Patent ID: 7281136

Claim:
A method for designing an LSI, comprising the step of encrypting provided circuit design data, wherein the encrypting step includes the step of conducting circuit conversion to produce an encrypted circuit, the circuit conversion being conducted using an entire circuit represented by the circuit design data or a part of the circuit as an original circuit, the circuit conversion step includes the steps of providing at least one dummy circuit in parallel with the original circuit, the dummy circuit having a same number of inputs and a same number of outputs as those of the original circuit, providing a permutation circuit for permutating respective outputs of the original circuit and the dummy circuit, and providing a selector responsive to a selection signal for selecting a number of signals corresponding to the number of outputs of the original circuit from an output of the permutation circuit so as to produce the encrypted circuit, wherein the selection signal is used as a key signal, and such a value of the key signal that the output of the original circuit matches an output of the selector is used as a key of the encrypted circuit.