Controlled Bidirectional Quantum Secure Direct Communication

Table 1

Comparison of CQSDC and CBQSDC protocols with our protocol.

			Scheme
	Gao2005	Dong2011	Man2006	Dong2008	Ours
Protocol type	CQSDC	CQSDC	CBQSDC	CBQSDC	CBQSDC
Resource cost of two directional transmission	6 Q and 6 C	6 Q and 6 C	6 Q and 6 C	6 Q and 6 C	5 Q and 6 C
Secret message type	C/Q	C/Q	C	C	C/Q
Received classical bits	1 C	1 C	2 C	2 C	1 C
Received quantum bits	1 Q	1 Q	0	0	1 Q
Controller	Yes	Yes	Yes	Yes	Yes
Classical message exchange	Yes	Yes	Yes	Yes	Yes
Quantum information exchange	Yes	Yes	No	No	Yes
No transmission	Yes	Yes	No	Yes	Yes
Honest condition between legitimate users	No	No	No	No	Yes

C: classical bits; Q: quantum bits.