In this paper, the cryptanalytic strength of two Hwang- Rao Secret Error-Correcting Code (SECC) schemes is examined under a known-plaintext attack. In particular, we found the existence of key information redundancy in all SECCs used in the electronic codebook (ECB) mode. Also, our investigations indicate the existence of synergism in the SECC schemes, that is, the security of SECC (containing three transformations, Ψ and E and P) is much stronger than the individual strength of either Ψ or E or P.