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Expecting a software developer(a specialist) to necessarily possess knowledge of encryption technologies is naive. For example a Java developer specializing in UI's is never going to have the need to delve into the world of file encryption. A network specialist is never going to need to know the difference between an Array and a List.
Decide what the position requires, advertise the job referencing the requirements, and focus on the job requirements when you are interviewing the candidates. Everything else is extraneous, a distraction, and a waste of everybody's time. .