Semi-quantum protocols that allow some of the users to remain classical areproposed for a large class of problems associated with secure communication andsecure multiparty computation. Specifically, first time semi-quantum protocolsare proposed for key agreement, controlled deterministic secure communicationand dialogue, and it is shown that the semi-quantum protocols for controlleddeterministic secure communication and dialogue can be reduced to semi-quantumprotocols for e-commerce and private comparison (socialist millionaireproblem), respectively. Complementing with the earlier proposed semi-quantumschemes for key distribution, secret sharing and deterministic securecommunication, set of schemes proposed here and subsequent discussions haveestablished that almost every secure communication and computation tasks thatcan be performed using fully quantum protocols can also be performed insemi-quantum manner. Further, it addresses a fundamental question in context ofa large number problems- how much quantumness is (how many quantum parties are)required to perform a specific secure communication task? Some of the proposedschemes are completely orthogonal-state-based, and thus, fundamentallydifferent from the existing semi-quantum schemes that areconjugate-coding-based. Security, efficiency and applicability of the proposedschemes have been discussed with appropriate importance.
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