Re: [bitcoin-dev] Revisiting NODE_BLOOM: Proposed BIP

[Peter Todd <pete@petertodd.org>]

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On Fri, Aug 21, 2015 at 04:46:17AM +0000, Matt Corallo wrote:
> Peter: Since I stole most of this text from your old BIP, should I leave
> you as an author?

That's fine by me.

> BIP: ?
> Title: NODE_BLOOM service bit
> Author: Matt Corallo <bip@bluematt.me>, Peter Todd <pete@petertodd.org>
> Type: Standards Track (draft)
> Created: 20-08-2015
> 
> Abstract
> ========
> 
> This BIP extends BIP 37, Connection Bloom filtering, by defining a
> service bit to allow peers to advertise that they support bloom filters
> explicitly. It also bumps the protocol version to allow peers to
> identify old nodes which allow bloom filtering of the connection despite
> lacking the new service bit.
> 
> 
> Motivation
> ==========
> 
> BIP 37 did not specify a service bit for the bloom filter service, thus
> implicitly assuming that all nodes that serve peers data support it.
> However, the connection filtering algorithm proposed in BIP 37, and
> implemented in several clients today, has been shown to provide little
> to no privacy, as well as being a large DoS risk on some nodes. Thus,
> allowing node operators to disable connection bloom filtering is a
> much-needed feature.

I'd reference that paper on bloom filters re: the "little to no privacy"
issue. There's also a post in the bitcoinj mailing list somewhere IIRC
talking about the default settings, and how they don't provide any
privacy.

> Specification
> =============
> 
> The following protocol bit is added:
> 
>     NODE_BLOOM = (1 << 2)
> 
> Nodes which support bloom filters should set that protocol bit.
> Otherwise it should remain unset. In addition the protocol version is
> increased from 70002 to 70011 in the reference implementation. It is
> often the case that nodes which have a protocol version smaller than
> 70011, but larger than 70000 support bloom filtered connections without
> the NODE_BLOOM bit set, however clients which require bloom filtered
> connections should avoid making this assumption.
> 
> NODE_BLOOM is distinct from NODE_NETWORK, and it is legal to advertise
> NODE_BLOOM but not NODE_NETWORK (eg for nodes running in pruned mode
> which, nonetheless, provide filtered access to the data which they do have).
> 
> If a node does not support bloom filters but receives a "filterload",
> "filteradd", or "filterclear" message from a peer the node should
> disconnect that peer immediately. For backwards compatibility, in
> initial implementations, nodes may choose to only disconnect nodes which
> have the new protocol version set and attempt to send a filter command.
> 
> While outside the scope of this BIP it is suggested that DNS seeds and
> other peer discovery mechanisms support the ability to specify the
> services required; current implementations simply check only that
> NODE_NETWORK is set.

Good to note Mike Hearn's Cartography seed protocol here.

> Design rational
> ===============
> 
> A service bit was chosen as applying a bloom filter is a service.
> 
> The increase in protocol version is for backwards compatibility. In
> initial implementations, old nodes which are not yet aware of NODE_BLOOM
> and use a protocol version < 70011 may still send filter* messages to a
> node without NODE_BLOOM. This feature may be removed after there are
> sufficient NODE_BLOOM nodes available and SPV clients have upgraded,
> allowing node operators to fully close the bloom-related DoS vectors.

Ah good! That solves the backwards compatibility quite nicely.

-- 
'peter'[:-1]@petertodd.org
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