Classical Encryption Techniques

A comprehensive implementation and study of Classical Encryption Techniques, covering both Substitution Ciphers and Transposition Ciphers. This repository demonstrates the core principles of early cryptographic systems that laid the foundation for modern encryption.

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Overview

Classical encryption techniques transform plaintext into ciphertext using systematic methods. These techniques are broadly divided into:

• Substitution Techniques – Replace characters with other characters
• Transposition Techniques – Rearrange the positions of characters

This project includes implementations, explanations, and examples of the most important classical ciphers.

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Substitution Ciphers

1. Caesar Cipher

A simple shift cipher where each letter is shifted by a fixed number of positions in the alphabet.

Example:

Plaintext:  HELLO
Shift:      +3
Ciphertext: KHOOR

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2. Monoalphabetic Cipher

Each letter in the plaintext is mapped to a unique letter in the ciphertext.

• Fixed substitution for entire message
• More secure than Caesar, but vulnerable to frequency analysis

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3. Playfair Cipher

A digraph substitution cipher that encrypts pairs of letters using a 5x5 matrix.

• Reduces frequency analysis weakness
• Handles plaintext in pairs instead of single characters

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4. Hill Cipher

A mathematical cipher based on matrix multiplication.

• Uses linear algebra
• Encrypts blocks of letters
• Requires invertible key matrix

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5. Polyalphabetic Ciphers

a. Vigenère Cipher

Uses multiple Caesar ciphers based on a repeating keyword.

Formula:

Ci = (Pi + Ki) mod 26

b. Vernam Cipher (One-Time Pad when key is random)

• Uses a random key equal in length to plaintext

• Theoretically unbreakable if:

  • Key is truly random
  • Key is used only once

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6. One-Time Pad (OTP)

An extension of Vernam Cipher with perfect secrecy.

✔ Advantages:

• Impossible to crack mathematically

Limitations:

• Key distribution problem
• Requires very long random keys

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Transposition Ciphers

1. Rail Fence Cipher

Writes plaintext in a zig-zag pattern across multiple rows.

Example (Depth = 3):

H   L   O
 E L W R D
  L   O

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2. Row-Column Transposition Cipher

Plaintext is written in rows and read column-wise using a key.

• Key determines column order
• Can be single or double transposition

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3. General Transposition (One-line Definition)

A cipher that rearranges the positions of characters without changing their actual values.

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Comparison

Feature	Substitution Cipher	Transposition Cipher
Operation	Replace characters	Rearrange positions
Security	Moderate	Moderate
Vulnerability	Frequency analysis	Pattern detection
Complexity	Low to Medium	Low

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Features

• Implementation of multiple classical ciphers
• Encryption and Decryption support
• Clean modular code structure
• Educational examples and explanations

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🛠️ Technologies Used

• C++ / JavaScript / Python (depending on your implementation)
• Basic Linear Algebra (for Hill Cipher)
• String manipulation techniques

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Project Structure

/ciphers
    caesar.cpp
    monoalphabetic.cpp
    playfair.cpp
    hill.cpp
    vigenere.cpp
    vernam.cpp
    otp.cpp
    railfence.cpp
    rowcolumn.cpp

README.md

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How to Run

C++ Example:

g++ caesar.cpp -o caesar
./caesar

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Learning Outcomes

• Understanding historical encryption systems
• Difference between substitution and transposition
• Basics of cryptanalysis
• Foundation for modern cryptography

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Disclaimer

These techniques are not secure for modern applications and are implemented strictly for educational purposes.

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Contribution

Contributions are welcome. Feel free to:

• Improve implementations
• Add new ciphers
• Optimize algorithms

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Contact

Hamza Amir hamzaamir9733@gmail.com

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⭐ Support

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