Abstract: The method of verifying an opinion includes, by an account module, receiving a request for identification information of the opinion (Ballot Stamp) from the user terminal; requesting a first random value to the user terminal; receiving a first homomorphic ciphertext from the user terminal; generating a second random value; storing a first value; generating a second homomorphic ciphertext from the Ballot Stamp; receiving a third homomorphic ciphertext obtained from a tag from an opinion verifying program module; and transmitting the second homomorphic ciphertext and the third homomorphic ciphertext to the user terminal. The method further includes, by the opinion verifying program module, receiving the tag obtained by decrypting the third homomorphic ciphertext, Ballot Stamp, and the opinion message, from the user terminal; and determining the opinion as being verified if the value calculated by the first arithmetic operation to the random value and Ballot Stamp is identical to the tag.