Hi, I'm Chandan Paul
I build and own backend systems end to end API design, data modeling, deployment. On live products I've cut API response times from 800ms to 120ms with Redis caching and queue workers, and shipped complete payment backends across Stripe, PayPal, SSLCommerz, and Toss.
Who I Am
4 years shipping
industrial products
Four years in, most of my work has been the part users never see: REST APIs, service layers, queue workers, and the third-party integrations that quietly hold a product together. I've delivered for government, travel, e-commerce, and enterprise clients — mostly Laravel, with Django REST and NestJS where the job called for it.
Payments are where I go deepest. Subscription billing, metered usage, refund and chargeback flows, and replay-safe webhook pipelines — the kind of work where one idempotency bug costs real money. I've integrated both global and Bangladesh-local gateways, and handled the reconciliation and failure paths behind them.
My master's in Information & Cybersecurity at the University of Dhaka shapes how I design everything else. My thesis, PhishLens, fine-tuned a Llama 3 8B multimodal model for real-time phishing detection, outperforming single-modality baselines across datasets.
Chandan Paul
Full-Stack Backend Engineer
What I Work With
Skills & Technologies
Payments & Integrations
Languages
Databases
Frameworks
Security
Tools
Soft Skills
Career
Work Experience
Freelance
Full Stack Developer
Independent contract work for small businesses and startups
- As per requirements
Building and maintaining production-grade web applications for clients across multiple industries.
- Designed and built Laravel REST APIs consumed by Flutter and React.js clients
- Cut API response times from 800ms to 120ms using Redis caching and queue workers
- Built payment backends with subscription billing, refunds, and replay-safe webhook handling
- Integrated third-party services: Stripe, SSLCommerz, FCM, Brevo, Twilio
- Reviewed code and mentored junior developers
What I've Built
Software Projects
NestJS backend for a Korean luxury silver e-commerce platform, handling dual product lines (standard and fully customizable items), deposit-based payments via Toss, and Kakao AlimTalk/SMS order notifications.
- Dual product-line logic (standard + custom orders with delivery/pickup rules)
- Deposit-based payment flow via Toss with 24-hour expiry
- Kakao AlimTalk & SMS notifications with automatic failover
- Order fulfillment state machine across production, pickup & delivery
Smart Governance System
Ministry of Commerce, Bangladesh
Government platform that digitized manual workflows of trade organizations — document submission, status tracking, and official communication.
- Requirement analysis with ministry officers
- Laravel controllers & Eloquent models
- Bootstrap-based UI with dynamic forms
Sole-architected backend using Service Layer pattern, serving Flutter and React.js clients. Built for reliability under production load.
- Service Layer pattern with REST API
- SSLCommerz payment & webhook
- Redis caching + queue workers
- Health checks and structured logging
Laravel API backend serving a Flutter mobile app and React admin panel for Crown Cement, covering campaign registrations, OTP-based authentication across local and international channels, WhatsApp/SMS notifications, and a construction knowledge content system.
- Built dual-channel OTP authentication - SSL Wireless for local numbers, Twilio WhatsApp/SMS for international
- Designed campaign registration and Meet & Greet workflows with role-based admin permissions
- Integrated Firebase push notifications and WhatsApp/SMS messaging pipelines
- Set up CI/CD via GitHub Actions for automated deployment on shared hosting
- Resolved production data migration and shared-hosting infrastructure constraints
Tour Booking platform for an Albania-based tour agency, handling tour packages, destination browsing, and deposit-based bookings with Stripe and PayPal payment processing.
- Built booking and payment flow supporting deposit-based reservations
- Integrated Stripe and PayPal for international payment processing
- Developed tour package, destination, and category management system
- Implemented admin panel for managing bookings and content
Asset Tracker
Internal asset management system built with Django REST Framework and Vue.js, tracking company assets with QR-based mobile scanning and a dynamic, permission-based access control system.
