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Over The Hill
Challenge
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
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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"
Solution
This looks like a Hill Cipher. We use sympy to decode this in python:
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from sympy.crypto.crypto import decipher_hill
from sympy import Matrix
alphabet = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ123456789_{}"
key = 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"
print decipher_hill(ciphertext, key, alphabet)
Flag
IceCTF{linear_algebra_plus_led_zeppelin_are_a_beautiful_m1xture}