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35 lines
1.0 KiB
35 lines
1.0 KiB
# Python2 ver.
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# If you use Python3 interpreter, the trouble will be in print format
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# [KSL Playground][Crypto][IDCC2018 DecryptME] written by Mr. Goodnight
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# Link: https://euectf.stikom-bali.ac.id/challenges#[IDCC]%20DecryptME
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# Flag: IDCC{S1mpl3_4nd_stR4ight}
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from base64 import *
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# Encryption algorithm
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# ciphertext = plaintext + keys
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with open('./enkripsi', mode = 'r') as f:
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ciphertext = f.read()
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# plaintext = ciphertext - keys
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# Make my own function to decrypt the ciphertext
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def decrypt(ciphertext, keys):
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plaintext = ""
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for num,char in enumerate (ciphertext):
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plaintext += chr((ord(char) - ord(keys[num % len(keys)])) % 127)
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return plaintext
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# keys = ciphertext - plaitext
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# Find the key by using known string attack
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# Then I found out that the key is raja
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known_string = b64encode("IDCC{")
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keys = ""
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for num,char in enumerate (known_string):
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keys += chr((ord(ciphertext[num]) - ord(char)) % 127)
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# Run the decrypt function the decode it
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keys = "raja"
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flag = b64decode(decrypt(ciphertext, keys))
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print ("Flag: {f}".format(f = flag))
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