Crypto Trading Interface Development

I'm seeking an experienced backend developer to create a trading interface for crypto assets, compatible with both Android and iOS platforms.

Key Requirements:
- Interaction with Ethereum and Bitcoin blockchains
- Support for Buy/Sell order functionalities
- User authentication via email and password

Ideal Skills and Experience:
- Proficiency in blockchain technology, especially Ethereum and Bitcoin
- Experience in developing trading platforms
- Strong backend development skills
- Familiarity with user authentication protocols

The interface should be downloadable via Play Store (APK) and iOS (through configuration).

Please ensure the user experience is seamless and secure, as the target audience will be crypto-savvy individuals.