A field programmable gate array (FPGA) and a decryption circuit are implemented within a common integrated circuit (IC) or within separate ICs enclosed within a common IC package. The decryption circuit decrypts an input FPGA program encrypted in accordance with a particular encryption key and then writes the decrypted FPGA program into the FPGA. Thus an FPGA program encrypted in accordance with a particular encryption key can be used to program only those FPGAs coupled with a decryption circuit capable of decoding the encrypted FPGA program in accordance with that particular encryption key. Since the decryption circuit and the FPGA are implemented in the same IC, or within the same IC package, the decrypted FPGA program the decryption circuit produces cannot be readily intercepted and copied.