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Starting from the basic ideas of undergraduate optics and quantum mechanics, it is shown that simple optical elements (like, polarizing beam splitter, mirror, neutral density filter) can be used to realize many proposals of quantum communication and computation. Especially, Mach Zehnder interferometer can be used to realize Elitzur-Vaidman bomb testing scheme and many schemes of unconditionally secure quantum key distribution, some of which are counterfactual, too. Subsequently, a scheme of controlled quantum dialogue is introduced and the same is used to obtain a set of protocols for other cryptographic tasks, such as, quantum dialogue, quantum secure direct communication, deterministic secure quantum communication, quantum key distribution, quantum key agreement. Interesting applications of these protocols are discussed in the context of quantum voting, quantum e-commerce, quantum private comparison (socialist millionaire problem), etc. Further, specific attention is given to the nature and amount of quantumness (nonclassicality) needed for implementation of a quantum cryptographic task. It is shown that all the well known quantum cryptographic tasks can be performed without using conjugate coding (i.e., by using orthogonal states alone), and most of them can be implemented using semi-quantum schemes. A brief comment will also be made on the possible optical realizations of these schemes and the challenges associated with that, specially, the challenges posed by Markovian and non-Markovian noise |