How does Bitcoin offer privacy even though every transaction is announced publicly?

By keeping public keys anonymous — the public sees that some amount moved between two keys, but not who owns them, much like a stock ticker showing each trade's time and size but not the parties.

Traditional banking hides transactions but reveals your identity to the bank. Bitcoin flips this: transactions are public, but identities are detached from the keys.

Best practice is a fresh key pair per transaction so payments can't be linked to one owner. Two caveats: multi-input transactions necessarily reveal that their inputs share an owner, and if one key is ever tied to a real identity, linked transactions can be de-anonymised.

Go deeper:

• Public-key cryptography — Wikipedia — key pairs and why a fresh public key per payment keeps transactions from being linked to one owner.