZ? No I
>> > don't, > please use ABC". Let's not do that.
>>
>>
>>
>> >As just one datapoint, Google would have a hard time supporting ECC,
>> > since it's not in the Java core library. We don't use bouncycastle.
>>
>>
>>
>> I agree that there can be license issues that one could encounter with ECC
>> (as we all did with RSA), there are already customers that require ECC, and
>> so there is a need to have alternative algorithms that you don’t have to
>> support. We already have the issue of “do you support” with claims and token
>> types, etc
>>
>>
>>
>> From: oauth-bounces@ietf.org [mailto:oauth-bounces@ietf.org] On Behalf Of
>> Dirk Balfanz
>> Sent: Tuesday, September 28, 2010 10:23 AM
>> To: Mike Jones
>> Cc: oauth@ietf.org
>> Subject: Re: [OAUTH-WG] Comparing the JSON Token drafts
>>
>>
>>
>> On Mon, Sep 27, 2010 at 5:46 PM, Mike Jones <Michael.Jones@microsoft.com>
>> wrote:
>>
>> Dirk and I both posted JSON Token drafts on Thursday.  They are at
>> http://balfanz.github.com/jsontoken-spec/draft-balfanz-jsontoken-00.html
>> (which I’ll refer to as Dirk’s draft) and
>> http://self-issued.info/docs/draft-goland-json-web-token-00.html (which I’ll
>> refer to as JWT).  This note points out some of the differences (and
>> commonalities) in the interest of building consensus towards a unified
>> approach.
>>
>>
>>
>> Commonalities:
>>
>> ·         Both have ways of expressing the signature algorithm, token
>> issuer, token expiration time, and intended audience.
>>
>> ·         Both use a form of base64url encoding of the JSON claim data.
>>
>> ·         Both require support for the HMAC SHA-256 signature algorithm,
>> and describe how to sign with RSA SHA-256 as well.
>>
>>
>>
>> Differences:
>>
>> ·         Dirk’s draft uses a base64url encoding that may include one or
>> two ‘=’ pad characters.  The JWT draft uses base64url encoding without
>> padding.
>>
>> ·         JWT uses shorter claim names in the interest of brevity (“iss”,
>> “exp”, and “aud”, versus “issuer”, “not_after”, and “audience”).
>>
>> ·         JWT also describes how to sign with ECDSA SHA-256, plus HMAC,
>> RSA, and ECDSA with longer key lengths.
>>
>> ·         Dirk’s tokens must be signed, whereas signing JWTs is optional.
>>
>> ·         Dirk’s draft provides for a key_id parameter and a means of
>> serializing keys.
>>
>> ·         Dirk’s draft utilizes a Magic Signatures envelope, whereas the
>> only “envelope” component of a JWT is the encoded signature.
>>
>> ·         Dirk’s draft proposes that a particular discovery mechanism be
>> used with JSON tokens.
>>
>>
>>
>> Let me tackle the differences one at a time, in hopes of driving towards a
>> consensus position.
>>
>>
>>
>> Hi there - thanks for writhing this up. Comments below:
>>
>> ·         To pad or not to pad:  The ‘=’ pad characters add length, are
>> not URL-safe (and therefore must be escaped when used in URLs, adding more
>> length), and add no information.  Therefore, I would propose that we agree
>> not to use padding (as permitted by RFC 4648, Section 5), especially since a
>> no-padding implementation is trivial, as shown in JWT Section 13.
>>
>>
>>
>> I don't feel strongly about this, but remember John Panzer's cautionary
>> tales here: Apparently, padding-less encoding is not well-supported in some
>> frameworks, which can lead to confusion.
>>
>>
>>
>> ·         Claim name length: Given that a core goal of both specs is short
>> tokens, I would propose that we use the shorter reserved claim names.
>> Having short tokens is especially important when used with mobile browsers,
>> where URL length restrictions may be severe.  (People are always free to use
>> longer ones in any particular application context if they have a reason to
>> do so.)
>>
>>
>>
>> I don't feel strongly about this, but I think many people do want to have
>> more descriptive names here.
>>
>>
>>
>> ·         Elliptic curve crypto and longer key lengths:  The JWT spec
>> defines how to use ECC as well as HMAC and RSA.  Given ECC’s inclusion in
>> NSA Suite B and that it has engineering advantages over RSA (shorter key
>> lengths and more efficient computations), it makes sense that any modern
>> spec incorporating cryptography allow its use as an option.  Likewise, it
>> makes sense for the spec to define how to use longer key lengths on an
>> optional basis.
>>
>> So this one I do feel more strongly about: We should only include crypto
>> mechanisms that everybody MUST support. Otherwise, we'll have to invent some
>> sort of negotiation step in the protocol: "do you support alg XYZ? No I
>> don't, please use ABC". Let's not do that.
>>
>>
>>
>> As just one datapoint, Google would have a hard time supporting ECC, since
>> it's not in the Java core library. We don't use bouncycastle.
>>
>>
>>
>> ·         Unsigned tokens:  In some application contexts, it may make
>> sense to send unsigned tokens if carried in a signed and/or encrypted
>> container or channel.  Allowing for unsigned tokens means that double
>> signing need not occur.
>>
>> That one just confuses me :-) What's the difference between OAuth without
>> signatures and unsigned tokens? Is the latter not just a more complicated
>> way of doing the former?
>>
>>
>>
>> ·         Key identification:  I agree that having means of identifying
>> and distributing keys are critical for to end-to-end security of signed
>> tokens.  That’s a separate point from whether the key identification and
>> distribution mechanisms should be part of the token format specification, or
>> treated separately.  I would advocate that it be treated separately (as was
>> done with SWTs as well), but am open to discussion on this point.
>>
>> ·         Discovery:  Like key distribution, I believe that an agreement
>> on discovery mechanisms is critical to many use cases.  But like key
>> distribution, I’d like us to take that up in a separate specification,
>> rather than tightly binding the use of JSON tokens to a particular discovery
>> mechanism.
>>
>>
>>
>> Here is where I'm coming from: I find the public-key versions of the
>> signatures much more intriguing - they allow for easier key management, key
>> rotation, etc. To actually reap the benefits of key rotation, though, we
>> need to say how to find out what the currently-used key is. If we don't,
>> then a lot of the potential advantage of using public keys evaporates. I'm
>> concerned that, lacking the discovery spec, developers will start
>> hard-coding keys into their servers, and we'll end up in a situation where
>> we can't rotate keys when Something Bad happens.
>>
>>
>>
>> ·         Envelope structure:  Dirk’s draft proposes that the signed
>> content be wrapped in a particular kind of envelope.  Among other things,
>> this envelope can help prevent a token from being repurposed from one
>> context to another, by having a clear (and cryptographically verified)
>> declaration that “This is a JSON token”.  I understand this motivation and
>> am open to discussions on how to best achieve it, while still providing as
>> little mechanism as possible (but no less J).
>>
>> Well, you've seen my proposal on how to achieve it :-), but I'm also open
>> to better ways, if someone comes up with one...
>>
>>
>>
>> Dirk.
>>
>>
>>
>>
>>
>> Dirk, and others, please jump in!
>>
>>
>>
>>                                                                 -- Mike
>>
>>
>>
>>
>>
>>
>>
>>
>
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-- 
Nat Sakimura (=nat)
http://www.sakimura.org/en/
http://twitter.com/_nat_en