AES offers minor changes over DES, essentially the key is longer, but in turn th

Question

AES offers minor changes over DES, essentially the key is longer, but in turn the number of rounds is smaller.

Mark the appropriate comment:
a) True, but also AES offers a key size variety, which DES does not.
b) No! DES is symmetric, and AES is asymmetric, they are essentially different!
c) AES is based on completely different mathematical operations compared to DES, different substitution procedures and different transposition procedures.
d) AES is essentially a Triple-DES, with a double DES key: 128bits = 2*64 bits

I think the answer is C but I just want to be sure...

Answer B - is incorrect AES is symmetric

Please exaplain...when select the right answer. Thank you

Explanation / Answer

Solution:-

Answer is option 'C' .

AES algorithm is quite different from DES encryption algorithm.

DES algorithm is a block cipher, it uses plain text of 64 bits and a 56 bit key. DES consists of a16-round series of substitution and permutation. It divides the plain text in two halves of 32bits. In each round, initial permutation and final permutation is performed.after initial permutation, S-box substitution and XOR performed, then final permutation takes place. There are 16 round.

Decryption is essentially the same process, performed in
reverse.

Advanced Encryption Standard (AES)
AES uses 10, 12, or 14 rounds. The key size that can be
128,192 or 256 bits depends on the number of rounds. AES
uses several rounds in which each round is made of several
stages. To provide security AES uses types of
transformation.

Initially plain text goes into the first stage that is
Add Round Key stage. After that the output of first stage goes through nine main rounds, before reaching the final round. In each round there is four transformations which are
performed are as following as:-
1. Sub-bytes
2. Shift-Rows
3. Mix-columns
4. Add round key
In the last round there is no Mix-Column transformation. The output of last round is the cipher text.
So AES used different calculation from DES. It is quite different. It doesn't divides the plain text but works on bytes of plain text. IT performs different substitution and transposition methods.

So it is defined that AES is a replacement of DES not a higher version. It uses substitution, transposition shifts in completely different manner.

So answer (C) is correct.

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