What is AES Encryption and Decryption in Information Security?

AES encryption defines the phase of hiding electronic information using an approved 128-bit, 192-bit, or 256-bit symmetric encryption algorithm from the Advanced Encryption Standard (AES), also called a FIPS 197.

In the 1990s, the US Government required to standardize a cryptographic algorithm which was to be used globally by them. It is known as the Advance Encryption Standard (AES).

Several proposols were submitted and after multiple debate, an algorithm known as Rijndael was accepted. Rijandael was invented by Joan Daemen and Vincent Rijmen. The need for appearing up with a new algorithm was actually because of recognized weakness in DES.

The 56-bit keys of DES were no longer considered safe against attacks depends on exhaustive key searches and the 64-bit blocks were also treated as weak. AES is based on 128-bit blocks with 128-bit keys.

There are the following points while define the AES structure are as follows −

  • The feature of this structure is that it is not a feistel structure. In feistel structure, half of the data block is used to change the other half of the data block and thus the halves are exchanged.

  • Two of the AES finalists, such as Rijandael do not need a Feistel Structure but process the complete data block in parallel during each round using substitution and permutation.

  • The key that is supported as input is expanded into an array of fourty four 32-bit words, w [i]. There are four distinct words (128-bits) serve as a round key for each round.

  • There are multiple stages are utilized, one of the permutation and three of substitution −

    • Substitution bytes − It used as an S-box to implement a byte-by-byte substitution of the block.

    • Shift rows − A simple permutation.

    • Mix columns − A substitution that creates use of arithmetic over GF (28).

    • Add round key − A smooth bitwise XOR of the modern block with the portion of the diffuse key.

  • For both encryption and decryption, the cipher starts with an add round key stage, followed by nine rounds that contains all four stages followed by a 10th round of three stages.

  • It can only add round key stage that create use of the key. For this reasons, the cipher starts and end with an add round key stage. Any other stage, applied at the starting or end, is reversible without knowledge of the key and so would add no security.

  • The add round key stage is a form of vernam cipher and by itself would not be dangerous. The other three stages support confusin, diffusion and non-linearity but by themselves would support no security because they do not required the key.

Updated on: 15-Mar-2022


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