CTF Mugardos 2015 Writeup – Crypto100

And lets reopen the blog with the first writeup of the CTF that took place in 2015 at the Kernel in Mugardos.

Statement:

When does the trope open? 100 points

When does the trope open? I wanna dance!

Format of the answer:
– SHA256 of the flag
– Lowercase
– No spaces

Solution:

In this challenge they provided the following image:

crypto100

My first impression was, ¿What the …? Thinking that maybe the organization didn’t copy/paste each stickmen I did several searches in google for fonts done with them. Found several ones but  an specific one matched exactly and on its detailed information said that it was based on a message shown in one of Sherlock Holmes novels.

Font: http://www.fontspace.com/martin-bergman/dancingmen

As the website already shown the alphabet with all the stickmens that we needed I directly translated each stickmen to its corresponding letter obtaining the following message:

jvxlif hlv jz ruvdrj tzwirdfj vjkf tfe rcxle dvkfuf tcrjztf tfdf trvjri jvir dltyf drj wfidrj gfi jz rtrjf cr tcrmv vj mzmrvcglcgf

A quick Caesar bruteforce showed that it was a Caesar with key 17. We got the following message:

seguro que si ademas ciframos esto con algun metodo clasico como caesar sera mucho mas formas por si acaso laclave es vivaelpulpo

In English it will be: “if we also cypher this with a classic method like Caesar it will be mucho more forms just in case the password is longliveoctopus”

Doing the SHA256 of the string “vivaelpulpo” it will show the flag we need.

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