A key enrollment method of a physically unclonable function (PUF) circuit including a plurality of PUF cells includes receiving a first level key from PUF cells, performing bit encoding on the first level key using a bit coding table based on Hamming weights of a plurality of bits in the first level key to generate a second level key, storing first helper data associated with the second level key in a non-volatile memory, performing block encoding on the second level key using an error correction code to generate a third level key, and storing second helper data associated with the third level key in the non-volatile memory.