Cryptography: Decryption, AES, RSA, and Algorithm Comparison

This document presents a comprehensive solution to a cryptography assignment. The solution begins with a decryption problem involving monoalphabetic and row transposition encryption, providing step-by-step workings to reveal the plaintext. The second part delves into AES-128, demonstrating the state array transformations, including initial AddRoundKey, SubBytes, and ShiftRows. Furthermore, the RSA algorithm is explored, with calculations for the decryption key and encryption of a message. Finally, the solution highlights the key differences between DES and RSA algorithms, including their respective strengths and weaknesses and an instance of an attack for each method. The document includes a bibliography with relevant sources.

Running head: CRYPTOGRAPHY
CRYPTOGRAPHY
Name of the Student
Name of the University
Author Note

CRYPTOGRAPHY 1
Question 1:
Encrypted text: KNTGETRZTXRUQFACTIOSJNZAGTQ
K1 = QWERTYUIOPLKJHGFDSAZXCVBNM
K N T G E T R Z T X R U Q F A C T I O S J N Z A G T Q
Q W E R T Y U I O P L K J H G F D S A Z X C V B N M
Output: LYEOCEDTEUDGAPSVEHIRMYTSOEA
1 L U I
2 Y D R
3 E G M
4 O A Y
5 C P T
6 E S S
7 D V O
8 T E E
9 E H A
K2 = 627158943
6 E S S
2 Y D R
7 D V O

2CRYPTOGRAPHY
1 L U I
5 C P T
8 T E E
9 E H A
4 O A Y
3 E G M
K2 = 627158943
Final output: VOILA YOU DECRYPTED THE MESSAGE.
Question 2:
1)
a)
[ 00 04 08 0 C
01 05 09 0 D
02 06 0 A 0 E
03 07 0 B 0 F ]
b)
Key =
[ 01 01 01 01
01 01 01 01
01 01 01 01
01 01 01 01 ]

3CRYPTOGRAPHY
[ 00 04 08 0 C
01 05 09 0 D
02 06 0 A 0 E
03 07 0 B 0 F ] (+)
[ 01 01 01 01
01 01 01 01
01 01 01 01
01 01 01 01 ] =
[ 01 05 09 0 D
00 04 08 0 C
03 07 0 B 0 F
02 06 0 A 0 E ]
c)
[ 01 05 09 0 D
00 04 08 0 C
03 07 0 B 0 F
02 06 0 A 0 E ] =
[ 7C 6 B 01 D 7
63 F 2 30 FE
7 B C 5 2 B 76
77 6 F 67 AB ]
d)
[ 7C 6 B 01 D 7
63 F 2 30 FE
7 B C 5 2 B 76
77 6 F 67 AB ] =
[ 7 C 6 B 01 D 7
F 2 30 FE 63
2 B 76 7 B C 5
AB 77 6 F 67 ]
2)
a)
p = 47, q = 53,
n = p*q = 2491 (12 Bit)
e = 19
φ(n) = (p − 1) × (q − 1) = 2392
gcd(e, φ(n)) = 1
e × d = 1 (mod φ(n))
For the chosen values of p, q, and e, we get d as:
d = 1259

4CRYPTOGRAPHY
b)
The message M = 03
The cipher text is 723.
3)
a)
e= 5, n = 1343
gcd(e, φ(n)) = 1
e × d = 1 (mod φ(n))
d = 749.
b)
The DES is basically a symmetric crypto-graphic related algorithm. On the other side the
RSA is basically an asymmetric crypto-graphic algorithm or public key. The decryption and
encryption is done with the single key that is DES. On the other side, the users can use
separate keys such as private and public in the RSA algorithm. The RSA algorithm uses 2600
bits keys and the DES algorithm uses 56 bits of key. The RSA algorithm is more secure than
the DES algorithm. The RSA algorithm is used widely in the electronic commerce protocols
as well as it is believed for being more security provided with sufficient long keys as well as
the utilization of up to date implementation.

5CRYPTOGRAPHY
Bibliography:
Bhanot, R., & Hans, R. (2015). A review and comparative analysis of various encryption
algorithms. International Journal of Security and Its Applications, 9(4), 289-306.
Bokhari, M. U., Shallal, Q. M., & Tamandani, Y. K. (2017). A Performance Analysis of
Hybrid Technique using DES and RSA algorithms. In Computing for Sustainable
Global Development (INDIACom), 2017 4th International Conference on IEEE.
Gambhir, A., & Arya, R. (2016, December). Performance Analysis of DES Algorithm and
RSA Algorithm with Audio Steganography. In International Conference on
Communication and Signal Processing 2016 (ICCASP 2016). Atlantis Press.
Patil, P., Narayankar, P., Narayan, D. G., & Meena, S. M. (2016). A comprehensive
evaluation of cryptographic algorithms: DES, 3DES, AES, RSA and
Blowfish. Procedia Computer Science, 78, 617-624.
Rihan, S. D., Khalid, A., & Osman, S. E. F. (2015). A performance comparison of encryption
algorithms AES and DES. International Journal of Engineering Research &
Technology (IJERT), 4(12), 151-154.
Wahid, M. N. A., Ali, A., Esparham, B., & Marwan, M. (2018). A Comparison of
Cryptographic Algorithms: DES, 3DES, AES, RSA and Blowfish for Guessing
Attacks Prevention. Journal Computer Science Applications and Information
Technology, 3, 1-7.