76 المجلة العراقية لتكنولوجيا المعلومات.. المجلد. 8 - العدد. 2 - 2018 Modified LOKI97 Algorithm Based on DNA Technique and Permutation Assist. Prof. Dr. Alaa Kadhim M.Sc. Shahad Husham University of Technology / Computer science department E-mail: [email protected] ABSTRACT As is common, in the cryptography, that any encryption algorithm may be vulnerable to breakage, but that conflicts with the most significant goal of any encryption algorithm, which is to conserve sensitive information that will be transmitted via an unsafe channel, therefore the algorithms must be designed to be resistant against the attacks and adversaries, by increasing the complexity of some internal functions, raised the number of rounds or using some techniques such as artificial intelligence to develop this algorithm. In this paper, has been proposed an approach to develop the classical LOKI97 algorithm by enhancement some of its internal functions for increasing the confusion and diffusion to possess resistance against the attacker. 77 المجلة العراقية لتكنولوجيا المعلومات.. المجلد. 8 - العدد. 2 - 2018 المستخلص كما هو شائع في التشفير ان خوارزميه التشفير قد تكون عرضه للكسر ولكن هذا يتعارض مع الهدف اﻻكثر اهميه في خوارزميه التشفير والتهيئه لحمايه المعلومات الحساسه في الرساله تنتقل ضمن قناه غير امنه ولذلك يجب ان تكون الخوارزميه مصممه لتكون مقاومه ضد محاوﻻت الكسر من خﻻل زياده التعقيد ببعض الوضائف الداخليه وزياده عدد الدورات واستخدام بعض التقنيات الذكاء اﻻصطناعي لتطويرهذه الخوارزمية. في هذا البحث , تم اقتراح تطوير خوارزمية LOKI97 , من خﻻل تطوير بعض دوالها لزيادة درجة تعقيدها مما يجعلها تمتلك أرتباك وانتشار عالي , لتكون أكثر قوة ضد اﻻخت ارق . Keywords: Block Cipher, LOKI97, Permutation, DNA Technique 1. Introduction Maintaining and protecting information security has been and still which is the main objective of information security programs such the large organizations and companies spend thousands of dollars and working hours to maintain their information systems. Since attacks are a daily occurrence on their sources of information and systems as well as the evolution of these attacks, the need for information security development goes hand in hand with the evolution of these attacks [1]. In the current era, it became clear that a most important means of protecting sensitive information and accurate data is using cryptography. The cryptography is considered a powerful and effective way to protect information as well as send it quickly and 78 المجلة العراقية لتكنولوجيا المعلومات.. المجلد. 8 - العدد. 2 - 2018 to check the process of sending and receiving it correctly. Where the cryptography can now be regarded as the cornerstone of his peace of the computers and telecommunications because it provides the secure services needed by any party wishing to secure its digital data [2]. 2. LOKI97 Overview [3] The family of a block cipher of (Loki89, Loki91) is designed to be as replacing of data encryption standard (DES) algorithm, and it is very similar to DES in its structure. LOKI97 is one member of the LOKI family, designing by Lawrie Brown. This algorithm, is a new Feistel cipher of 16 round and using a data of 128 bits by employ a complex non-linear function (F). It is using 128, 192, or 256-bit keys. The LOKI97 is designing as a development of Loki 91, by increasing the number of rounds up to 16 and increase the data input from 64-bits to 128-bits, and made the function (F-function) more complicated that is using also in the key schedule. The following figure showed the main F-function of LOKI97. 79 المجلة العراقية لتكنولوجيا المعلومات.. المجلد. 8 - العدد. 2 - 2018 3. The Proposed Work In LOKI89,91 some weaknesses appeared such as key scheduling that have been handled in LOKI97, it has also been increasing the length of the block in addition to the complexity of the F-function and use this nonlinear complex function in its key scheduler. In LOKI97 algorithm, there are some fragility in internal functions component. In this paper, the proposal has 80 المجلة العراقية لتكنولوجيا المعلومات.. المجلد. 8 - العدد. 2 - 2018 improved some functions which are keyed-permutation, permutation function and S-box. The proposal of developing the LOKI97 algorithms is consisting of five internal functions which were included two layers of S- boxes (AES S-box). The first and second phases were a dynamic shifting function and a dynamic DNA addition function. The dynamic shift function that used in this proposal, is featured by awarding a high diffusion. As for the DNA technique, has been used because it is characterized by many advantages such as its privilege of huge capacity in the data storage, in addition to its speed, where the conventional computers can perform nearly (millions of instructions per second), while, as clarified by Adelman, DNA strands has made the computations at a speed of about 10 ^ 9 or better, which can be said to be about 100 times faster than quickest computers. The last phase in the proposed algorithm is the LOKI- permutation function, which is the same permutation function, has been used in the classical LOKI97 algorithm. The following presented figure (2) illustrated the proposed work. 81 المجلة العراقية لتكنولوجيا المعلومات.. المجلد. 