CSE4232: Cryptography and Network Security Lab

This repository contains the lab works of CSE4232 – Cryptography and Network Security Lab course.
All programs are implemented in Python with clear encryption and decryption processes demonstrated for each algorithm.

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Lab Experiments

1. Caesar Cipher

• Implemented the Caesar Cipher (shift of 3).
• Performed encryption and decryption to retrieve the original plaintext.

2. Polygram Substitution Cipher

• Implemented Polygram Cipher with a block size of 3.
• Encrypted plaintext by substituting character blocks.
• Reversed operation to recover the plaintext.

3. Transposition Cipher

• Implemented Columnar Transposition Cipher.
• User inputs the width (key) to determine column arrangement.
• Performed both encryption and decryption.

4. Double Transposition Cipher

• Applied two successive transposition ciphers using two keys.
• Verified correct decryption of ciphertext back to original text.

5. One Time Pad (OTP)

• Used a truly random nonrepeating key file.
• Implemented bitwise XOR for encryption and decryption.
• Verified perfect secrecy property.

6. Lehmann Primality Test

• Implemented Lehmann’s algorithm to determine if a number P is prime.

7. Rabin–Miller Primality Test

• Implemented the Rabin–Miller probabilistic primality test.
• Compared performance and accuracy with Lehmann’s test.

8. MD5 Hash Function

• Implemented MD5 one-way hash algorithm.
• Demonstrated how the same input produces identical 128-bit hash values.

9. Secure Hash Algorithm (SHA)

• Implemented SHA-1/SHA-256 one-way hashing.
• Compared with MD5 in terms of hash length and security.

10. RSA Algorithm

• Implemented RSA public-key cryptosystem.
• Supported both integer and string (ASCII converted) plaintexts.
• Demonstrated encryption and decryption using generated keys.

11. Diffie–Hellman Key Exchange

• Simulated secure key exchange between two users over an insecure channel.
• Illustrated the concept of shared secret generation.

12. Pretty Good Privacy (PGP) (not implemented yet)

• Implemented simplified PGP operations:
  • Authentication (Digital signature simulation)
  • Confidentiality (Hybrid encryption using symmetric + asymmetric keys)
• Demonstrated full data transmission workflow.

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