  In majority of protocols of secure quantum communication (such as, BB84, B92,
etc.), the unconditional security of the protocols are obtained by using
conjugate coding (two or more mutually unbiased bases). Initially all the
conjugate-coding-based protocols of secure quantum communication were
restricted to quantum key distribution (QKD), but later on they were extended
to other cryptographic tasks (such as, secure direct quantum communication and
quantum key agreement). In contrast to the conjugate-coding-based protocols, a
few completely orthogonal-state-based protocols of unconditionally secure QKD
(such as, Goldenberg-Vaidman (GV) and N09) were also proposed. However, till
the recent past orthogonal-state-based protocols were only a theoretical
concept and were limited to QKD. Only recently, orthogonal-state-based
protocols of QKD are experimentally realized and extended to cryptographic
tasks beyond QKD. This paper aims to briefly review the orthogonal-state-based
protocols of secure quantum communication that are recently introduced by our
group and other researchers.
