From: Rusty Russell <rusty@rustcorp.com.au>
To: Russell O'Connor <roconnor@blockstream.io>,
	Bitcoin Protocol Discussion <bitcoin-dev@lists.linuxfoundation.org>
In-Reply-To: <CAMZUoKmXTONMqJ=0Vv7+e=q0CBL5h6Tio-5ec0bmZ+U4psOmCg@mail.gmail.com>
References: <871s0c1tvg.fsf@rustcorp.com.au>
	<CAMZUoKmXTONMqJ=0Vv7+e=q0CBL5h6Tio-5ec0bmZ+U4psOmCg@mail.gmail.com>
Date: Thu, 06 Jun 2019 12:38:50 +0930
Message-ID: <87r287o1fh.fsf@rustcorp.com.au>
MIME-Version: 1.0
Content-Type: text/plain
Subject: Re: [bitcoin-dev] [PROPOSAL] Emergency RBF (BIP 125)
Precedence: list

"Russell O'Connor" <roconnor@blockstream.io> writes:
> Hi Rusty,
>
> On Sun, Jun 2, 2019 at 9:21 AM Rusty Russell via bitcoin-dev <
> bitcoin-dev@lists.linuxfoundation.org> wrote:
>
>> The new "emergency RBF" rule:
>>
>>  6. If the original transaction was not in the first 4,000,000 weight
>>     units of the fee-ordered mempool and the replacement transaction is,
>>     rules 3, 4 and 5 do not apply.
>>
>> This means:
>>
>> 3. This proposal does not open any significant new ability to RBF spam,
>>    since it can (usually) only be used once.  IIUC bitcoind won't
>>    accept more that 100 descendents of an unconfirmed tx anyway.
>>
>
> Is it not possible for Alice to grief Bob's node by alternating RBFing two
> transactions, each one placing itself at the bottom of Bob's top 4,000,000
> weight mempool which pushes the other one below the top 4,000,000 weight,
> and then repeating with the other transaction?  It might be possible to
> amend this proposal to partially mitigate this.

Good point.  This will cost Alice approximately one tx every block, but
that may still be annoying.  My intuition says it's hard to play these
games across swathes of non-direct peers, since mempools are in constant
flux and propagation is a bit random.

What mitigations were you thinking?

Cheers,
Rusty.