BB84 with several intercepts and resend attacks using partially non-orthogonal basis states through a depolarising channel

Abstract

The paper presents the partially non-orthogonal basis states effect in presence of several intercept and resend attacks through a depolarising channel. The quantum error and the mutual information are computed for arbitrary angles of the non-orthogonal basis states and the depolarising channel parameter. It is found that the information security depends strongly on the non-orthogonal basis states angle, the depolarising channel parameter, the intercepts and resend attack probability and the eavesdropper number. Besides, it is found that for any eavesdropper's number and basis states angle, the protocol is more secure if the depolarisation parameter is lower than a threshold value and the maximum value of the quantum error decreases by increasing the depolarising parameter and/or the eavesdropper's number. While for the depolarisation parameter above the threshold value the protocol is not secured independently of any values of the non-orthogonal basis states angle and/or the eavesdroppers' number.