The article first introduces the specific steps of a quantum-secure direct communication scheme that sends a single photon at a time. Based on the basic steps of the scheme, it is gradually extended to a quantum secure direct communication scheme that transmits single-photon sequences in two and four times, with emphasis on the coding rules corresponding to each scheme. The purpose is that through the above scheme, it can be intuitively seen in the subsequent efficiency analysis that with the increase of the number of transmissions, the classification of single photons can be increased, and the encoding capacity of each single photon and the transmission efficiency of quantum states in the entire communication can be greatly improved. Finally, a universal scheme and coding rules for quantum secure direct communication by sending single photons in integer powers of 2 are proposed, and the scheme is proved to be safe and feasible after security analysis. Through the efficiency analysis, the communication efficiency of this scheme is higher than that of the existing scheme, and the implementation of this scheme only uses a single photon, does not involve quantum entanglement, and has more application value.

In response to the demand for identity authentication in quantum secure direct communication, this paper proposes a quantum secure direct communication scheme based on a mixture of single photon and Bell state, combined with bidirectional identity authentication. Before communication begins, both parties share a series of secret information to prepare a series of single photon and Bell state particles. Encoding four single photons and four Bell states yields eight types of encoded information, followed by identity authentication. The first step in identity authentication is to use a single photon to verify the legitimacy of the receiver. If the error exceeds the given threshold, it indicates the presence of eavesdropping. Otherwise, the channel is safe. Then, Bell state particles are used to verify the legitimacy of the sender, and the threshold is also used to determine whether there is eavesdropping. The method is the same as before. If the error rate is higher than the given threshold, it indicates the existence of third-party eavesdropping. Otherwise, it indicates that the channel is secure. As for the specific verification method, it will be explained in detail in the article. Afterwards, Bell state particles are mixed with a single photon as the transmission carrier, and eavesdropping detection particles are added every time the quantum state is sent. However, once the eavesdropper intercepts the transmitted particles, due to incomplete information obtained, the eavesdropper is unable to recover the original information, and the eavesdropping behavior will be immediately detected, thus terminating communication. In this scheme, single photon and Bell states are fully utilized, and hybrid communication can effectively improve transmission efficiency, encoding ability, and quantum bit utilization. Security analysis shows that this scheme can resist common external and internal attacks such as interception/measurement replay attacks, auxiliary particle attacks, and identity impersonation attacks. The analysis of efficiency and encoding capacity shows that the transmission efficiency of this scheme is 1, the encoding capacity is 3 bits per state, and the quantum bit utilization rate is 1. Compared with other schemes, this scheme has significant advantages because it uses different particles for bidirectional authentication, making it more difficult for attackers to crack, and thus has higher security than traditional schemes.

Aiming at the problem that traditional quantum secure direct communication schemes need to assume the legitimacy of both parties in advance, a GHZ state based quantum secure direct communication scheme with identity authentication is proposed. The scheme first encodes GHZ state particles into eight types, divides them into three parts, and sends them in three times. Each time, eavesdropping is added to detect whether the particle detection channel is secure, and the second time, identity authentication is added to verify the identity of the receiver. Specifically, according to the value of the ID key IDA, the specified particles (such as | 0>particles or |+>particles) are found in the two particles, Then mark their position L and traverse down until all the identity keys are traversed to obtain a position sequence L. After sending the two particles to Bob for eavesdropping detection, Bob measures the L position of the two particles with the corresponding basis according to the value of the identity key, codes the measurement results, and compares them with the identity key IDA to complete the identity authentication. After sending the particles for the third time, The receiver extracts all the detected particles, and then jointly measures the GHZ state particles, and recovers the original information through the originally given coding rules, so as to realize quantum safe direct communication. The design of this scheme is simple and efficient, and communication can be realized without complex unitary transformation. The correctness analysis proves that the scheme is correct in theory. The security analysis of interception/measurement retransmission attack, trojan horse attack, denial of service attack, auxiliary particle attack, identity impersonation attack and other attacks proves that the scheme can resist common internal attacks and external attacks, and solve the problem of information leakage. The transmission efficiency of the scheme is 1, the quantum bit utilization is 1, and the coding capacity is a quantum state carrying 3 bits of information, Compared with some previous schemes, this scheme has obvious advantages in these three aspects. The biggest advantage is that the sender does not need to assume the legitimacy of the receiver when sending information, so it has high practical application value.