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Current advancement in electronic technology have made it possible to transmit and disseminate electronic services such as (Pharmaceutical, Defence...) proficiently and conveniently to remote places. In fact, a majority of private data today exist in digital format for efficient storing and recovery. Computer technology made it incredibly realistic to obtain and exchange data. Yet, the simplicity of such services enhances some safety issues i.e. (confidentiality, availability and reliability). To fix the security problems, multiple methodologies for the preservation of legal proprietorship of the confidential information have been documented. And encryption is one among them. Cryptography is another word for data encryption. The method of encoding messages in a way that hackers are unable to read it is called encryption, but it can be authorized personnel. The method of transforming the unintelligible data back to original form is called decryption (Fedushko et al., 2020). An encryption algorithm also employs a secret key which has an impact on algorithms output. Encryption algorithms can be grouped into two categories and those are Private key algorithm and Public key algorithm.
In private key encryption, a single key is employed by both sender and receiver for encryption and decryption of the data for safe data transmission. The private key is shared among the parties before of the transfer of the data. Private key encryption is frequently used in government, private sector applications and defence. The strength of private key encryption is proportional to length of the key; longer the key challenging to decipher. Examples of private key algorithms are: Data Encryption Standard (DES), Advanced Encryption Standard (AES), Blowfish, Rivest Cipher 2 and Rivest Cipher 6.
In public key encryption, two different keys are used; public key and private key. For encryption, the public key is used and is available openly where as private key is used for decryption and is not disclosed. This type of algorithms is computationally expensive and are 100 times slower when compared to private key algorithms and is usually employed to encipher only the keys instead of the whole data. Examples include RSA, LUC and ElGamal (Forouzan and Mukhopadhyay, 2012).
As cryptography plays a crucial part in the security of information transmission, the national institute of standards and technology selected AES algorithm as the standard algorithm for encryption of information. It was selected on the basis of performance, security and proficiency in hardware and software implementation. The AES algorithm is a block cipher using private key. The block size of data in AES algorithm is 128 bits. It provides three different key sizes of 128 bits, 192 bits and 256 bits (Satoh et al., 2001). The number of rounds in the operation of the algorithm is dependent on the key size. 14 rounds for key size of 256 bits, 12 rounds for key size of 192 bits and 10 rounds for key size of 128 bits (Gangadari and Ahamed, 2015). The first step is initialization step which is computed by adding (128 bits) data with first round key which is followed by Sub Bytes, Shift Rows, Mix Columns and Add Round Key. The input 128 bits data are expressed in 4x4 square matrix which contains size 8 bits elements (Rudra et al., 2001). The decryption side of the algorithm includes exactly inverse steps that of the encryption. For Byte Substitution, Inverse S-BOX is used (Sarti et al., 2017). The remaining transformation are Add Round Key, Inverse Shift Rows, and Inverse Mix Columns.