B92 protocol analysis related to the same basis eavesdropping

Carry out research on the variation rule of the average mutual information between Alice and Eve I
_AE
, Alice and Bob I
_AB
and bit error rate q
_e
(AE), q
_e
(AB), when the eavesdropper Eve uses the same measurement basis as Bob, eavesdropping the communication between Alice and Bob on the basis of intercepting-retransmission pattern. Based on the symmetrical characteristic of source sequence, making research on the variation features of I
_AE
, I
_AB
, and then make respective simulation with tool of Matlab. Research results provide the guarantee for optimal quantum communication of legal users and theoretical guidance for detecting presence of eavesdroppers on the basis of average mutual information.