InfoSec | Crypto Challenges | CarolinaCon 2018

After we paid our registration fee and received our con bag, we were told that the crypto challenge was on the back of the program. We looked at the back of the program and saw what we, incorrectly, assumed was the starter:

This was, in fact, the entire crypto challenge and took us a little longer to solve than we originally anticipated.

Part 1:

We promptly began working on this puzzle and started at the top:

KSZQCAS HC HVS QOFCZWBOQCB TCIFHSSB QFMDHC DINNZS. SOQV GHOUS KWZZ USH KCFRWSF OBR GVWTHWSF PIH WH KWZZ AOYS GSBGS.

A cursory frequency analysis indicated that this was most likely the result of a rotation cipher. The multiple occurrences of "ZZ" and the two letter words were fairly good indicators. We began iterating through Caesar Shift N values until we arrived at a deciphered message when N=12:

WELCOME TO THE CAROLINACON FOURTEEN CRYPTO PUZZLE. EACH STAGE WILL GET WORDIER AND SHIFTIER BUT IT WILL MAKE SENSE.

Part 2:

With the first part of the message deciphered, we proceeded to the second part of the message:

RRK, UQ XLEX ZDV TYEPCPDETYR, ZDV KV QRW? DQG QRW B YOTMRK ANONANWLN VQ WKH IXEVZU VAFFRK GAZNUX (BHW), ZKR OXMYEBKQOC BRX VQ TPEC JEMV IZIR ZNUAMN JG KU QRW ZXNSL B XTIGNIQZ IOVNKX XLMW CIEV.

At first, this message also resembled the result of a simple rotation cipher. However, we quickly realized that wasn't the case after we'd iterated through all values of N without a clear message being revealed. For example, this was the result when N=12:

DDW, GC JXQJ LPH FKQBOBPQFKD, LPH WH CDI? PCS CDI N KAFYDW MZAZMZIXZ HC IWT UJQHLG HMRRDW SMLZGJ (NTI), LWD AJYKQNWCAO NDJ HC FBQO VQYH ULUD LZGMYZ VS WG CDI LJZEX N JFUSZUCL UAHZWJ JXYI OUQH.

While iterating through values of N, we did notice that some words would be deciphered, but the complete message was never deciphered. See what happened when N=2:

PPI, SO VJCV XBT RWCNANBCRWP, XBT IT OPU? BOE OPU Z WMRKPI YLMLYLUJL TO UIF GVCTXS TYDDPI EYXLSV (ZFU), XIP MVKWCZIOMA ZPV TO RNCA HCKT GXGP XLSYKL HE IS OPU XVLQJ Z VRGELGOX GMTLIV VJKU AGCT.

We saw similar occurrences for other values of N, but never a completely deciphered message. Fortunately, the previous message contained a hint:

EACH STAGE WILL GET WORDIER AND SHIFTIER

Between the hint and what we observed by iterating through values of N, it seemed that there was some relationship between word length (wordiness) and the value of N (shiftiness). We concluded that we could decipher different parts of the message using different values of N and then combine the deciphered words to reveal the entire message. We also concluded that the value of N used would decipher words with the same number of letters as N. So, we were able to determine the following:

Reassembling the words revealed the deciphered message:

OOH, SO THAT WAS INTERESTING, WAS IT NOT? AND NOT A SINGLE REFERENCE TO THE CRYPTO PUZZLE AUTHOR (YET), WHO ENCOURAGES YOU TO PLAY FAIR EVEN THOUGH HE IS NOT USING A PLAYFAIR CIPHER THIS YEAR.

At least we knew we wouldn't have to worry about using the playfair cipher this time!

Part 3:

Having successfully deciphered the first two parts of the message, we looked at the third part:

MYZ LYV WKZN YQXBGLLGD SA CB ZVGFW UEI BRMGLMQS NJVRNTDL BDVW L GIL. VWKV DINK AKMN TQFM UEI EAWP QBHHYE HFFS JBFIEV YMI XDUTT CNQF. PM, UEI EGFHM VXHWT BDRR VQI UEI DEVFAJ KOWXCUWKJZX NYP UEI BFQI ER UEI PVVAKHCDHPBZ CMA ZLPEIH'Z RLEVDFODEV VHGFX MI UEI ACL. DZUUC UY CMA TIU WJGFW.

Due to the presence of punctuation and the letters being grouped in common word lengths, we concluded this was another rotation cipher. We tried using the methods employed previously; however, we did not get any meaningful results. We began to suspect that the message was the result of a keyed Caesar Shift and performed a frequency analysis and calculated the index of coincidence. Ultimately, we determined that the key length was most likely 37 characters.

