🔐 Hima Chat – Cryptography-Focused Secure Messaging System

Hima Chat is a secure chat application built specifically to demonstrate and apply cryptography concepts in real-world communication systems.
The project focuses on encryption, key sharing, and secure message storage, rather than UI design or clean-code practices.

---

📌 Project Purpose

The main goal of this project is to:

• Apply cryptographic algorithms in a real chat scenario
• Protect sensitive data from attackers by storing encrypted messages only
• Simulate secure key agreement between sender and receiver
• Design the system to be extensible for adding new encryption algorithms

⚠️ This project is cryptography-oriented.
Topics such as clean code, advanced architecture patterns, or UI optimization are out of scope.

---

🧠 Core Cryptography Concepts Used

• Symmetric Key Encryption
• Shared Secret Keys
• Plain Text → Cipher Text Transformation
• Secure Data Storage (Encrypted at Rest)
• Decryption Only with Matching Key & Algorithm

---

🛠️ Technologies Used

Backend

• C#
• ASP.NET Core MVC

Frontend

• Razor Pages
• HTML / CSS

Database

• SQL Server

Development Tools

• Visual Studio

---

🧩 System Overview

The system is divided into two main cryptography-related modules:

1️⃣ Secure Chat Creation

• Sender and Receiver must:
  • Choose the same encryption algorithm
  • Use the same secret key
• This shared configuration represents the cryptographic agreement

2️⃣ Encrypted Messaging

• Messages are encrypted before being stored
• Only encrypted data (Cipher Text) is saved in the database
• Decryption is possible only if:
  • The correct key is used
  • The correct encryption algorithm is selected

---

🗄️ Database Design (Security-Oriented)

🧑 Users Table

Column	Description
Email	User identifier
FName	First Name
LName	Last Name
Password	Stored securely

---

🔑 SymmetricKeys (Chats) Table

Column	Description
EmailFrom	Sender
EmailTo	Receiver
Key	Shared secret key
EncryptionType	Selected algorithm
Time	Chat creation time

---

💬 Messages Table

Column	Description
Id	Message ID
EmailFrom	Sender
EmailTo	Receiver
CipherText	Encrypted message
TimeMessage	Timestamp

⚠️ No plain text messages are stored in the database.

---

🔄 Application Flow (Cryptography Lifecycle)

1️⃣ User logs in

---

2️⃣ Sender creates a new chat

---

3️⃣ Sender & Receiver agree on:

• Encryption Algorithm
• Secret Key
  4️⃣ Sender writes a message (Plain Text)
  5️⃣ System encrypts the message → Cipher Text
  6️⃣ Cipher Text is stored in the database
  7️⃣ Receiver:
• Uses the same key & algorithm
• Decrypts Cipher Text → Plain Text

✔️ Without the correct key and algorithm, messages are unreadable

---

🔌 Encryption API Design (Extensibility)

The system is designed to make adding new encryption algorithms simple and scalable.

To Add a New Encryption Type:

1️⃣ Create a new class with the same name as the encryption type

2️⃣ Implement the following static methods:

public static string Encrypt(string plainText, string key);
public static string Decrypt(string cipherText, string key);