  Two protocols for deterministic secure quantum communication (DSQC) using
GHZ-like states have been proposed. It is shown that one of these protocols can
be modified to an equivalent but more efficient protocol of quantum secure
direct communication (QSDC). Security and efficiency of the proposed protocols
are analyzed in detail and are critically compared with the existing protocols.
It is shown that the proposed protocols are highly efficient. It is also shown
that all the physical systems where dense coding is possible can be used to
design maximally efficient protocol of DSQC and QSDC. Further, it is shown that
dense coding is sufficient but not essential for DSQC and QSDC protocols of the
present kind. We have shown that there exist a large class of quantum state
which can be used to design maximally efficient DSQC and QSDC protocols of the
present kind. It is further, observed that maximally efficient QSDC protocols
are more efficient than their DSQC counterparts. This additional efficiency
arises at the cost of message transmission rate.
