U18IT604 : Cryptography & Network Security
CDT10: Class room Discussion
Topic
Topics: AES structure, AES transformation
functions
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CDT10: AES structure, AES transformation
functions
Lecture Outcome
After completion of this session, you will be able to
LO1: Apply AES in real time application
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Advanced Encryption Standard
• AES is a specification for the encryption of
electronic data established by the U.S National
Institute of Standards and Technology (NIST) in
2001.
• AES is widely used today as it is a much
stronger than DES and triple DES despite being
harder to implement.
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Advanced Encryption Standard
• What is the Advanced Encryption Standard?
• The AES Encryption algorithm (also known as the
Rijndael algorithm) is a symmetric block cipher
algorithm with a block/chunk size of 128 bits.
• .
• It is based on a substitution-permutation network, also
known as an SP network. It consists of a series of linked
operations, including replacing inputs with specific
outputs (substitutions) and others involving bit shuffling
(permutations).
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Advanced Encryption Standard
• AES is a block cipher.
• key size can be 128/192/256 bits.
• Encrypts data in blocks of 128 bits each.
• It takes 128 bits as input and outputs 128 bits of
encrypted cipher text as output.
• The number of rounds depends on the key length as
follows :
• 128 bit key – 10 rounds
• 192 bit key – 12 rounds
• 256 bit key – 14 rounds
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• criteria for being chosen as the next AES algorithm
included the following:
• Security. Competing algorithms were to be judged on
their ability to resist attack as compared to other
submitted ciphers. Security strength was to be
considered the most important factor in the competition.
• Cost. Intended to be released on a global, nonexclusive
and royalty-free basis, the candidate algorithms were to
be evaluated on computational and memory efficiency.
• Implementation. Factors to be considered included the
algorithm's flexibility, suitability for hardware or software
implementation, and overall simplicity.
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• This data security measure is efficient and
widely implemented in securing internet
communication, protecting sensitive data,
and encrypting files.
• AES, a cornerstone of modern
cryptography, is recognized globally for its
ability to keep information safe from cyber
threats.
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• AES STRUCTURE
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How Does AES Work?
a 4x4 matrix holds the data in a single block, with each cell
holding a single byte of information. The matrix shown in
the image above is known as a state array.
• .
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• (or) Sub-Bytes: In this step, it converts each byte of the
state array into hexadecimal, divided into two equal
parts. These parts are the rows and columns, mapped
with a substitution box (S-Box) to generate new values
for the final state array.
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• Shift Rows: It swaps the row elements among each
other. It skips the first row. It shifts the elements in the
second row, one position to the left. It also shifts the
elements from the third row two consecutive positions
to the left, and it shifts the last row three positions to the
left.
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Shift Rows
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MixColumns Transformation
• forward mix column transformation,called MixColumns,
operates on each column individually.
• Each byte of a column is mapped into a new value that
is a function of all four bytes in that column.
• The transformation can be defined by the following
matrix multiplication on State matrix
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State matrix (XOR)round key
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AES key expansion
128bits- key (Round key generation)
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Sbox
example 65
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Round constant
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Galois Fields
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