OFAC compliance for DeFi developers

DeFi developers should screen at the front end, design for smart-contract risk, and study the Tornado Cash precedent.

TL;DR

TL;DR: DeFi compliance centers on screening before a user transacts and understanding that OFAC has designated code itself, as in the Tornado Cash case.

Front-end screening

The most practical control for a DeFi team is front-end screening. Before a wallet can initiate a transaction, check the address against the 947 OFAC-listed crypto wallets and block flagged ones. The same API that returns ALLOW or BLOCK in under 100 ms works here, and it applies the 50 Percent Rule for ownership.

Smart contract risk

Smart contracts raise harder questions, because once deployed, code runs without an operator. OFAC's approach has been to designate the service itself. The Tornado Cash designation is the defining precedent: OFAC added the mixer and associated addresses to the SDN list, which blocks US persons from interacting with it and puts developers on notice that code is in scope.

The lesson

The lesson is to treat sanctions risk as a design constraint, not an afterthought. Screen at the entry point, log the decision, and document the reasoning. Strict liability applies, and civil penalties start at $356,000 per violation, so early screening is far cheaper.

Practical first steps

Start with front-end screening, then document it. Block flagged addresses before signing, log every decision, and write down the reasoning so a reviewer can follow it. Because OFAC treats code as in scope, the documentation matters as much as the code: it shows the screening was a deliberate control, not an accident.