Using CoinJoin is an incredibly important part of using bitcoin privately, but if you’re not careful with your CoinJoin change, you can damage your own privacy as well as the privacy of others using the platform. That being said, here are 7 safe ways to spend CoinJoin change privately.
What Is CoinJoin Change?
Your CoinJoin change, more commonly known as “doxxic change“, is the “odd” or leftover change output generated from a Whirlpool tx0 transaction. While CoinJoin change doesn’t do anything to compromise your privacy directly on its own, if you ever group it with other inputs in a single transaction, you risk your privacy by linking the histories of both inputs together.
This can become especially problematic if you have UTXOs from both KYC and non-KYC sources.
“Doxxic” change, after all, comes from the term “doxxing” — when a person exposes someone else’s personally identifiable information (PII) online or offline, usually without their permission or knowledge.
When spending CoinJoin change, you want to avoid doxxing yourself to keep you and your bitcoin safe. In order to prevent accidentally leaking any personal information, you need ways to spend CoinJoin change privately without compromising any of your personal information.
Why Should I Spend My CoinJoin Change?
Put simply: to protect you from yourself!
Most of the time, when people lock themselves out of their bitcoin or have it stolen from them, it’s typically due to user error, as harsh as that sounds. Bitcoin is new technology, leaving plenty of room to fumble and make easy mistakes if you’re not careful.
One of those primary mistakes may be accidentally doxxing yourself. The purpose of CoinJoin is to protect you and your bitcoin’s privacy, but if you leave your CoinJoin change sitting around in your wallet unspent, you open yourself up to the risk of accidentally spending that private CoinJoin change with KYC or otherwise compromised bitcoin.
To take care of that, let’s learn how to spend CoinJoin change in an effective, private manner.
How To Spend CoinJoin Change
Using CoinJoin change requires some technical understanding, so be sure you understand the fundamentals of Bitcoin privacy and are open to learning something new before proceeding. Whenever dealing with funds (especially privacy-sensitive funds like CoinJoin change), it’s crucial that you’re careful and intentional with your actions.
1. CoinJoin In A Smaller Pool
If your doxxic change output is large enough that you can use it in a smaller CoinJoin pool, send it to one of your unused deposit wallet address and mix into a smaller CoinJoin pool.
For example: If you have a 3.7 million sat UTXO, you can enter the 1 million sat mixing pool. The tx0 transaction will generate the following outputs:
- A Whirlpool fee of 50,000 sats
- The miner fee
- 3 premix UTXOs of ~1 million sats each
- A doxxic change output of ~650,000 sats
You can then send this change output back to an unused address in your deposit wallet to enter the 100k sat CoinJoin pool.
The CoinJoin change generated from the tx0 transaction of entering the smaller 100,000 sat pool would be less than 45,000 sats which could easily be sent to one of the other services listed below.
Keep in mind: NEVER combine your doxxic change outputs with your postmix UTXOs as it undermines all privacy measures you’ve taken thus far. Thankfully, Samourai Wallet makes it nearly impossible to do, but just understand how intentional you must be with your doxxic change outputs.
2. Send CoinJoin Change Through Lightning
The Lightning network acts as a sort of Tor-like onion routing for Bitcoin payments, since each node that you route through doesn’t necessarily know the original source of the bitcoin. The more Lightning nodes that you route through, the more privacy you can enjoy.
If you send doxxic change to a Lightning wallet, you can send it to another Lightning wallet you control to make an on-chain payment to one of your unused deposit wallet addresses. This will get you a different UTXO than you sent to the first Lightning wallet. As soon as it is confirmed on-chain in your Sparrow wallet, you can enter a CoinJoin pool with a new UTXO. Using Lightning this way can be a good way to use a burner wallet to preserve your privacy.
If you don’t run your own Lightning node, you can use any of these plug-n-play Lightning wallets:
- Muun: Non-custodial mobile wallet for both on-chain and Lightning payments.
- Phoenix: Non-custodial mobile wallet for both on-chain and Lightning payments.
- Wallet Of Satoshi: Completely custodial mobile wallet for both on-chain and lightning payments.
3. Send CoinJoin Change To Stacker News
If you decide to send your CoinJoin change through Lightning, you might consider creating an account on Stacker.News, fund your account, and upvote quality posts or even to boost some of your own posts.
While the primary purpose of Stacker News is to use sats to upvote quality posts and comments, if you use the platform often enough and make quality posts, one of your contributions could potentially go viral and earn some sats from others on the platform. It’s not uncommon to see posts that have earned thousands of sats.
Not only are you properly managing your spare CoinJoin change, but you’re contributing to the Bitcoin circular economy online by supporting the latest social networks growing on Lightning.
4. Swap Your CoinJoin Change
Another great way to spend CoinJoin change privately is to swap any of your doxxic change UTXOs for different ones.
One of the key advantages that swaps have over CoinJoins is that they rely on two separate transactions that are not linked to each other in any way. CoinJoins are collaborative spends that generate identical outputs, making it impossible to know for certain which sender owns which output.
There are a few different ways to do this, each of which come with their own set of tradeoffs.
