[OAUTH-WG] MAC Discussion

[Hannes Tschofenig <[e-mail]>]

Justin wrote: 
"
I believe that there's value in per-message signing completely apart from the channel level encryption. 
"

May well be. But we have to figure out what exactly the reasons are why there is value. 

Bill wrote:
"
I find the idea of starting from scratch frustrating. MAC solves a set of specific problems and has a well defined use case.
"

This would be a very quick process if we had ever done our home work properly. 

So, what are the problems it tries to solve? Yesterday I found an old presentation about MAC and the basic argument was that it has better performance than TLS. While that's true it is not a good argument per se. However, performance is not the only factor to look at and the negative performance impact caused by TLS is overrated.  

Here is the slide set I am talking about: 
http://www.tschofenig.priv.at/Why_are_we_Signing.pdf

In many cases I had noticed that more time was spent with the pictures (in slides and blog post) than with the content. That's not good IMHO. 

Bill, we can hardly call a specification "complete" if many of us don't know what problem it solves. John phrases it nicely as "Part of the problem with MAC has been that people could never agree on what it was protecting against." I am also interested in hearing about deployment constraints that people have. Blaine always said that many developers cannot get TLS to work. I am sure that's true but OAuth 2.0 requires TLS to be used anyway to secure the interaction with the authorization server. 

Note: I am not saying that we are not going to standardize something like the MAC token (maybe with different details) but let us spend a little bit of time to figure out what threats we want to deal with.