Recently, Zhang, Li, and Guo have proposed a particular eavesdropping attack [Phys. Rev. A { \bf 63}, 036301 (2001), quant-ph/0009042] which shows that my quantum key distribution protocol based on entanglement swapping [Phys. Rev. A { \bf 61}, 052312 (2000), quant-ph/9911025] is insecure. However, security against this attack can be attained with a simple modification. In addition, a simpler version of the protocol using four qubits is introduced.
Categories: quant-ph