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Sarah was a cryptologist for the CIA. One night, as she was getting ready to leave for the day, her supervisor rushed in and handed her and her team a single sheet of paper.

"We've got less than three hours until this goes down. I need you to decode this ASAP!"

Her division had been monitoring a potential major arms deal for some time, waiting for tips as to when and where it would take place.

The note read:

MEET @ 9:00 PM TONIGHT

GNXRSVEFGUVAGSEBZNZVYXLSEHVGLQEVAX

HYRNBCHNZCZNYYHIZCPYCHUYOLIJYUHJLYWCHWN

OFJHFGMVLIYBQSZWFRIZWGGYMCOBMYSXFMBDMS

NDFQVMYGUGWPCOJNIQJSGFYMROQTJYMEZMNLITMH

CWQIAUDSZZOGMDGJCOUIZMFFIUUWYSNHKIZGUXCXDFCJTYXHWS GTSMWDSZJNNZIMOFBYLMPJNQYCGQWZBQZWGJGOAOVYTYISTIY FFIAIOMIZIMWOJYPIQWHYZFIAIEJIXUAMMYQNVILDYFFUACOYJ

FUQBYSFZIABMCZOUMVZVFFLBCDYTNYDIAGN

JVWAYLMRLZQGGDTTGQPJ

KVRDRZFNXLRCZCMWCGMV

But where? The division knew of many different locations this interaction might go down at. The arms dealers often referred to different locations using code names. The division had noticed that all these names were things or places on a farm.

Where did the CIA need to be at 9:00 PM that night?

Hint 1

Line two gives a year that leads to the cipher used in line three

Hint 2 Revised

The line, "THE CLUE AND THE KEY A MONOLITHIC TRANSLATION," as deciphered by @Stiv, refers to both a specific cipher and the key to be used in the cipher. "MONOLITHIC TRANSLATION" is a synonym for the cipher, while it describes the key, which has already been mentioned below. The cipher is very common and simple, and is present on many generic lists of types of ciphers.

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Partial answer

the first line of the rot-13 decoded message is:
TAKEFIRSTHINTFROMAMILKYFRUITYDRINK
Adding spaces: TAKE FIRST HINT FROM A MILKY FRUITY DRINK
I think it is Frappé.

Then

The word Frappé has 6 letters (and it starts with the 6th letter of the alphabet). Applying rot-6 to the second line:
NEXTHINTFIFTEENOFIVEINAEUROPEANPRECINCT
With spaces: NEXT HINT FIFTEEN O FIVE IN A EUROPEAN PRECINCT

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  • $\begingroup$ Possible typo in the second part: rot13(V oryvrir vg vf ebg-fvk gung tvirf gur qrpelcgvba lbh sbhaq, abg ebg-gjragl) $\endgroup$ Jun 22 '20 at 15:05
  • 1
    $\begingroup$ @BarryPoppins sure it is. That also possibly explains the first part (?) $\endgroup$
    – melfnt
    Jun 22 '20 at 15:17
  • $\begingroup$ Ah! well reasoned! sounds plausible... $\endgroup$ Jun 22 '20 at 15:27
  • $\begingroup$ rot13(Lbhe svefg pbqrjbeq nyfb ortvaf jvgu gur 6gu yrggre bs gur nycunorg - fb n frpbaq ernfba gb hfr 6 va gur arkg fgrc...) $\endgroup$
    – Stiv
    Jun 23 '20 at 22:14
  • $\begingroup$ @stiv sure, do you have any idea on how to go on? $\endgroup$
    – melfnt
    Jun 24 '20 at 6:03
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A partial answer, taking this one step further from @melfnt's work so far, in which they have already discovered that:

Line-1 translates via rot-13 to 'TAKE FIRST HINT FROM A MILKY FRUITY DRINK'.

Inferring the answer "Frappé" and noticing it has both 6 letters and begins with the 6th letter of the alphabet, this is a hint to translate Line-2 with rot-6 to get 'NEXT HINT FIFTEEN O FIVE IN A EUROPEAN PRECINCT'.

My findings:

This is a reference to Giovan Battista Bellaso, an Italian cryptographer born in the Province of Brescia (Italy) in 1505. He is known for inventing a cipher which has been misattributed during the course of history to Blaise de Vigenère - the Vigenère cipher.

If we apply a Vigenère cipher decryption to Line-3 using the key 'VYFFUMI' we get the following message: "THE CLUE AND THE KEY A MONOLITHIC TRANSLATION". (Why 'VYFFUMI'? Because this can be translated by rot-6 again to 'BELLASO', the surname of the cipher's inventor referenced above...)

At this point I am not entirely sure how to proceed to translate Line-4, but:

Considering that translating Line-3 required an application of the rot-6 previously used in Line-2, I would not be surprised if this next step combines another use of the Vigenère cipher with some other technique that is being clued by 'MONOLITHIC TRANSLATION'...

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    $\begingroup$ My only thoughts about the clue from Line-3 so far is that this may be a reference to rot13(gur Ebfrggn Fgbar naq genafyngvat orgjrra qvssrerag ynathntrf) but I have no clear thought on how yet to proceed... $\endgroup$
    – Stiv
    Jun 29 '20 at 11:25
  • $\begingroup$ maybe rot13(zbabyvguvp genafyngvba) refers to a rot13(zbabnycunorgvp pvcure) and we have to use rot13("yuvgvp" be "zbabyuvgvp" nf n xrl (?)) $\endgroup$
    – melfnt
    Jul 3 '20 at 10:00

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