P-1. This question is about AES (Advanced Encryption Standard) algorithm. a) Use
ID: 3869629 • Letter: P
Question
P-1. This question is about AES (Advanced Encryption Standard) algorithm.
a) Use ShiftRow() transformation to obtain the next state:
Solution:
Current State Next State
4e 3d 6f ef
e4 ff 67 8a
5b c5 cc aa
44 23 78 2a
b) Give only the topmost row of the state after doing AddRoundKey() transformation:
Current State Round Key Topmost Row
4e 3d 6f ef a3 4b 6e ff
e4 ff 67 8a c3 23 b4 ee
5b c5 cc aa 7e 84 93 ef
44 23 78 2a 55 3e f5 d7
Explanation / Answer
Hi,
In AES, shift row() is one of the steps where rows are shifted by certain positions(indicated by row number)
hence
row0 4e 3d 6f ef //shift by 0 4e 3d 6f ef
row1 e4 ff 67 8a //shift by 1 ff 67 8a e4
row2 5b c5 cc aa //shify by 2 cc aa 5b c5
row3 44 23 78 2a //shift by 3 2a 44 23 78
b. add round key, in this each of the 16 bytes of state is XORed against each of the 16 bits of the round key
for top row we have
4e 3d 6f ef
XOR XOR XOR XOR
a3 4b 6e ff
result: ed 76 01 10/
Thumbs up if this was helpful, otherwise let me know in comments
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