# Modified Generalized Feistel Network Block Cipher for the Internet of Things
###### Abstract  
With the advent of the Internet-of-Things (IoT) technologies, millions of low-resource devices are constantly used at the network's edge. As a result, the large amount of private and sensitive data generated by these devices must be securely transported, stored, and processed, posing a challenge because these resource-constrained IoT devices cannot meet the criteria of conventional encryption ciphers. Due to this limitation on IoT-enabled devices, lightweight cryptography has emerged as a new area of study. Lightweight block ciphers, a subfield of lightweight cryptography, include the substitution-permutation network (SPN) and Feistel-based networks. Feistel networks are further divided into two types: classical Feistel networks and generalized Feistel networks (GFN). While classical Feistel ciphers divide a message into two sub-blocks, GFN divides a message into k sub-blocks for some k > 2 called the partition number. One popular form of GFN is the so-called Type-II. Unfortunately, this type of Feistel structure needs a large number of rounds to obtain a full diffusion property. A full diffusion means all output sub-blocks are affected by all input sub-blocks. Therefore, this paper proposed a new lightweight block cipher by modifying the GFN structure, focusing on providing optimal security to the cipher with a small number of rounds. The algorithm was subjected to a series of statistical and cryptographic randomization analyses in order to investigate the avalanche effect on the ciphertext and the algorithm's random properties, such as confusion, diffusion, and independence. The avalanche criterion and output randomness results show that this algorithm meets the fundamental security requirement for a lightweight block cipher. lightweight block cipher; modified Feistel; randomness test; avalanche test +
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the increased connectivity of these devices has made it easier for cybercriminals to gain unauthorized access to private information on the networks, as certain devices may be susceptible to attacks. Therefore, cryptography, a branch of mathematics related to creating secure communication protocols for data transmission, is used as a crucial component of information security to protect communication systems. In today's digital age, cryptography plays a critical role, particularly in the Internet of Things (IoT), where connected devices are vulnerable to numerous security threats, such as hacking and eavesdropping. As the number of connected devices in the IoT continues to increase, the need for secure communication protocols has become more pressing, making cryptography an indispensable tool for ensuring the confidentiality, integrity, and authenticity of data transmitted over IoT networks. However, conventional cryptography algorithms are unsuitable for use in resource-constrained IoT devices due to their high resource demands. Consequently, lightweight cryptography is employed for smart objects in the IoT environment as a replacement for traditional cryptography techniques. For IoT security, a number of lightweight cryptography techniques are available, including lightweight block ciphers, lightweight hash functions, lightweight message authentication codes, and lightweight stream ciphers, with lightweight block ciphers being the most frequently used. Over the years, several lightweight block ciphers, such as PRESENT [4], LED [5], RECTANGLE [6], SKINNY [7], and SPECK [8], have been developed with simple structures and a high throughput for efficient implementation. While several new lightweight block ciphers have recently been proposed, they have yet to undergo extensive cryptanalysis to be considered as state-of-the-art. Additionally, in low-power and lossy networks, security remains a significant concern, necessitating the need for more innovation in developing lightweight algorithms. A lightweight block cipher must possess confusion and diffusion properties in its design components to provide sufficient security to the algorithm [9].