English [Sharif University CTF 2016] [Crypto 50 – Rail Fence Cipher] Write Up

Description

Decrypt and find the flag.
Ciphertext is: AaY–rpyfneJBeaaX0n-,ZZcs-uXeeSVJ-sh2tioaZ}slrg,-ciE-anfGt.-eCIyss-TzprttFliora{GcouhQIadctm0ltt-FYluuezTyorZ-

Resolution

Rail Fence Cipher is pretty straighforward, we use http://www.geocachingtoolbox.com/index.php?page=railFenceCipher and try every rails number till we get a plaintext since we know the flag format will be SharifCTF{flag_is_here}. The shift was 21 rails.
And the plaintext is:

A-fence-is-a-structure-that-encloses-an-area,-SharifCTF{QmFzZTY0IGlzIGEgZ2VuZXJpYyB0ZXJt},-typically-outdoors.

Flag is : “QmFzZTY0IGlzIGEgZ2VuZXJpYyB0ZXJt“.

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