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.