Re: [OAUTH-WG] MAC Tokens body hash

Eran Hammer-Lahav <> Mon, 15 August 2011 16:47 UTC

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From: Eran Hammer-Lahav <>
To: "William J. Mills" <>, Phil Hunt <>
Date: Mon, 15 Aug 2011 09:46:56 -0700
Thread-Topic: [OAUTH-WG] MAC Tokens body hash
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Subject: Re: [OAUTH-WG] MAC Tokens body hash
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Let’s just keep ‘ext’ and drop ‘bodyhash’. Seems like this should resolve the issue.


From: William J. Mills []
Sent: Monday, August 15, 2011 9:46 AM
To: Eran Hammer-Lahav; Phil Hunt
Cc: OAuth WG
Subject: Re: [OAUTH-WG] MAC Tokens body hash

"add" doesn't really say it to me either.  "ah", short for "additional hash" is somewhat more mnemonic for me, but then I think "ext" isn't horrible because it's a frequent abbreviation for extension.


From: Eran Hammer-Lahav <<>>
To: William J. Mills <<>>; Phil Hunt <<>>
Cc: OAuth WG <<>>
Sent: Sunday, August 14, 2011 11:28 PM
Subject: RE: [OAUTH-WG] MAC Tokens body hash
How about ‘add’? as in “Used to include additional data in the MAC normalized string”.


From: William J. Mills []<mailto:[]>
Sent: Thursday, August 04, 2011 6:06 PM
To: Eran Hammer-Lahav; Phil Hunt
Cc: OAuth WG
Subject: Re: [OAUTH-WG] MAC Tokens body hash

It's the proverbial 'void *client_data;' equivalent.  All names for that to date suck, my favorite is 'rock'.

From: Eran Hammer-Lahav <<>>
To: Phil Hunt <<>>
Cc: OAuth WG <<>>
Sent: Thursday, August 4, 2011 4:42 PM
Subject: Re: [OAUTH-WG] MAC Tokens body hash
Ok. We seem to be using different definitions of what application data mean, but have the same use cases in mind. I'll come up with a different name or just keep ext.


On Aug 3, 2011, at 12:42, "Phil Hunt" <<>> wrote:
Only allowing (implied or not) app data is needlessly narrow in scope.

Extending MAC to include claims or session information is a perfectly valid thing to do. It improves scalability and reduces the need to look up artifact data.

Note:  I'd like to share more on this, but I'm prioritizing the Threat Model document. Never-the-less, the above should be a sufficient example about why extensibility is useful.



On 2011-08-03, at 11:03 AM, Eran Hammer-Lahav wrote:

My proposal is to change ‘ext’ to ‘app’, keep the same prose as ‘ext’, and add the use case of ‘bodyhash’ as an example. I’m not too stuck on the name, but my thinking is that ‘app’ relays the right message that this is a place where developers can stick any application data they want included. ‘ext’ conveys the idea of extensions which I’m not so thrilled about.

In other words, I’d like a developer reading this to feel comfortable using it right away for securing addition bits such as a JSON payload, but I don’t like the idea of someone publishing an I-D with a full syntax and canonicalization requirements for say, singing an entire request, headers and all. I feel that would be much better accomplished by defining a new HTTP authentication scheme.

Philosophically, I think extensible authentication schemes are a bad idea.


From: William J. Mills []<mailto:[]>
Sent: Wednesday, August 03, 2011 10:28 AM
To: Phillip Hunt; Eran Hammer-Lahav
Cc: Ben Adida; OAuth WG; Adam Barth(<>)
Subject: Re: [OAUTH-WG] MAC Tokens body hash

In thinking about this I'm coming around to the viewpoint that a single additional predefined spot is sufficient.  If the app developer wants to include addtional data there (iun the specified format) that's fine.  If what they want to do is include a signature of other payload that's fine too.

I'm not in love with the name "app" though, "ext" is better.

From: Phillip Hunt <<>>
To: Eran Hammer-Lahav <<>>
Cc: Ben Adida <<>>; OAuth WG <<>>; "Adam Barth(<>)" <<>>
Sent: Tuesday, August 2, 2011 7:14 PM
Subject: Re: [OAUTH-WG] MAC Tokens body hash


On 2011-08-02, at 18:02, Eran Hammer-Lahav <<>> wrote:
The idea is to drop 'ext' and 'bodyhash' due to being underspecified and therefore causing more harm than good. I added 'ext' to allow for application specific data to be included in the signed content. However, the name suggests this is an extension point for future specifications. I believe authentication schemes should not be extensible in ways that affect their security or interop properties and without additional text (registry, process, etc) for the 'ext' parameter, it will cause more issues than help.

Instead of the 'ext' parameter I am suggesting the 'app' parameter which will do the same, but will be better positioned as an application-specific data. The prose will go a step further and recommend that the parameter value include a hash of the data, not the data itself. This is to ensure the parameter does not become part of the payload which is inappropriate for HTTP requests.
-1 what you describe appears to be a separate feature from ext

As for the 'bodyhash' parameter, I would like to remove it because it is underspecified (we had an actual deployment experience showing that it doesn't produce interoperable implementations due to the many HTTP body transformation applied in most frameworks). Solving this issue is not possible due to the many different types of bodies and frameworks (and clearly operating on the "raw" body doesn't work). Instead, developers can use the new 'app' parameter to accomplish that.


As for the normalized string, it will be adjusted to reflect these changes when they are made, so no placeholders which will require code change. Considering this is -00, it is clearly not a stable document.
Will these changes work with your use cases?

-----Original Message-----
From: Skylar Woodward []<mailto:[]>
Sent: Tuesday, August 02, 2011 4:02 PM
To: Eran Hammer-Lahav
Cc: OAuth WG; Ben Adida; 'Adam Barth (<>)'
Subject: Re: [OAUTH-WG] MAC Tokens body hash

(not necessarily for losing a way to sign the body, but for simplicity and
avoiding some of the potential inconsistencies w/ bodyhash).

Is your plan to reserve an empty line 6 for the Normalized Request String
(which was used for bodyhash) or eliminate it, brining the total to six


On Jul 30, 2011, at 3:43 AM, Eran Hammer-Lahav wrote:

I plan to drop support for the bodyhash parameter in the next draft based
on bad implementation experience. Even with simple text body, UTF
encoding has introduced significant issues for us. The current draft does not
work using simple JS code between a browser and node.js even when both
use the same v8 engine due to differences in the body encoding. Basically,
the JS string used to send a request from the browser is not the actual string
sent on the wire.

To fix that, we need to force UTF-8 encoding on both sides. However, that
is very much application specific. This will not work for non-text bodies.
Instead, the specification should offer a simple way to use the ext parameter
for such needs, including singing headers. And by offer I mean give
examples, but leave it application specific for now.

I am open to suggestions but so far all the solutions I came up with will
introduce unacceptable complexity that will basically make this work useless.

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