## 2 Related Work  
In here, we discuss the major encryption algorithms proposed for transmission of data in IoT networks. Specifically, we discuss the design and implementation of these algorithms and highlight their issues and drawbacks. We also discuss the design, implementation and issues with the TEA and its latest versions in detail. One of the earliest works in this area was the RC5 symmetric key block cipher [24]. RC5 uses variable sized blocks, 32, 64, 128 bits etc. The rounds used are 0-255 with key size of 0 to 2040 bits. The case RC5 is determined suitable for wireless sensor network (WSN) applications, but the key schedule must be calculated a priori based on 104 additional bytes of RAM for each key. Also, the variable-bit rotation instruction used by RC5 is rarely supported by the embedded systems [24]. Skipjack algorithm is another block cipher algorithm developed by the US National Security Agency. Skipjack and its variants, TinySec and MiniSec, are used for transmission of data in WSNs. But the algorithm is not efficient in embedded IoT devices with multiple issues in implementation [25; 26; 27]. [PERSON] et al. gave the scalable encryption algorithm (SEA) [28] generated for processing units that have limited the instruction set. It provides cost-effective encryption and authentication, but does not address secure search of the substring. [PERSON] et al. proposed the HIGHT algorithm [29] that is very useful for pervasive computing devices like devices of a wireless sensory system or network. It uses Feistel network and basic operations like addition mod 2\({}^{8}\) or XOR. There are 32 rounds with 128-bit key and 64-bit block size. But the noted algorithm is vulnerable to saturation attack. [PERSON] et al. proposed SIT--a lightweight encryption algorithm [30] that provides enhanced security for data transmission between IoT devices. SIT uses a combinational form of Feistel structure and network with a uniform substitution-permutation. But the detailed study on performance evaluation and cryptanalysis for possible attacks have not been performed. [PERSON] et al. [31] proposed the hybrid encryption algorithm for lightweight data in cloud storage. This was an improved method on the RSA algorithm and it combined with advanced encryption standard (AES) to introduce a hybrid encryption algorithm. The proposed algorithm improves the efficiency of generating large primes. But the algorithm was mainly focused on enhancing the data confidentiality in the cloud. M-SSE proposed by [PERSON] et al. [32] is different from existing searchable symmetric encryption algorithms as it provides privacy in both forward and backward directions using a technique of multi-cloud computing. But the algorithms and its variations are prone to information leakage. International data encryption algorithm (IDEA) [33] is a block symmetric algorithm that uses 64-bit plain text and a key size of 128 permuted into 52 sub-keys of 128 bits. It includes a Feistel structure and has eight rounds. The degree of diffusion and non-linearity properties of the round function decides the strength of the Feistel structure. IDEA does not use substitution and permutation boxes and is based on operations like XOR, addition and multiplication, thus reducing the memory overhead. The use of the multiplication operation provides diffusion. IDEA does not support any change in the Feistel structure and hence is not flexible. MARS [34] is another symmetric block algorithm that uses 128-bit plaintext with key size varying between 128-448 bits. It follows Feistel structure and has only one substitution box. This algorithm is faster than DES and it is susceptible to many attacks. The involvement of various components makes MARS very complex to analyze and implement in hardware. [PERSON] et al. proposed the modified TEA algorithm (MTEA) [35], which improves the security of TEA and power consumption. The linear feedback shift register (LFSR) is used as a pseudo-random number generator to improve the security of the TEA and power utilization.