# A Lightweight Image Cryptosystem for Cloud-Assisted Internet of Things
###### Abstract  
Cloud computing and the increasing popularity of 5G have greatly increased the application of images on Internet of Things (IoT) devices. The storage of images on an untrusted cloud has high security and privacy risks. Several lightweight cryptosystems have been proposed in the literature as appropriate for resource-constrained IoT devices. These existing lightweight cryptosystems are, however, not only at the risk of compromising the integrity and security of the data but also, due to the use of substitution boxes (S-boxes), require more memory space for their implementation. In this paper, a secure lightweight cryptography algorithm, that eliminates the use of an S-box, has been proposed. An algorithm termed Enc, that accepts a block of size n divides the block into L n R bits of equal length and outputs the encrypted block as follows: \(E=(L\bigotimes R)\bigoplus R\), where \(\bigotimes\) and \(\bigoplus\) are exclusive-or and concatenation operators, respectively, was created. A hash result, \(hasR=SHA256(P\bigoplus K)\), was obtained, where SHA256, P, and K are the Secure Hash Algorithm (SHA\(-\)256), the encryption key, and plain image, respectively. A seed, S, generated from \(enchash=Enc(hashenc,K)\), where hashenc is the first n bits of hasR, was used to generate a random image, Rim. An intermediate image, \(intimage=Rim\bigotimes P\), and cipher image, \(C=Enc(intimage,K)\), were obtained. The proposed scheme was evaluated for encryption quality, decryption quality, system sensitivity, and statistical analyses using various security metrics. The results of the evaluation showed that the proposed scheme has excellent encryption and decryption qualities that are very sensitive to changes in both key and plain images, and resistance to various statistical attacks alongside other security attacks. Based on the result of the security evaluation of the proposed cryptosystem termed Hash XOR Permutation (HXP), the study concluded that the security of the cryptography algorithm can still be maintained without the use of a substitution box. cloud; cryptography; S-box; cloud-assisted IoT; resource constrained +
Footnote †: journal: Applied sciences  
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devices anytime and anywhere [8], make cloud computing a very suitable technology in IoT applications which are, though resource constrained, needed in real-time applications, where quick and precise responses with vital security are required [9]. These capabilities, provided by cloud computing to IoT applications, make IoT applicable to almost all works of life [10]. Hence, the integration of IoT and cloud computing technology is referred to as cloud-assisted IoT (CIoT) [11], which was called cloudIoT by the authors of [12]. Cloud-enabled IoT frameworks have recently become prominent [13]. However, connecting different remotely operated IoT devices to the cloud via the internet raises security and privacy concerns for users [14; 15]. Both the IoT and the cloud sides of the CIoT are vulnerable to security attacks; hence, the need for security of the data on both sides. The growing awareness of data security during transmission, or when it is stored on the cloud, explains the reason for the high demand for cryptography algorithms [16]. Conventional cryptography algorithms, due to their high demand for computing resources for storage and processing, are not suitable for resource-starved IoT devices [10]. Resource-starved IoT applications, such as wireless sensor nodes (WSNs) [17; 18], radio-frequency identification (RFID) networks [19], and secure robotic communications [20], require the area-optimized implementation of the cryptographic algorithm [21]. A lighter version of the cryptography scheme that requires a low computational storage and power will be more appropriate for these resource-starved IoT devices [22].