To: bitcoin-dev@lists.linuxfoundation.org
From: Andreas Schildbach <andreas@schildbach.de>
Date: Mon, 22 Jul 2019 00:56:33 +0200
Message-ID: <qh2qj1$7sg4$1@blaine.gmane.org>
References: <59fad2b6-9b15-ffec-116e-91d27ce29f80@mattcorallo.com>
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In-Reply-To: <59fad2b6-9b15-ffec-116e-91d27ce29f80@mattcorallo.com>
Content-Language: en-US
Subject: Re: [bitcoin-dev] Bitcoin Core to disable Bloom-based Filtering by
	default
Precedence: list

An estimated 10+ million wallets depend on that NODE_BLOOM to be
updated. So far, I haven't heard of an alternative, except reading all
transactions and full blocks.

It goes without saying pulling the rug under that many wallets is a
disastrous idea for the adoption of Bitcoin.

> well-known DoS vectors

I asked many people, even some "core developers" at meetings, but nobody
ever was able to explain the DoS vector. I think this is just a myth.

Yes, you can set an overly blurry filter and thus cause useless traffic,
but it never exceeds just drinking from the full firehose (which this
change doesn't prohibit). So where is the point? An attacker will just
switch filtering off, or in fact has never used it.

> It is not anticipated that
> this will result in a significant lack of availability of
> NODE_BLOOM-enabled nodes in the coming years

Why don't you anticipate that? People almost never change defaults,
especially if it's not for their own immediate benefit. At the same
time, release notes in general recommend updating to the latest version.
I *do* anticipate this will reduce the number of nodes usable by a large
enough amount so that the feature will become unstable.

> clients
> which rely on the availability of NODE_BLOOM-supporting nodes on the
> P2P network should consider the process of migrating
> to a more modern (and less trustful and privacy-violating) alternative
> over the coming years.

There is no such alternative.

I strongly recommend postponing this change until an alternative exists
and then give developers enough time to implement, test and roll out.

I also think as long as we don't have an alternative, we should improve
the current filtering for segwit. E.g. testing the scripts themselves
and each scriptPubKey spent by any input against the filter would do,
and it also fixes the main privacy issue with server-side filtering
(wallets have to add two items per address to the filter).