Encryption, Decryption, Encoding & Decoding Java Suite

A comprehensive Java implementation of classic cryptography algorithms, encoding/decoding schemes, and hashing mechanisms built from scratch using core Java logic without relying on external security libraries.

---

Table of Contents

• Overview
• Project Architecture & Directory Structure
• Supported Algorithms & Implementation Details
  • 1. Encryption & Decryption (/Encryption & /Decryption)
  • 2. Encoding & Decoding (/Encode & /Decode)
  • 3. Hashing (/Hashing)
• Prerequisites
• Compilation & Execution Guide
  • Encryption Examples
  • Decryption Examples
  • Encoding Examples
  • Decoding Examples
  • Hashing Examples
• Detailed Walkthrough of Modules
• License

---

Overview

This repository contains clean, core Java programs designed to demonstrate fundamental cryptographic operations and data representation transformations. Each module is self-contained with standard interactive console inputs (java.util.Scanner), making it ideal for educational purposes, security foundational studies, and algorithm analysis.

---

Project Architecture & Directory Structure

Encryption-Decryption-Encoding-Decoding/
├── Encryption/                # Symmetric and substitution cipher algorithms
│   ├── Ceaser_Cipher.java     # Caesar Cipher encryption
│   ├── ROT13.java             # ROT13 substitution encryption
│   ├── Vigenere_cipher.java   # Vigenère polyalphabetic cipher encryption
│   └── XOR.java               # Bitwise XOR cipher encryption
├── Decryption/                # Reverse operations for cryptographic algorithms
│   ├── Ceaser_cipher.java     # Caesar Cipher decryption
│   ├── ROT13.java             # ROT13 decryption
│   ├── Vigenere_cipher.java   # Vigenère cipher decryption
│   └── XOR.java               # Bitwise XOR cipher decryption
├── Encode/                    # Binary and text encoding schemes
│   ├── Base_64.java           # Custom 6-bit chunking Base64 encoder
│   ├── binary.java            # ASCII character to 8-bit binary string encoder
│   ├── MorseCode.java         # Alphanumeric text to Morse Code (. / -) encoder
│   ├── Unix_to_Unix.java      # UUEncoding (Unix-to-Unix binary-to-text) encoder
│   └── URL.java               # Percent-encoding for special URL characters
├── Decode/                    # Reverse transformations for encoding schemes
│   ├── Base64.java            # Base64 decoder back to plain text
│   ├── Binary.java            # 8-bit binary string to plain ASCII decoder
│   ├── MorseCode.java         # Morse Code (. / -) to ASCII text decoder
│   ├── Unix-to-Unix.java      # UUDecoding back to ASCII text
│   └── URL.java               # URL percent-decoding back to plain text
├── Hashing/                   # One-way cryptographic hash functions
│   └── SHA_256.java           # Custom SHA-256 block infrastructure & 512-bit message padding
├── LICENSE                    # MIT License
└── README.md                  # Detailed documentation

---

Supported Algorithms & Implementation Details

1. Encryption & Decryption (/Encryption & /Decryption)

• Caesar Cipher (Ceaser_Cipher.java / Ceaser_cipher.java)

  • Mechanism: Shifts alphabetic characters by a user-defined integer key modulo 26 ((c - 'a' + key) % 26).
  • Preservation: Preserves case (uppercase and lowercase letters are handled separately); non-alphabetic characters remain unchanged.

• ROT13 (ROT13.java)

  • Mechanism: A fixed special case of the Caesar cipher using a fixed key shift of 13 positions ((c - 'a' + 13) % 26).
  • Symmetric nature: Shifting twice by 13 results in the original text (26-letter alphabet).

• Vigenère Cipher (Vigenere_cipher.java)

  • Mechanism: Polyalphabetic substitution cipher using a repeated keyword.
  • Key Expansion: Automatically extends/repeats the key string to match the length of the plaintext string before applying modular shifts.

• XOR Cipher (XOR.java)

  • Mechanism: Bitwise XOR (^) operation between character ASCII binary representations and key binary representations expanded across 8-bit byte frames.

2. Encoding & Decoding (/Encode & /Decode)

• Base64 (Base_64.java / Base64.java)

  • Mechanism: Converts text into 8-bit binary chunks, concatenates them into a unified bit stream, groups them into 6-bit blocks, and maps each 6-bit index to the Base64 index table (A-Z, a-z, 0-9, +, /). Appends 0 padding bits where required.

• Binary Encoding (binary.java / Binary.java)

  • Mechanism: Converts each ASCII character of the input string into a padded 8-bit binary representation (e.g., 'A' $\rightarrow$ 01000001).

• Morse Code (MorseCode.java)

  • Mechanism: Maps letters (A–Z), numbers (0–9), and special punctuation (., ,, ?, !, /, etc.) to standard International Morse Code signals composed of dots (.) and dashes (-).

