# A Secure and Efficient Lightweight Symmetric Encryption Scheme for Transfer of Text Files between Embedded IoT Devices

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## Abstract

**:**

## 1. Introduction

## 2. Related Work

^{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. Usman 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. Liang C 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 Chongzhi Gao 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. Abdelhalim 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. The pseudo-random number generator frequently changes the MTEA key in each round. Zhdanov and Sokolov proposed an algorithm [36] based on the principles of many-valued logic and variable block length. The encryption process is performed iteratively with five rounds. The number of rounds can be varied, with round 1 consisting of gamma and permutations procedures, remaining rounds include substitution and gamma procedures. The proposed method can process binary information after representing as a ternary vector. But there is no method developed that does this conversion directly. LEA (lightweight encryption algorithm) is a block encryption algorithm [37] that is designed to provide confidentiality in lightweight environment like mobile devices. This algorithm uses plain text of 128 bits and varying modes can be selected depending on the size of the key (128, 192, or 256 bits). Based on the modes, the number of rounds can be changed between 24, 28, and 32 bits. This algorithm does not use S-box, instead addition, rotation and XOR arithmetic operation is processed in 32-bit unit [38]. Abdullah et al. proposed a super-encryption cryptography [39] with IDEA (international data encryption algorithm) and WAKE (word auto key encryption) algorithm. The technique of super encryption combines two or more symmetric cryptographic algorithms so as to provide more security to data. Anderson et al. proposed the serpent algorithm [40] that was an AES candidate. The main aim of this algorithm is to maximize the avalanche effect within the cipher text. Serpent has substitution permutation structure that uses 128-bit plain text and accepts keys of 128, 192, or 256 bits. The 32 rounds of serpent make it a bit slower and complex to implement on small blocks. Data encryption standard (DES) is one of the widely used symmetric key block cipher that uses the Feistel structure. The plaintext of 64-bit and a key size of 56 bits are used for the encryption process that includes 16 rounds. The DES algorithm does not allow flexibility in Feistel structure and hence does not support any changes in it [41].

_{16}and would be selected as 2

^{31}/ Ø (Ø is named the golden ratio). During the encryption process, the plaintext is partitioned into two parts Left[0] and Right[0]. Each of the parts utilizes another half part for doing the encryption process. There will be 64 rounds along with two other rounds that constitute one cycle, so there are 32 cycles. After the 64th round, both parts will be composed to create the cipher text. In each of the rounds, all the inputs include “Left[i − 1]” and “Right[i − 1]” which is derived from the previous round and sub-key Ki extracted from the 128-bit key K. The constant delta =0 × 9E3779B9 is chosen to be 2

^{31}/Ø. This is to confirm that the sub-keys are distinct and that the accurate value of it does not have a cryptographic significance. In each round, the integer "addition" modulo of 2

^{32}is applied instead of XOR. The round function F uses addition, bitwise XOR, left and right shift operation.

## 3. Novel Tiny Symmetric Encryption Algorithm (NTSA)

^{31}/Ø) where Ø is the golden ratio. The golden ratio Ø is 1.618033988749895 and computed as (1 + √ 5)/2.

Algorithm 1 Novel tiny symmetric encryption algorithm (NTSA) symmetric encryption algorithm |

Encrypt (plaintext v, key k): |

1: Start 2: Assign key constant kc = 0 3: Assign cycle = 0 4: kc = kc + ksc 5: 32-bit block v0 is recomputed as v0 += ((v1 LSHIFT 4) AND k0) XOR (v1 AND kc) XOR ((v1 RSHIFT 5) AND k1) 6: Partial key k1 is recomputed as k1 += (k0 XOR(xtract(v0))) where function xtract() returns value of array indexed v0. 7: 32-bit block v1 is recomputed as v1 += ((v0 LSHIFT 4) AND k2) XOR (v0 AND kc) XOR ((v0 RSHIFT 5) AND k3) 8: Partial key k3 is recomputed as k3 += (k2 XOR(xtract(v1))) where function xtract() returns value of array indexed v1. 9: Increment cycle by 1 10: Repeat step 4 through step 9 until cycle = 32 11: Assign value of k1 to newk1 and k3 to newk3 12: Return newk1 and newk3 |

^{31}/Ø) where Ø is the golden ratio. The golden ratio Ø is 1.618033988749895. The 32-bit block plaintext v0 and v1 are recomputed each time for 32 cycles and partial keys k1 and k3 are recomputed for even and odd rounds respectively to induce key confusion. The computation of v0, k1, v1, k3 are shown in the following equations.

