[OpenID] D-H vs SSL

[Martin Atkins]

Ben Laurie wrote:
> On Thu, Mar 19, 2009 at 2:17 PM, Andrew Arnott <andrewarnott at gmail.com> wrote:
>> Maybe it's just me, but I don't like the terminology we're using.  DH and
>> SSL are only redundant when used together.
> 
> I don't understand why. As I said, DH over SSL gives you a shared
> secret, which SSL alone does not. Of course there are cheaper ways to
> arrive at a shared secret over SSL, but that's not the point.
> 
>>  Otherwise they're complementary.
>>  If SSL cannot be used, for whatever reason, DH is mandatory.
> 
> But does not protect against MitM, and so is not equivalent. Which is
> not what "complementary" means to me.
> 

I believe what's being discussed here is using the secure channel to 
exchange a shared secret in "cleartext" (as far as the application layer 
is concerned).

This is actually already permitted by the spec, but the spec does not 
say that it is *required* to use the "cleartext" session mode when on a 
secure channel. This is the change that I think is being proposed here.