mirror of https://github.com/dirtbags/moth.git
53 lines
1.4 KiB
Python
53 lines
1.4 KiB
Python
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def cipherBlockChainingE(key, IV, C, text):
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"""Cypher block chaining encryption. Works in blocks the size of IV.
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@param key: the key for the Cipher.
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@param IV: initialization vector (bytes object).
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@param C: the cypher function C(text, key).
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@param text: A bytes object of the text. The length of the text
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must be a multiple of the length of the IV.
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"""
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mod = len(text) % len(IV)
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assert mod == 0, 'The text length needs to be a multiple of the key '\
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'length. %d of %d' % (mod, len(IV))
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feedback = IV
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block = len(IV)
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out = bytearray()
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while text:
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p, text = text[:block], text[block:]
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c = bytearray(block)
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for i in range(block):
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c[i] = p[i] ^ feedback[i]
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c2 = C(c, key)
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out.extend(c2)
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feedback = c2
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return bytes(out)
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def cipherBlockChainingD(key, IV, C, text):
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"""Cipher block chaining decryption. Arguments are the same as for the
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encrypting function."""
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mod = len(text) % len(IV)
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assert mod == 0, 'The text length needs to be a multiple of the IV '\
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'length. %d of %d' % (mod, len(IV))
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feedback = IV
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block = len(IV)
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out = bytearray()
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while text:
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c, text = text[:block], text[block:]
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p = C(c, key)
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p = bytearray(p)
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for i in range(block):
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p[i] = p[i] ^ feedback[i]
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out.extend(p)
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feedback = c
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return bytes(out)
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