A method of processing a ciphertext, the method includes: acquiring a part of a plurality of encrypted elements included in the ciphertext, each of the plurality of encrypted elements being an encrypted element in which values of a plurality of elements in a multidimensional determination target vector are respectively encrypted by homomorphic encryption; decrypting the acquired part of the plurality of encrypted elements; and determining validity of the determination target vector based on a relationship between at least one value obtained by the decrypting and both of 0 and 1.