To build a reliable VPN client,consider the following organized approach:

1. Understand and Implement Diffie-Hellman Key Exchange:

   • Use Diffie-Hellman algorithm for secure key exchange between client and server.
   • Generate unique keys for both parties using modular exponentiation.

2. Implement Traffic Encryption:

   • Encrypt each packet of data using techniques like AES-256 with MAC or ciphertext.
   • Use modern encryption standards to secure data transmission.

3. Use Tunnel Key:

   • Generate tunnel keys using Diffie-Hellman between client and server.
   • Use tunnel keys to encrypt video streams and decrypt data at the server end.

4. Provide Strong Authentication:

   • Implement token-based verification with short-lived tokens.
   • Use Two-Factor Authentication (TFA) for added security.

5. Device Agnostic Support:

   • Design the client to support various devices (e.g., smartphones, tablets, PCs) and browsers.
   • Ensure compatibility with multiple protocols like HTTP and HTTPS.

6. Secure Protocols:

   • Use SSL/TLS or HTTPS to secure the entire connection.
   • Employ advanced encryption protocols for data protection.

7. Handle Multiple Users:

   • Implement mechanisms to prevent mutual trust and ensure security even with concurrent users.
   • Use consensus algorithms or rate limiting to manage user interactions.

8. User Interface and Security:

   • Provide a user-friendly interface with intuitive settings and troubleshooting tools.
   • Stay updated with security patches and improvements to maintain client reliability.

9. Consider Trade-offs:

   • Balance between security and performance based on user needs.
   • Choose protocols that suit their specific use cases.

By integrating these elements, you can build a reliable VPN client that offers secure, device-agnostic, and performant connectivity.