🔐 Cryptography Algorithms Collection

This repository contains Java implementations of classical cryptography algorithms, categorized into Substitution Ciphers and Transposition Ciphers. These algorithms are fundamental in understanding the evolution of modern cryptography and are widely used for educational and research purposes.

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✳️ Substitution Ciphers

Substitution ciphers work by replacing elements of the plaintext with corresponding elements of ciphertext based on a certain system.

✅ Single Substitution

➡️ In these ciphers, each letter of the plaintext is replaced with another letter consistently throughout the message.

• Monoalphabetical
  • 🔸 Atbash Cipher: Reverses the alphabet (A ↔ Z, B ↔ Y, etc.).
  • 🔸 Caesar Cipher: Shifts each letter by a fixed number of places in the alphabet.
  • 🔸 Affine Cipher: Uses mathematical functions (ax + b) mod 26 to encrypt letters.
  • 🔸 August Cipher: A variation of Caesar/Monoalphabetic substitution (implementation included).

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✅ Multiple Substitution

➡️ These are more secure than single substitution ciphers as they use multiple alphabets to encrypt the message.

🔁 Polyalphabetical

• 🔸 Vigenère Cipher: Uses a repeated key to shift letters based on the Vigenère table.
• 🔸 Gronsfeld Cipher: A numeric variant of the Vigenère cipher, often using digits 0–9.
• 🔸 Beaufort Cipher: Similar to Vigenère but uses reversed table logic.
• 🔸 Auto Key Cipher: Key is extended using the plaintext itself.
• 🔸 Running Key Cipher: Uses a long key like a book or paragraph, making repetition harder.

🔤 Polygraphic

• 🔸 Hill Cipher: Uses matrix multiplication and modular arithmetic to encrypt blocks of letters simultaneously.

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🔄 Transpositional Ciphers

These ciphers rearrange the characters of the plaintext instead of substituting them.

• 🔸 Rail Fence Cipher: Characters are written in a zigzag pattern across multiple "rails" and then read row-wise.
• 🔸 Route Cipher: Writes text into a grid and reads it in a specific traversal pattern (e.g., spiral, zigzag).