AES is a block cipher intended to replace DES for commercial applica- tions. It uses a 128-bit block size and a key size of 128, 192, or 256 bits.

Chapter
5 **ADVANCED ENCRYPTION STANDARD**

o **Finite
Field Arithmetic**

o **AES Structure**

·
General Structure
Detailed Structure

o **AES
Transformation Functions**

·
Substitute Bytes
Transformation

·
ShiftRows
Transformation

·
MixColumns
Transformation

·
AddRoundKey
Transformation

o **AES Key Expansion**

·
Key Expansion
Algorithm Rationale

o **An AES Example**

·
Results Avalanche
Effect

o **AES Implementation**

·
Equivalent Inverse
Cipher Implementation Aspects

KEY
POINTS

◆ AES is a block cipher intended to replace DES for
commercial applica- tions. It uses a 128-bit block size and a key size of 128,
192, or 256 bits.

◆ AES does not use a Feistel structure. Instead, each full
round consists of four separate functions: byte substitution, permutation,
arithmetic opera- tions over a finite field, and XOR with a key.

The Advanced
Encryption Standard (AES) was published by the
National Institute of Standards and Technology
(NIST) in 2001.
AES is a symmetric block cipher that is
intended to replace DES as the approved
standard for a wide range of applications. Compared to public-key
ciphers such as RSA, the structure of AES and most symmetric ciphers is quite
complex and cannot be explained as easily as many other
cryptographic algorithms. Accordingly, the reader may wish to begin with a simplified
version of AES, which is described
in Appendix 5B. This version allows the reader to perform
encryption and decryption by hand and gain a good understanding of the working of the algorithm details. Classroom experience indicates that a study of this
simplified version enhances
understanding of AES.1 One possible
approach is to read the chapter
first, then carefully read
Appendix 5B, and
then re-read the main body of the chapter.

Appendix H looks at the evaluation criteria used by NIST to select from among
the candidates for AES, plus the rationale
for picking Rijndael,
which was the winning
candidate. This material is useful in understanding
not just the AES design but the criteria by which to judge any symmetric
encryption algorithm.

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Cryptography and Network Security Principles and Practice : One Symmetric Ciphers : Advanced Encryption Standard : Advanced Encryption Standard(AES) |

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