3.9 How Chain Analysis Tries to Track You

The Bitcoin ledger is fully public — every transaction ever made is visible to anyone. That openness is great for verification, but it also means companies can try to build maps that link addresses to real people. Firms like Chainalysis, Elliptic, and TRM Labs sell exactly that service to exchanges, banks, and governments.

They don't break Bitcoin's cryptography — they look at patterns. The big ones:

• Common-input ownership: when multiple coins are spent together in one transaction, they're almost certainly owned by the same person.

• Change detection: in a typical payment, one output is the payment and the other is your change. Software guesses which is which based on amounts and patterns.

• Address reuse: every time you reuse an address, you tie more activity to the same identity.

• KYC linkage: the moment you buy or sell on an exchange that knows your name, every coin attached to that exchange withdrawal can be linked to you.

Once a single address is linked to your identity, the surveillance firm can crawl forwards and backwards through your transaction history. That's why privacy hygiene — fresh addresses, careful coin selection, and the techniques in the next lessons — actually matters.