**3. Conclusion**

This chapter presents a classification and systematisation of modern quantum technology of information security. The characteristic of the basic directions of quantum cryptography from the point of view of the quantum technologies used is given. A qualitative analysis of the advantages and imperfections of concrete quantum protocols is made. Today the most developed direction of quantum secure telecommunication systems is QKD protocols. In research institutes, laboratories and centres, quantum cryptographic systems for secret key distribution for distant legitimate users are being developed. Most of the technologies used in these systems are patented in different countries (mainly in the U.S.A.). Such QKD systems can be combined with any classical cryptographic scheme, which provides information-theoretic security, and the entire cryptographic scheme will have informationtheoretic security also. QKD protocols can generally provide higher information security level than appropriate classical schemes.

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Other secure quantum technologies in practice have not been extended beyond laboratory experiments yet. But there are many theoretical cryptographic schemes that provide high information security level up to the information-theoretic security. QSDC protocols remove the secret key distribution problem because they do not use encryption. One of these is the ping-pong protocol and its improved versions. These protocols can provide high information security level of confidential data transmission using the existing level of technology with security amplification methods. Another category of QSDC is protocols with transfer qubits by blocks that have unconditional security, but these need a large quantum memory which is out of the capabilities of modern technologies today. It must be noticed that QSDC protocols are not suitable for the transfer of a high-speed flow of confidential data because there is low data transfer rate in the quantum channel. But when a high information security level is more important than transfer rate, QSDC protocols should find its application.

Quantum secret sharing protocols allow detecting eavesdropping and do not require data encryption. This is their main advantage over classical secret sharing schemes. Similarly, quantum stream cipher and quantum digital signature provide higher security level than classical schemes. Quantum digital signature has information-theoretic security because it uses quantum one-way function. However, practical implementation of these quantum technologies is also faced to some technological difficulties.

Thus, in recent years quantum technologies are rapidly developing and gradually taking their place among other means of information security. Their advantage is a high level of security and some properties, which classical means of information security do not have. One of these properties is the ability always to detect eavesdropping. Quantum technologies therefore represent an important step towards improving the security of telecommunication systems against cyber-terrorist attacks. But many theoretical and practical problems must be solved for wide practical use of quantum secure telecommunication systems.
