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Advanced encryption standard (AES) refers to a specification used in the encryption of data, which is usually in presented in electronic form. It was established by National Institute of Standards and Technology in the United States. According to Hephaestus Books (2011), the advanced encryption standard was designed by Vincent Rijmen and Joan Daemen and was first published in 1998. It uses a block size of 128 bits and works on the basis of Rijndael cipher. Rijndael refers to a family of different ciphers which have different key and block sizes. AES adoption by the government of the United States also led to its adoption worldwide. AES is thus used over the world in the encryption of data. Although it uses the Rijndael algorithm, AES itself is proven to be more effective because of its ability to resist attacks hence enhancing security.

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AES Overview

The Rijndael algorithm works on a design principle combining substitution in addition to permutation. It is efficient and fast both in terms of hardware and software. Daemen and Rijmen (2013) affirm that one of the characteristics that distinguishes AES from its predecessor DES is that AES does not work using Feistel framework. The Rijndael algorithm was identified as the new Advanced Encryption Standard (AES) because of various reasons. Firstly, the Rijndael algorithm is capable of resisting known attacks. Moreover, it is simple and also quick in the formation of codes because less computation is involved and only one key is generated to be used as many times as possible. In addition, the algorithm is versatile, as it can use varying block and key sizes. On the other hand, Chen and Gong (2012) opine that it is not dynamic in approach as the generated key can be expanded and hence sent to many other receivers. Therefore, to get the data, the receivers ought to have received the key. It was originally used for non-classified governmental information in the United States. However, as a result of its success, it has been used to protect the confidential information of American government. Since the attacks have been unsuccessful, the application of AES is fully justified.

Key Generation

There are various types of keys generated in the Rijndael algorithm. They include symmetric and asymmetric key algorithms. The Symmetric-key algorithms employ the similar (secret) key for information protection, removal, and verification. Hephaestus Books (2011) highlights the view that these keys are referred to as secret keys because they are only known and used by the people concerned. More than one entity can share the secret key. Moreover, the secret keys can also be shared with trusted parties, whereas the parties should not share the keys with any unauthorized personnel. Generation of symmetric key algorithms depends on the type of algorithm to be used; hence, its length is determined. In particular, symmetric keys can be generated from passwords.

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Under this circumstance, the kind of passwords selected should have huge value entropy. The given entropy should support the generated key if it is generated from passwords. Symmetric keys can also be created as the combination of multiple keys as well as data. Daemen and Rijmen (2013) indicate that symmetric keys can be derived from keys that have been pre-shared too. Therefore, the strength of security of such key depends on the strength of security of the key that has been pre-shared. These keys can also be obtained directly from outputs of the Random Bit Generator (RBG)

Asymmetric key algorithms are also referred to as public keys. They include a private key that corresponds with public keys. The key that is put in use depends heavily on the process of cryptographic that is to be performed. Whether the cryptographic process involves verification of information or the generation of signatures. Daemen and Rijmen (2013) explain that each pair of private and public keys associates with one entity commonly referred to as “key pair owner”. The public key can be made known and used by a large group of people, whereas the private key is entirely managed by the owner of the key pair.

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Encryption Process

Before the algorithm is applied to data, the sizes of the block and the key must be identified. AES can only work with specified block sizes. Chen and Gong (2012) are of the view that these sizes include 128, 168, 192, 224, and 256 bits. AES also works with specified key sizes. The key sizes are 128, 192, and 256 bits (Hephaestus Books, 2011). The standard encryption works with AES-128. This refers to both key and block sizes of 128 bits. The block size is denoted as Nb, while the key size is denoted as Nk. Nb is a denotation of column numbers the block contains in which a single column row contains four cells with a size of eight bytes. The diagram below is an illustration of the breaking up of data into blocks.

Every single character is kept in one cell of the block. As illustrated above, the cells that are blank in the block are not essentially blank, as they are a representation of the texts spaces. Depending on the implementation of the logarithm, the characters can be stored as either integer values, binary values, or hexadecimal values. All the three ways of representation show similar data. For effective functioning of the Rijndael algorithm, Daemen and Rijmen (2013) explain that the given data should be a representation of a multiple of the size of the block. This is required for the completion of the block. If the data does not represent a multiple of the size of the block, padding must be employed. Padding refers to a process whereby extra bits are included to original data by addition means. One way of padding involves the addition of similar bytes to the point where the needed size is achieved.

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Another form involves padding the zeros in the block and, therefore, the last byte being a representation of the zero numbers in the block. More so, a key that is commonly referred to as the cipher key is needed for the effective functioning of Rijndael algorithm. The cipher key should have a size similar to the size of the block. Hephaestus Books (2011) note that the cipher key is kept as a block same to the texts that is plain. Upon storing data into the blocks and choosing the cipher key, the Rijndael encryption algorithm can be put at work. Generally, the Rijndael algorithm undergoes several rounds in the transformation of data in each block. It uses six rounds in addition to the maximum number of blocks and keys, which rounds up to ten.

This calculation is the result of adding six rounds and four keys and blocks, thereby summing up to ten. Chen and Gong (2012) reiterate that the state of the results, or, in other terms, the initial block, is usually added to a key which is expanded. Hephaestus Books (2011) hold the view that this key is extracted from the cipher key that initially existed. This is followed by the rounding process consisting of operating shifts, a mixcolumn, and the S-box; the state that results from this process is then added to the expanded key. This process is repeated for the whole ten rounds exempting operation of the mixcolumn in the final round. The outcome that comes out of this entire process is the encryption process, and it results to a block that is encrypted.


In conclusion, the Advanced Encryption Standard is currently being utilized for the enhancement of security through generation of the secret key in the United States as well as the entire world. Accordingly, it has replaced Data Encryption Standard that was initially being utilized (DES). This is especially because DES exhibited numerous inefficiencies and insecurities emanating from attacks. The Rijndael algorithm was the one chosen to be used for the standard encryption; this type of algorithm works in the combination of substitution of the S-box and the rotation of the rows and columns combining the working of a mixcolumn. The Rijndael algorithm plays a critical role in both the encryption and decryption processes.

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