We struggled to find a key that long until we saw G.Mark's hint on Twitter late that night:

We looked at the conference schedule and saw that he was only giving one presentation. We noticed that without spaces or punctuation, his presentation title was 37 characters:

blockchainthenewdigitalswissarmyknife

Using that as the cipher key resulted in the following alphabet:

BLOCKHAINTEWDGSRMYFJPQUVXZ

Once that was determined, we were able to use the same method from Part 2 to decipher the message:

NOW YOU HAVE IMPRESSED ME BY USING THE SHIFTING ALPHABET WITH A KEY. THAT IDEA CAME FROM THE GCHQ PUZZLE BOOK NUMBER ONE THREE ZERO. SO, THE FINAL STAGE WILL USE THE GERMAN TRANSLATION FOR THE WORD OF THE ILLUSTRATION AND SUNDAY'S FRANCISCAN SAINT OF THE DAY HURRY UP AND GET GOING.

This deciphered message contained several hints which would be critical to successfully deciphering the final part.

Part 4:

The deciphered message in Part 3 provided us with two good hints that we would need to decipher the final part of the message. The hints were:

The German translation for the word of the illustration

Sunday's Franciscan Saint of the Day

The second hint was a bit more straightforward, so we addressed that one first. Having had a significant amount of exposure to the Catholic Church when I was younger, I knew that the different religious orders with the Church had their own lists of Saints, and that the Franciscans were one of those orders. That knowledge made it relatively simple to find that the Patron Saint of Sunday within the Franciscan Orders is Cesar de Bus. An image search for "Cesar de Bus" quickly revealed that the man depicted in the portrait on the program is Cesar de Bus. Based on this, we assumed this meant the message in part four would employ the use of the Caesar Shift.

Having discovered the meaning behind the portrait on the program, the only other illustration left was the speed limit sign. It was clear that was the illustration for which we needed to have the German translation. Fortunately, I studied German for many years, which made this relatively simple. The translation for Speed Limit is "Geschwindigkeitsbegrenzung" and the translation for fourteen is "Vierzehn."

Armed with good hints to complete our task, we looked at part four of the message. We immediately encountered an issue; it wasn't written in English!

Again, being well-versed in the German language, I recognized the Old German typed letters. We were able to quickly overcome this initial obstacle and transcribe the provided text into Latin letters:

Ska ihkk fvgdgfk jy bsav qcwynkhqupl! Xcpn ephxj gws btki rmz ver dl vgfk hmf gws nkq.

Since the rest of the message was deciphered using some form of Caesar Shift and one of the hints for this part was "Cesar," we thought that would be a good starting point for this part of the message. Unfortunately, the Caesar Shift and the shifting Caesar Shift did not work. We then attempted to use the keyed Caesar Shift to decipher the last part of the message.

Using the key from the last part of the message did not produce anything. We then tried "Geschwindigkeitsbegrenzungvierzehn" as the key, but that didn't produce any results, either. At this point it became clear that this part of the message could not be deciphered using the Caesar Shift.

Since we were provided two hints in the last part of the message, we started to think that we might need two things in order to decipher the message. We also acknowledged that the deciphering method became more complex, within the realm of Caesar Shifting, as we worked on each part of the message, so we should expect that to be true for part four. Considering those things, we then attempted to use a keyed Vigenére cipher to reveal the final part of the message. The Vigenére is a more complex version of the Caesar Shift, since it has a variable N value which changes for each letter. Additionally, the keyed version of this cipher requires two things: a keyed alphabet and a passphrase.

In order to decipher the final part of the message, we used the keyed Vigenére cipher with the following parameters:

Keyed Alphabet - Geschwindigkeitsbegrenzung

Passphrase - caesardebus

The deciphered message:

You have arrived at your destination! Tell gmark you know the age of oban and you win.

Both of us being connoisseurs of fine whisky, we immediately knew the answer to the final question. So we hastily set out to find G. Mark and inform him that the Age of Oban is 14. Fortunately, when we located him, we learned that we were the first to complete the challenge.

After a pleasant conversation about the challenge and what we did to solve it, the conference, and ourselves over a bit of Scotch, we were officially declared the winners. We were given the bottle of Oban (well, what was left of it...) and a copy of the GCHQ Puzzle Book. Then it was time to pose for the camera:

A few months later we also received a nice plaque: