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!

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.

Solve stats

/112

No solved challenges yet.

Today's Challenge

Submissions (latest 3)

tsuji1

SOLVED!

Mar 22, 5:53 AM

baumroll1234

SOLVED!

Mar 22, 5:39 AM

hiikunz

SOLVED!

Mar 22, 5:17 AM

Leaderboard

Period

Try the first challenge

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

Upcoming challenges reveal the , , and in advance.

Mar 2026

Solved

Unsolved

Upcoming

Mon

Tue

Wed

Thu

Fri

Sat

Sun

kakur41

Alpaca Quest

Rev

Medium

109 solves

minaminao

hit-and-hit

Misc

Medium

81 solves

tchen

Alpaca Rangers

Web

Medium

134 solves

kurenaif

One Byte Padding Oracle Attack

Crypto

Hard

69 solves

tchen

Rock Paper Scissors Lizard Spock

Web

Hard

90 solves

minaminao

pyjs

Misc

Hard

77 solves

admin

Alpaca meets QR

Misc

Welcome

232 solves

kakur41

Bars

Web

Easy

231 solves

tan90909090

glibc's secret function

Rev

Easy

162 solves

minaminao

Flag Printer 2026

Misc

Easy

166 solves

tchen

Alert my Flag

Web

Medium

139 solves

mora

magic number

Misc

Medium

108 solves

theoremoon

high and low

Crypto

Hard

80 solves

ark

guess.js

Misc

Hard

93 solves

minaminao

FLAG OVER

Misc

Medium

106 solves

ark

💯

Misc

Medium

106 solves

pppp4649

Find XOR key

Crypto

Easy

117 solves

colza

kappa overflow

Pwn

Medium

109 solves

tchen

Another Login Challenge

Web

Medium

108 solves

asusn

Heuristic IPPON

Misc

Easy

146 solves

minaminao

flag.txt

Misc

Hard

100 solves

pppp4649

The future path

Crypto

Medium

83 solves

tchen

Free Coupon

Web

Medium

116 solves

ark

PPPPParse

Misc

Medium

88 solves

rsk0315

Flags for the FLAG

Misc

Easy

119 solves

colza

canary leak

Pwn

Medium

75 solves

chocorusk

Alpacker

Rev

Hard

62 solves

k0080

vuln4vuln

Pwn

Hard

40 solves

kanon

Planned topicXOR

Crypto

Medium

Coming soon

Want a harder challenge?

Go to B-SIDE

Writeups

Writeup for Daily AlpacaHack 3/15-3/21 kakur41 ja The future path +6 2 hours ago
Writeup for Alpacker baumroll1234 ja Alpacker 14 hours ago
Writeup for canary leak colza author ja canary leak yesterday
Writeup for canary leak baumroll1234 ja canary leak yesterday
Writeup for Flags for the FLAG rsk0315 author ja Flags for the FLAG 2 days ago
Writeup for PPPPParse baumroll1234 ja PPPPParse 3 days ago
Writeup for Free Coupon baumroll1234 ja Free Coupon 4 days ago
Writeup for a fact of CTF masaki-fukura ja a fact of CTF 4 days ago
Writeup for Daily AlpacaHack 3/9-3/15 labpump ja FLAG OVER +6 4 days ago
Writeup for The future path pppp4649 author ja The future path 4 days ago

Rows:

a fact of CTF

Topic: Python, PrimeReleased: Dec 2, 2025

831 solves

Crypto

Easy

Author:

xornet

Show Tags

The very first challenge ever completed for AlpacaHack was never released because we adjusted the difficulty for the first Crypto round. (Organizers' note)

Beginner Hint

This challenge is in the Crypto (Cryptography) category.
AlpacaHack currently features four main categories: Crypto, Pwn, Rev, and Web; everything else goes into Misc.
Start by downloading the attached a-fact-of-CTF.tar.gz and extracting it.
In chall.py, the environment variable FLAG is read. This is the flag.
The flag is then transformed using prime numbers.
The output of chall.py is output.txt.
The goal is to recover the flag from the value in output.txt.

a-fact-of-CTF.tar.gz

description solves writeups