CoinJoin and Mixing: Understanding Bitcoin On-Chain Privacy

Table of Contents

1. Introduction
2. Why Mixing Is Necessary
3. What Is CoinJoin?
4. Historical and Current CoinJoin Tools
5. PayJoin: The Subtle Alternative
6. Other Mixing Techniques
7. Risks and Legal Considerations
8. Detailed Technical Workings
9. Recommended Tools in 2025
10. Future Outlook
11. Summary Table
12. FAQ
13. Conclusion
14. Internal Links
15. Sources and Resources

Suggested URL: /privacy/coinjoin-mixing-bitcoin

Category: Privacy and Anonymity

Summary: Complete guide to Bitcoin mixing techniques: CoinJoin, PayJoin, and alternatives. Technical workings, available tools, and the state of play after the 2024 shutdowns.

Introduction

Bitcoin is traceable, but mixing allows you to break the links between transactions.

Bitcoin is often described as "pseudonymous" rather than anonymous. Every transaction is publicly recorded on the blockchain, allowing anyone -- and especially chain analysis companies -- to trace the flow of funds.

Mixing techniques aim to break these traceability links by blending the bitcoins of multiple users. Among them, CoinJoin has established itself as the most robust and widely used solution.

However, 2024 marked a turning point: the shutdown of Wasabi Wallet and regulatory pressures upended the mixing ecosystem. This article takes stock of the available techniques, how they work, and their future.

1. Why Mixing Is Necessary

Every Bitcoin transaction is public, traceable by professional chain analysts.

1.1 The Problem of Bitcoin Traceability

On the Bitcoin blockchain, every transaction reveals:

1.2 The Chain Analysis Industry

Companies like Chainalysis, Elliptic, and CipherTrace have developed sophisticated tools to:

• Identify address owners
• Trace fund flows between addresses
• Group addresses belonging to the same entity (clustering)
• Provide this information to governments and exchanges

Techniques used:

1.3 Practical Consequences

Without privacy protection:

• Your employer can see your purchases if you are paid in BTC
• Your complete financial history is accessible
• Your wealth becomes a potential target
• Third parties can refuse your BTC deemed "tainted"

2. What Is CoinJoin?

A collaborative transaction that mixes the bitcoins of multiple users to break traceability.

2.1 Fundamental Principle

CoinJoin, proposed by Gregory Maxwell in 2013, exploits a property of Bitcoin: a transaction can have multiple inputs from multiple owners.

Normal transaction:

Alice (1 BTC) ─────────────────► Recipient (1 BTC)

CoinJoin transaction:

Alice   (1 BTC)  ──┐
Bob     (1 BTC)  ──┼──► 4 outputs of 1 BTC each
Charlie (1 BTC)  ──┤     (no one knows who received what)
David   (1 BTC)  ──┘

The analyst sees 4 inputs and 4 identical outputs, but cannot determine which input corresponds to which output.

2.2 Conditions for Effectiveness

For a CoinJoin to be effective:

2.3 The Anonymity Set

The anonymity set measures the number of possible outputs for each input.

Example:

• CoinJoin with 50 participants and identical outputs
• Anonymity set = 50
• Probability that a specific output came from a specific input = 2%

The larger the anonymity set, the better the privacy.

3. Historical and Current CoinJoin Tools

Wasabi and Samourai shut down in 2024, JoinMarket remains the decentralized reference.

3.1 Wasabi Wallet (2018-2024)

History: Wasabi democratized CoinJoin with its WabiSabi protocol, enabling mixes with anonymity sets of 100+.

Shutdown: In 2024, Wasabi shut down its coordinator, citing regulatory pressure and legal risks.

Legacy: The code remains open source; alternative coordinators exist but with less liquidity.

3.2 JoinMarket

How it works: A decentralized marketplace where "makers" offer their bitcoins for mixing, and "takers" pay to join.

Advantage: Censorship-resistant because it is decentralized.

Disadvantage: Technical interface, less accessible to beginners.

3.3 Whirlpool (Samourai Wallet)

Situation: In April 2024, the developers of Samourai Wallet were arrested by the U.S. DOJ. The Whirlpool service is compromised.

