Cross-Platform Encrypted Messaging App

I'm looking for a skilled developer to create a secure messaging application similar to WhatsApp, available on both iOS and Android platforms.

Essential features include:
- End-to-end encryption for all messages and calls
- Group chats functionality
- Multimedia sharing capabilities (photos, videos)

Ideal candidates should have:
- Proven experience in developing secure messaging apps
- Strong knowledge of encryption technologies
- Expertise in mobile app development for iOS and Android
- Ability to implement group chat and multimedia sharing features

Please provide examples of similar projects you've completed and your approach to ensuring security and privacy.