Deterministic links are the graveyard to your privacy 💀
Deterministic links are the connection between the inputs and outputs of given transaction(s). The links are measured between 0 to 100, represents the probability of likability to set of addresses. The lower, the better, for privacy. Let's dive into it with simple examples.
What do we see in this TX? Some addresses with some amount of Bitcoin has been almost fully spent to the second output address, and the rest was sent back as change. Could you interpret it else wise? I guess not, based on the heuristic that the bigger value is the amount sent.
Now, what about this TX? We see two inputs and 4 outputs, where two of the outputs have the exact same amount; We will get into this later on. How could we figure this one? We could say that both of the inputs belong to one wallet, which fully spent these UTXOs to other four.
The more sophisticated interpretation could be a CoinJoin of two users, where together sent to somewhere 10K SATs and the rest went back as change to both of them. It's pretty clear that the bigger input of 0.1BTC, if sent 10K SATs, would have a change of 0.0985BTC (fees inc.). Doesn't matter if the first or third 10K SATs is also the amount that was sent/came back as change from this address. Actually, no matter how we could describe this scenarios, it will always link the first input to the second output & second input to the fourth output. These pair of inputs and outputs are deterministically linked, at 100%, and others has lower chances, but still got some. Even if CoinJoining, it's still important to pick the right order of UTXOs to be sent.
That's why Samourai wallet & Sparrow wallet restricts different orders to be sent over Chaoots. The lower the differences, the higher entropy the TX will have; The less links to be generated, the higher privacy users gain.
Want to use your Bitcoin more privately? Find collaborators for StonewallX2 in: Make Every Spend A Coinjoin Telegram group. These metric of course could be expanded to include a set of TXs instead of just one specific, which could lead to other links in turn. Looking to better understanding? Check out @LaurentMT's post here.