Re: Exercising Version Negotiation

Eric Rescorla <ekr@rtfm.com> Thu, 22 March 2018 14:26 UTC

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From: Eric Rescorla <ekr@rtfm.com>
Date: Thu, 22 Mar 2018 14:25:53 +0000
Message-ID: <CABcZeBMVNy151rFntLutSPtctPsd2Ei3Qy-ChuEXVMVpz4pgdQ@mail.gmail.com>
Subject: Re: Exercising Version Negotiation
To: Ryan Hamilton <rch@google.com>
Cc: IETF QUIC WG <quic@ietf.org>
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It would exercise the former.

-Ekr


On Thu, Mar 22, 2018 at 2:10 PM, Ryan Hamilton <rch@google.com> wrote:

> When you say Version Negotiation, do you mean the process of sending an
> receiving a version negotiation packet, or simply the act of speaking two
> different versions? Your proposal seems to be the latter but I don't think
> I follow how it would exercise the former, though maybe that's intentional?
>
> On Thu, Mar 22, 2018 at 5:03 AM, Eric Rescorla <ekr@rtfm.com> wrote:
>
>> Following up on the discussion at the mic, I do think it is useful to
>> exercise the VN function, but I don't think it's useful to have those
>> versions be different, because that creates perverse incentives.
>>
>> Here's what I suggest instead: create two versions (we can call them QUIC
>> v1+i  and QUIC v1-i), each with its own code point [0]. They should be
>> essentially identical except for two trivial differences, intended to
>> ensure that if you screw up version negotiation, you get failed interop.
>>
>> - The constant in the handshake salt (5.2.2)
>> - The HKDF expansion constants
>>
>> I suggest we handle each of these by just inverting the bits.
>>
>> We would then suggest to people that they somewhat randomize their
>> preferences (e.g., 99% of the time prefer v1+i, 1% of the time prefer
>> v1-i). This will almost always result in matching versions, but will
>> occasionally result in a mismatch, thus forcing us to test VN.
>>
>> -Ekr
>>
>> [0] Obviously we can do this for draft versions. We just say that the two
>> versions are
>> ff0000XX and ffffffXX.
>>
>>
>>
>>
>>
>>
>>
>