Computer Security: Cryptography Design Application

This project includes the design and implementation of custom stream and block ciphers with encryption/decryption demos, naming, workflow diagrams, and usage justification. It also proposes a hybrid cryptography application combining symmetric and asymmetric methods.

Block Cipher

EDES_zero is a fully commented, step-by-step educational implementation of the Data Encryption Standard (DES) algorithm, written in C++.
It demonstrates how DES operates internally, including key generation, expansion, substitution, and permutation processes.

File Name	Description
EDES_zero.cpp	Main source file containing the complete DES algorithm and demo program

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Compilation & Execution

To compile the program, use the following command:

g++ EDES_zero.cpp -std=c++17 -O2 -o EDES_zero

./EDES_zero

Example Output

EDES_zero. Input plaintext and 8-byte key.
Enter plaintext: HelloDES
Enter 8-character key (will be used as 64-bit key): mysecret

--- ENCRYPTION ---
Padded plaintext (len=8): HelloDES
Binary: 01001000 01100101 01101100 01101100 01101111 01000100 01000101 01010011

Key (64-bit binary): 01101101 01111001 01110011 01100101 01100011 01110010 01100101 01110100
K1: 00011011 00000000 11110000 11101110 11111100 10101010
...
=== Encrypting block 1 ===
  After IP: 11001010 11100001 01010111 ...
  --- Round 1 ---
  Subkey K1: 00011011 ...
  ...
Ciphertext (hex): 8f1a2bce21d4e765

Recovered plaintext: HelloDES

Stream Cipher

Tornado-25 is a fully commented, educational implementation of a noise-based stream cipher, written in C++. It demonstrates how stream ciphers operate using keystream generation, XOR-based encryption, and Base64 encoding for readable output.

File Name	Description
Tornado-25.cpp	Main source file containing the complete Tornado-25 stream cipher and demo program

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Compilation & Execution

To compile the program, use the following command (in Google Colab):

!g++ Tornado-25.cpp -o Tornado-25

./Tornado-25

Example Output

Original Message: THE MANAGER IS HERE
Encrypted (Base64): ks3ZyuWlRpu7AK6sjYZMHEjjFQ==
Decrypted Message: THE MANAGER IS HERE

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System Requirements

• C++17 compatible compiler (e.g., g++, clang++)
• Operating System: Linux, macOS, or Windows
• No external libraries required

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License

This project is open-source and free to use for educational purposes.