The challenge was part of the NorthSec 2018 edition. This write-up has also been shared on the ctf repository, which seems to be slowly replaced by ctftime.org
- Category: forensic
- Points: 3
- Description: Can you decrypt the message on that picture?
For this challenge, you had to download the font displayed in the image and decrypt the message. Here is a table for the translation
After a lot of pain, and three eye surgeries… We resolve with some cryptic message that is spaced a bit like a normal language.
tivvgrmt hglk gsv urihh szou lu gsv uozt rh gsv mfnyvi gdl nfmwivw zmw hvevm ulooldvw yb gsv gdvougs ovggvi lu gsv zokszyvg. hglk mvcg rh gsv mfnyvi 3 zmw gsvm gsv hrcgs ovggvi lu gsv zlkszyvg ulooldvw yb gsv mrmvgvvmgs ovggvi hglk zoo oldvixzhv
You can see some pattern in the language, maybe some kind of permutation like in rot13. But it yielded gibberish for any kind of permutation.
You can decode it using an
atbash decipher to get the
message that lets you create the flag:
greeting stop the firss half of the flag is the number two mundred and seven followed by the twelfth letter of the alphabet. stop next is the number 3 and then the sixth letter of the aophabet followed by the nineteenth letter stop all lowercase
I think they obviously left some errors in the text, this font being very difficult to read.
That didn’t make me doubt and after following the instructions, it gave the flag
The Atbash Cipher simply reverses the plaintext alphabet to create the ciphertext alphabet. It was a substitution cypher used apparently to encrypt hebrew alphabet.