An encryption apparatus includes a table generator configured to generate a key table based on each of a plurality of encryption keys, the plurality of encryption keys having different attributes, generate a key-independent table independent of the plurality of encryption keys, and generate an encryption algorithm based on the key table and the key-independent table; and a transmitter configured to transmit the key table and the key-independent table to a client terminal, wherein the table generator and the transmitter are implemented by using at least one hardware processor.