More word to nts.adoc

[Hal Murray]

> Not only, any data in encrypted extension fields that goes back to the server
> is encrypted with the c2s key (from the P portion of the paylod in section
> 5.6 of the RFC).

The cyphertext of figure 4 contains both the encrypted version of any headers 
we want to encrypt and the authentication data.  Do we encrypt any headers 
using this mechanism?  (I haven't noticed anything, but I could have missed 
something.)

We need to encrypt the new cookies returning from the NTP server.  Are they 
using this mechanism, or are they encrypted out-of-band from this step?  We 
can probably find an answer by reading the code.

The out of band approach allows a simple server implementation to construct 
the response in place, on top of the request.  If we use the AEAD encryption, 
we have to move things around.


>> The new cookies returned from the NTP server are encrypted.
>> I think that's at a different layer.
> Yes, on the client side it's just an opaque blob since it can't be decrypted
> by the client. 

There are 2 layers of encryption for cookies.  The data in the raw cookie is 
encrypted by the server.  When we say "cookie", we are referring to that 
encrypted version rather than the raw version.

When the NTP server is returning new cookies to the client, they are encrypted 
so that a spy can't track the client if it moves to a new IP Address before it 
uses the cookie.


-- 
These are my opinions.  I hate spam.