Re: [TLS] Comments on EndOfEarlyData

[Britta Hale <[e-mail]>]

On 16. mai 2017 20:59, Eric Rescorla wrote:
>> However, this intuition is incorrect. Alerts signal the end-of-use of
>> keys, not the prohibition of further communication under other keys.
>> Keys should be deleted and no further data should be sent on the
>> connection.
>
> This last sentence seems to reinforce the motivating intuition here,
> namely that the alert signals the end of the *connection*, and so it's
> odd to have EOED indicate a key change within a connection.
>
Avoiding getting caught on the word "connection", EOED signals the end of key 
use like other alerts, which is the central issue. Notably, EOED does 
not signal key change, unlike a KeyUpdate message or Finished message - even 
the name indicates that it is for "end of data". Its behavior is fundamentally 
like an alert's, indicating only end-of-key use for application data. 

>> Specifically, the 0-RTT handshake is
>> followed by 0-RTT data and finally an EndOfEarlyData alert to end use of
>> that key, while in parallel the remainder of the handshake and
>> subsequent session key act almost as a further resumption (i.e. under a
>> different key).
>>
> I can see how you could look at it this way, but I'm not sure that that's
> the natural way to look at it. If you're not doing DH, then these are
> very much derived from the same PSK and the same client-side
> nonce.
>
In that case, they are both then related to the master key of the previous 
session, which may well have ended with a close_notify, i.e. a properly 
finished key use signaled by an alert.