[Lightning-dev] PoDLEs revisited

Lloyd Fournier lloyd.fourn at gmail.com
Wed Feb 3 06:33:44 UTC 2021


On Fri, Jan 29, 2021 at 10:51 AM Rusty Russell <rusty at rustcorp.com.au>
wrote:


> Less true after taproot though?
>

The heuristic from [1] is not affected by Taproot.
Taproot will be helpful for keeping private channels private against the
method in [2] though.

> [1] https://arxiv.org/abs/2007.00764
> > [2] https://arxiv.org/pdf/2003.12470.pdf
> > [3] https://graphsense.info/
> >
> > I am told there is a new revision of [1] coming out any day now that will
> > present a few more tricks and have contributions directly from a
> scientist
> > at Chainalsysis (the company).
>
> I'll add to my reading list (or wait for one of my colleagues to provide
> the TL;DR!).
>
>
Let me TL;DR quickly the core idea quickly as it's not too difficult to
grasp.

1. You are node n_1
2. You fund a public channel to node n_2 called c1
3. You use the change to fund a public channel to node n_3 called c2
4. The network sees that n_1 is involved in both c_1 and c_2. They're both
public channels so the channel_id gives away the on-chain funding utxo.
Everyone can conclude that the owner of n_1 was also the funder of both and
therefore owns the change output of the funding of c_2.

Consider a variant of this heuristic where instead of using funding change
they use the output of a cooperative close of c_1 to to fund c_2. By the
same reasoning you can identify the owner of n_1 funded the channel but you
can also now know  that n_2 is the owner of the other utxo of the close of
c_1.

The point of this is if you are a node that is churning UTXOs from the
funding change or the closing UTXO into other public channels you
necessarily associate those UTXOs with your node id and any descendent
utxos. This is the point of UTXO probing too but with this you get the info
for free by just passively observing the new channel gossip. I think this
makes UTXO probing useless as long we can assume that public nodes that
accept dual funding requests from random people on the internet (and
therefore vulnerable to probing) are also likely to use their wallet funds
to fund channels in the future.

LL
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