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

From: Kazuho Oku <kazuhooku@gmail.com>
Date: Thu, 11 May 2017 20:35:33 +0900
Message-ID: <CANatvzzGNxXd=dMNOC1bADieFzcBZYhUAcgdC9n4mQK24MCZnA@mail.gmail.com>
To: Stefan Eissing <stefan.eissing@greenbytes.de>
Cc: Willy Tarreau <w@1wt.eu>, Mark Nottingham <mnot@mnot.net>, Erik Nygren <erik@nygren.org>, "ietf-http-wg@w3.org Group" <ietf-http-wg@w3.org>, "Ponec, Miroslav" <mponec@akamai.com>, "Kaduk, Ben" <bkaduk@akamai.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.

>
>
>> 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 11:36:06 UTC

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