^{31}/Ø). The golden ratio Ø is 1.618033988749895. The 32-bit blocks v1 and v0 are recomputed each time for 32 cycles and partial keys k3 and k1 are recomputed for odd and even rounds respectively to induce key confusion. The computation of k3, v1, k1 and v0 are shown in the following equations.

Algorithm 2. NTSA symmetric decryption algorithm |

Encrypt (plaintext v, key k): |

1: Start 2: Assign key constant kc = 0XC6EF3720 3: Assign k1 = newk1 and k3 = newk3 4: Assign cycle=0 5: Partial key k3 is recomputed as k3 - = (k2 XOR(xtract(v1))) where function xtract() returns value of array indexed v1. 6: 32-bit block v1 is recomputed as v1 - = ((v0 LSHIFT 4) AND k2) XOR (v0 AND kc) XOR ((v0 RSHIFT 5) AND k3) 7: Partial key k1 is recomputed as k1 - = (k0 XOR(xtract(v0))) where function xtract() returns value of array indexed v0. 8: 32-bit block v0 is recomputed as v0 - = ((v1 LSHIFT 4) AND k0) XOR (v1 AND kc) XOR ((v1 RSHIFT 5) AND k1) 9: kc = kc − ksc 10: Increment cycle by 1 11: Repeat step 5 through step 10 until cycle=32 12: Return |

^{O}0,1; O indicates an odd round, and 0,1 indicate the 0th cycle, round 1;

^{E}1,1; E indicates an even round, and 1,1 indicate the 1st cycle, round 1.

^{O}0,1, the second half of the plaintext v1 is used and shift, AND, and XOR operations are performed on v1. Similarly, for computing v

^{E}1,1, the first half (32 bits) of plain text v0 is used and shift, AND and XOR operations are performed on v0.

## 4. Experimental Results and Discussion

#### 4.1. Performance Comparison of NTSA with TEA, XTEA and XXTEA

#### Avalanche Effect

## 5. Conclusions

## Author Contributions

## Acknowledgments

## Conflicts of Interest

## References

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Algorithm | Developer | Block/Stream Cipher | Key Size | Attack | Algorithm Structure |
---|---|---|---|---|---|

DES [41] | IBM | Block cipher (64 bits) | 56 bits | Brute Force Attack | 16 rounds Feistel Structure |

3DES [49] | IBM | Block cipher (64 bits) | 112 or 168 bits | chosen-plaintext attack | 48 rounds Feistel Structure |

IDEA [33] | Lai and James | Block cipher (64 bits) | 128 bits | weak keys | 8 rounds Feistel Structure |

RC5 [24] | Ron Rivest | Block cipher (32,64,128 bits) | 0–2040 bits | differential attack | (12 round suggested) Feistel Structure |

TEA [45] | Wheeler and Needham | Block cipher (64 bits) | 128 bits | equivalent key attack | Variable round Feistel Structure |

XTEA [46] | Wheeler and Needham | Block cipher (64 bits) | 128 bits | related key differential attack | Variable round nested Feistel Structure |

XXTEA [47] | Wheeler and Needham | Block cipher (64 bits) | 128 bits | chosen-plaintext attack | unbalanced Feistel Network |

SKIPJACK [50] | National Security Agency (NSA) | Block cipher (64 bits) | 80 bits | slide attack | 32 rounds, unbalanced Feistel Structure |

AES [40] | Daemen and Rijmen | Block cipher (128 bits) | 128, 192, 256 bits | known plaintext | 20 rounds Feistel Structure |

MARS [34] | IBM | Block cipher (128 bits) | 128, 192, 256 bits | meet-in-the-middle | 32 rounds Feistel Structure |

HIGHT [29] | Hong et al. | Block cipher (64 bits) | 128 bits | Impossible Differential attack | light weight block algorithm, effective in hardware |

