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A girl called Claire suddenly disappeared two weeks ago. She left strange notes before she left. Her parents asked everybody to help find their girl.

Last diary entries:

[12.02.2019]
Prep for mom and dad:
ABCD
AABC
BBCD
CDEF

[13.02.2019]
I can't see his face, he always wears black. Maybe he is French?

[14.02.2019]
The strange man still follows me.
I hope his favorite color isn't blue because it's part of the key.
I might not see the yellow of the sun again.
My favorite color is the key.
People give it a meaning, it is what I need right now.

Goodbye Note:

Nvpt V mfx ovjeetcku
M oaun xlnz kli zge pmikj egeujw xuk jxvrkk

Can you decrypt the Goodbye Note based on her diary entries?

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1 Answer 1

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The message is

Help I got kidnapped I know that the man lives across the street

The cipher is

A Vigenère cipher with key "GREEN". I guessed the key by trying a few 'normal' colours (which isn't great, I'll admit...)
'People give it a meaning, which is what I need right now': Green is the colour of hope

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6
  • $\begingroup$ Well yeah correct, good job. Maybe this one was a bit too easy. $\endgroup$
    – Nati
    Oct 9, 2019 at 12:33
  • $\begingroup$ @eru-cs I still didn't understand how you solved? $\endgroup$
    – ahmed
    Oct 9, 2019 at 13:10
  • $\begingroup$ @ahmed rot13(Jryy, V gbbx gur fragrapr 'Zl snibhevgr pbybhe vf gur xrl' dhvgr yvgrenyyl: guvf pvcure erdhverf n bar-jbeq qrpelcgvba xrl, naq guvf jbeq vf n pbybhe. V gura fhfcrpgrq vg jnf n Ivtraèer pvcure nf vg'f n irel pbzzba pbqr jubfr xrl vf n fvatyr jbeq. Gura V whfg gevrq n srj pbzzba pbybhef hagvy vg znqr nal frafr. Ohg vs lbh jnag gb fbyir nf vagraqrq: 1)'V ubcr uvf snibevgr pbybe vfa'g oyhr orpnhfr vg'f cneg bs gur xrl.': Va fhofgenpgvir pbybhe flagurfvf, terra = oyhr + lryybj 2)'Crbcyr tvir vg n zrnavat, vg vf jung V arrq evtug abj.': terra vf gur pbybe bs ubcr.) $\endgroup$
    – user62757
    Oct 9, 2019 at 13:18
  • $\begingroup$ @eru-cs No help. Which language is this? $\endgroup$
    – ahmed
    Oct 9, 2019 at 13:30
  • 1
    $\begingroup$ Rot13 is Caesar cipher with offset 13 (it's commonly used on this site to avoid spoilers in comments). To code or decode just shift each letter by 13 positions. If you type "rot13" into your search engine, you'll find online decoders $\endgroup$
    – user62757
    Oct 9, 2019 at 13:33

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