Encryption device using mask value to convert plain text into encrypted text

A decryption circuit which generates decrypted text from encrypted text using a key, said decryption device comprising:

• a random number generation circuit which generates a random number;
• a randomized input data generation circuit which receives the encrypted text, and generates randomized input data that is obtained by adding, to input data that is obtained by performing predetermined processing on the encrypted text using the key, a predetermined input mask value determined depending on the random number;
• a first randomized inverse element data generation circuit which receives the randomized input data generated by said randomized input data generation circuit and the input mask value, and generates randomized output data that is obtained by adding, to an inverse element of the input data in a predetermined first finite field, an output mask value that is an inverse element of the received input mask value in the first finite field;
• and
• an output data processing circuit which receives the randomized output data generated by said first randomized inverse element data generation circuit, and generates the decrypted text from the received randomized output data.

An encryption method which is performed by an encryption circuit to generate encrypted text from plain text using a key, said encryption method comprising:

• generating a random number, said generating being performed by a random number generation circuit;
• receiving the plain text and generating randomized input data that is obtained by adding, to input data that is obtained by performing predetermined processing on the plain text using the key, a predetermined input mask value determined depending on the random number, said receiving of the plain text and generating of randomized input data being performed by a randomized input data generation circuit;
• receiving the randomized input data generated in said receiving of the plain text and generating of the randomized input data and the input mask value and generating randomized output data that is obtained by adding, to an inverse element of the input data in a predetermined first finite field, an output mask value that is an inverse element of the received input mask value in the first finite field, said receiving of the randomized input data and generating of randomized output data being performed by a first randomized inverse element data generation circuit;
• and
• receiving the randomized output data generated in said receiving of the randomized input data and generating of the randomized output data and generating the encrypted text from the received randomized output data, said receiving of the randomized output data and generating of the encrypted text being performed by an output data processing circuit.

An integrated circuit which generates encrypted text from plain text using a key, said integrated circuit comprising:

• a random number generation unit configured to generate a random number;
• a randomized input data generation unit configured to receive the plain text, and generate randomized input data that is obtained by adding, to input data that is obtained by performing predetermined processing on the plain text using the key, a predetermined input mask value determined depending on the random number;
• a first randomized inverse element data generation unit configured to receive the randomized input data generated by said randomized input data generation unit and the input mask value, and generate randomized output data that is obtained by adding, to an inverse element of the input data in a predetermined first finite field, an output mask value that is an inverse element of the received input mask value in the first finite field;
• and
• an output data processing unit configured to receive the randomized output data generated by said first randomized inverse element data generation unit, and generate the encrypted text from the received randomized output data.