- Dynamic role-based permission system (default-deny)
- Mobile QR scan endpoint for asset lookup
- Async SMTP fix with timeout handling
- Docker-based deployment & cross-team coordination
Multi-service corporate website for a Saudi Arabia-based company spanning construction, skilled manpower supply, garments, and IT solutions, with a linked e-commerce storefront.
- Multi-service content architecture (construction, manpower, garments, IT)
- Bootstrap-based responsive frontend
- Multi-language content support (Arabic testimonials, English UI)
- Linked e-commerce storefront integration
Simple Cash-on-Delivery e-commerce funnel for the Bangladesh market, with a Filament-powered admin panel for order and delivery management.
- COD order flow with tiered delivery pricing (Dhaka / outside-Dhaka)
- FilamentPHP admin panel for order management
- Bengali-language customer-facing checkout
- Terms, refund policy & order confirmation flow
Ticket and incident management system with role-based permissions, automated escalation rules, and PDF/Excel reporting, deployed to production
- Role-based access control (Spatie permissions)
- Automated ticket escalation rules
- PDF/Excel report generation
- Production deployment
Video Hosting Platform
Video hosting and streaming platform with CDN-based delivery, background video processing, and a published mobile app.
- Full technical scope withheld under client agreement
Security Work
Cybersecurity Projects
PhishLens — Multimodal Phishing Detection System
Multimodal phishing detection framework combining URL analysis (DeBERTa), HTML structure analysis (ELECTRA), visual page analysis (CLIP/YOLOv8), and LLM-based explainability (Llama 3 8B) to detect phishing sites with human-readable reasoning, outperforming single-modality baselines. Developed as a master's thesis targeting IEEE TDSC/TIFS publication.
Multi-Agent RAG Poisoning Research
Security research into how poisoned documents propagate through multi-agent RAG pipelines, where each agent trusts and re-states the previous agent's output. Built the three-agent LangGraph pipeline and the end-to-end baseline evaluation harness benchmarking local Llama models against Claude on HotpotQA and SQuAD.
Web Application Vulnerability Assessment
Performed black-box VAPT on a sample e-commerce application. Identified OWASP Top 10 vulnerabilities including SQL injection, XSS, and IDOR.
TryHackMe — Pre-Security Path
Completed the Pre-Security learning path covering networking, Linux fundamentals, and web fundamentals.
ShieldGuard — Malicious Chrome Extension Detector
Full-stack cybersecurity platform for detecting and risk-scoring malicious Chrome extensions, combining threat intelligence, malicious domain matching, and AI-powered permission analysis. Built to demonstrate full-stack and security engineering skills.
SecureChat — End-to-End Encrypted Messaging
Real-time chat application with client-side end-to-end encryption for direct messages, using ECDH key exchange and AES-256-GCM via the Web Crypto API. The server stores only ciphertext , no plaintext ever reaches the backend.
VaultLock — Password Manager
Client-side encrypted password manager using PBKDF2 key derivation and AES-256-GCM via the Web Crypto API. Vault data is encrypted in the browser before it ever reaches the server, which stores only ciphertext and per-user salts.
Credentials
Certifications
Cisco Certified Network Associate
Cisco · Cisco Certification Exam
Mastering Cybersecurity: A Complete Guide from Beginner to Expert
TechSight · TechSight
IELTS Academic (CEFR B2)
British Council
Academic Background
Education
Professional Master's in Information & Cybersecurity
University of Dhaka
Graduate coursework spanning software security, digital forensics, applied cryptography, cloud security, and cybersecurity law, culminating in a capstone research project on multimodal phishing detection.
Bachelor of Computer Science & Engineering
Independent University, Bangladesh
Built a strong foundation in computer science fundamentals — data structures, algorithms, databases, and system design — with an elective focus on cryptography and network security that led directly into graduate cybersecurity study. Minor in International Business.
Get In Touch
Let's Talk
Have a project in mind, want to collaborate, or just want to say hello? I'm always open to discussing new opportunities.