4
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You took part in a bank heist and wait for your share.
Finally this message comes in:

uMZ6rvnaWF88YQmbHNk3QdoxMj1hPn_htiEbOkNYlTA=

Loc:
gAAAAABdw_LDAgmuZdvcVAV_E-ld96n06pZqAGwEs8mMNW58L-xrNJ90a45WZcJfQd1xOWJPZ_XfsSEXSfSD6epdp1B6d1nVZ7qQTbVAXr8X9irA5I0BGDc=

I wait for you there.

Where do you need to go?

Hint 1:

The first string is the key, the second is the cipher.

Hint 2:

The second string is called a "token" and was created with the Base-64 format.

Hint 3:

This encryption method guarantees that a message encrypted using it cannot be manipulated or read without the "secret key".

Hint 4:

The "=" at the end indicates the format is in Base64.

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  • $\begingroup$ … so it is some known encryption like Rijndael, DES, TripleDES, TwoFish, Serpent…(or so) each has 8 modes like ECB, CBC and so…or something else - it is a lot to try… also with some missing/extra characters? $\endgroup$
    – Jan Ivan
    Nov 18, 2019 at 12:45
  • $\begingroup$ Yes it's a known encryption method, but no characters are missing or extra @JanIvan $\endgroup$
    – Nati
    Nov 18, 2019 at 14:50
  • $\begingroup$ "_" and "-" are not Base64 usual symbols. One of them would be 62nd symbol, second 63rd symbol and for tools use, it needs to be replaced by "+" and "/" I guess? $\endgroup$
    – Jan Ivan
    Nov 22, 2019 at 8:58
  • $\begingroup$ That's true @JanIvan, but you don't have to replace anything, it's part of the key or token. The enrypting method contains multiple steps and one of them is formatting the token in base64. The key generated is a URL-safe, also base64-encoded key. Find the method and you simply can decode it to it's normal format. $\endgroup$
    – Nati
    Nov 22, 2019 at 9:20

1 Answer 1

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The answer to the riddle is:

A Fernet token, which can be decrypted using boilerplate code in the Python cryptography package's fernet module

How did I find out?

I searched Google for base64 starts with "gAAAAA" which turned up a NoobCTF writeup on medium.com which mentions that gAAAAA is characteristic of a Fernet token.

Then... what's the plaintext?

Lat41.805012 Long12.612277, which presumably refers to a location near an elementary school in Rome, Italy

I hope this question wasn't an attempt to get us to crack a geocache puzzle for you!

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  • 2
    $\begingroup$ I love it when puzzles on here are solved many years later. $\endgroup$
    – JLee
    Aug 14, 2023 at 23:48
  • $\begingroup$ Don't worry, it wasn't a geocache puzzle. I was just obsessed with encryption of any kind. Well done!^^ $\endgroup$
    – Nati
    Aug 17, 2023 at 7:35

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