Impact: Demonstrated that centralized coordinators are vulnerable to prosecution.

3.4 State of Play in 2025

4. PayJoin: The Subtle Alternative

A discreet two-participant CoinJoin that breaks classic analysis heuristics.

4.1 Principle

PayJoin (or P2EP -- Pay-to-EndPoint) is a two-participant CoinJoin disguised as a normal transaction.

Normal transaction:

Alice (1 BTC) ──► Merchant (0.5 BTC) + Alice change (0.5 BTC)

PayJoin:

Alice (1 BTC) + Merchant (0.3 BTC) ──► Merchant (0.8 BTC) + Alice change (0.5 BTC)

The merchant adds one of their own inputs, breaking the "common input ownership" heuristic.

4.2 Advantages

4.3 Implementations

• BTCPay Server: Supports PayJoin natively
• Sparrow Wallet: Can initiate PayJoins
• BlueWallet: Experimental support

4.4 Limitations

• Requires the recipient's cooperation
• Poorly adopted by merchants
• Smaller anonymity set than a classic CoinJoin

5. Other Mixing Techniques

Centralized mixers are obsolete; atomic swaps and submarine swaps serve as alternatives.

5.1 Centralized Mixers (Obsolete)

Classic centralized mixers work as follows:

1. You send BTC to the mixer
2. The mixer sends you back "clean" BTC
3. The mixer keeps a log (or claims not to)

Problems:

• Risk of theft (exit scam)
• Logs potentially retained
• Targeted by authorities (ChipMixer, Blender shut down)
• Funds "tainted" because they passed through a known mixer

Verdict: Obsolete and dangerous in 2025.

5.2 Atomic Swaps

Decentralized cross-chain exchange (e.g., BTC <-> XMR) without an intermediary.

Advantage: Breaks traceability by passing through another chain.

Limitation: Technical complexity, limited liquidity.

5.3 Submarine Swaps

Exchange between Bitcoin on-chain and the Lightning Network.

BTC on-chain ──► Lightning ──► BTC on-chain (different address)

Breaks the traceability continuity between the two on-chain transactions.

6. Risks and Legal Considerations

Legal for privacy purposes, but risk of rejection by certain exchanges.

6.1 Legal Situation in France

6.2 Practical Risks

Exchanges and "tainted coins":

• Some exchanges refuse BTC that have passed through known mixing services
• Automatic flagging by Chainalysis
• Possible account freeze and request for justification

Enhanced KYC:

• Request for proof of origin of funds
• Justification of complete transaction history

6.3 Best Practices

1. Document your transactions: Keep proof of legitimate origin
2. Use unmixed outputs for exchanges: Keep a "clean" portion
3. Declare your capital gains: Mixing does not exempt you from tax obligations
4. Understand the risks: Some services may refuse your funds

7. Detailed Technical Workings

From registration to broadcast, understanding each step of the CoinJoin protocol.

7.1 Steps of a CoinJoin

Phase 1: Registration

• Participants register with the coordinator (or the marketplace for JoinMarket)
• Each participant provides their desired inputs and outputs

Phase 2: Transaction Construction

• The coordinator (or protocol) builds the joint transaction
• All inputs and outputs are aggregated

Phase 3: Signing

• Each participant signs their part of the transaction
• Use of Schnorr signatures for better privacy (post-Taproot)

Phase 4: Broadcast

• The complete transaction is broadcast to the network
• Participants receive their mixed outputs

7.2 Structure of a CoinJoin Transaction

Inputs:
├── Alice:   0.1 BTC (signature A)
├── Bob:     0.1 BTC (signature B)
├── Charlie: 0.1 BTC (signature C)
└── David:   0.1 BTC (signature D)

Outputs:
├── ???: 0.099 BTC (fees deducted)
├── ???: 0.099 BTC
├── ???: 0.099 BTC
└── ???: 0.099 BTC

(+ change outputs if necessary)

7.3 Importance of Equal Outputs

If outputs are of different amounts, correlation becomes possible again:

Bad example:
Inputs: 0.5 + 0.3 + 0.2 BTC
Outputs: 0.5 + 0.3 + 0.2 BTC
→ Obvious correspondence by amounts

8. Recommended Tools in 2025

JoinMarket and Sparrow Wallet as decentralized solutions post-2024 shutdowns.

