# Decipher the clues, escape the prison!

The guard at the prison, where you have been locked up for misuse of USB ports, has given you one chance to escape, by typing in a certain word. A keyboard is put down in front of you, and you are shown a sheet that reads as follows:

You never know where the key will be hidden, it could be right between your eyes...
[20][1E][23][1F]

THE WORD

Much like a Vigenere cipher, yet the letters are numbers!

[1L][1H][2M][16][13][08][06][17][15][18][10]

What should you type in?

HINT 1

The part about 'right between your eyes' applies to the word only, not the text in the first code block.

HINT 2

The guard is quite nice and has given you, being a USB expert, nothing too hard.

HINT 3

Surely someone knows a cipher like a Vigenere cipher but with numbers as letters.

• "right between your eyes" refers to either "nose" (the length of which matches the exact amount of [] blocks in the first row). or it is some red herring... hmm... Dec 18, 2015 at 15:16
• @BojidarMarinov or it might be the letter 'G' coz it is in the middle of the keyboard in all the alphabets. Dec 18, 2015 at 16:54
• Pretty sure he's referring to a Gronsfeld cipher. Jan 8, 2016 at 18:00
• @dpwilson Of course it is! Jan 8, 2016 at 20:08
• I feel like I'm close, but I just can't figure out the "USB expert" hint. :/ I've looked at the USB logo, read quite a few USB "fun facts". Skimmed through the Wikipedia page, but found nothing of use. One thing I thought about was whether the presence of a keyboard has a significance. Maybe the alphabets used in the Gronsfeld cipher are "QWERTY.." instead of "ABCDE..". I've tried changing letters to numbers by having E = 0, M = 8; E = 1, M = 9; letter = number of its column on keyboard (e.g. QAZ all = 1) - to then have numbers between 0-25 or 1-26 in the square brackets, but that didn't work. Jan 15, 2016 at 16:57

I think the word is

SPECTRUM

The first block is

just a hint that the encrypted text is base 16.

Since I am a USB expert,

I know how to read in base 16. And when I convert the legal blocks in [1L][1H][2M][16][13][08][06][17][15][18][10] from base 16 to base 10, it results as 22 19 8 6 23 21 24 16. When we convert these decimal numbers to letters in English alphabet, we get WTIGXVYQ.

Then, by using

Caesar cipher, I shift the letters by 22 to get SPECTRUM

• Interesting find, but I suspect this is only a partial answer, since it doesn't make use of the first code block, nor does it use a Gronsfeld cipher. Jan 23, 2016 at 22:47
• Does the second part not count as Gronsfeld? I think first block is just a distraction Jan 23, 2016 at 23:23
• Converting bases is not Gronsfeld. Caesar is a special case of Gronsfeld, but I doubt that's what the question is referring to. I hope the first block isn't a red herring, but then what do I know? Jan 23, 2016 at 23:41
• Not about converting the base, but converting numbers to Letters, as far as I know is Gronsfeld. I might be wrong, of course. Jan 24, 2016 at 0:31
• Gronsfeld is Vigenere but using numbers instead of letters. Jan 24, 2016 at 1:05