United States sanctions programs historically named people, companies and vessels. They now also name blockchain addresses, and that addition changed how compliance works for anyone processing crypto transactions.
Listings identify addresses directly
The Office of Foreign Assets Control maintains lists of sanctioned parties, and entries can carry associated digital currency addresses as identifiers alongside names and locations.
Once listed, an address becomes property of a blocked person for compliance purposes. US persons are generally prohibited from transacting with it.
Because the ledger is public, checking whether a counterparty address appears on a list is straightforward, which is unusual compared with screening conventional payments.
The obligation is strict
Sanctions liability does not generally require intent. Processing a prohibited transaction can be a violation even where the party did not know the counterparty was listed.
That standard pushes firms toward screening every transaction rather than investigating only those that appear suspicious.
Screening at the moment of transfer is also necessary because listings change, and an address that was clean at onboarding may not be clean later.
Exposure travels through the chain
Screening a direct counterparty is not sufficient when funds move through several addresses. Analytics tools trace how many transfers separate an address from a listed one.
Firms set internal thresholds for how much indirect exposure triggers review, which is a policy judgment rather than a published legal line.
Mixing services complicate this because they deliberately break the linkage, so funds emerging from one carry unclear history regardless of their origin.
Smart contracts raise a harder question
Addresses can belong to autonomous contracts rather than to people, and a contract accepts deposits from anyone without any operator making a decision.
Listing such an address means the prohibition applies to interacting with software, including for users whose own funds were already inside it.
This has been contested, and the disputes turn on whether immutable code can be property owned by a designated person, a question conventional sanctions law was not written to answer.
Practical compliance is layered
Exchanges screen deposits and withdrawals, blocking or freezing funds where a match occurs and filing reports through established channels.
Front-end interfaces to decentralized protocols often screen connecting addresses, which blocks access to the interface while leaving the underlying contract reachable.
Sanctions rules also require reporting blocked property, so a firm that freezes funds acquires an affirmative filing obligation rather than simply declining the transaction.
Blocked assets must then be held rather than returned, which is why a frozen balance is not released once a user explains themselves. Release generally requires a license from the administering office.