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With the booming of new information technologies, all kinds of information are expanding rapidly (Xu et al., 2014). However, the protection technology of information security is still in the initial stage of development, so there will inevitably be security problems such as information theft, tampering and disclosure when a large number of sensitive information is processed, transmitted and stored on the network. Therefore, reliable and efficient technology of encryption has become a research hotspot in all walks of life (Natalia & Alexander, 2018). Quantum circuits have the characteristics of high complexity and no feedback. The encryption system based on quantum circuits can improve the encryption efficiency. Its anti-attack ability is 
times of the traditional method. If the system is applied to the IoT technology, it can effectively guarantee information security and increase the difficulty of decoding.
Regarding the research on the encryption system of quantum circuits, document (Chen et al., 2018) proposes a construction method of quantum circuits for multiplication in finite field, and constructs encryption algorithm based on the method. However, it only completes the hardware design of the encrypted part and the decrypted part based on quantum circuit. In reference (Liu & Zhu, 2008), a quantum circuit implementation method is proposed for S-box transformation in AES algorithm, and the idea of constructing encryption algorithm based on quantum circuits is proposed. Literature (Liang, 2015) proposes a Quantum fully homomorphic encryption scheme based on universal quantum circuits and does research on the process of quantum information. In reference (Datta & Sengupta, 2013), the authors describe the advantages and feasibility of applying reversible Logic to cryptography and coding theory on the basis of confirmatory study. Document (Zhang et al., 2018) proposes a method of synthesis and optimization for linear nearest neighbour quantum circuits by parallel processing which can reduce the quantum cost for the design of quantum circuits. In reference (Wang et al., 2018), a hybrid particle swarm optimization algorithm based on adaptive learning strategy is proposed to improve the convergence accuracy and speed of quantum circuits. In reference (Wang et al., 2019), an adaptive weight vector guided evolutionary algorithm for preference-based multi-objective optimization is proposed, which can optimize the arrangement of two-dimensional quantum logic circuits and generate the simplest circuits. The existing literatures provide a theoretical idea for the research of encryption system based on quantum circuits. However, the encryption system needs a complete encryption and decryption module in practical application, and the encryption and decryption process needs the key. The complexity and security of the key largely determine the encryption complexity and anti-attack ability of the encryption system, so the complete design of the encryption and decryption module and the key extension part is particularly important; Furthermore, the encryption system must have an interface to interact with users or devices in practical application, so the design of the interface part is also essential.
To solve these problems, the encryption system of quantum circuits designed in this paper consists of four parts: encryption module, decryption module, key extension module and interface module. The construction of encryption module, decryption module and key extension module are all based on quantum circuits. The encryption and decryption modules are composed of four parts: Add Round Keys, Substitute Bytes, Shift Rows and Mix Columns. The key extension module is composed of G function and algorithm design. Meanwhile the interface module is designed by hardware language which can adapt to the characteristics of quantum circuits and work with encryption and decryption modules. Figure 1 illustrates the framework of the encryption system which shows the logical relationship of the four modules. The encryption and decryption modules can encrypt and decrypt information. The key extension module and interface module are used to work with the encryption module and the decryption module to improve the performance of them. The key extension module is connected to the encryption and decryption modules to provide the required keys for them. Similarly, the I/O interface module is connected to the encryption and decryption modules to enable users to exchange information with them conveniently. The design idea of encryption and decryption modules is similar to that of key extension module, so this paper mainly introduces the design of key extension module and I/O interface module.