As part of its food security policy, South Korea has been pursuing food self-sufficiency using high tariffs and high administrative prices in key agricultural and food markets. Using a dual approach to trade and trade restrictiveness indices, we analyze the impact of these market distortions on welfare and trade volume. Then, we compute optimum distortions, which minimize the welfare cost of observed self-sufficiency and production objectives. We rationalize these optimum distortions to what could be claimed as legitimate protection under a "food security" (FS) box in World Trade Organization negotiations. FS-box protection is sensitive to changes in the definition and the extent of the FS objectives. We show that FS via production targets and reliance on imports would be more palatable to consumers and trade partners, while preserving rents to the farm sector.