You wake up in a bed - not yours - your eyes squinting from the bright sun in the window. It’s an escape room, you ponder. I need to find a clue. A piece of paper is taped to the window, containing an encrypted first word:
KZIPIPJL VNWRRYQRWRBM UO PSBMSF OA IPBM TUIPYIET JLWRTUVNIPPSETSF.
There is a single letter we need, to escape out free. You only get one try, so think about it for your prize.
First posted on my Twitter.
The single letter is:
O.
First observation:
The cipher text has two rather long words of 12 and 16 letters respectively. It also lacks single- and three-letter-words, which often provide a way into cracking a cipher, especially when they are at the beginning ("I", "you", "the", "a"), but there are two two-letter words, which might be prepositions.
In fact, all word lengths are even, which suggests that we are dealing with letter pairs:
KZ IP IP JL / VN WR RY QR WR BM / UO / PS BM SF / OA /
IP BM / TU IP YI ET / JL WR TU VN IP PS ET SF
Second observation:
Several pairs occur more than once. For example, there are five IP's. And no other pairs begin with an I or end with a P. It seems that there is a connection between the two letters and that the first letter determines the second. (The reverse is not true: both QR and WR end in an R.)
The cipher:
The cipher uses the three rows of letters of a QWERTY keyboard, strung out in a single line, like so:
...QWERTYUIOPASDFGHJKLZXCVBNM...
Then for each pair, we take what's between the first and second letter in that string of letters. For example the first pair KZ yields the letter L, which is in the middle of the sequenceKLZ.
L O O K / B E T WE E N / I / A N D / P / O N / Y O U R / K E Y B O A R D
That gives us the letter O, of course, which is fitting: O is the most frequent letter in the message, encoded by IP.
(I first suspected that there is a typo in the second word, but a pair can encode more than a single letter if the keyboard layout permits it. E follows W in the keyboard string, so we can encode WE as QR as the central stretch of the sequenceQWER. Neat. I guess that the key string is circular, so that M and Q would become NQ and MW, but the message doesn't use these letters.)
Mild criticism of the puzzle:
The keyboard is a useful device for puzzles, because for most of us, it's in plain sight, but we don't really think of it. But, but, ... your story describes an escape-the-room setting – without a keyboard. It's probably not so easy to remember all the details of the keyboard layout. Also, how does the protagonist communicate the answer? If you placed a keyboard in the setting, that might solve this problem and provide a hint. Well, never mind, that's just something that irked me.
