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MukulParasar/README.md

Hi, I'm Mukul 👋

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

🚀 Featured Project

UPI Offline Mesh

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: upi-offline-mesh-production-5c2a.up.railway.app  |  GitHub →

Java Spring Boot AES-GCM RSA-OAEP Idempotency Distributed Systems

🛠️ Tech Stack

Backend: Java, Spring Boot, REST APIs, Spring Security, Spring Data JPA
Database: PostgreSQL, MySQL, H2
Tools: Git, IntelliJ, Docker (basics), Postman
CS Fundamentals: DSA, OOP, System Design (basics)

📈 Problem Solving

  • 100+ DSA problems solved in Java
  • Focus: Arrays, Hashmaps, Binary Search, Sliding Window, Two Pointers
  • Platform: LeetCode → mukul_parashar

🎯 Currently

  • Deepening backend systems knowledge — idempotency, concurrency, API design
  • Building toward ML/AI engineering after strong SWE fundamentals

🔗 Connect

LinkedIn  ·  LeetCode

Pinned Loading

  1. upi-offline-mesh upi-offline-mesh Public

    Offline UPI payments over a Bluetooth mesh — Spring Boot backend with hybrid encryption, atomic idempotency, and a mesh simulator. No internet required.

    Java 1

  2. chatbot-api chatbot-api Public

    WhatsApp chatbot backend simulation using Java Spring Boot with REST API, predefined responses, logging, and live deployment on Railway.

    Java 1

  3. leetcode-java-solutions leetcode-java-solutions Public

    LeetCode solutions in Java showcasing consistent DSA practice with clean, efficient code for interview prep. For a structured and topic-wise view, please see the README.

    Java 1

  4. DSA-Bootcamp-Java DSA-Bootcamp-Java Public

    Forked from kunal-kushwaha/DSA-Bootcamp-Java

    This repository consists of the code samples, assignments, and notes for the Java data structures & algorithms + interview preparation bootcamp of WeMakeDevs.

    Java

  5. student-registration-system student-registration-system Public

    Full-stack Student Registration System built with React, Spring Boot, and MongoDB Atlas.

    Java 1

  6. task-manager-api task-manager-api Public

    JavaScript