A challenge was posted via thirteen.club on Friday the 13th (September 2019) with a bounty of $50 in XMR.
The puzzle contains ascii art of Jason from the Friday the 13th movies, with what look like hex encoding below it.
54 57 39 79 61 58 52 31 63 6a 6j 67 64 47 55 67 55 32 46 73 64 58 52 68 62 58 56 7i
Several hints were posted, with one being at the botton of the page hidden in an HTML comment.
<!--
hint 1: the number thirteen
hint 2: Di = (Ei - Ki + 26) mod 26
hint 3: interwoven Caesar ciphers
Winners shall receive an email address or forwarder on thirteen.club. Whomever
solves this puzzle first receives $50 in XMR if you DM @dustyfresh the key
Thread: https://twitter.com/dustyfresh/status/1172542505713328128
!-->
These hints were posted with several tweets that offered some trolling, and more hints. Let's break each hint down:
#1 the number thirteen, okay that's not too helpful, is it?
#2 If we google Di = (Ei - Ki + 26) mod 26 we can see that it makes reference to some sort of shift cipher, the most common being Caesar's cipher.
#3 interwoven caesar ciphers.. if we google that we are able to see a lot of references to The Vigenère cipher
The author made more hints available via various tweets, if we paid attention. This tweet in particular references "The club's coat of arms" with the roman numeral XIII (13)..
If we take the broken hex and add it to Cyberchef and play around with vigenere we can shift the hex around but it requires a key..
Okay.. so given those hints let's try and use vigenere with the number 13. When we do this cyberchef informs us that the key must consist of only letters.
So we try XIII as the key, and then try to the Fromhex option in cyberchef we see that the following string is returned to us:
TW9yaXR1cmkgdGUgU2FsdXRhbXVz
This looks A LOT like base64, so then we try to decode it:
$ printf "TW9yaXR1cmkgdGUgU2FsdXRhbXVz"| base64 -d
Morituri te Salutamus
The answer to the challenge is Morituri te Salutamus, which is latin for: "Those of us who are about to die salute you."
I hope that you enjoyed this challenge, and I urge you to learn more about the club. More challenges and club information to be posted soon ;)
More on the thirteen club:
- https://medium.com/the-practical-mythologist/the-thirteen-club-what-did-a-jolly-gentlemens-club-have-to-do-with-friday-13th-6f85f1c8fcf
- https://www.theparisreview.org/blog/2015/03/13/morituri-te-salutamus/
- https://www.atlasobscura.com/articles/thirteen-club-superstition-new-york
Cypherpunks are welcome here