Subject: Re: [bitcoin-dev] Proposal to stop processing of unrequested transactions in Bitcoin Core

From: Antoine Riard <[email-masked]>
Date: Fri, 12 Feb 2021 06:49:42 -0500

Hi Jeremy,

If I understand correctly your concern, you're worried that change would
ease discovery of the node's tx-relay topology ? I don't scope transaction
origin inference, if you suppose the
unrequested-tx peer sending is the attacker it must have learnt the
transaction from somewhere else which is more likely to be the tx owner
rather than the probed node.

As far I can think of this change, a peer might send an unrequested
transaction to this node and observe that it's either a) processed, the
node has learnt about the txid from another peer or b) rejected, the node
has never learnt about the txid. The outcome can be queried by sending a
GETDATA for the "is-unrequested" txid.

I think the same result can already be achieved by sending an INV and
observing if a GETDATA is replied back to guess the presence of another
peer with already the knowledge of the txid. Or alternatively, just connect
to this other peer and wait for an announcement.

What else can we think of ?

>From my side, compared to the already-existing heuristics, I don't see how
this change is easing attackers' work. That said, I don't deny our
transaction announcements/requests logic is worthy of more study about its
privacy properties, especially when you acknowledge the recent overhaul of
the transaction request and the upcoming Erlay changes.

Cheers,
Antoine

Le jeu. 11 févr. 2021 à 16:15, Pieter Wuille <[email-masked]> a
écrit :

>
> I'm not sure of the existing behavior is of when we issue a getdata
> request, but noting that there could be a privacy implication of this sort
> of change. Could you (or someone else) expand on why this is not a concern
> here?
>
>
> What kind of privacy concern are you talking about? I'm not sure I see how
> this could matter.
>
> Cheers,
>
> --
> Pieter
>
>