8.1 For CoinJoin

8.2 Complementary Tools

8.3 Recommended Workflow

1. Run your own Bitcoin node
2. Use Sparrow Wallet for coin control
3. Perform CoinJoins via JoinMarket
4. Use separate addresses post-mix
5. Never consolidate mixed outputs with unmixed outputs

9. Future Outlook

Taproot improves discretion; CISA and decentralization are shaping the future of mixing.

9.1 Impact of Taproot

Taproot (activated in 2021) improves CoinJoin:

• Schnorr signatures: A single common signature for all participants
• Smaller footprint: CoinJoins look more like normal transactions
• MAST: Complex scripts hidden

9.2 Cross-Input Signature Aggregation (CISA)

A future proposal allowing the aggregation of all input signatures into a single one. This would reduce fees and improve the privacy of all CoinJoins.

9.3 Increased Decentralization

The post-2024 trend is toward total decentralization:

• No centralized coordinator = no single point of failure
• JoinMarket leads the way
• New protocols in development

10. Summary Table

Comparative summary of the different mixing techniques available in 2025.

FAQ

Q1: Is CoinJoin illegal?

No. Using CoinJoin to protect your privacy is legal in France and in most Western countries. What is illegal is using any tool (CoinJoin or otherwise) to launder money or commit tax fraud.

Q2: Can exchanges refuse my bitcoins after a CoinJoin?

Yes, some exchanges may flag funds that have passed through known mixing services. This is a commercial policy, not a legal obligation. Keep some "unmixed" BTC for interactions with exchanges.

Q3: Is JoinMarket safe to use?

JoinMarket is decentralized and open source, which reduces the risk of compromise. However, like any tool, it requires proper use. Run your own node and follow best practices.

Q4: What anonymity set should I aim for?

Generally, an anonymity set of 50+ is considered good. Purists aim for 100+. The important thing is not to "demix" afterward by consolidating with unmixed outputs.

Q5: Does mixing eliminate all traces?

No. Mixing significantly improves privacy but is not perfect. Sophisticated analysis can sometimes identify patterns. Combine it with other practices (Tor, personal node, coin control).

Conclusion

CoinJoin remains the most powerful tool for improving the privacy of on-chain Bitcoin transactions. Despite the shutdown of Wasabi and the prosecution of Samourai, decentralized alternatives like JoinMarket persist and continue to develop.

Key takeaways:

1. Mixing is legal for protecting your privacy
2. JoinMarket is currently the best decentralized option
3. PayJoin offers a subtle alternative for payments
4. Never consolidate mixed and unmixed outputs
5. Tax reporting obligations remain despite mixing

The future of mixing lies in total decentralization and native integration into wallets, making privacy accessible to everyone without the risk of a central point of failure.

Internal Links

• Privacy Coins - Monero, Zcash -- Alternative: natively private cryptocurrencies
• Lightning Network - Privacy -- Privacy on Layer 2
• VPN and Tor for Crypto -- Network protection
• Coldcard Guide -- Key security
• Multisig 2-of-3 -- Advanced protection

Related Articles -- Privacy

• Lightning Network Privacy and Confidentiality
• Privacy Coins: Monero, Zcash, and Alternatives
• VPN and Tor for Crypto Transactions

Sources and Resources

Technical Documentation

• Original CoinJoin: bitcointalk.org (Gregory Maxwell, 2013)
• JoinMarket: github.com/JoinMarket-Org/joinmarket-clientserver
• PayJoin BIP78: github.com/bitcoin/bips/blob/master/bip-0078.mediawiki

Tools

• Sparrow Wallet: sparrowwallet.com
• Jam (JoinMarket GUI): jamapp.org
• BTCPay Server: btcpayserver.org

Analysis

• Bitcoin Privacy Guide: bitcoiner.guide/privacy
• Academic Research: Publications on Bitcoin traceability

Article written in December 2025. The mixing ecosystem evolves rapidly. Check the status of tools before use.