Encrypted computation comprising a blind rotation

A cryptographic encrypted computation device for outsourcing computations, the computations comprising performing blind rotations on ciphertexts, the device comprising:

• a storage for storing a ciphertext, the ciphertext encrypting a plaintext value;
• and
• a processor subsystem configured to receive input data in encrypted form over a communication interface, obtain the ciphertext from the input data, the ciphertext encrypting a plaintext value, and perform a blind rotation of the ciphertext according to a test polynomial, wherein
• the blind rotation results in an encrypted polynomial product of the test polynomial and a bootstrapping monomial modulo a modulus and modulo a quotient polynomial, wherein the bootstrapping monomial represents the plaintext value as an exponent;
• and wherein
• the processor subsystem is further configured to output the encrypted polynomial product;
• and
• wherein:
• the quotient polynomial divides a number-theoretic transform (NTT) polynomial that allows a number-theoretic transform modulo the modulus;
• performing the blind rotation comprises performing a polynomial multiplication using the number-theoretic transform;
• and
• the test polynomial is defined such that the encrypted polynomial product has a desired output value for the plaintext value as a fixed coefficient, and return a computation result in encrypted form over the communication interface and/or store the computation result on the storage device, the computation result being obtained from the encrypted polynomial product.