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

> Am 11.05.2017 um 13:38 schrieb Kazuho Oku <kazuhooku@gmail.com>:
> 
> 2017-05-11 20:37 GMT+09:00 Stefan Eissing <stefan.eissing@greenbytes.de>:
>> 
>>> 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.
> 
> Yes. That is what I have been thinking. Thank you for clarifying that.

Excellent, very nice thinking, Kazuho! This strategy really solves any
interop issues for origin servers. Nice.

In case of proxies/intermediates, the case is different, I think. 

If a proxy receives 0-RTT data, it can only make direct use of it inside
upstream 0-RTT data on a new connection. If it sends 0-RTT data on an
established connection, the server cannot detect the replay weakness.

A proxy, on forwarding 0-RTT data on an established connection, must first
verify the client handshake.

Does that make sense?


>>>> 
>>>> 
>>>>> 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
>> 
> 
> 
> 
> -- 
> Kazuho Oku

Received on Thursday, 11 May 2017 11:46:40 UTC