Current Case Files

Case File 0.1

Nothing to see here yet, but keep your eye on this page, it is where we will post extra clues and hints to help explain the story and help you to crack the challenges.

The document in part A is a letter from Francois to Sarah, posted in reply to her questions about the broken photographic plate. It is lightly encrypted and if you look you can see that Francois has left the word shapes in place, which makes it easy to start to see patterns. There are a lot of three letter words of the form FTQ for example, and that is a very big clue! (Which three letter word appears most often in English text?)

Part B is made much trickier by the lack of word shapes, but you can use the same trick as you did for part A and look for common three letter strings to try and crack this cipher. It is another Caesar shift, so should be straightforward. Even better, just knowing the most likely common letter in English should be enough, and you can look that up in the Cryptanalyst handbook in the library.

Did you use the frequency counter on our tools page? If you did you should have seen that the character counts look a lot like the ones in the standard English alphabet, but shifted along as shown here. What does that tell you?

The most common three letter word in the cipher text is NZP so it is an excellent guess that this stands for “the”. A check on the frequency analysis tool tells you that N and P are very common in the text, with P being the most common, so that is consistent with them standing for t and e respectively. If we then make those substitutions using the substitution tool we get text that looks like this, and we can begin to recover the message! For example you will find the partially deciphered text includes the word “thDt” which suggests that maybe D stands for the letter a. Making that change we get something starting like the image here. As usual, lower case letters are plain text and upper case are cipher text. You could make a guess at how the letter might start to help you guess some more letters, or you can do something more sophisticated by tabulating the three and four letter words to see if you can make some more educated guesses. That takes you into the fabulous world of trigram and quadgram analysis and you can read much more about it in the guides in our library.

The mysterious EC appears to have been staying in the stylish new Hōtel Continental when he wrote his letter to the Prince of Wales. He hasn’t dated it because this was just his draft of the text. He had to encrypt it before it could be sent. He might have stayed at the somewhat more traditional Hotel Meurice, which was known as the Hôtel des Rois after Queen Victoria stayed there in 1855, but sadly the Prince and his mother did not get on and I suspect he found the new Hōtel Continental more congenial. It was modern and exciting, and I suspect the Prince might have liked the foreword looking atmosphere and the clientele.

Mrs Hartford is clearly a woman of style and substance. She knows what she needs and is accustomed to getting it. Here is the letter that Eli received, and you can see why he was impressed. (Mrs Hartford kept the typed decrypt in her personal files, which is why we have it here at BOSS. Perhaps that raises more questions than it answers, but we will leave it there for now.

As promised here is a note from Eli to Prof Vandiver. It has been enciphered by a Caesar shift cipher so you don’t actually read it if you don’t want to. If you read it carefully there are two important clues about how to tackle Challenge 3B. See if you can spot them!

Here is the decrypt of Eli’s message in case you had trouble deciphering Case File 3.1 (though I know that is not likely given we told you how it was encrypted.) You might find it helps with Challenge 3B.

Tackling Challenge 3B we sEli’s letter to Prof Vandiver mentions that the frequency analysis didn’t help and that should have told him something. Taking a look at the graph you can see what he means! The frequencies between the cipher text and natural English are incredibly close! That suggests that the cipher letter E probably stands for the plaintext letter e and the cipher letter T probably stands for t and so on. But in that case, why can’t we just read it? If the letters are all right they must be in the wrong order instead! It looks like Eli’s adversary might be using a transposition cipher.

TEZEM HNETI EIRND RTEBA AKSFA MTOOT WRAOR RDIBN BGAAN TWHIG EOCMS HOETL DAANS TOHOT SRHUB NOEUY ODDTE PSPAI WAERE PARNC DVEIO EOYNM YUOTB LWLIU DETEN NFDIO ROSUY SLOFE EEWNM SISGD UYCOO INELA FOOWL HAIWR FEYIL AUNWO CWAET XFYIN PUWUO STOHI AEPPM IRNSE WNNEA BMUEA ETNHT LOLUY EATVH MREEO RBTEM EUTSO NAATH UECMM SEIAH FRYIE UUSJO AHDET KAECB ISHTA YAORE VHEAU AETLR SVIEI OBORN NLMYK EYYBA OUUCO TDASL TWHIY MHRET MMBEE ORNNE TOHFE VSEEI PHPAR DNAEE TDWIN DUBLO RVYEE FAODB UYAOR ODRFN FSAIU NYEON UHGOT ITFDH EENRF DSOOT OTGGN ITNTE OANCG ECNIS NEDAC KAILT OGATN NYEON SUITO HEETD ARNGO TZIAI HNETO TAGSL HYOWU ERDIT LXAPE NNGII SIEMH OFBTL LGEDI ERDNA HHAET ADYWR THHAT EDSOE ITKLN CEUXE YEOSS SAOLU DETEN IBNRO ETKHG OYTTE TEOSH OEORR TWHIM WOEUY DETEN TGBEO OCUKA UEIQR NMTEP OERFB YAONE EETGN SNYOS SNTDA SRPTA NKGIO URNOA YIOFD DHNAU OBKRT TNWIE UWLOE BNETD HNITI SPIOS NIAOT ODUYN UECLR IYGBK NITSD IANKT ATTHG OUFTO ROWUY SGYEA HUOSO TLHDU ONFKI SHAIT EAALS NNGIR OPRPO IUTNT DABNY AGTRE LFTUE TAHTH SLSEE ONMCO RSEFE COHFE EROGA OERMN ITNHE EKPEG ROMUY HUSTO DUOTH ETTGN LOOLF AENDW NDTOD IACNP

Transposition ciphers can be very hard to break, but in this case the cipher is not too bad. Moreover Eli gave us a big clue! The message contains the phrase “relatives in Brooklyn” and that should be fairly distinctive. As long as the permutation uses fairly short blocks we might be able to find a group of cipher text characters that contains some part of that phrase jumbled up.