AES-128 Encryptor

Overview

This project is a C++ implementation of the AES-128 encryption algorithm. It takes a plaintext string as input, divides it into 16-byte blocks, applies padding if necessary, and then encrypts each block using the AES-128 cipher. The encryption process involves key expansion, byte substitution, row shifting, column mixing, and XOR operations.

Features

• Key Expansion: Expands the original 128-bit key into multiple round keys for the encryption process.
• Block Division and Padding: Splits the input into 16-byte blocks and applies PKCS#7 padding for any partial block.
• AES-128 Encryption: Encrypts each block using the AES algorithm, including initial and final transformations.

Project Structure

• AES128.cpp: The main file, orchestrates the encryption process.
• padBlock.h / padBlock.cpp: Handles padding of the last block.
• stringToHex.h / stringToHex.cpp: Converts strings to hexadecimal format for processing.
• keyExpansion.h / keyExpansion.cpp: Expands the initial 128-bit key into 10 additional round keys.
• xorEncrypt.h / xorEncrypt.cpp: Performs XOR operations with the expanded keys.
• subByte.h / subByte.cpp: Applies the AES S-box for byte substitution.
• shiftRows.h / shiftRows.cpp: Shifts rows as part of the encryption process.
• mixColumns.h / mixColumns.cpp: Mixes columns as part of the encryption.
• rotateWord.h / rotateWord.cpp: Rotates bytes in word units for key expansion.

How It Works

The encryption follows these main steps:

1. Key Expansion:

   • Expands a 16-byte (128-bit) original key into 11 keys using the AES key schedule. These expanded keys are used for each encryption round.

2. Block Sectioning and Padding:

   • Divides the plaintext into 16-byte blocks.
   • Pads the final block if its size is less than 16 bytes using PKCS#7 padding.

3. Encryption Process:

   • Each block undergoes the following transformations:
     • Initial AddRoundKey: XORs the block with the first expanded key.
     • 9 Main Rounds:
       • SubByte (S-Box substitution)
       • ShiftRows (row shifting)
       • MixColumns (column mixing)
       • AddRoundKey (XOR with expanded key)
     • Final Round (10th):
       • SubByte
       • ShiftRows
       • AddRoundKey
   • After processing, each encrypted block is printed in hexadecimal format.

How to Build and Run

Requirements

• Compiler: g++ or any C++ compiler with C++11 support.
• Makefile: A Makefile is included for easy building.

Instructions

1. Clone or Download the project files.
2. Compile the project using the following command:

   make

   or directly with g++:

   g++ -std=c++11 -o AES128 AES128.cpp padBlock.cpp stringToHex.cpp keyExpansion.cpp xorEncrypt.cpp subByte.cpp mixColumns.cpp shiftRows.cpp rotateWord.cpp

3. Run the Program:

   ./AES128

Expected Output

The program will output the encrypted blocks in hexadecimal format.

Example:

Encrypted Block 1: [hexadecimal values]
Encrypted Block 2: [hexadecimal values]
...

Notes

• Encryption Mode: This program uses ECB mode (Electronic Codebook), where each block is encrypted independently using the same key.
• AES Standard: This project is intended for educational purposes and demonstrates the steps of the AES-128 encryption algorithm.

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Future Updates

• Decryptor: This program will allow the user to decrypt the encrypted message.
• User Interface: This program will allow the user to interact with the code through a simple interface which will allow it to select the text to encrypt/decrypt, key and optinos between encryption and decryption.