L2 switch, L3 routing, L4/L7 load balancer — where the layer numbers attached to everyday networking terms come from. How the OSI model maps to TCP/IP, and what each number refers to.

SwapDo, a deepfake-based face synthesis meme service. A record of five months as a developer and team lead in a startup team.

HTTP is stateless. Maintaining user authentication requires storing state somewhere. This post covers the structure, trade-offs, and storage strategies of server-side sessions and client-side JWT tokens.

There was a time I called JWT an authentication method and said I logged in with OAuth, and the terms kept blurring together. This post lines up Basic, Digest, API Key, Session, Token, OAuth, OIDC, and SSO by two questions: authentication vs authorization, and where the proof of identity lives.

A startup born from a casual League of Legends habit. From architecture design to desktop apps, a record of two people building a service that grew to 10,000 users over five months.

Entering the GDG Korea Android 11 Hackathon solo, building both server and app in three weeks.

Korea Railroad Industry Information Center’s public-data hackathon. A three-person team built an Android app that surfaces hidden rest spaces inside subway stations, over three weeks.