FILE SIZE | ENCRYPTION TIME (in milliseconds) | |||
---|---|---|---|---|

(IN KILO BYTES) | TEA | XTEA | BLOCK TEA (XXTEA) | NTSA |

0.37 | 0.059 | 0.174 | 0.083 | 0.041 |

0.95 | 0.125 | 0.244 | 0.155 | 0.112 |

1.6 | 0.214 | 0.451 | 0.271 | 0.201 |

2.6 | 0.351 | 0.683 | 0.429 | 0.289 |

6.8 | 0.771 | 1.384 | 1.768 | 0.551 |

8.6 | 0.817 | 2.120 | 1.192 | 0.801 |

12.2 | 0.916 | 2.306 | 1.379 | 0.857 |

16.2 | 1.544 | 3.744 | 1.981 | 1.211 |

26.7 | 1.802 | 4.176 | 2.712 | 1.603 |

FILE SIZE | DECRYPTION TIME (in milliseconds) | |||
---|---|---|---|---|

(IN KILO BYTES) | TEA | XTEA | BLOCK TEA (XXTEA) | NTSA |

0.37 | 0.058 | 0.136 | 0.068 | 0.055 |

0.95 | 0.123 | 0.289 | 0.156 | 0.112 |

1.6 | 0.209 | 0.474 | 0.254 | 0.201 |

2.6 | 0.332 | 0.691 | 0.371 | 0.323 |

6.8 | 0.753 | 1.369 | 1.73 | 0.655 |

8.6 | 0.806 | 2.095 | 1.16 | 0.789 |

12.2 | 0.903 | 2.228 | 1.365 | 0.890 |

16.2 | 1.537 | 3.698 | 1.959 | 1.234 |

26.7 | 1.78 | 4.241 | 2.799 | 1.645 |

FILE SIZE | ENCRYPTION TIME (in milliseconds) | |||
---|---|---|---|---|

(IN KILO BYTES) | TEA | XTEA | BLOCK TEA (XXTEA) | NTSA |

0.37 | 0.059 | 0.125 | 0.068 | 0.51 |

0.95 | 0.126 | 0.264 | 0.158 | 0.109 |

1.6 | 0.198 | 0.423 | 0.232 | 0.189 |

2.6 | 0.332 | 0.686 | 0.384 | 0.221 |

6.8 | 0.696 | 1.584 | 0.743 | 0.548 |

8.6 | 0.948 | 1.669 | 1.171 | 0.899 |

12.2 | 1.277 | 2.807 | 1.535 | 1.02 |

16.2 | 1.12 | 3.263 | 1.864 | 1.10 |

26.7 | 2.209 | 5.207 | 2.224 | 1.983 |

FILE SIZE | DECRYPTION TIME (in milliseconds) | |||
---|---|---|---|---|

(IN KILO BYTES) | TEA | XTEA | BLOCK TEA (XXTEA) | NTSA |

0.37 | 0.058 | 0.143 | 0.068 | 0.49 |

0.95 | 0.125 | 0.276 | 0.179 | 0.101 |

1.6 | 0.195 | 0.43 | 0.233 | 0.174 |

2.6 | 0.324 | 0.673 | 0.388 | 0.311 |

6.8 | 0.678 | 1.57 | 0.75 | 0.556 |

8.6 | 0.936 | 1.641 | 1.21 | 0.889 |

12.2 | 1.241 | 2.764 | 1.538 | 1.03 |

16.2 | 1.111 | 3.184 | 1.956 | 1.10 |

26.7 | 2.179 | 5.178 | 2.193 | 1.989 |

KEY SIZE | ENCRYPTION TIME (in milliseconds) | |||
---|---|---|---|---|

(IN BITS) | TEA | XTEA | BLOCK TEA (XXTEA) | NTSA |

32 | 0.125 | 0.287 | 0.145 | 0.07 |

48 | 0.125 | 0.264 | 0.162 | 0.083 |

64 | 0.125 | 0.246 | 0.17 | 0.088 |

96 | 0.126 | 0.265 | 0.158 | 0.093 |

128 | 0.126 | 0.264 | 0.158 | 0.097 |

160 | 0.114 | 0.271 | 0.154 | 0.100 |

192 | 0.125 | 0.279 | 0.144 | 0.100 |

240 | 0.125 | 0.279 | 0.145 | 0.113 |

KEY SIZE | DECRYPTION TIME (in milliseconds) | |||
---|---|---|---|---|

(IN BITS) | TEA | XTEA | BLOCK TEA (XXTEA) | NTSA |

32 | 0.124 | 0.281 | 0.146 | 0.068 |

48 | 0.136 | 0.257 | 0.15 | 0.087 |

64 | 0.123 | 0.214 | 0.152 | 0.088 |

96 | 0.123 | 0.259 | 0.158 | 0.091 |

128 | 0.125 | 0.276 | 0.179 | 0.090 |

