Controlled semi-quantum dialogue protocol based on Bell states

Abstract A controlled semi-quantum dialogue protocol is proposed that uses semi-quantum cryptography and the concept of ‘control’. In this scheme, the supervisor Charlie prepares a large number of entangled photon pairs and separates them into an <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>S</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>A</mml:mi> </mml:mrow> </mml:msub> </mml:math> for verification and an <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>S</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>B</mml:mi> </mml:mrow> </mml:msub> </mml:math> for encoding. The quantum-capable party Alice and the classical communication party Bob proceed to encode on the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>S</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>B</mml:mi> </mml:mrow> </mml:msub> </mml:math> sequence only after confirming the security of the channel. Finally, Alice performs measurements and announces the results to finalise the communication. This protocol ensures that secret information is exchanged between Alice and Bob only with Charlie’s permission, while Charlie has no access to the communicators’ secret information during the whole process. In terms of security, the protocol contains two strict security checks and accounts for noise, making it robust against both internal and external attacks, which greatly improves the security and reliability of the protocol. Finally, the efficiency analysis demonstrates that the protocol outperforms other existing protocols in terms of efficiency and its actual efficiency can approach the theoretical limit through optimization.