An integrated circuit includes a core circuit and a function lock circuit. The core circuit includes at least one function block circuit. The function lock circuit is coupled to the core circuit. The function lock circuit includes a random number source, an entanglement circuit, and a memory. The random number source is configured to generate a random code. The entanglement circuit is coupled to the random number source and the core circuit and configured to generate an unlocking code according to the random code and a command signal. The memory is coupled to the entanglement circuit and configured to store the unlocking code. The at least one function block circuit of the core circuit is determined to be locked/unlocked according to a presence of the unlocking code.