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SecureStream: Hybrid Video Encryption System

SecureStream is a prototype software complex for secure streaming multimedia data transmission. The project is developed on the .NET 8 platform (Windows Forms) using a modern hybrid cryptosystem combining ChaCha20-Poly1305 and X25519.

The project was developed as part of a master's thesis on the protection of multimedia data in corporate networks.

📋 Key Features

• Hybrid Encryption: Combines the speed of a stream cipher with the reliability of asymmetric cryptography.
• Perfect Forward Secrecy: Uses ephemeral (one-time) keys. Compromise of a long-term key does not allow decryption of data from past sessions.
• Data Authentication (AEAD): Usage of Poly1305 guarantees data integrity. Any attempt to modify the file (even by 1 byte) results in a decryption error.
• Entropy Visualization: A unique module for real-time visual analysis of encryption quality ("white noise" effect).
• High Performance:
  • Uses the TAP (Task-based Asynchronous Pattern) to ensure UI responsiveness.
  • Optimized memory management using Span<byte> to reduce Garbage Collector load.

🛠 Tech Stack

• Language: C#
• Framework: .NET 8, Windows Forms.
• Cryptography: Bouncy Castle (algorithm implementation).
• IDE: Visual Studio 2022.

🔐 Cryptographic Architecture

The system uses the following primitives:

1. Key Agreement:
   • Protocol: ECDH on Curve25519 (X25519).
   • Provides a 128-bit security level with a 32-byte key.
2. Encryption:
   • Algorithm: ChaCha20 (stream cipher).
   • Speed: 1.20–2.40 cpb (with AVX2 instructions).
3. Key Derivation Function (KDF):
   • Algorithm: SHA-256 for hashing the shared secret.

Secure Container Structure (.enc)

Each encrypted file has a header for autonomous decryption by the recipient:

Field	Size	Description
Length	4 bytes	Length of the public key
Ephemeral PubKey	32 bytes	Sender's one-time public key (X25519)
Nonce	12 bytes	Unique salt to protect against replay attacks
Payload + Tag	Variable	Encrypted data + 16 bytes Poly1305 tag

🚀 Installation and Setup

1. Clone the repository:

   git clone https://github.com/FullyRealist/SecureVideoAppECDH.git

2. Open the project: Launch the .sln solution file in Visual Studio 2022.
3. Dependencies: Ensure the BouncyCastle.Cryptography package is installed via NuGet.
4. Run: Compile and run the project (F5). On the first run, the application will automatically generate a user key pair in the keys_ecdh.conf file.

🖥 Usage

1. Click "Select File" (Обрати файл) and choose a video file.
2. Click "Encrypt" (Зашифрувати).
   • The program will generate a unique ephemeral key.
   • The visualization window will show "white noise," demonstrating high ciphertext entropy.
3. To view, select the .enc file and click "Decrypt" (Розшифрувати).
   • The video will play only if the Poly1305 integrity check is successful.

⚠️ Disclaimer

This project is a research prototype. Although industry-standard algorithms (RFC 7539, RFC 7748) are used, the software implementation has not undergone a professional security audit.

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© 2025. Odesa National Maritime University.