Swap On Fixed Float
You can use a service like Fixed Float that allows users to trade on-chain bitcoin for bitcoin on Lightning or vice versa. This can be useful for anyone who doesn’t want to set up one of the Lightning wallets mentioned above.
You can send on-chain bitcoin and receive bitcoin directly to your Lightning wallet OR you can send bitcoin on the Lighting network and receive bitcoin directly with one of your unused deposit wallet addresses. This way, you can join a CoinJoin whirlpool with new UTXOs that aren’t associated with you.
If you decide to send from on-chain to Lightning, you can consolidate your Lightning balance until you have enough to join a CoinJoin pool.
Swap Using Mercury Wallet
If your doxxic change output is large enough, you can swap it with Mercury wallet. Mercury is a new Bitcoin layer-2 scaling technology (based on the concept of statechains) that enables two independent owners of private keys to swap them securely for a new UTXO, without requiring an on-chain transaction. This enables users to transfer full custody of an amount of BTC to anyone almost instantly, with increased privacy, and without having to pay miner fees.
One of the benefits of swapping CoinJoin change with Mercury is that not only is there no connection between those two counter-parties who are swapping, but there isn’t even an on-chain transaction to begin with. Instead the 2 parties are blindly swapping private keys.
Swap With Another Bitcoiner
If you know someone who also owns some bitcoin, you can ask them if they want to do a coin swap with your CoinJoin change. This involves both parties exchanging their coins without any third-party involvement but it comes with the potential loss of privacy if the counter-party ends up being a bad actor. So of course, only swap CoinJoin change with people you trust.
5. Buy A VPN Service
Since you’re reading this article, I am going to assume that you are concerned about using bitcoin as privately as you possibly can. If so, it only makes sense that you may be interested in spending CoinJoin change on a VPN service. There are number of VPN services that accept bitcoin as payment but a bunch of them seem to require you to provide some of your personal information like an email address and even your name.
Even though some of these VPN services accept bitcoin as payment, some of them only accept it via a KYC payment gateway. Not only is that completely against the ethos of Bitcoin, it’s also a direct violation of step 6 of this project (avoid KYC off-ramps).
Mullvad offers a $5 flat rate VPN service that requires none of your personal information and they offer a 10% discount for paying with bitcoin. If you want to maximize your privacy when paying for a VPN, it’s best practice to use coin control send 1 entire doxxic UTXO so that you don’t create any change and potentially start a peeling chain.
A VPN service is an important tool if you are trying to use bitcoin anonymously or even if you just want some added privacy online.
6. Buy Gift Cards
You can also spend CoinJoin change on gift cards through services like Fold (Affiliate), Bitrefill, and The Bitcoin Company. This is a great way to deal with your CoinJoin change without having to go through the hassle of conjoining it again or exchanging it for fiat. Just find the perfect gift card and pay with your change. Done.
7. Donate Your CoinJoin Change
The easiest way to spend CoinJoin change is to donate it to one of the many open source projects in the Bitcoin space or even to some of the amazing content creators out there.
If you are going to donate your CoinJoin change with an on-chain payment, it makes the most sense to only donate to a brand new address or with a PayNym. For maximum privacy, it’s best to avoid ever sending to a static donation/tipping address. If you’re going to donate via Lightning, it doesn’t really matter how you donate since it shouldn’t compromise any of your privacy.
Some of the best projects in the Bitcoin space are open source. If you would like to support the developers who make bitcoin what it is today, consider using CoinJoin change on them:
- Donate to RoboSats
- Donate to Sparrow Wallet
- Donate to SeedSigner
- Donate to BTCPay Server
- Donate to Zeus
- Donate To Pleb Projects
…or find other ways to donate to your favorite Bitcoin projects.
Donate To Pleb Content Creators
The plebs are the lifeblood of the Bitcoin community. They are the decentralized Bitcoin marketing team. Without them, there wouldn’t be any articles, books, videos, podcasts, memes, infographics, art, and music. All of that amazing content comes from the plebs who work for basically free to help the world achieve hyperbitcoinization.
The next time you see a donation link or a PayNym from one of your favorite Bitcoin content creators, maybe take the time to send them one of your doxxic UTXOs to help them to continue producing content while also preserving your own privacy.
Final Thoughts
As bitcoin grows in prominence, so should the importance of your privacy as a sovereign Bitcoin holder.
With the increased popularity of CoinJoin and other Bitcoin privacy tools, along with resources like these to help learn about them, it’s easier than ever to learn about CoinJoin and take advantage of the benefits other similar Bitcoin privacy tools offer. There are a few ways to ensure that your CoinJoin change is private. By CoinJoining in a smaller pool, buying a VPN service, buying gift cards, sending it through Lightning, or swapping it, you can be sure that your data is safe.
Maybe you’ve only just started your journey to enhance your bitcoin’s privacy. Have you learned how to consolidate your UTXOs? Manage your seed phrase security?
Like bitcoin’s nature as layered money, Bitcoin privacy comes in layers as well. There are plenty of ways for you to bolster the strength of your Bitcoin security, which may very well be necessary as Bitcoin adoption accelerates. So stay aware of new developments, and take the initiative to ensure that your bitcoin is safe for the long term.
Stay private out there!
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