Re: [bitcoin-dev] Rebroadcast mechanism in Bitcoin P2P network

From: Aymeric Vitte <aymeric@peersm•com>
To: Pieter Wuille <bitcoin-dev@wuille•net>,
	Bitcoin Protocol Discussion
	<bitcoin-dev@lists•linuxfoundation.org>
Subject: Re: [bitcoin-dev] Rebroadcast mechanism in Bitcoin P2P network
Date: Sun, 12 Dec 2021 12:48:18 +0100	[thread overview]
Message-ID: <86d49c80-2f8f-245c-5fdb-17c6ca6b5f2b@peersm.com> (raw)
In-Reply-To: <dSBrti8VFr0lMNgTHw8pD-mAPLm0E4auJa234o0FNY67EUuEy1Dfb93INNIzoUb3j2dWSJjZtG7qncci1LhKAHOXzAzbEWOtXjnggr19J6w=@wuille.net>

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Indeed, I reiterate that using the Tor network for Bitcoin or whatever
protocol not related to the Tor Browser (ie browsing and HS) does not
make sense, for plenty of reasons

But using the Tor protocol outside of the Tor network (and inside
browsers for wallets for example) does:
https://github.com/Ayms/node-Tor#presentation and
https://github.com/Ayms/node-Tor#phase-4-and-phase-5, anonymizing nodes
can just be already existing bitcoin nodes, example:
https://github.com/bitcoin/bitcoin/pull/18988#issuecomment-646564853


Le 11/12/2021 à 17:21, Pieter Wuille via bitcoin-dev a écrit :
>> It is that the solution to privacy is to use privacy-enhancing network
>> communications, such as TOR. I am not against a mechanism to rebroadcast
>> transactions more robustly if the mempool of adjoining nodes has
>> forgotten about them, but the truth is, all transactions originate from
>> some node, and there are methods that allow an individual node to be
>> identified as the likely source of a transaction unless privacy-enabled
>> networks are utilised. Having a different method to cause rebroadcast
>> does not obfuscate the origin.
> You're talking about distinct aspects of transaction privacy.
>
> The rebroadcasting approach as it exists on the network, where wallets are responsible for their own rebroadcasting, directly reveals to your peers a relation between nodes and transactions: whenever any node relays the same transaction twice, it almost certainly implies they are the origin.
>
> This is just a node-transaction relation, and not necessarily IP-transaction relation. The latter can indeed be avoided by only connecting over Tor, or using other privacy networks, but just hiding the relation with IP addresses isn't sufficient (and has its own downsides; e.g. Tor-only connectivity is far more susceptible to partition/Eclipse/DoS attacks). For example seeing the same node (even without knowing its IP) rebroadcast two transaction lets an observe infer a relation between those transactions, and that too is a privacy leak.
>
> I believe moving to a model where mempools/nodes themselves are responsible for rebroadcasting is a great solution to improving this specific problem, simply because if everyone rebroadcasts, the original author doing it too does not stand out anymore. It isn't "fixing privacy", it's fixing a specific leak, one of many, but this isn't a black and white property.
>
> Cheers,
>
> --
> Pieter
>
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