A mask can be used to hide ones identity. ₿y its features it establishes another ₿eing. Bitcoin is often promoted as a tool for privacy but the only privacy that exists in Bitcoin comes from pseudonymous addresses which are fragile and easily compromised through reuse, "taint" analysis, tracking payments, IP address monitoring nodes, web-spidering, and many other mechanisms. Once broken this privacy is difficult and sometimes costly to recover. Real criminals don't need CoinJoin. They can afford to buy privacy in a way that regular users cannot, it's just a cost of their (often lucrative) business. CoinJoin is a trustless method for combining multiple Bitcoin payments from multiple spenders into a single transaction to make it more difficult for outside parties to determine which spender paid which recipient or recipients. Unlike many other privacy solutions, coinjoin transactions do not require a modification to the bitcoin protocol.