kei5uke

Hello

3 min read

Matrix code rain 

kei5uke@blog:~$ whoami
> full-stack software engineer by day, CTF player by night
> passion: breaking things (ethically), then building them better
> status: hacking boxes and writing it all down

I’m kei5uke, a full-stack software engineer who also does security testing from time to time.

I live at the intersection of building software and breaking software — writing production code with one hand while finding its weaknesses with the other. When I’m not shipping features, I’m grinding CTFs, solving machines, and turning every shell I pop into a lesson.

Why this blog exists

Every machine I hack gets a writeup — the recon, the foothold, the privilege escalation, and the dead ends in between. If you want to learn offense, you have to practice offense, and the best way to sharpen it is to write about it.

Want to see what I’ve pwned so far? → All writeups live in CTF 🚩

CV

Contact Information

Email: keisuke.konno.tech AT gmail.com
GitHub: kei5uke

Skills

  • Programming Languages
    • Frequently used: JavaScript, TypeScript, Python, C
    • Previous experience: Java, PHP, C++, R, Go
  • Full-stack development (frontend and backend)
  • Infrastructure as Code: Ansible
  • Basic network engineering: TCP/IP, LAN/WAN
  • Algorithms and data structures
  • Implementation of machine learning and deep learning algorithms

Experience

Software Engineer / Penetration Tester

NTNU | HUNT Cloud, Norway · September 2025 - Present

  • Working on secure cloud platforms for sensitive data in medical and health research.

Software Engineer (AI/ML)

Flowstep OÜ, Estonia · 2024

  • Developed a web application that helps designers create better UI/UX using LLMs and computer vision.
  • Built the full stack with React and Node.js.
  • Fine-tuned a vision transformer model (SAM) for computer vision features using PyTorch and OpenCV.

Software Engineer (Full-stack)

Hemlex OÜ, Estonia · August 2022 - December 2023

  • Developed an educational web application for teachers and students.
  • Designed pages and components with React and TypeScript.
  • Implemented a RESTful API with Node.js and Express.js, including JWT-based authentication.
  • Tested the frontend and backend with Cypress and Jest.
  • Conducted OWASP-based security testing for XSS, SQL injection, authentication flaws, CSRF, broken access control, and more.

Research Intern, e-Healthcare Technology Lab

Turku University of Applied Sciences, Finland · August 2019 - February 2020

  • Built an e-healthcare application that lets patients with disabilities control home appliances with their brain waves.
  • Implemented it in Python using a deep learning model (Long Short-Term Memory network).
  • Conducted time-series analysis of patients’ biometric data, such as brain waves, body temperature, and skin resistance.
  • Wrote Bash scripts to collect sensor data from IoT devices.

Education

Master of Science in Cybersecurity

Tallinn University of Technology, Estonia · 2023 - 2025

Exchange Study

Norwegian University of Science and Technology, Norway · 2025

Bachelor of Science in Cyber Security Engineering

Tallinn University of Technology, Estonia · 2020 - 2023
Thesis: Multi-class Classification of Botnet Detection by Active Learning

Foundation Degree in Network Engineering

National Institute of Technology, Sendai College, Japan · 2015 - 2020
Thesis: Biometric Engineering Research: Biometric Measurement and Its Application

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