Re: HTTP profile for TLS 1.3 0-RTT early data?

> Am 11.05.2017 um 13:35 schrieb Kazuho Oku <kazuhooku@gmail.com>:
> 
> 2017-05-11 20:33 GMT+09:00 Stefan Eissing <stefan.eissing@greenbytes.de>:
>> 
>>> Am 11.05.2017 um 13:31 schrieb Kazuho Oku <kazuhooku@gmail.com>:
>>> 
>>> 2017-05-11 17:19 GMT+09:00 Stefan Eissing <stefan.eissing@greenbytes.de>:
>>>> 
>>>>> Am 11.05.2017 um 07:33 schrieb Willy Tarreau <w@1wt.eu>:
>>>>> 
>>>>> Hi Mark,
>>>>> 
>>>>> On Thu, May 11, 2017 at 10:23:12AM +1000, Mark Nottingham wrote:
>>>>>> If an origin doesn't have robust retry/replay protection in place for
>>>>>> non-idempotent requests, it seems operationally simpler and safer for them to
>>>>>> disable 0RT, rather than refusing it on a request-by-request basis. That's
>>>>>> the discussion I think we should have here...
>>>>> 
>>>>> That's exactly the situation I'm facing for now with haproxy. A few
>>>>> users have asked us to support 0RTT and by lack of way to 1) decide
>>>>> which requests are really safe, and 2) tell the client it must replay
>>>>> them using 1RTT, for now I refused to enable it. The load balancer
>>>>> and the origin server will have a different view of the acceptability
>>>>> of 0RTT, and all the chain must be able to accept or reject them, and
>>>>> let the client retry.
>>>> 
>>>> Even the "origin server" might not be aware what the application's
>>>> committal and guarantee here is.
>>>> 
>>>> My thoughts for an implementation is:
>>>> 
>>>> - it has to work without the "upper" layer / next hop being aware of it
>>>> - it has to fail in a defined HTTP way. The HTTP request is tagged as
>>>> possibly replayed, regardless of the actual transport. The answer
>>>> needs to also work on that transport.
>>>> - The negative answer to a 0-RTT request might come early, might come
>>>> late. For h2, other streams might have been opened, even answered,
>>>> in the meantime.
>>>> - The sender selecting 0-RTT should only do so, if it understands the
>>>> retry answer. (Once that is defined)
>>>> - The sender may well want to select 0-RTT only if it considers the
>>>> data to be safe for replays *and* it expects the server to come to
>>>> the same conclusion.
>>>> - So, ideally, sender and receiver have the same notion about what HTTP
>>>> data is acceptable for 0-RTT.
>>> 
>>> This is an interesting discussion!
>>> 
>>> I believe that there is no need for us to require a _client_ to resend
>>> a HTTP request, even in case it sends a HTTP request in 0-RTT and then
>>> turns out that the application running behind tells the "origin
>>> server" that it cannot handle 0-RTT request.
>>> 
>>> IMO what the origin server should do is buffer the 0-RTT request
>>> (note: in TLS 1.3, a server can cap the size of 0-RTT data), and if
>>> the application refuses to handle the request due to the fact that it
>>> has been sent in 0-RTT, wait until the client proves itself to be a
>>> legitimate client (by sending an 1-RTT data), and then resend the
>>> buffered request to the application.
>> 
>> Hmm, how many RTTs will this proof take?
> 
> 1RTT. The latency will be the same as when the client did not use 0-RTT.
> OTOH, the obvious benefit of the proposed approach is less use of
> bandwidth since there is no need for a client to resend the request.

Ok, so when the server sees the first non-0-RTT byte from the client, the
handshake was accepted and the 0-RTT data can be regarded as genuine.

The PING merely triggers the data transfer in case the client does not
send anything on its own, I assume.

>> 
>> 
>>> In HTTP/2, the proof can be obtained by sending a PING frame from the
>>> server after sending ServerFinished message (of TLS 1.3) and waiting
>>> for the response to the PING frame.
>>> 
>>> So, while I agree that it is beneficial to have an agreement on how
>>> the interaction scheme between the origin server and the application
>>> running behind (possibly as an informational RFC), I do not see a
>>> strong reason that we need to introduce some kind of profile due the
>>> introduction of 0-RTT data in TLS 1.3.
>>> 
>>>> -Stefan
>>>> 
>>>>> 
>>>>> I tend to think that a 4xx status code would make sense and would be
>>>>> useful to pass the verdict back to the client. For example we could
>>>>> return "418 not idempotent".
>>>>> 
>>>>> Willy
>>>>> 
>>>> 
>>>> 
>>> 
>>> 
>>> 
>>> --
>>> Kazuho Oku
>> 
> 
> 
> 
> -- 
> Kazuho Oku

Received on Thursday, 11 May 2017 11:38:07 UTC