You are gathered around the latest victim with your partner. This has been the fourth one this month, and yet you are no closer to solving the mystery. The victim is a history student, apparently lead into one of the janitorial closets and killed. The method isn't obvious and you are still waiting from a report from the morgue about any of the previous ones. Your partner notices something.

Look! There's a small slip of paper in the victim's hand!

Indeed there is. You take a closer look at it and discover it has a note on it. Maybe it is a crucial clue.

521b why how

It makes no sense. You can't see any meaning to this note. You consult your partner about the previous victims, trying to find a pattern.

The first victim was a computer scientist.

The second victim was a mathematician.

The third victim was a chemist.

The fourth victim, this one, was a historian.

There's no correlation, no motivation you can see that would connect them. You prepare to leave to mull over this information when you spot a note on the wall. Surely that wasn't there before. You would have noticed it earlier. It says:


This must be a clue! You take it from the wall and begin work on decrypting it.

What does the note say?

Hint 1:

You ask what each of the victims were studying to get more insight into the killer's motives. The first victim was studying text encoding. The second victim was studying Fermat's last theorem. The third victim was studying atomic bonds. The last victim was studying secret communication in the 20th century.

Hint 2:

Understanding how the victims relate to the note is essential to figuring out what encryption has been used.

Hint 3:

Consider the order in which the victims were killed and the order in which something is encoded.

  • $\begingroup$ Does it involve a substitution cipher. $\endgroup$ May 22, 2016 at 10:03
  • $\begingroup$ @SharadGautam No substitution cipher has been used. I'm going to add another hint. $\endgroup$ May 22, 2016 at 10:11
  • $\begingroup$ A killer choosing their victims depending on what they study must be seriously deranged. Not have I ever heard of this in a book or movie either! $\endgroup$
    – fffred
    May 22, 2016 at 12:22
  • $\begingroup$ Anyway, are you sure the mathematician was studying Fermat's last theorem? Not the little theorem? That would match RSA encryption. $\endgroup$
    – fffred
    May 22, 2016 at 19:45
  • $\begingroup$ @fffred RSA is not featured in this puzzle. This one is possibly too difficult to understand, so I'll add more hints to try to clarify if better. $\endgroup$ May 22, 2016 at 22:38

1 Answer 1



521b why how

I believe this is the setting for an Enigma cipher, which generates the following cipher text: RGWG RUDH VVRG RHFU PVVT VRCA JKVS RXPW YVPX TKRK UVJS MCNH QHMI DYNA FICC ZVTB RFCG YFRU QIOR AHFO QJON JJJ
depending on the order with which you use 'why' and 'how'. From here I am not sure where to go though

Old wrong answer
Here is a partial to get the ball rolling:


This is the han character 创 (chuàng) in UTF-16 hex encoding (as per the victim being interested in text encoding in the Computer Science field). According to google translate, used as a noun it means wound, cut, trauma or injury. This may mean the murder involved a knife or blunt-force trauma.

That's all I have so far

  • $\begingroup$ Nice attempt, though not right. Look at which victim the note was found on and reconsider what it could be. $\endgroup$ May 23, 2016 at 13:30
  • $\begingroup$ Well I am at a loss, I though the point was that 521b was CS, 'why' was Math, 'how' was chemistry, and the cipher was history. Not sure how the majors relate now $\endgroup$ May 23, 2016 at 13:35
  • $\begingroup$ Consider the fact that the note was only found with the historian and what the historian was studying as a first step for decrypting. The other majors will come later. $\endgroup$ May 23, 2016 at 13:37
  • $\begingroup$ Using the 3 first characters for the "message setting", an enigma emulator results in XHEDHYKEOAEPJCGFCCLPKLGQWGLMVWPASWAAVOKUAKFHXOBDZRPANHVNIPPLTJNWYSEQKFSYJHWDJGJOGMTA $\endgroup$
    – fffred
    May 23, 2016 at 16:47
  • $\begingroup$ @fffred What settings did you use? Did you set the reflector wheel to b, wheel order to 5 2 1, ring setting to w h y (or h o w) and and ground setting to h o w (or w h y)? This is what I did $\endgroup$ May 23, 2016 at 16:53

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