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IceCTF - 65 - Over the Hill - Cryptography

noraj (Alexandre ZANNI)
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Information#

Version#

By Version Comment
noraj 1.0 Creation

CTF#

Description#

Over the hills and far away... many times I've gazed, many times been bitten. Many dreams come true and some have silver linings, I live for my dream of a decrypted flag. crypted

Description#

  1. Challenge's title is Over the Hill like the Hill cipher polygraphic substitution. Looking for ciphering matrix in a search engine will help you find it.
  2. Since coding is own method can take some time and because dCode won't work for Hill cipher: we will write a script using SymPy python library.
  3. Crypto examples avaible here.
  4. Install SymPy: pip install sympy.
  5. Here's the script:
from sympy.crypto.crypto import decipher_hill
from sympy import Matrix

alphabet = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ123456789_{}"

matrix = [[54, 53, 28, 20, 54, 15, 12, 7],
          [32, 14, 24, 5, 63, 12, 50, 52],
          [63, 59, 40, 18, 55, 33, 17, 3],
          [63, 34, 5, 4, 56, 10, 53, 16],
          [35, 43, 45, 53, 12, 42, 35, 37],
          [20, 59, 42, 10, 46, 56, 12, 61],
          [26, 39, 27, 59, 44, 54, 23, 56],
          [32, 31, 56, 47, 31, 2, 29, 41]]

ciphertext = "7Nv7}dI9hD9qGmP}CR_5wJDdkj4CKxd45rko1cj51DpHPnNDb__EXDotSRCP8ZCQ"

key = Matrix(matrix)

pt = decipher_hill(ciphertext, key, alphabet)

print(pt)
  1. And here's the flag: IceCTF{linear_algebra_plus_led_zeppelin_are_a_beautiful_m1xture}.
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