160 | 0.113 | 0.267 | 0.155 | 0.101 |

192 | 0.126 | 0.26 | 0.159 | 0.119 |

240 | 0.123 | 0.259 | 0.157 | 0.119 |

KEY SIZE | ENCRYPTION TIME (in milliseconds) | |||
---|---|---|---|---|

(IN BITS) | TEA | XTEA | BLOCK TEA (XXTEA) | NTSA |

32 | 1.173 | 2.287 | 1.649 | 1.009 |

48 | 1.178 | 2.572 | 1.393 | 1.010 |

64 | 1.248 | 2.089 | 1.178 | 1.006 |

96 | 1.208 | 2.32 | 1.502 | 1.10 |

128 | 1.067 | 2.301 | 1.534 | 1.04 |

160 | 1.137 | 2.608 | 1.076 | 1.03 |

192 | 1.39 | 2.327 | 1.148 | 1.11 |

240 | 1.439 | 2.866 | 1.413 | 1.2 |

KEY SIZE | DECRYPTION TIME (in milliseconds) | |||
---|---|---|---|---|

(IN BITS) | TEA | XTEA | BLOCK TEA (XXTEA) | NTSA |

32 | 1.127 | 2.249 | 1.641 | 1.08 |

48 | 1.195 | 2.572 | 1.396 | 1.083 |

64 | 1.241 | 2.084 | 1.179 | 1.112 |

96 | 1.226 | 2.299 | 1.477 | 1.117 |

128 | 1.029 | 2.265 | 1.583 | 1.020 |

160 | 1.093 | 2.645 | 1.074 | 1.025 |

192 | 1.363 | 2.278 | 1.163 | 1.155 |

240 | 1.402 | 2.827 | 1.414 | 1.388 |

KEY SIZE | ENCRYPTION TIME (in milliseconds) | |||
---|---|---|---|---|

(IN BITS) | TEA | XTEA | BLOCK TEA (XXTEA) | NTSA |

32 | 2.253 | 4.459 | 2.339 | 1.772 |

48 | 1.883 | 3.734 | 2.111 | 1.789 |

64 | 1.933 | 3.349 | 2.485 | 1.812 |

96 | 2.812 | 4.856 | 2.246 | 1.856 |

128 | 2.209 | 5.207 | 2.224 | 1.825 |

160 | 2.925 | 3.687 | 2.731 | 1.887 |

192 | 1.869 | 4.562 | 1.958 | 1.662 |

240 | 1.989 | 4.213 | 2.43 | 1.912 |

KEY SIZE | DECRYPTION TIME (in milliseconds) | |||
---|---|---|---|---|

(IN BITS) | TEA | XTEA | BLOCK TEA (XXTEA) | NTSA |

32 | 2.212 | 4.422 | 2.387 | 1.701 |

48 | 1.854 | 3.713 | 2.136 | 1.746 |

64 | 1.888 | 3.307 | 2.516 | 1.777 |

96 | 2.726 | 4.892 | 2.289 | 1.834 |

128 | 2.179 | 5.178 | 2.193 | 1.820 |

160 | 2.883 | 3.668 | 2.711 | 1.811 |

192 | 1.853 | 4.498 | 1.935 | 1.812 |

240 | 1.934 | 4.073 | 2.456 | 1.936 |

© 2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

## Share and Cite

**MDPI and ACS Style**

Rajesh, S.; Paul, V.; Menon, V.G.; Khosravi, M.R.
A Secure and Efficient Lightweight Symmetric Encryption Scheme for Transfer of Text Files between Embedded IoT Devices. *Symmetry* **2019**, *11*, 293.
https://doi.org/10.3390/sym11020293

**AMA Style**

Rajesh S, Paul V, Menon VG, Khosravi MR.
A Secure and Efficient Lightweight Symmetric Encryption Scheme for Transfer of Text Files between Embedded IoT Devices. *Symmetry*. 2019; 11(2):293.
https://doi.org/10.3390/sym11020293

**Chicago/Turabian Style**

Rajesh, Sreeja, Varghese Paul, Varun G. Menon, and Mohammad R. Khosravi.
2019. "A Secure and Efficient Lightweight Symmetric Encryption Scheme for Transfer of Text Files between Embedded IoT Devices" *Symmetry* 11, no. 2: 293.
https://doi.org/10.3390/sym11020293