Joinstr

Oct 25, 2025

The transparency of the Bitcoin blockchain makes it possible to trace transaction history. CoinJoins break these links by mixing multiple simultaneous transactions, restoring a level of confidentiality comparable to cash.

However, traditional solutions rely on a central coordinator as a single point of failure. Wasabi and Samourai ceased operations in 2024 under regulatory pressure.

Joinstr eliminates this weakness by using the decentralized Nostr network for coordination. This open source application enables truly sovereign CoinJoins, where no central authority can censor, monitor or interrupt the service.

What is Joinstr?

Joinstr is an open source tool that revolutionizes the CoinJoins approach by leveraging the Nostr protocol as a coordination infrastructure. Unlike centralized solutions requiring a dedicated server, Joinstr relies on a distributed network of Nostr relays to enable participants to coordinate directly between peers.

Decentralized architecture : The Nostr network replaces the central coordinator. Participants create or join "pools" by posting encrypted announcements via the Nostr relays. This information (amounts, participants, addresses) remains unintelligible to the relays, ensuring that no central entity can monitor, censor or filter CoinJoins.

SIGHASH_ALL|ANYONECANPAY mechanism: Joinstr exploits this Bitcoin signature flag, allowing each participant to sign only his or her input while validating all outputs. Each user generates his or her PSBT locally, then distributes it via Nostr. Each user generates his PSBT locally, signs it, then distributes it via Nostr. Your bitcoins remain under your exclusive control until the final signature.

Philosophy: Joinstr follows the Bitcoin cypherpunk ethos, aiming for three goals: resistance to censorship (no authority can stop the service), total non-custodiality (you keep your private keys), and equal treatment (no UTXO can be discriminated against).

Main features

Flexible pools: Unlike fixed denominations, any user can create a pool with the exact amount desired and the target number of participants, optimizing the use of UTXO without artificial splitting.

Transparent fees: No coordination fees. Only Bitcoin transaction fees are shared equally between participants (a few thousand satoshis per person).

Ephemerality: No user data retained. Information transits via encrypted ephemeral Nostr messages, immediately forgotten after the transaction.

Available platforms

This tutorial focuses on the Android application, the only currently stable and recommended solution. A Electrum plugin exists but has compatibility problems that make it unstable. A web interface is under development.

Bitcoin Core configuration

Joinstr Android requires a connection to a Bitcoin node via RPC. You must first configure Bitcoin Core on your computer to accept connections from your phone.

Note: For more details on the complete configuration of Bitcoin Core, see our dedicated tutorials :

Bitcoin Core (Linux)Running your own node with Bitcoin Core on Linux

Bitcoin Core (macOS & Windows)Install Bitcoin Core on Mac or Windows

Network requirements

Locate your local IP address

Your Android phone must be able to reach your Bitcoin node on the local network. Find the IP address of your computer:

On macOS :

ifconfig | grep "inet " | grep -v "127.0.0.1" | awk '{print $2}' | head -n 1

Simple alternative:

ipconfig getifaddr en0
# or for WiFi: ipconfig getifaddr en1

On Linux :

hostname -I | awk '{print $1}'

On Windows :

ipconfig

Find the IPv4 address (format 192.168.x.x or 10.0.x.x)

RPC configuration

Edit bitcoin.conf

Locate your bitcoin.conf file:

Linux: ~/.bitcoin/bitcoin.conf
macOS: ~/Library/Application Support/Bitcoin/bitcoin.conf
Windows: %APPDATA%\Bitcoin\bitcoin.conf

Open the file with your favorite text editor and add this configuration to activate the RPC server.

Recommended configuration for getting started (bookmark) :

# Enable signet (test network)
signet=1
prune=550

# Enable the RPC server
server=1
rpcbind=0.0.0.0

# Allow connections from your local network
# Adjust according to your network (192.168.x.0/24 or 10.0.x.0/24)
rpcallowip=192.168.1.0/24

# RPC Credentials (CHANGE THESE VALUES!)
rpcuser=your_username
rpcpassword=your_strong_password

# Specific signet configuration
[signet]
rpcport=38332

mainnet configuration (for production use) :

# RPC Server
server=1
rpcbind=0.0.0.0
rpcallowip=192.168.1.0/24

# RPC Credentials
rpcuser=your_username
rpcpassword=your_strong_password

# Mainnet Port
rpcport=8332

Important :

Signet is highly recommended for your first tests: the application is still in development (beta), and bugs may still exist. Signet lets you test free of charge, without risking real funds
Replace 192.168.1.0/24 with your network subnet (e.g. if your IP is 192.168.68.57, use 192.168.68.0/24)

Security: Generate a strong password :

openssl rand -base64 32

Initialization

Restart and check

Shut down Bitcoin Core completely
Restart it to apply the configuration

When Bitcoin Core starts up for the first time, it will download and synchronize the bookmark blockchain. This operation is much faster than on mainnet (only a few minutes). Please wait until synchronization is complete before proceeding.

