S14 E8: Fadi Barbàra on DMix & Bitcoin Privacy

Fadi Barbàra is a researcher from the University of Turin who works on Bitcoin privacy. His new project, DMix, promises to offer better privacy than CoinJoins by integrating a pre-mix transaction that makes use of Taproot multisigs. Fadi's background and introduction (00:02:11) Discussion about Fadi Barbara's work on DMix and Bitcoin privacy, his research in Turin at a state-funded university, and his journey into Bitcoin. Explanation of DMix and how it works (00:10:13) Overview of DMix as a two-transaction protocol, the use of CoinJoin in the second transaction, and the three-phase process of the mix. The transaction threshold signature (00:14:40) Explanation of how transaction threshold signatures work and the difference between a multisig and an aggregated signature. The goal of DMix (00:18:53) Comparison between DMix and other coinjoin protocols, with a focus on the goal of removing the need for a coordinator or centralization. Scalability and the limit of mixes (00:26:49) Discussion on the technical limit of mixes based on transaction size, the trade-off between decentralization and popularity, and the potential for larger transaction sizes. Dmix as a privacy facilitator (00:29:44) Discussion on how the mix in DMix improves privacy by creating unlinkability and the trade-off between privacy and protocol rules. Incentivizing participation in the mixing system (00:33:39) Exploration of the research phase regarding financial incentives for users to keep their coins in the mixing system and the importance of liquidity. Toxic change and its elimination in DMix (00:38:23) Explanation of how DMix handles toxic change by creating a greatest common divisor of the coins being exchanged, ensuring no toxic output in the final mix transaction. Address Reuse and Blockchain Privacy (00:43:18) Fadi Barbara discusses the importance of address reuse in blockchain privacy and the ongoing study of address reuse on the blockchain. Trust in DMix and Anonymity Set (00:45:42) Fadi addresses the issue of trust in DMix and the potential risk of participants belonging to chain analysis. He also discusses the use of multi-party computation to enhance privacy. DMix in Closed and Open Settings (00:50:57) The speaker discusses the suitability of DMix in closed settings, such as exchanges, and the ongoing efforts to make it suitable for open settings where anyone can participate. The proposed soft forks and Drivechains (00:57:04) Discussion about the potential solutions to Bitcoin's privacy problems through proposed soft forks and Drivechains. Controversy between Wasabi and Samourai wallet (00:58:20) Exploration of the differences and opinions on Wasabi and Samourai, their strengths, weaknesses, and potential for improvement. Statechains and coin swap idea (01:03:26) Evaluation of the concept of statechains and coin swap as a method of transferring ownership of coins without on-chain transactions, including the benefits and challenges associated with the approach. Using DMX in conjunction with existing solutions like CoinJoin or CoinSwap (01:11:35) Vlad asks Fadi if DMix can be used alongside other privacy solutions or if it is meant to replace them. Confidential transactions and the need for soft or hard forks (01:12:26) Fadi Barbara discusses how confidential transactions, which require changes at the protocol level, are necessary for achieving better privacy. He also mentions that the Elements project is currently testing these features. How listeners can help and contribute to the development of DMix (01:20:08) Vlad asks Fadi Barbara how listeners can support the development of DMix, including spreading the word, donating, and providing criticism and feedback.