Abstract
Recently, Zhang, Li, and Guo have proposed a particular eavesdropping attack [Phys. Rev. A 63, 036301 (2001)] that shows that my quantum key distribution protocol based on entanglement swapping [Phys. Rev. A 61, 052312 (2000)] 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.