It is sometimes desirable to protect a design used in a PLD from being copied. According to the present invention, the design is encrypted, then loaded into a PLD, then decrypted, and then loaded into the configuration memory of the PLD. An attacker could relocate the design to a visible part of the PLD and learn the design. The present invention prevents design relocation by attaching address information to the encryption key or by encrypting an address where the design is to be loaded as well as encrypting the design itself. Thus, if an attacker tries to load the design into a different part of the PLD, the encrypted design will not decrypt properly.