Abstract: An encryption processing apparatus that processes a ciphertext, the apparatus including a processor that executes a process including: performing a homomorphic operation related to a predetermined operation for three or more of the ciphertexts for which an error range is set to make a range of an error added to a plaintext after the homomorphic operation fall within a predetermined value; and calculating a new ciphertext by applying a predetermined polynomial to a ciphertext that is a result of the homomorphic operation, wherein the calculation includes factorizing each of a plurality of the polynomials into a common polynomial common to the polynomials and an uncommon polynomial not common to the polynomials, and calculating a plurality of the new ciphertexts by using a plurality of ciphertexts calculated by applying the common polynomial to the result of homomorphic operation, and using the uncommon polynomial.

Abstract: A fully homomorphic encryption processing device processing a ciphertext is disclosed, the ciphertext has an integer as a plaintext. The encryption processing device includes a processor that executes a process including: obtaining a ciphertext by using a first polynomial and a second polynomial respectively including a second function and a third function, the second function and the third function being generated by decomposing a first function as a calculation object. The processor also applies the first polynomial to a first ciphertext to obtain a second ciphertext. The processor further applies the second polynomial to a ciphertext obtained by calculation based on applying a predetermined polynomial to the first ciphertext to obtain a third ciphertext. The processor performs a homomorphic operation using the second ciphertext and the third ciphertext to obtain a fourth ciphertext corresponding to a result of calculation of the first function which uses the first ciphertext as input.

Abstract: An encryption processing device processes a ciphertext that has two values as a plaintext and is a ciphertext of fully homomorphic encryption that allows a logical operation without decryption. The encryption processing device executes a predetermined operation including calculating a plurality of new ciphertexts based on the ciphertexts input thereto. The encryption processing device comprising a processor which executes a process including performing a first homomorphic operation for the input ciphertext, calculating a first ciphertext having a polynomial by using a predetermined polynomial for a result of the first homomorphic operation to extract a second ciphertext having a coefficient of a plaintext polynomial of the first ciphertext, extracting a third ciphertext having another coefficient of a plaintext polynomial of the first ciphertext, and performing a homomorphic operation using the second ciphertext and the third ciphertext to calculate a fourth ciphertext.

Abstract: An encryption processing device processing a ciphertext is disclosed. The ciphertext is a fully homomorphic ciphertext that has a value obtained by adding an error with a predetermined variance to a predetermined value, as a plaintext associated with an integer and that enables a predetermined operation between integers without decryption, and the predetermined operation is division of a first ciphertext as a dividend and a second ciphertext as a divisor. The encryption processing device includes a processor which executes a process including calculating a third ciphertext corresponding to a reciprocal of the divisor by using a first polynomial for the second ciphertext, and performing multiplication based on the first ciphertext and the third ciphertext to calculate a fourth ciphertext corresponding to a result of division of the first ciphertext and the second ciphertext as a result of multiplication.

Abstract: An encryption processing device that processes a ciphertext, the ciphertext being a fully homomorphic ciphertext that has a value obtained by adding an error with a predetermined variance to a predetermined value, as a plaintext associated with an integer and that enables a predetermined operation between integers to be performed without decryption, the device including a processor which executes a process including generating, based on a first ciphertext as a multiplier, a third ciphertext having a first stepped polynomial as a plaintext and performing an operation based on the third ciphertext and a second ciphertext as a multiplicand to calculate a ciphertext corresponding to a result of multiplication between plaintexts of the first ciphertext and the second ciphertext as a fourth ciphertext of an operation result.

Abstract: An operation by a full adder that achieves fully homomorphic encryption is speeded up. Ciphertexts are ciphertexts of fully homomorphic encryption that allow a logical operation to be performed without decryption. A sorting process is performed which rearranges the ciphertexts arranged in a predetermined order in accordance with a predetermined method. In the sorting process, a homomorphic operation based on a first ciphertext and a second ciphertext is performed. From a result of this homomorphic operation and a ciphertext obtained based on a predetermined polynomial, new first and second ciphertexts are calculated. When the first and second ciphertexts and the new first and second ciphertexts satisfy a predetermined condition, the first ciphertext and the second ciphertext are swapped.