• UUEncoding (Unix_to_Unix.java / Unix-to-Unix.java)

  • Mechanism: Historical Unix-to-Unix encoding scheme that converts binary/text streams into 6-bit printable ASCII characters (offset by ASCII code 32), adding length byte headers and grave accent (`) padding.

• URL Percent Encoding (URL.java)

  • Mechanism: Replaces reserved or non-alphanumeric characters (such as space , !, #, $, &, =) with their corresponding %HEX ASCII representations (e.g., space becomes %20).

3. Hashing (/Hashing)

• SHA-256 (SHA_256.java)
  • Mechanism: Custom low-level implementation of SHA-256 block creation and message preprocessing:
    1. Converts UTF-8 input string to binary bits.
    2. Applies 512-bit block calculation.
    3. Performs primary padding (1 bit appended as 0s), intermediate zero-padding, and 64-bit Big-Endian length attachment.
    4. Constructs block infrastructure (blockInfraStructure) mapping 32-bit unsigned words ($W_0 \dots W_{15}$).

---

Prerequisites

• Java Development Kit (JDK): JDK 8 or higher (JDK 11 / JDK 17 / JDK 21 recommended).
• Terminal / Command Prompt / Shell access.

Verify your local Java installation:

java -version
javac -version

---

Compilation & Execution Guide

Navigate to the project root directory before executing compilation commands:

cd /Users/pasu/Desktop/Encryption

Encryption Examples

Caesar Cipher

# Compile
javac Encryption/Ceaser_Cipher.java

# Run Encryption
java -cp Encryption Ceaser_cipher

Sample Prompt:

Plaintext: Hello World
Key: 3

Plaintext: Hello World
Ciphertext: Khoor Zruog
--------------------------

ROT13

javac Encryption/ROT13.java
java -cp Encryption ROT13

Vigenère Cipher

javac Encryption/Vigenere_cipher.java
java -cp Encryption Vigenere_cipher

---

Decryption Examples

Caesar Cipher Decryption

javac Decryption/Ceaser_cipher.java
java -cp Decryption Ceaser_cipher

Sample Prompt:

ciphertext: Khoor Zruog
Key: 3

Ciphertext: Khoor Zruog
Plaintext: Hello World
--------------------------

Vigenère Cipher Decryption

javac Decryption/Vigenere_cipher.java
java -cp Decryption Vigenere_cipher

---

Encoding Examples

Base64 Encoding

javac Encode/Base_64.java
java -cp Encode base64_encode

Binary Encoding

javac Encode/binary.java
java -cp Encode binary

Morse Code Encoding

javac Encode/MorseCode.java
java -cp Encode MorseCode_encode

---

Decoding Examples

Base64 Decoding

javac Decode/Base64.java
java -cp Decode base64_decode

Binary Decoding

javac Decode/Binary.java
java -cp Decode Binary_decode

Morse Code Decoding

javac Decode/MorseCode.java
java -cp Decode MorseCode_Decode

---

Hashing Examples

SHA-256 Preprocessing & Block Structure

javac Hashing/SHA_256.java
java -cp Hashing SHA_Hash

Sample Output:

Input: Hello World
Combined Length of Total Blocks: 512
Total blocks used: 1

---

Detailed Walkthrough of Modules

Category	File	Main Class	Core Technique
Encryption	Ceaser_Cipher.java	Ceaser_cipher	Alphabet Modular Shift
Encryption	ROT13.java	ROT13	13-Position Shift
Encryption	Vigenere_cipher.java	Vigenere_cipher	Keyword Polyalphabetic Shift
Encryption	XOR.java	XOR	Bitwise XOR (^) on 8-bit ASCII
Decryption	Ceaser_cipher.java	Ceaser_cipher	Reverse Modular Shift
Decryption	ROT13.java	ROT13	13-Position Reverse Shift
Decryption	Vigenere_cipher.java	Vigenere_cipher	Key-based Reverse Substitution
Decryption	XOR.java	XOR	Symmetric Bitwise XOR
Encode	Base_64.java	base64_encode	8-bit to 6-bit Base64 Table Mapping
Encode	binary.java	binary	ASCII Byte to 8-bit Binary String
Encode	MorseCode.java	MorseCode_encode	Lookup Map to Dots and Dashes
Encode	Unix_to_Unix.java	UUEncoding	Unix Binary-to-ASCII Encoding
Encode	URL.java	URL_encoding	Reserved Char to Percent-Encoding
Decode	Base64.java	base64_decode	Base64 Index to 8-bit Byte Reconstruction
Decode	Binary.java	Binary_decode	8-bit Binary Chunk to ASCII Char
Decode	MorseCode.java	MorseCode_Decode	Dot/Dash Tokens to ASCII
Decode	Unix-to-Unix.java	UUDecoding	Unix UUDecode Stream to ASCII
Decode	URL.java	URL_decoding	Percent-Hex Tokens to ASCII
Hashing	SHA_256.java	SHA_Hash	SHA-256 Preprocessing, Padding & Block Split

---

License

This repository is licensed under the MIT License. Feel free to use, modify, and distribute for learning and development.