Senior Crypto Developer (Java / Blockchain)

📍 Location: Warsaw, Poland (Hybrid 2-3 days/week from the Warsaw office)
💼 Employment Type: B2B Contract
🚀 Start Date: Immediate

About the Role

We are looking for an experienced Senior Crypto Developer to join an innovative team building next-generation blockchain and crypto-enabled payment solutions. You'll be responsible for designing, developing, and maintaining secure, scalable, and high-performance distributed systems while contributing to the full product lifecycle—from architecture through deployment and ongoing support.

This role is ideal for someone with deep Java backend expertise, strong blockchain knowledge, and experience delivering enterprise-grade financial applications.

Responsibilities

• Design, develop, and maintain crypto product capabilities end-to-end.

• Build scalable, secure, and highly available distributed systems.

• Develop and integrate REST APIs, orchestration services, and third-party integrations.

• Implement blockchain-based solutions using modern crypto technologies.

• Work with smart contracts and Ethereum Virtual Machine (EVM)-based platforms.

• Participate in architecture discussions and technical design decisions.

• Ensure software quality through unit testing, performance testing, and CI/CD pipelines.

• Monitor application performance and implement observability, alerts, and high availability strategies.

• Collaborate with cross-functional teams to deliver secure and reliable solutions.

• Contribute to ongoing product improvements and production support.
  

Required Skills & Experience

• 12+ years of professional software development experience.

• Strong backend development expertise using Java.

• Experience building large-scale distributed systems and microservices.

• Strong understanding of:

  • Blockchain technologies (Bitcoin, Ethereum, Hyperledger, etc.)

  • Distributed Ledger Technologies (DLT)

  • DeFi applications

  • Security protocols

  • Private key custody

• Hands-on experience with:

  • Solidity

  • Ethereum Virtual Machine (EVM)

  • Smart contract development

  • Assembly (preferred)

• Strong knowledge of Secure Software Development Lifecycle (SSDLC).

• Experience with Git, CI/CD pipelines, automated testing, and performance optimization.

• Understanding of monitoring, logging, and high-availability architectures.

• Experience working within payment systems or financial services is highly desirable.

• Excellent communication skills and ability to collaborate with technical and business stakeholders.

• Strong analytical and problem-solving skills.
  

Nice to Have

• Full-stack development experience.

• Strong frontend development using Angular.

• Experience with cloud platforms and containerized environments.

• Knowledge of payment processing flows and financial regulations.