Common-input-ownership heuristicCommon-input-ownership heuristic

(An intro to PayJoin)

Meet Alice, a new employee at a chain analysis firm

Her job?
Track and analyze transactions on the Bitcoin network

Alice’s first onboarding session: "common-input heuristic"

All inputs of a given tx are assumed to be owned by the same owner

To explain it:

Let’s say Bob buys a coffee from Carol with 1 BTC

Looking at this Tx, it's clear that the outputs are:

• 1 BTC payment to Carol
• 2 BTC change back to Bob

That’s how input correlation works —
This is what surveillance companies use to violate your privacy

So here’s the question:

What if we could break this heuristic…
but still make the tx look totally normal?

PayJoinPayJoin

PayJoin is one way to disrupt this heuristic, allowing a tx to be interpreted in various ways

So now, the same tx — but with PayJoin looks like this:

Can you tell who owns what now?
Yeah... pretty hard.

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