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🔐 Data Encryption Standard (DES) Algorithm Simulation

This project demonstrates the DES (Data Encryption Standard) encryption and decryption algorithm using C. It simulates the key generation, initial/final permutations, and 16-round Feistel structure of DES.

📖 Overview

DES is a symmetric block cipher that encrypts plaintext data in 64-bit blocks using a 64-bit key (56 effective bits). It was a widely used encryption standard before being replaced by AES.

🔍 Key Concepts

  • Symmetric Cipher: Same key for encryption and decryption
  • Block Size: 64-bit blocks
  • Key Size: 64-bit (56 bits effective)
  • Rounds: 16 Feistel rounds with subkeys

🔁 DES Encryption Process

  1. Initial Permutation (IP):
    Rearranges 64-bit plaintext using a fixed IP table.

  2. Key Generation:

    • Drop parity bits from 64-bit key → 56-bit key
    • Split into two 28-bit halves
    • Perform left shifts
    • Generate 16 subkeys (48-bit each)

  3. 16 Feistel Rounds:

    • Split data into Left (L) and Right (R)
    • Expand R (32 → 48 bits)
    • XOR with round key
    • S-box substitution → 32-bit output
    • P-box permutation
    • XOR with L and swap halves

  4. Final Permutation (FP):
    Apply inverse of IP to get the ciphertext.

🔄 Decryption

Same steps as encryption but apply the subkeys in reverse order (K16 → K1).

💡 Example

🔢 Plaintext: "HELLO123" → ASCII → Binary

H: 01001000
E: 01000101
L: 01001100
L: 01001100
O: 01001111
1: 00110001
2: 00110010
3: 00110011

Combined 64-bit plaintext: 01001000 01000101 01001100 01001100 01001111 00110001 00110010 00110011

🔐 Sample Key (Hex): 133457799BBCDFF1

Final Output Cipher (Hex): 29C3 50F3 47D8 70CA

🧠 Project Structure

DES_Algorithem/
├── des.c           # Main C program implementing DES
├── README.md       # Project documentation

##📌 Notes DES is considered insecure for modern use due to brute-force vulnerabilities. Historically used in the financial and government sectors. Replaced by AES for higher security standards.

📄 License This project is licensed under the MIT License. Feel free to use and modify it for educational purposes.

🙋‍♂️ Author Sarvam Patel Computer Engineering Student | Developer | Open to Internships 🔗 GitHub: https://github.com/CoreTech7704 🔗 LinkedIn: https://www.linkedin.com/in/sarvam-patel-89a414300/