CoinJoinXT

CoinJoinXT is non-custodial privacy technique which is closely related to CoinJoin. It allows for any number of entities to between them create a so-called proposed transaction graph (PTG) which is a list of connected transactions. In the PTG the bitcoins belonging to the entities are sent to and fro in all the transactions, but at the end of the PTG they are all returned to their rightful owners. The system is set up so that the process of the PTG being mined is atomic, so either the entire PTG is confirmed on the blockchain or none of it is, this means none of the participating entities can steal from each other.

The proposed transaction graph has the freedom to be any list of transactions that obfuscate the transaction graph. For best results the PTG would perfectly mimic the natural transaction graph due to normal economic activity in bitcoin, and so an adversary would not know where the PTG started or ended, resulting in a massive privacy gain.

Like CoinJoin, CoinJoinXT is easy to make DOS-resistant and doesn't require a prohibitive number of interaction steps. Unlike CoinSwap there is no liveness or non-censorship requirement so funds are secure even if bitcoin is under temporary censorship. However CoinJoinXT uses a lot of block space compared the privacy gain. And CoinJoinXT requires a malleability fix so all the transactions in the PTG have to be segwit-only. As of 2019 only around 40% of transactions are segwit, so an observer of the blockchain could easily eliminate non-PTG transactions by checking whether they are legacy or segwit.