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I recently made a self referential cipher (meaning that the key is the same as what is being decoded) a while back and was planning on putting it on here after making the cipher a bit more difficult. I actually decided to have a few more layers put on my puzzle before posting it on here as to not make it too easy. So, after putting it through Morse code a [redacted] amount of times, I present to you my self-referential cipher:

-....- -....- / -....- .-.-.- -....- .-.-.- / -....- .-.-.- -....- .-.-.- / -....- -....- .-.-.- / -..-. / .-.-.- .-.-.- .-.-.- / -....- .-.-.- -....- .-.-.- / -....- .-.-.- -....- .-.-.- / -..-. / -....- .-.-.- -....- .-.-.- / .-.-.- -....- / -..-. / -....- .-.-.- -....- / -....- .-.-.- -....- .-.-.- / .-.-.- -....- -....- / -....- -....- .-.-.- -....- / -....- -....- .-.-.- -....- / .-.-.- -....- / -....- -....- / -..-. / -....- .-.-.- -....- -....- / .-.-.- -....- -....- / -..-. / -....- .-.-.- -....- / .-.-.- .-.-.- / .-.-.- -....- -....- / -....- .-.-.- -....- / -..-. / .-.-.- .-.-.- / .-.-.- .-.-.- / -....- .-.-.- -....- / .-.-.- .-.-.- / .-.-.- .-.-.- / .-.-.- .-.-.- / .-.-.- -....- / -....- -....- / -....- -....- .-.-.- -....- / .-.-.- -....- / .-.-.- -....- -....- / -..-. / .-.-.- / -....- -....- .-.-.- -....- / .-.-.- / -....- -....- -....- / .-.-.- .-.-.- / .-.-.- .-.-.-

A perfect answer would include:

How to decrypt it

The final text.

Also the only reason I didn't just leave the cipher as it was for people to solve was only because it would just be too easy then IMO.

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1 Answer 1

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Taking off the Morse code produces: MCCG SCC CA KCWQQAM YW KIWK IIKIIIAMQAW EQEOII

Only even letters of the alphabet (ACEGIKMOQSUWY) appear. This is characteristic of a Vigenere cipher where the plaintext and key are identical. This is equivalent to an Affine cipher with M=2 and B=0, which is technically not allowed as an Affine key because there is no unique decipherment. That's fine because there are only two ways to decipher each letter. The two substitutions to use are:

Cipher:   ACEGIKMOQSUWY
Plain 1:  ABCDEFGHIJKLM
Plain 2:  NOPQRSTUVWXYZ

Apply each substitution to the ciphertext and choose the most likely of the two letters at each position to read out the plaintext.

Cipher:  MCCG SCC CA KCWQQAM YW KIWK IIKIIIAMQAW EQEOII
Plain 1: GBBD JBB BA FBLIIAG ML FELF EEFEEEAGIAL CICHEE
Plain 2: TOOQ WOO ON SOYVVNT ZY SRYS RRSRRRNTVNY PVPURR
Plain:   good job on solving my self referential cipher

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    $\begingroup$ How do you 'take off the Morse code' here? Thanks. $\endgroup$
    – Stiv
    Nov 14, 2023 at 6:57
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    $\begingroup$ @Stiv ROT13(-....- pna or fcyvg gb -.. .. - = QVG (pbashfvatyl hfrq sbe n qnfu), .-.-.- vf n Zbefr "." naq -..-. vf n Zbefr "/". Fb lbh pna qrpbqr gur Zbefr fgevat gb "QVGQVG QVG.QVG. QVG.QVG. QVGQVG. / rgp." juvpu orpbzrf "-- -.-. -.-. --. rgp" juvpu tvirf lbh gur "ZPPT ...") $\endgroup$
    – fljx
    Nov 14, 2023 at 10:03
  • $\begingroup$ @fljx Good job on not only solving the puzzle, but brute-forcing the Morse Code!! (I hid the vigenere cipher under 2 layers of morse code) Did not expect that to happen lol $\endgroup$
    – CrSb0001
    Nov 14, 2023 at 13:46
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    $\begingroup$ @CrSb0001 This isn't my answer. $\endgroup$
    – fljx
    Nov 14, 2023 at 13:50
  • $\begingroup$ @fljx oh sorry lol $\endgroup$
    – CrSb0001
    Nov 14, 2023 at 14:05

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