8 - العدد. 2 - 2018 3.1 Dynamic Shift Function The keyed permutation function which located in the main function of the LOKI97 algorithm has been replaced by the dynamic shift function. The dynamic circular left shift function is granted a high diffusion to the input bits, it receives 64 bits of input block and 32 bits of a key block then producing a cipher text of 64 bits as an output. It begins by dividing the input block to eight blocks of the length (8 bits), and this division is also done on the key block to gain eight blocks of length 4 bits. Then, every key block will convert from binary code to the equivalent 82 المجلة العراقية لتكنولوجيا المعلومات.. المجلد. 8 - العدد. 2 - 2018 decimal number, and setting every number as a switch key to the input blocks, this means, the shift will apply on every block of the input to the left direction according to the number of the equivalent key block. 83 المجلة العراقية لتكنولوجيا المعلومات.. المجلد. 8 - العدد. 2 - 2018 For example, if the input block was (10010110), the key block is (1001), convert the key block to decimal to be (9), this means performs the left shifting process on the block (9th times). 84 المجلة العراقية لتكنولوجيا المعلومات.. المجلد. 8 - العدد. 2 - 2018 So, the block will be (00101101). When applied the inverse algorithm to retrieve the original block, the shifting process performs in the right direction so the block (00101101) will shift as the key block (1001), (9th times to the right) to be (10010110). 3.2 Dynamic DNA Addition Function: In this proposal has been dispensed with the idea of the compression, by deleting the expansion function in the LOKI97 standard algorithm that gives a 96 bits as an input to this S-box. So the expansion function will have replaced by the dynamic DNA addition function. The dynamic DNA addition function is a proposed function designed to be depend on the dynamic key. This function will have received a key of 32 bits, this key will be subjected to several processing to suit the several stages of this function. The function works according to several steps, in every step will use a key of different length, firstly, the input block is a 64 bits is divided into 32 blocks of (2 bits), then these blocks will be transformed to the equivalent decimal number. These numbers are compensated according to the proposed specific table by using the key. As for the key, as mentioned above, the key will be processing many times. At the beginning, the 32 bits of the key will be expanded to 64 bits by performing the Xor operation between all two adjacent bits (the last bit will be Xor with 0) to 85 المجلة العراقية لتكنولوجيا المعلومات.. المجلد. 8 - العدد. 2 - 2018 get an additional 32 bits, then will be concatenated them with the bits of the original key to form the 64 bits at the end. Then, the second process is splitting the 64 bits of the key into two arrays (odd and even arrays of the 32 bits to each array) and perform the Xor operation between them in gaining the 32 bits and concatenating them with the key of 64 bits to getting 96 bits. In the first stage, the key of 96 bits will be used in the first step of the enciphering, which is dividing the 96 bits into 32 blocks of (3 bits) and transforming these blocks to equivalent decimal number to construct the decimal key blocks. Now, matching the decimal input blocks with the rows of the proposed DNA table (1), while the decimal key blocks will be matched with column of the same table and compensation the resulting code to getting a new sequence of 32 DNA codes. While in the second stage, the key of (64 bits) was used here. It will perform the division of the key into 32 blocks of the length 2 bits, then, coded the 32 blocks by DNA classic codes, which that the 00 is coded to the (A) and 01,10,11 will coded in C, G, T respectively, then will be getting a sequence of DNA code of the key. In the third stage, the DNA-addition operation the table (2) was performed on the two DNA sequences of the input and the key. 86 المجلة العراقية لتكنولوجيا المعلومات.. المجلد. 8 - العدد. 2 - 2018 87 المجلة العراقية لتكنولوجيا المعلومات.. المجلد. 8 - العدد. 2 - 2018 Algorithm (3): Dynamic DNA addition Algorithm Input: 64 bits as input block.