Building your own instant messaging app is totally possible, but security should be a top priority from the start. Here are some essential safety measures to consider:

Security Measures for Messaging Apps
End-to-End Encryption (E2EE)

Use Signal Protocol (used by WhatsApp, Signal) for strong encryption.
Encrypt messages before they leave the device, so only sender and receiver can read them.
Secure Authentication

Implement OAuth 2.0 or JWT (JSON Web Tokens) for authentication.
Consider multi-factor authentication (MFA) to prevent unauthorized access.
Self-Destructing Messages

Allow messages to be deleted automatically after a set time to enhance privacy.
Metadata Protection

Even if messages are encrypted, metadata (who you talk to, when, etc.) can be exposed. Use Tor or a decentralized model to reduce tracking.
Secure Storage

Store messages encrypted at rest using AES-256 encryption.
Avoid storing unnecessary user data.
Network Security

Use TLS (Transport Layer Security) to encrypt data in transit.
Implement certificate pinning to prevent man-in-the-middle (MITM) attacks.
Permissions & Privacy Controls

Allow users to control who can message them.
Request only necessary permissions (e.g., avoid accessing contacts unnecessarily).
Open Source & Audits

If possible, open-source your encryption implementation for transparency.
Have security audits performed by experts.
Can You Build One on Your Own?
Yes, but it depends on:

Your experience: If you're comfortable with backend development, encryption, and networking, you can do it solo or with a small team.
Your goal: If it’s a personal project or for learning, you can start with existing frameworks.
Tech Stack & Resources
Backend:
Programming Languages: Node.js (Express), Python (Django), Golang
Database: Firebase, PostgreSQL, MongoDB
WebSockets: Socket.io (Node.js) or WebRTC for P2P
Frontend:
Mobile: React Native, Flutter, or native Android (Kotlin)/iOS (Swift)
Desktop/Web: React.js, Vue.js
Encryption Libraries:
Signal Protocol (via libsignal)
OpenPGP.js (for browser-based encryption)
Hosting & Deployment:
Cloud: AWS, Firebase, DigitalOcean
Messaging Server: XMPP (e.g., ejabberd), Matrix (decentralized)
Getting Started
Define Features (e.g., text, voice, video, self-destructing messages).
Choose a Stack (start with Firebase + WebSockets for simplicity).
Implement Encryption (use Signal’s protocol).
Build a Prototype (MVP with basic chat functionality).
Test Security (use penetration testing tools like OWASP ZAP).