My professor Dr. Cryptic gave us a quiz today in class, and on it there was an extra credit opportunity. Most of the questions weren't too difficult to figure out; however no one in the class could decrypt the extra credit message. How do I decrypt the extra credit question?

The quiz:

  1. Decode the following messages:

    • "This uses a cipher."
    • "Guvf nyfb hfrf n pvcure."
    • "Fdtyr xfwetawp ntaspcd ymwqe ftuzse tmdpqd"
  2. Can you decode these too?

    • "14211302051819 011805 062114"
    • "0513020504040504 03091608051819 110215 181102141502"
  3. This one is a bit more tricky. (Not really but here is a hint 110525)

    • "Estd nx sqhbjx"

Follow the instructions in the following message. After doing so, you will receive 15 points of extra credit on the final for the class.

  • Wg quwrhyw dnnad fjdtcc rq lgu zrqdd xeo vxvl ahcwj dl kuubw iauu hxqswqymqdedd vixg lldcm cr fdzim whal vuyt wr vnduch wg sxy orrv chceh..

He also gave one final remark after passing out the test saying, "Remember, I am the key to unlocking knowledge. By using all of what I have taught you, you will be able to unlock even more."

  • $\begingroup$ First attempt at creating a cipher so any constructive criticism is welcome. Hopefully it isn't too hard or too easy. $\endgroup$ – Dragonrage Aug 18 '16 at 17:21
  • $\begingroup$ Sorry for the mess up on the cipher. Next time I will quadruple check it. $\endgroup$ – Dragonrage Aug 18 '16 at 20:20
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    $\begingroup$ My only criticism is that it's a bit bland IMO. I don't mean this as an insult - it's just that Caesar ciphers, A1Z26, and Vignere have been done to death. $\endgroup$ – Deusovi Aug 19 '16 at 0:10
  • $\begingroup$ @Deusovi hmm, ok. I shall have to think of something more unique next time then. I have actually never head of Vignere before. I just made up the cipher. $\endgroup$ – Dragonrage Aug 19 '16 at 0:32

I've got sections 1-3 so far:

"This uses a cipher." (Not enciphered.)

"Guvf nyfb hfrf n pvcure."

"This also uses a cipher." (rot13)

"Fdtyr xfwetawp ntaspcd ymwqe ftuzse tmdpqd"

"Using multiple ciphers makes things harder." (caesar 15 / caesar 14)

"14211302051819 011805 062114"

"numbers are fun" (two-digit alphabet lookup)

"0513020504040504 03091608051819 110215 181102141502"

"Embedded ciphers are harder" (first part is lookup, second part is lookup / caesar 16)

"Estd nx sqhbjx" "110525"

"This is tricky." (each word is caesar enciphered with a different value: 15, 21, 1) "110525" by lookup reads: "key" As Ronan noticed, (15 + 11) = (21 + 5) = (1 + 25) = 26.

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  • 1
    $\begingroup$ A note, the three different values for part 3 come from decoding the hint using the same technique as part 2a. $\endgroup$ – Ronan Aug 18 '16 at 17:57
  • $\begingroup$ I did not spot that. I've updated my answer with credit to you. $\endgroup$ – Juan Tomas Aug 18 '16 at 18:07

The decoded text for the last part is

To receive extra credit on the final you mmst bring at least five nonpishable food items to class next week to donate to the food drive.

The key is


which is

"cryptic" ("I am the key") advanced by one letter (rot-1)

However I solved it in a ridiculous way which means I missed something.

I used a vigenere autokey and typed the key over and over until it was as long as the plaintext.
Also there were three instances where I had to type dszqjd (without a "u").
So I am guessing this was encoded by hand (also "nonpishable" looks like it should be different).

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  • $\begingroup$ Oof! Missed it by that much! $\endgroup$ – Juan Tomas Aug 18 '16 at 19:19
  • $\begingroup$ Yea, I hand encoded it. Looks like I messed up a little bit. I will try to fix that. $\endgroup$ – Dragonrage Aug 18 '16 at 19:28
  • $\begingroup$ "Must" and "nonperishable"? $\endgroup$ – Ian MacDonald Aug 18 '16 at 20:08
  • $\begingroup$ Updated the cipher to be correct. I accidentally missed a rotation and messed everything up after it. Sorry about that $\endgroup$ – Dragonrage Aug 18 '16 at 20:19

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