Practical List 📃

1. Caesar & Hill Ciphers

Implement Caesar and Hill cipher. Both are substitution cipher. Analyze the strength of the cipher in terms of brute force attack and cryptanalysis attack. Suggest one way to improve and strengthen the cipher and analyze with respect to cryptanalysis attack.
Ceasar cipher-
Your plaintext is Hello, Welcome. The key used is 3. How Ceaser cipher will work?
Test case :
A B C
D E F
Hill Cipher -

    [ 17 17 5]    
K = [ 21 18 5]    
    [ 2  2  19]       

Plaintext = pay
Ciphertext = RRL

2. Rail Fence & Transposition cipher

Implement rail Fence and transposition cipher. Both are permutation cipher. Analyze the strength of the cipher in terms of crypt analysis.
Rail fence.
Test case : Meetme
Ciphertext : MEMETE
Transposition
Key : 4312567
Plaintext: attackpostponeduntiltwoam
Ciphertext: TTNAAPTMTSUOAODWCOIXKNLYPETZ

3. Playfair Cipher

Implement Playfair Cipher. The plaintext is paired in two characters. Discuss the advantage of polyalphabetic cipher over monoalphabetic cipher.
Key = MONARCHY
Plaintext = ar mu hs ea
Ciphertext = RM CM BP IM

4. Vigenere Cipher

Write a program to implement Vigenere Cipher..

5. Vernam Cipher

Write a program to implement Vernam Cipher.

6. GCD

Implement Euclid algorithm to find GCD.
GCD(16,12) = 4
GCD(12,4) = 0
Then 4 is the GCD(16,12)

7. Euler’s totient

Implement Euler’s totient function ф(n). It is defined as the number of positive integers less than n and relatively prime to n. Find ф(35) and ф(37). Observe the value and analyze the behavior of totient function.

8. Euclidean Algorithm

Implement extended Euclidean Algorithm for finding inverse.

9. RSA Algorithm

Implement RSA algorithm.
Take two prime numbers p, q
n=pxq
Initially take encryption key such that it is relatively prime with ф(n).
Find out decryption key.
Take plaintext message M, Ciphertext C=Me mod n.
To get plaintect from ciphertext M=Cd mod n.
Test case :
Two prime numbers 17,11
Encryption key = 7
Decryption key = 23
M=88, C=11

References

• ❤️ Crypto Hack
• Coursera Cryptography I, Stanford, Dan Boneh
• Crypto Pals Crypto Challenges

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