The assumption that public chains are anonymous is incorrect and has caused real harm to people who acted on it.
Pseudonymity
Addresses are not names, and all activity associated with them is permanently public.
Which means one link between an address and an identity exposes the entire history.
That link is commonly created at an exchange, where identity verification is required.
Heuristics used to cluster addresses
Common input ownership — spending from multiple addresses in one transaction suggests one controller.
Change address identification.
Timing and amount correlation.
Which are the basis of commercial chain analysis and work well enough to be relied upon by law enforcement.
Address reuse
Using one address repeatedly links everything together.
Which is the single most common and most avoidable privacy failure.
Wallets generating a new address per transaction address this by default in some designs and not others.
Ring signatures and stealth addresses
Some protocols hide the sender among a set of possible senders and generate one-time destination addresses.
Which provides privacy at the protocol level rather than as an option.
Analysis techniques against these have been published, and the designs have been revised in response.
Zero-knowledge approaches
Allow proving a transaction is valid without revealing amounts or parties.
Which is the strongest available approach cryptographically.
Privacy depends on the size of the anonymity set — if few people use the shielded feature, membership itself is revealing.
Mixing services
Pool funds from many users to break the link between deposit and withdrawal.
Which has attracted substantial regulatory and enforcement attention, including sanctions against specific services.
Using them carries legal risk in several jurisdictions independent of intent, and receiving funds that passed through them can create difficulties with exchanges.
Network-level exposure
Broadcasting a transaction reveals network information regardless of chain-level privacy.
Which is a separate layer and is addressed by different tools.
Practical position
Anyone with a genuine safety need for financial privacy should understand that these systems are considerably more transparent than their reputation suggests.
Legal obligations differ by jurisdiction, and this is technical description rather than legal advice.
Coin control
Selecting which inputs to spend, avoiding combining funds from unrelated sources.
Which is supported by some wallets and ignored by most users.
Combining a privacy-preserved output with an identified one links them permanently.
Payment channels
Transactions conducted off-chain between parties settle only on opening and closing.
Which provides some privacy as a side effect of not publishing every transaction.
Routing information can still be observed by intermediate nodes, so the improvement is partial.
View keys
Some privacy protocols allow selective disclosure of transaction history to a chosen party.
Which addresses the practical need to demonstrate holdings to an auditor or tax authority.
It is a useful design property that general public chains lack, since they disclose to everyone by default.
Exchange interaction
Depositing to and withdrawing from identity-verified services creates the strongest links.
Which is unavoidable for most people converting to and from conventional currency.
Understanding that this link exists is more useful than attempting to obscure it.
Realistic expectations
These systems provide less privacy than cash and more than a bank account provides to the public.
Which is a specific position rather than the anonymity commonly assumed.
Regulatory direction
Travel rule requirements and reporting frameworks increase the identity information attached to transfers between services.
Which reduces practical privacy for anyone using regulated venues.
This is the direction of travel in most major jurisdictions rather than a temporary position.
What actually helps
Not reusing addresses, separating unrelated activity, and understanding that the ledger is permanent.
Which is modest and is considerably better than assuming anonymity that does not exist.
Metadata beyond the chain
Exchange accounts, device identifiers, network addresses and social posts all contribute to linkage.
Which means chain-level techniques address only part of the exposure.
Publicly posting an address links it to whatever identity that account carries, permanently.
Closing point
Assume the ledger is permanent and public, because it is.
Which is the correct starting assumption for any decision about what to do on one.
Businesses and disclosure
Companies transacting on public chains expose supplier relationships, payroll timing and treasury positions to competitors.
Which is a commercial problem distinct from individual privacy and is a stated barrier to institutional adoption.
Selective disclosure designs address it directly, and adoption of them remains limited.
Final note
The gap between reputation and reality here is unusually wide, and acting on the reputation has consequences.
Legal position
Privacy and evasion are different things, and the tools discussed here have legitimate uses and legal risk depending on jurisdiction.
Which is worth establishing before use rather than afterwards.
This is technical description and is not legal advice.
Anyone assuming otherwise should test the assumption against a chain analysis demonstration before relying on it for anything that matters.
The permanence is the part most people underestimate: a transaction made today remains readable and linkable indefinitely, long after the circumstances that made it seem unremarkable have changed.