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76 lines
2.0 KiB
Python
76 lines
2.0 KiB
Python
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"""
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https://en.wikipedia.org/wiki/Running_key_cipher
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"""
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def running_key_encrypt(key: str, plaintext: str) -> str:
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"""
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Encrypts the plaintext using the Running Key Cipher.
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:param key: The running key (long piece of text).
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:param plaintext: The plaintext to be encrypted.
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:return: The ciphertext.
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"""
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plaintext = plaintext.replace(" ", "").upper()
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key = key.replace(" ", "").upper()
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key_length = len(key)
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ciphertext = []
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ord_a = ord("A")
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for i, char in enumerate(plaintext):
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p = ord(char) - ord_a
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k = ord(key[i % key_length]) - ord_a
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c = (p + k) % 26
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ciphertext.append(chr(c + ord_a))
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return "".join(ciphertext)
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def running_key_decrypt(key: str, ciphertext: str) -> str:
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"""
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Decrypts the ciphertext using the Running Key Cipher.
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:param key: The running key (long piece of text).
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:param ciphertext: The ciphertext to be decrypted.
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:return: The plaintext.
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"""
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ciphertext = ciphertext.replace(" ", "").upper()
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key = key.replace(" ", "").upper()
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key_length = len(key)
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plaintext = []
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ord_a = ord("A")
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for i, char in enumerate(ciphertext):
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c = ord(char) - ord_a
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k = ord(key[i % key_length]) - ord_a
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p = (c - k) % 26
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plaintext.append(chr(p + ord_a))
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return "".join(plaintext)
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def test_running_key_encrypt() -> None:
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"""
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>>> key = "How does the duck know that? said Victor"
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>>> ciphertext = running_key_encrypt(key, "DEFEND THIS")
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>>> running_key_decrypt(key, ciphertext) == "DEFENDTHIS"
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True
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"""
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if __name__ == "__main__":
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import doctest
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doctest.testmod()
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test_running_key_encrypt()
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plaintext = input("Enter the plaintext: ").upper()
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print(f"\n{plaintext = }")
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key = "How does the duck know that? said Victor"
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encrypted_text = running_key_encrypt(key, plaintext)
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print(f"{encrypted_text = }")
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decrypted_text = running_key_decrypt(key, encrypted_text)
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print(f"{decrypted_text = }")
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