Patent ID: 10630472

Abstract:
The present invention relates to a method for providing encrypted data on a client, a cloud or the like, performed in a memory available to a computation device comprising the steps of a) Providing for each user a user specific encryption key for encrypting user-specific plaintext, b) Computing a common decryption key with a pre-determined function using the user specific encryption keys as input for said function, and wherein the common decryption key is computed based on at least two product groups of the same prime order, c) Encrypting each user-specific plaintext with the corresponding user-specific encryption key resulting in user-specific ciphertexts, d) Computing a common ciphertext with said function using the user-specific ciphertexts as input for said function, e) Providing the common ciphertext and the common decryption key for decryption, preferably to a user, wherein step c) is performed such that encryption is homomorphic in the user-specific plaintext as well in the user-specific encryption keys, wherein said function is a polysized function supporting poly-many additions and a single multiplication.