JoinMarket CoinJoin Analyzer

Analyze JoinMarket Bitcoin CoinJoin transactions. Using greedy pre-processing and Integer Linear Programming (ILP).

Features

• Deterministic preprocessing: Greedy heuristic for unambiguous input-output matches
• Symmetry-breaking ILP: Eliminates permutation duplicates, finds all distinct solutions
• Memory-safe: 10GB limit enforcement
• Interrupt handling: Ctrl+C saves progress
• Incremental saves: Solutions written after each discovery
• Production-ready: Modular architecture, comprehensive tests, CLI interface

Installation

pip install -e .

Usage

CLI

# Analyze a transaction
joinmarket-analyze 0cb4870cf2dfa3877851088c673d163ae3c20ebcd6505c0be964d8fbcc856bbf

# Custom parameters
joinmarket-analyze <txid> --max-fee-rel 0.1 --max-solutions 500

# Help
joinmarket-analyze --help

# Output is automatically saved to solutions_<txid_prefix>.json

Scanner (Mass Analysis)

The joinmarket-scan tool allows you to scan blocks for JoinMarket transactions, analyze them, and store results in a SQLite database.

# Scan specific block range
joinmarket-scan 924300 924305

# Scan last 100 blocks
joinmarket-scan -100

# Resume scanning (skips already scanned blocks)
joinmarket-scan 0

# Check stats in the database
sqlite3 joinmarket_stats.db "SELECT count(*) FROM coinjointx;"

# Run in parallel (e.g., 4 jobs)
joinmarket-scan 924300 924305 --jobs 4

The scanner saves partial results if the exact solution cannot be found but the greedy algorithm successfully identifies the taker. This allows collecting fee statistics even for complex transactions.

Docker

# Run with a transaction ID
docker run --rm ghcr.io/m0wer/joinmarket_analyzer:master 0cb4870cf2dfa3877851088c673d163ae3c20ebcd6505c0be964d8fbcc856bbf

# Run with memory limit (recommended)
docker run --rm -m 10g ghcr.io/m0wer/joinmarket_analyzer:master <txid> --max-solutions 500

# Using docker-compose
docker-compose run --rm joinmarket-analyzer <txid>

Python API

from joinmarket_analyzer import analyze_transaction

solutions = analyze_transaction(
    txid="0cb4870cf2dfa3877851088c673d163ae3c20ebcd6505c0be964d8fbcc856bbf",
    max_fee_rel=0.05,
    max_solutions=1000
)

for solution in solutions:
    print(f"Taker: Participant {solution.taker_index + 1}")
    print(f"Maker fees: {solution.total_maker_fees:,} sats")

Working Example

docker run --rm ghcr.io/m0wer/joinmarket_analyzer:master \
  0cb4870cf2dfa3877851088c673d163ae3c20ebcd6505c0be964d8fbcc856bbf \
  --max-fee-rel 0.001 --max-solutions 10

View Output

Taker: Participant 4 (pays 21,368 sats)
  💰 Participant 1 (maker)
    Inputs: [0]
    Outputs: Equal=6,357,366 sats, Change[2]=113,283,033 sats
    Fee receives: 458 sats
  💰 Participant 2 (maker)
    Inputs: [1]
    Outputs: Equal=6,357,366 sats, Change[6]=2,089,662,830 sats
    Fee receives: 413 sats
  💰 Participant 3 (maker)
    Inputs: [3]
    Outputs: Equal=6,357,366 sats, Change[19]=765,432,353 sats
    Fee receives: 623 sats
  🎯 Participant 4 (taker)
    Inputs: [4]
    Outputs: Equal=6,357,366 sats, No change output
    Fee pays: 21,368 sats
  💰 Participant 5 (maker)
    Inputs: [5]
    Outputs: Equal=6,357,366 sats, Change[11]=3,044,723 sats
    Fee receives: 5,153 sats
  💰 Participant 6 (maker)
    Inputs: [6]
    Outputs: Equal=6,357,366 sats, Change[3]=10,187,122 sats
    Fee receives: 559 sats
  💰 Participant 7 (maker)
    Inputs: [7]
    Outputs: Equal=6,357,366 sats, Change[8]=90,781,833 sats
    Fee receives: 636 sats
  💰 Participant 8 (maker)
    Inputs: [8]
    Outputs: Equal=6,357,366 sats, Change[12]=8,045,121 sats
    Fee receives: 973 sats
  💰 Participant 9 (maker)
    Inputs: [9]
    Outputs: Equal=6,357,366 sats, Change[7]=100,823,618 sats
    Fee receives: 687 sats
  💰 Participant 10 (maker)
    Inputs: [11]
    Outputs: Equal=6,357,366 sats, Change[20]=8,125,627 sats
    Fee receives: 191 sats
  💰 Participant 11 (maker)
    Inputs: [2, 10]
    Outputs: Equal=6,357,366 sats, Change[1]=87,861 sats
    Fee receives: 693 sats
Total maker fees collected: 10,386 sats
Network fee: 10,982 sats

Algorithm

Greedy Preprocessing

1. Single-input matching (iterative): Match inputs to change outputs where only one valid pairing exists
2. Multi-input fallback: Sequential assignment for remaining inputs
3. Reduces search space: Pre-assigns deterministic participants before ILP

ILP Formulation

• Variables: Input assignments x[i,p], change assignments c[p,j], taker indicator t[p]
• Symmetry breaking: Orders participants by minimum input index
• Partition cuts: Excludes found solutions and all permutations
• Constraints: Balance equations, fee bounds, dust thresholds, maker fee non-positivity

Testing

# Unit tests
pytest tests/unit/ -v

# E2E tests (requires network)
pytest tests/e2e/ -v

# All tests with coverage
pytest --cov=joinmarket_analyzer --cov-report=html

Development

# Install with dev dependencies
pip install -e ".[dev]"

# Linting
pre-commit run --all-files

Requirements

• Python 3.9+
• PuLP (CBC solver)
• Pydantic 2.x
• Loguru
• Requests

Citation

If you use this tool in research, please cite:

@software{joinmarket_analyzer,
  title = {JoinMarket CoinJoin Analyzer},
  year = {2025},
  url = {https://github.com/m0wer/joinmarket-analyzer}
}

Future Work & Research

This tool lays the groundwork for more advanced privacy research:

• Entropy Evaluation: Measure how "ambiguous" change outputs are. If multiple valid solutions exist, the Taker is harder to pinpoint.
• Algorithm Design: Evaluate and improve taker algorithms to intentionally create ambiguous change structures.
• Market Statistics: Analyze historical CoinJoins to gather statistics on fee limits used by takers and earnings by makers.

Notes

• Assumes JoinMarket protocol structure (equal outputs, optional change)
• CBC solver timeout: 60s per iteration
• Uses mempool.sgn.space API for transaction data (requires network access)

License

MIT License