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What the chain makes public
Most chains are a public noticeboard. Anyone can see transfers, amounts, and addresses. Private means something narrower than people hope.
Private means something narrower than people hope. The trail can still be tied to you.
A worked case
A person posts their address under their real name, then says the payment was anonymous because the chain does not store names. The name was in the post. The chain supplied the amounts.
What anyone can see
From an address, a patient person can follow coins through exchanges, other addresses, and contracts. Your name is not on the chain. Your behaviour can still point at you.
What private is not
A new address is not a new identity if you funded it from the old one. A privacy feature you do not understand is not privacy.
Do not put a salary, a home payment, and a public social account on the same trail if you need them apart.
The chain is a noticeboard
Bitcoin and Ethereum publish transfers. Amounts, addresses, and times are there for anyone who downloads the history or pays an explorer to show it. What is not there is your legal name, until you put it there, or a company does. Posting an address under your real name, buying through an exchange that has your passport, or reusing one address for a salary and a private payment are how the noticeboard becomes a diary.
Companies built an industry on reading that diary. Chainalysis and its competitors sell the reading to exchanges, police, and tax offices. You do not have to like the industry to understand the consequence: a payment is not anonymous because you did not type your name into the wallet. The exchange that cashes you out already has the name, and it can freeze the account the trail leads to.
Private, in this world, means a narrower thing than people hope. It might mean a coin with better hiding, or a break in the trail. It does not mean invisible. The privacy course says what those tools are. It is not a manual, and this one is not either.
Read it yourself
These links are the record. They are not a recommendation, and they are not instructions. A news story or a court paper can still be wrong about a detail. The check does not change because a famous name is in the story.
Apply the check
Open a question. The line is about this topic. It is not a verdict that anything is safe.
Whoever analyses the trail, and whoever you pay.
The protocol, for what is recorded. You, for what you publish.
An exchange that links the address to a bank account and then freezes it.
Check yourself
If your name is not on the chain, is the payment anonymous?
Not by default. The trail can still be tied to you.
After this you can assume a transfer is readable by anyone, unless you have a specific reason to think otherwise.