Daily AlpacaHack

A daily CTF challenge with a fun new puzzle every day

What is Daily AlpacaHack?

We publish one simple, beginner-friendly or educational CTF challenge every day! Selected problems from external CTFs are released occasionally.

Join Anytime

Solve within 24 hours of release to appear on the leaderboard.

Not a Competition

Discussion with friends or AI is welcome (account sharing is prohibited).

Solution Sharing Rules

Sharing solutions is allowed only after 24 hours have passed since release (mirrored past challenges are excluded).

Solve stats

/49

0 solves (within 24h)

0 solves (after 24h)

No solved challenges yet.

Today's Challenge

Submissions (latest 3)

ken1220

SOLVED!

13:08:44

asdfsu

SOLVED!

13:06:41

usermendo

SOLVED!

12:41:55

Leaderboard

51.

17 solves

58.

16 solves

69.

15 solves

77.

14 solves

81.

13 solves

91.

12 solves

98.

11 solves

105.

10 solves

110.

9 solves

121.

8 solves

127.

7 solves

140.

6 solves

153.

5 solves

162.

4 solves

179.

3 solves

Try the first challenge

Is this your first CTF? Let's begin by tackling the first challenge released on Daily AlpacaHack.

Topics and categories are revealed in advance for upcoming challenges.

Jan 2026

Solved

Unsolved

Upcoming

Mon

Tue

Wed

Thu

Fri

Sat

Sun

kanon

one-p-rsa

Crypto

Easy

178 solves

soon-haari

RBG

Crypto

Very Hard

110 solves

admin

108

Misc

Easy

213 solves

admin

Happy New Year

Misc

Welcome

361 solves

kanon

super-tomato

Crypto

Easy

259 solves

hiikunz

Ruby Flag Checker

Rev

Easy

208 solves

minaminao

Fushigi Crawler

Web

Easy

232 solves

kurenaif

Encoding Basics

Crypto

Misc

Easy

215 solves

minaminao

jailiaj

Misc

Easy

201 solves

hiikunz

Square RSA

Crypto

Medium

181 solves

ark

secret-table

Web

Medium

199 solves

hiikunz

SwapSwap

Misc

Easy

210 solves

theoremoon

RSA2026

Crypto

Medium

166 solves

keymoon

crazython

Rev

Medium

150 solves

hiikunz

Basic Buffer Overflow

Pwn

Medium

137 solves

tchen

I wanna be the Admin

Web

Easy

173 solves

ark

free-comment

Misc

Hard

127 solves

hiikunz

Five Alpacas

Crypto

Easy

141 solves

k0080

Short Writer

Pwn

Hard

88 solves

minaminao

Base Length

Misc

Medium

107 solves

hiikunz

dice roll

Web

Medium

106 solves

chocorusk

Planned topicStream Cipher

Crypto

Medium

k0080

Planned topicSIMD

Rev

Hard

ark

Planned topicDocker

Misc

Easy

hiikunz

Planned topicClient-Side

Web

Medium

minaminao

Planned topicJail

Misc

Hard

yu212

Planned topicAES

Crypto

Medium

tchen

Planned topicJWT

Web

Medium

keymoon

Planned topicGit

Misc

Medium

chocorusk

Planned topicMatrix, SageMath

Crypto

Hard

tchen

Planned topicClient-Side

Web

Medium

k0080

Planned topicShellcode

Pwn

Medium

yu212

Planned topicLCG

Crypto

Hard

ark

Planned topicGeneral

Misc

Medium

Coming soon

Writeups

Writeup for I wanna be the Admin nemukemo ja I wanna be the Admin 20 hours ago
Writeup for Base Length mikusan ja Base Length 21 hours ago
Writeup for Short Writer mikusan ja Short Writer 21 hours ago
Writeup for Base Length kakur41 ja Base Length 21 hours ago
Writeup for free-comment (言語仕様等調べ付き) tan90909090 ja free-comment yesterday
Writeup for Short Writer kakur41 ja Short Writer yesterday
Writeup for Five Alpacas sh1m0 ja Five Alpacas yesterday
Writeup for Five Alpacas kakur41 ja Five Alpacas 2 days ago
Author's Writeup for Useful Machine tchen official en Useful Machine 3 days ago
Author's Writeup for I wanna be the Admin tchen official en I wanna be the Admin 3 days ago

Rows:

Emojify

Topic: Server-Side

441 solves

Web

Medium

Author:

ark

:pizza: -> 🍕

Beginner Hint 1: About Difficulty

This challenge is in the Web category, i.e., web applications.
Unlike yesterday's challenge, which was Easy, this one is Medium.
Daily AlpacaHack currently defines four difficulty levels: Easy, Medium, Hard, and Very Hard.
Medium is one step above Easy. If Daily AlpacaHack is your first exposure to CTF, solving it may be tough.
If you get stuck, feel free to lean on AI to find a starting point for the solution.
Even if you can't solve it, check other players' solutions (writeups) afterward to review and learn.
24 hours after release, a writeup tab will appear in the tab bar below.

Beginner Hint 2: Running the Challenge Locally

After extracting the attachment, you'll find compose.yaml, Dockerfile, and directories for three services.
Modern CTFs often ship a Docker Compose file so players can reproduce the remote environment locally.
From the root of the distribution, run docker compose up.
With default settings, the challenge server will start at http://localhost:3000/.
Use this local server to investigate vulnerabilities and to test the solver you build.

Beginner Hint 3: 問題を解くまでのアプローチ

まずはどのようなWebサービスが動いているかをソースコードを読んで把握するところから始めてみましょう。
ローカルで立ち上げた問題サーバーの振る舞いを確認しながら読むと理解が早いです。
サービスの挙動をおおよそ理解したら今度はゴールが何かを確認することをおすすめします。
フラグがどこにあって、何ができたらそのフラグを取得できるのかを考えると、その「何ができたら」を達成するのがこの問題の趣旨であるとわかります。
また、今回の問題サーバーはJavaScriptで書かれています。
JavaScriptの関数の細かい挙動などをあれこれ確認するには、JavaScriptを実行可能な対話環境があると便利です。
手元のターミナルでnodeコマンドを実行して色々実験してみましょう。
合わせて、使われているJavaScriptの関数の仕様を調べてみるのも有効でしょう。
MDNのドキュメント（https://developer.mozilla.org/ja/docs/Web ）は情報の精度や網羅性がしっかりしているので、情報リソースとしては有用です。

emojify.tar.gz

description solves writeups