  Quantum secure direct communication is one of the important mode of quantum
communication, which sends secret information through a quantum channel
directly without setting up a prior key. Over the past decade, numerous
protocols have been proposed, and part of them have been experimentally
demonstrated. However, the strict security proof is still in suspense. Two-way
protocol is seen as one of the most practical protocol, in this paper, the
security of the two-way quantum secure direct communication protocol will be
proved against general attacks when the noisy and lossy channel is taken into
account. There are two steps included in the proof, firstly, we need to prove
that the mutual information between Alice and Bob is larger than the mutual
information shared between Alice and the eavesdropper when the error rate in
control mode is less than the predetermined threshold. Secondly, once the error
rate is lower than the threshold, one can always find out a forward error
correction code to guarantee the security of information transmission.
