Improving Wójcik's eavesdropping attack on the ping–pong protocol

Abstract

The eavesdropping scheme proposed by Wójcik [Phys. Rev. Lett. 90 (2003) 157901] on the ping–pong protocol [Phys. Rev. Lett. 89 (2002) 187902] is improved by constituting a new set of attack operations. The improved scheme only induces half of the eavesdropping-induced channel loss in Wójcik's scheme, therefore, in a larger domain of the quantum channel transmission efficiency η, i.e., [ 0 , 75 % ] , the eavesdropper Eve can attack all the transmitted bits. The improvement of the ping–pong protocol security produced by Wójcik's is also suitable for our eavesdropping attack.