Once synchronized, create a new wallet by clicking on "Create a new wallet". Give it an explicit name like tuto_joinstr_signet.

Your wallet is now created and ready to receive bookmarked bitcoins for testing.

Get bookmarked bitcoins (test)

To test Joinstr on bookmark, you need free test bitcoins :

Use a public bookmark like :

In Bitcoin Core, generate a new receive address ("Receive" tab), copy it and paste it into the faucet form. Solve the captcha if necessary. You'll receive free bookmarked bitcoins within seconds.

Android application

Installation

Go to gitlab.com/invincible-privacy/joinstr-kmp/-/releases to download the latest APK version. On your Android browser, download the file, then open it to launch the installation. You'll need to allow installation from unknown sources in your phone's security settings if necessary.

Application configuration

On first launch, the Joinstr application will ask for permissions to control the built-in VPN. Accept both permission requests: OpenVPN control and VPN connection. These permissions are required for VPN integration, which protects your network privacy.

The Joinstr application is organized into three main tabs:

Home: Home screen
Pools: Creating and managing CoinJoin pools
Settings: Application configuration

Configure settings in the "Settings" tab:

1. Nostr Relay: Nostr relay address for pool coordination

Example: wss://relay.damus.io
Other recommended relays: wss://nos.lol, wss://relay.nostr.band, wss://nostr.fmt.wiz.biz
⚠️ Important: All participants must use the same Nostr relay to see and join the same pools. If you use a different relay, you will not see pools created on other relays

2. Node URL: IP address of your Bitcoin node (without port)

Format: http://VOTRE_IP_LOCALE
Example: http://192.168.68.57

3. RPC Username : The user name configured in rpcuser= on your bitcoin.conf

Example: satoshi

4. RPC Password : The password set in rpcpassword= on your bitcoin.conf

5. RPC Port : RPC port depending on network

Mainnet : 8332
Bookmark: 38332

6. Wallet: Select the Bitcoin Core wallet containing the UTXOs to be mixed

Example: tuto_joinstr_signet

7. VPN Gateway: Select a Riseup VPN server

Example: (Paris) vpn07-par.riseup.net
Others available: Amsterdam, Seattle, etc.
⚠️ Important: All participants in the same pool must use the same VPN Gateway to participate in CoinJoin. During the mixing round, all participants must appear with the same exit IP address to prevent network analysis from correlating participants

The Joinstr application integrates natively the Riseup VPN, simplifying coordination between participants.

Important :

Make sure your phone and computer are on the same local WiFi network
The VPN connection will be activated automatically when participating in a pool
Click on "Save " once you have set all the parameters

Practical use

Create or join a pool

You have two options for participating in a CoinJoin:

Option 1: Create a new pool

Click on "Create New Pool" in the "Pools" tab. Specify the denomination in BTC (e.g. 0.002 BTC) and the desired number of participants (minimum 2, recommended 3-5 for greater anonymity). The application then waits for other users to join your pool. Once the required number has been reached, the output registration process begins automatically, and you'll need to select your UTXO to mix and click on "Register".

⏱️ Important: Pools expire after 10 minutes of inactivity. If the required number of participants is not reached, the pool will be automatically closed.

Option 2: Join an existing pool

In the "View Other Pools" tab, browse the available pools created by other users. Select a pool corresponding to your amount and join it. Make sure you have configured the same Nostr relay and VPN Gateway as the other participants (see Configuration section).

UTXO selection rule: Your UTXO must be slightly higher than the pool denomination (between +500 and +5000 sats surplus).

Example: For a pool of 0.002 BTC (200,000 sats), use a UTXO between 200,500 and 205,000 sats.

The process is then fully automatic: once your input has been registered, the application waits for all participants to register their inputs. Once all inputs have been registered, the PSBT is created, automatically signed with your keys, then combined with the signatures of the other participants. Finally, the complete transaction is broadcast on the Bitcoin network. You receive the TXID (transaction identifier) once the broadcast is complete. No manual manipulation of PSBT is required on Android.

on-chain verification

Once the transaction has been broadcast, you will receive the TXID (transaction identifier). View it on mempool.space or your favorite browser. To test on a bookmark, use mempool.space/signet.

You can observe :

N entries: One per participant (in our example, 2 entries)
N identical outputs: exact amount of the denomination (here, 2 outputs of 0.00199800 BTC each)
Flow chart: mempool.space visually displays the mix of inputs and outputs
Features : The transaction can be identified as SegWit, Taproot, RBF, etc.

As all main outputs have the same amount, it's impossible to determine which belongs to whom. This is the fundamental principle of CoinJoin: the indistinguishability of outputs.

