Date: Tue, 06 Oct 2020 04:10:52 +0000
To: ZmnSCPxj <ZmnSCPxj@protonmail.com>,
 Bitcoin Protocol Discussion <bitcoin-dev@lists.linuxfoundation.org>
From: ZmnSCPxj <ZmnSCPxj@protonmail.com>
Reply-To: ZmnSCPxj <ZmnSCPxj@protonmail.com>
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Subject: Re: [bitcoin-dev] A thought experiment on bitcoin for payroll
	privacy
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Good morning Mr. Lee, and list,

> I can then look at the gossiped channels and see the size of the channel =
between the cut-throat company and the other employee, and from there, gues=
s that this is the bi-weekly salary of that employee.


This can be made an argument against always publishing all channels, so let=
 me propose something.

The key identifying information in an invoice is the routehint and the node=
 ID itself.

There are already many competing proposals by which short-channel-ids in ro=
utehints can be obscured.
They are primarily proposed for unpublished channels, but nothing in those =
proposals prevents them from being used for published channels.

The destination node ID is never explicitly put in the onion, only implied =
by the short-channel-id in order to save space.
However, the destination node ID *is* used to encrypt the final hop in the =
onion.
So the receiver node can keep around a small number of throwaway keypairs (=
or get those by HD) and use a throwaway to sign the invoice, and when it is=
 unable to decode by its normal node ID, try using one of the throwaway key=
pairs.

With both of the above, what remains is the feerate settings in the invoice=
.
If the company node gives different feerates per channel, it is still possi=
ble to identify which channel is *actually* referred to in the invoice.
What the receiver node can do would be to give a small random increase in f=
eerate, which basically overpays the company node, but obscures as well *wh=
ich* channel is actually in the invoice.

Regards,
ZmnSCPxj