Senior Backend Engineer (Java / Spring Boot / Zero-Knowledge)

About the Role

We are looking for a Senior / Middle Backend Engineer (Java) to join a Client’s team building a Zero-Knowledge backend.
The goal of this role is to build a “blind server” — a system that never sees user secrets and stores only encrypted data.

👉 Our priority is a Senior-level engineer, but we are also open to strong Middle candidates with solid backend fundamentals and growth potential.

Location: Remote
Cooperation Type: Full-time, long-term
Experience Level: Senior / Middle
Start: ASAP

Responsibilities

• Design, develop, and maintain high-load backend services using Java and Spring Boot
• Build scalable and secure APIs with a focus on privacy and performance
• Work with event-driven and real-time systems (WebSocket, gRPC, message brokers)
• Implement privacy-preserving and security-first backend logic
• Design and optimize data storage layers (PostgreSQL, Redis, Cassandra / ScyllaDB)
• Minimize metadata and sensitive server-side logging
• Implement anti-abuse mechanisms without PII
• Ensure high availability, fault tolerance, and scalability
• Participate in architecture discussions and technical decision-making
• Collaborate with mobile, security, and DevSecOps teams
• Write clean, maintainable, and well-documented code

Requirements

• 4+ years of backend engineering experience with Java
• Strong hands-on experience with Spring Boot
• Experience building RESTful or real-time APIs
• Experience working with PostgreSQL
• Experience with Redis or other in-memory stores
• Experience with high-load or distributed systems
• Solid understanding of backend security, authentication, and scalability
• Experience with message brokers or event-driven systems
• Ability to work independently and take ownership
• English: Upper-Intermediate or higher

Nice to Have

• Experience with Zero-Knowledge systems
• Experience with cryptography or privacy-first architectures
• Experience with Cassandra / ScyllaDB
• Experience with WebFlux / Reactive programming
• Experience with MQTT / XMPP / Centrifugo
• Experience with Blind Signatures or Private Set Intersection (PSI)

What We Offer

• Competitive compensation according to your experience (gross system)
• Fully remote work and long-term cooperation
• Opportunity to work on a privacy-first, security-critical product
• Ownership over core backend systems and architecture
• Fast hiring process and quick start
• Supportive engineering culture focused on quality, ownership, and impact

What happens after you apply

• Quick CV review
• Short recruiter call
• Technical interview with LITSLINK team 
• Fast decision & offer