public inbox for bitcoindev@googlegroups.com
 help / color / mirror / Atom feed
From: "Mr. Lee Chiffre" <lee.chiffre@secmail.pro>
To: bitcoin-dev@lists.linuxfoundation.org
Subject: [bitcoin-dev] Question about PayJoin effectiveness
Date: Tue, 9 Jun 2020 21:01:44 -0700	[thread overview]
Message-ID: <7c0dc46538f96032596163c4a9f03dc2.squirrel@giyzk7o6dcunb2ry.onion> (raw)

I am trying to learn about payjoin. I have a couple concerns on its
effectiveness. Are my concerns valid or am I missing something?

concern 1
If it is known to be a payjoin transaction anyone could determine the
sender the recipient and amount right?

Lets assume that everyone has a single utxo because payjoin becomes common
use and payjoin consolidates utxos through "snowballing". If Alice has a
UTXO of 0.05 btc and Bob has a UTXO of 1.15 btc. Bob can be assumed to
have more balance because he is a merchant and his customers payjoin him
payments alot.

If Alice and Bob do a payjoin with Alice paying 0.01 btc to Bob, it would
probably look like this right?

 0.05---> |____---->1.16
 1.15---> |    ---->0.04

It is very obvious here the amount sent and the sender.  Even if Alice did
combine another input it would still be very obvious. In this case Alice
has another utxo with 0.4 BTC

 0.40---> |
 0.05---> |____---->1.16
 1.15---> |    ---->0.44

This is still obvious that Alice paid Bob 0.01 BTC isn't it?



concern 2
If there is just one consolidated utxo after each payjoin, would it  be
easy to break the privacy of transaction chains?

Alice---payjoin--->Bob
Clark---payjoin--->Bob

or

Alice---payjoin--->Bob---payjoin--->Clark

For exmaple, lets say that Alice payjoins to Bob. Then later on Clark
payjoins with Bob. Based on the payjoin between Clark and Bob, Clark now
knows what UTXO was actually Bob's. And can then know which one was
actually Alices. By transacting a payjoin with someone, they could decloak
the payjoins before them right? If so, how far back the chain can they go?

The issue is not that someone knows the utxos of themselves and the entity
they payjoined with. The issue is that someone can figure out the payjoins
of others before them with the same entity.


I surely must be missing something here. What am I not understanding?

-- 
lee.chiffre@secmail.pro
PGP 97F0C3AE985A191DA0556BCAA82529E2025BDE35










             reply	other threads:[~2020-06-10  4:01 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-10  4:01 Mr. Lee Chiffre [this message]
2020-06-10  6:29 ` [bitcoin-dev] Question about PayJoin effectiveness ZmnSCPxj
2020-06-10  6:47   ` ZmnSCPxj
2020-06-10 17:49 ` Chris Belcher

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=7c0dc46538f96032596163c4a9f03dc2.squirrel@giyzk7o6dcunb2ry.onion \
    --to=lee.chiffre@secmail.pro \
    --cc=bitcoin-dev@lists.linuxfoundation.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox