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arXiv · 2609.27933

Shedding Light on Complex Bitcoin Mixer Transactions: 67-Fold Reduction in Unclassified Cases

Nikolay Larionov·Yekaterina Smolenkova·Yury Yanovich
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Abstract

Bitcoin's Unspent Transaction Output (UTXO) model enables public analysis of fund flows, but users often merge transactions into Shared Send Mixers (SSMs) to obscure these flows. Untangling SSMs to recover original subtransactions is an NP-complete problem. While a practical untangling algorithm exists, it fails to classify 1.4% of SSM transactions due to computational time limits. This paper introduces four novel heuristics that exploit structural weaknesses in real-world SSM transactions to resolve these timeout cases: preemptive grouping, connectable singleton, ambiguous pairing, and knapsack fallback. We provide theoretical proofs validating each heuristic and integrate them into an optimized pipeline. Applied to timeout transactions, our approach classifies 98.5% of previously unresolved cases, reducing the overall unclassified transaction rate from 1.4% to 0.021% of all SSM transactions. Our open-source implementation and comprehensive evaluation on the complete Bitcoin blockchain demonstrate that the heuristics effectively untangle previously intractable transactions, enabling more accurate flow analysis and deeper structural insights into cryptocurrency transaction patterns.

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Nikolay Larionov, Yekaterina Smolenkova, Yury Yanovich. 2026-08-22. Shedding Light on Complex Bitcoin Mixer Transactions: 67-Fold Reduction in Unclassified Cases. https://arxiv.org/abs/2609.27933

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