Exemple de transaction signet : 404a6a58a1682341c1197655fa492fa160bf63fca8c3b29be125e7360dbec44c

Please note: If your UTXOs were larger than the pool denomination, you will have foreign exchange outputs (surpluses). These exchange UTXOs remain traceable and must be managed separately from your anonymized outputs. Never combine them with your mixed outputs.

CoinJoin quality and anonymity packages

The efficiency of a CoinJoin is measured by its anonset: the number of outputs of identical value produced by the transaction. The higher this number, the more difficult it is to determine which input corresponds to which output.

Joinstr currently generates pools of 2 to 5 participants on average. These figures are lower than traditional centralized coordinators like Wasabi (50-100 participants) or Whirlpool (5-10 participants), but that's the price of decentralization.

💡 To understand anonymity sets and their calculation in detail, see our full course: Anonymity sets.

Joinstr vs. other CoinJoins

Aspect	Wasabi	Whirlpool/Ashigaru	JoinMarket	Joinstr
Participants per pool	50-100	5-10	Variable (P2P)	2-5
Coordinator	Centralized (closed 2024)	Centralized (active)	P2P maker/taker	None (Nostr)
Censorship resistance	Weak	Medium	Very high	Very high
Coordination fees	Percentage	Entry fee	Paid to makers	None
UTXO discrimination	Yes (blacklists)	No	No	No

💡 Other active CoinJoin solutions :

Ashigaru: Open-source implementation of the Whirlpool protocol with centralized coordinator but deployable in a decentralized way. Continues to operate after the seizure of Samourai Wallet in 2024.
JoinMarket: Decentralized P2P solution with no central coordinator, based on a maker/taker business model where "makers" provide liquidity and are remunerated by "takers".

Ashigaru TerminalUse Ashigaru on desktop to make coinjoins

The fundamental trade-off: Joinstr and JoinMarket are the only two solutions without a central coordinator. JoinMarket uses a P2P business model with financial incentives, while Joinstr uses Nostr for cost-free coordination. Joinstr sacrifices immediate large-scale anonymity in favor of simplicity (no maker/taker management) and the total absence of coordination fees.

Practical recommendation: To compensate for smaller pools, run several successive rounds of CoinJoin with different participants. Space out your rounds and change Nostr relays between each round to maximize your confidentiality.

Feel free to consult our complete course on bitcoin privacy for more information on this topic:

Privacy on Bitcoin

Intermediate

4.7(140)

Understand and master the principles of privacy protection when using Bitcoin

4.7(140)

Privacy on Bitcoin

Understand and master the principles of privacy protection when using Bitcoin

Advantages and limitations

Highlights

Enhanced privacy: The combination of Nostr communications encryption, shared VPN between participants, and the recommended use of Tor creates multi-layered protection that's hard to bypass.

Transparent, minimal costs: No coordination costs, only mining costs are shared equitably between participants. No percentage levied by any operator.

Constraints to consider

Variable liquidity: Smaller pools, can wait for participants to come together
Project in progress: Application in beta, bugs possible. Test first with small amounts on bookmark
Sybil attacks: Possibility of one opponent controlling several pool participants

Best practices

UTXO isolation: Never combine a mixed UTXO with an unmixed one. Use a separate wallet for your anonymized outputs.

Multiple rounds essential: Perform a minimum of 3 successive rounds with different participants. Vary amounts and timings to avoid patterns. Space rounds several hours apart.

Network protection: Systematically use Tor in addition to the built-in VPN. Generate ephemeral Nostr keys for each important session.

Cautious progress: Start bookmarking with small amounts.

Conclusion

Joinstr represents a truly decentralized Bitcoin privacy solution. By using Nostr for coordination, it eliminates dependence on central coordinators while preserving user sovereignty.

For users who value resistance to censorship and are prepared to perform several rounds of CoinJoin to compensate for smaller pools.

Against a backdrop of increasing financial scrutiny, decentralized tools to protect privacy are becoming essential.

Resources

Official documentation

Tutorials

Electrum plugin tutorial - Complete guide by Uncensored Tech

Community and support

Telegram Joinstr Group - Community support and bookmark corners
Technical discussion on DelvingBitcoin

Additional tools

Bookmark Faucet - Free test Bitcoins
Alt Signet Faucet - Faucet alternative
Mempool.space - Block explorer with privacy analysis

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Author

This tutorial has been written by Pierre

You can say thanks by tipping the professor.

Pierre

41Tutorials

Passionate about Bitcoin and convinced that education is the key, I wish to share with you the little knowledge I have and thus contribute to the adoption of Bitcoin. Otherwise, I'm a big fan of Pink Floyd, I'm learning to code, and I make memes. Looking forward to meeting you at the next meet-up! I am the creator of the training course BTC 205 - Non-KYC Purchase Solution.

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