Fig. 5From: RETRACTED ARTICLE: Can Two-Way Direct Communication Protocols Be Considered Secure?Mutual information plots for BB84 vs. two-way deterministic protocols. a One-way probabilistic protocol BB84. b Two-way deterministic protocols with either entangled Bell states or with LM05-like single photon states. Essential difference between them is that in a Eve causes polarization flips in the message mode, while in b Eve ideally does not cause any flip in the message modeBack to article page