Backend Developer building real systems with Java and Spring Boot — focused on distributed systems, payment infrastructure, and clean API design.
🎓 B.Tech CSE (2023–2027) | Uttaranchal University
Offline UPI payments routed through a Bluetooth-style mesh network — no internet required anywhere in the chain.
A Spring Boot backend that solves three genuinely hard problems: stopping untrusted relay phones from reading or tampering with payments (hybrid RSA-OAEP + AES-GCM), preventing the same payment from settling twice when multiple phones upload it simultaneously (atomic idempotency via ciphertext hashing), and blocking replay attacks (encrypted freshness timestamps). Includes a concurrency test that fires 3 threads at the same packet and asserts exactly 1 SETTLED, 2 DUPLICATE_DROPPED.
Live demo: https://upiofflinemesh.up.railway.app/ | GitHub →
Java Spring Boot AES-GCM RSA-OAEP Idempotency Distributed Systems
Backend: Java, Spring Boot, REST APIs, Spring Security, Spring Data JPA
Database: PostgreSQL, MySQL, MongoDB, H2
Tools: Git, IntelliJ, Docker (basics), Postman
CS Fundamentals: DSA, OOP, System Design (basics)
- 150+ DSA problems solved in Java
- Focus: Arrays, Hashmaps, Binary Search, Sliding Window, Two Pointers, Trees, Graphs
- Platform:
- LeetCode → mukul_parashar
- Codeforces → mukul_parashar
- GeeksforGeeks → parasharmukul
- Deepening backend systems knowledge — idempotency, concurrency, API design
- Building toward ML/AI engineering after strong SWE fundamentals