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  • Writer's pictureDimit Chadha

Advanced Encryption Standard

  • Original Name - Rijndael

  • Efficient Algorithm that supports both hardware & Software

  • Supports a block length of 128 bits data and key lengths of 128, 192, and 256 bits.

  • Supersedes DES – Data Encryption Standard

  • Supports Symmetric key Encryption.

  • Result of the encryption is base64 encoded to prevent character encoding problems.

  • AES encryption is used by U.S. for securing sensitive but unclassified material, so we can say it is enough secure.

  • Six time faster than triple DES.

  • It replaced DES as key size was too small (key length of 64 bits, however 8 bits are used for parity, therefore the effective key length is 56 bits.

  • based on ‘substitution–permutation network - series of linked operations, some of which involve replacing inputs by specific outputs (substitutions) and others involve shuffling bits around (permutations).

  • Performs all its computations on bytes rather than bits. Hence, AES treats the 128 bits of a plaintext block as 16 bytes. These 16 bytes are arranged in four columns and four rows for processing as a matrix

  • The number of rounds in AES is variable and depends on the length of the key. AES uses 10 rounds for 128-bit keys, 12 rounds for 192-bit keys and 14 rounds for 256-bit keys. Each of these rounds uses a different 128-bit round key, which is calculated from the original AES key

  • four processes conducted – [Add round key -Mix columns -Shift rows -Byte substitution]

  • Decryption – Reverse process –[ Byte substitution - Shift rows - Mix columns Add round key ]

  • Built-in flexibility of key length, which allows a degree of ‘future-proofing’ against progress in the ability to perform exhaustive key searches.


  • What are AES – Modes

  • Procedural rules for a generic block cipher. Different modes of operation of a block cipher.

  • Different modes result in different properties being achieved which add to the security of the underlying block cipher.

  • Modes are - ECB, CBC, CFB, OFB, CTR

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