---
title: "How an authenticator generates a login code"
url: "https://reamcp.dev/en/cases/how-an-authenticator-generates-a-login-code-f530d2"
source: "https://rea.tools/showcase/aegis"
source_type: "website"
author: "REA team"
author_handle: "REA team"
stars: 0
category: "CTF & learning"
categories: ["ctf-learning"]
tags: []
added: "2026-10-13T03:57:24.397Z"
updated: "2026-10-13T03:57:24.399Z"
locale: "en"
content_locale: "en"
---

# How an authenticator generates a login code

Follows the six-digit code calculation of the open-source Aegis authenticator through its released Android APK, and uses a demo clock to show why the code changes every 30 seconds.

## Description

Why it is listed: Official case study on an open-source (GPL) app in an authorized lab setting; educational.

## Original README

Inspect the Aegis Android APK with REA, recover its six-digit login-code calculation and try a reconstruction with an adjustable clock.