1. Introduction

Internet of Things (IoT) includes millions of connected devices that can sense, compute and communicate data^[1][2][3]. Every second, large amount of data is transferred among these devices.  Considering the sensitivity of applications in IoT network such as connected vehicles or wearable health devices, security of transmitted information has remained a major area of concern^[4][5]. Over these years, numerous cryptographic algorithms have been used to ensure the security of transmitted data. With numerous IoT devices having different computational capabilities, one of the major requirements for an efficient security protocol in IoT network is that it should be light weight. The processing time taken by the protocol should be minimal for less delay and better performance. Also the security algorithm needs to be less complex with minimal overhead. Because of these reasons many protocols used with normal computer networks does not give good performance in IoT networks and are not preferred. Considering these features, Tiny Encryption Algorithm (TEA)^[6] is the most widely used symmetric algorithm with Feistel cipher for secure transmission of data through the IoT network. The popularity of TEA is mainly due to the ease of implementation and less memory utilization compared to all other encryption algorithms. But one of the major issues with TEA is the usage of same keys through all the rounds of encryption which leads to reduced security. This is undoubtedly observed from the avalanche effect of TEA. Moreover, the time taken for encryption and decryption is high, leading to reduced efficiency of TEA. Although many versions of TEA have been proposed over these years ^[7][8], none of them have given concrete solutions to the above problems. 

This article proposes an algorithm named NTSA (Novel-T Symmetric Algorithm) that improves the security features of TEA by introducing more key confusions. Most of the works with TEA and its variations has focused only on decreasing the delay in delivery. Very few researches have been done on key alteration as a method to enhance the security of the transmission algorithm. In the proposed method we introduce multiple key alterations dynamically and secure the key from intruders. Since the key is computed dynamically, the key values are changed during the execution time and cannot be pre-computed. Furthermore, our proposed algorithm (NTSA) takes less time for encryption and decryption compared to TEA and thus provides both better security and efficiency for all the modern applications in IoT networks. In our next work we will discuss how thie method can be integrated to ad hoc, sensor and underwater networks. ^{[9][10][11][12]}

2. Novel Tiny Symmetric Encryption Algorithm (NTSA)

The TEA algorithm and its variations use the same key in all rounds of encryption and thus more prone to relative key attack where the attacker tries to realize some relationship between different keys used by the user. The proposed NTSA algorithm is intended to provide more confusion to the keys in each round dynamically. It uses 64-bit plaintext and key of 128 bits. There are 32 cycles and each cycle is composed of 2 rounds resulting in 64 Rounds. The plaintext is divided into two halves v0 and v1 with 32 bits each. The round function op is applied to each half of plaintext. The 128-bit key is divided into 4, 32 bit partial keys k1, k2, k3 and k4. Partial keys k1 and k3 are applied to the odd numbered round and partial keys k2 and k4 are applied to even numbered round. Compute key schedule constant ksc= floor (2³¹/ Ø) where Ø is the golden ratio. The golden ratio Ø is 1.618033988749895 and computed as [ (1+√ 5)/2].

 NTSA round function is as follows

 Round _i ( i is odd) 

       v0 += ((v1 LSHIFT 4) AND k0) XOR (v1 AND kc) XOR ((v1 RSHIFT 5) AND k1)

Round _i ( i is even)

       v1 += ((v0 LSHIFT 4) AND k2) XOR (v0 AND kc) XOR ((v0 RSHIFT 5) AND k3)

 For 1^st cycle: the partial keys are k0, k1, k2 and k3.

 From 2^nd cycle onwards

For odd round k0 is kept constant but k1 changes for all odd rounds as follows,

       k1 = k1+ (k0 XOR(xtract(v0)))

For even round k2 is kept constant but k3 changes for all even rounds as follows,

       k3 = k3+ (k2XOR(xtract(v1)))

 he function xtract() will compute an integer in the range 0 to 32 from v0 or v1 depending upon the parameter being passed. This integer value is an index to an array that is generated dynamically based on the key value selection. The xtract() function will return the value from the array that is pointed by the index value computed. Thus the key confusion is created dynamically and cannot be predicted prior to execution and the value changes on each execution of the algorithm. The NTSA Encryption and Decryption Model is shown in Figure 1.