We present in this article two secure multiplexing and demul- tiplexing schemes that use homomorphic properties from known public key cryptosystems. One scheme is suitable for cryptosystems with addi- tive homomorphic properties such as Paillier and Benaloh cryptosystems. The proposed scheme employs a modification of Hadamard codes to generate a set of orthogonal codes over Z3. The other one is suitable for cryptosystems with multiplicative homomorphic properties such as RSA and ElGamal. Both schemes might be used in voting and auction systems where anonymity of the individuals is crucial.