A method for data privacy in a VoIP system includes: generating a private key for an additive homomorphic encryption scheme; sending the private key to a plurality of client terminals to be used by each of the plurality of client terminals to encrypt a respective VoIP streaming data; receiving an encrypted VoIP streaming data from each of the plurality of client terminals, wherein each of the VoIP streaming data is encrypted using the same private key; performing an encrypted homomorphic addition on the encrypted VoIP streaming data to generate a mixed encrypted VoIP data stream; and sending the mixed encrypted VoIP data stream to the plurality of client terminals to be played back.