111 lines
2.8 KiB
Python
111 lines
2.8 KiB
Python
#!/usr/bin/env python
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import os
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from Crypto import Random
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from Crypto.Cipher import AES
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from base64 import b64encode, b64decode
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__author__ = 'rolandh'
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POSTFIX_MODE = {
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"cbc": AES.MODE_CBC,
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"cfb": AES.MODE_CFB,
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"ecb": AES.MODE_CFB,
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}
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BLOCK_SIZE = 16
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def build_cipher(key, iv, alg="aes_128_cbc"):
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"""
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:param key: encryption key
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:param iv: init vector
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:param alg: cipher algorithm
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:return: A Cipher instance
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"""
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typ, bits, cmode = alg.split("_")
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if not iv:
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iv = Random.new().read(AES.block_size)
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else:
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assert len(iv) == AES.block_size
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if bits not in ["128", "192", "256"]:
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raise Exception("Unsupported key length")
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try:
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assert len(key) == int(bits) >> 3
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except AssertionError:
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raise Exception("Wrong Key length")
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try:
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return AES.new(key, POSTFIX_MODE[cmode], iv), iv
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except KeyError:
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raise Exception("Unsupported chaining mode")
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def encrypt(key, msg, iv=None, alg="aes_128_cbc", padding="PKCS#7",
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b64enc=True, block_size=BLOCK_SIZE):
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"""
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:param key: The encryption key
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:param iv: init vector
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:param msg: Message to be encrypted
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:param padding: Which padding that should be used
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:param b64enc: Whether the result should be base64encoded
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:param block_size: If PKCS#7 padding which block size to use
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:return: The encrypted message
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"""
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if padding == "PKCS#7":
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_block_size = block_size
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elif padding == "PKCS#5":
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_block_size = 8
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else:
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_block_size = 0
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if _block_size:
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plen = _block_size - (len(msg) % _block_size)
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c = chr(plen)
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msg += c * plen
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cipher, iv = build_cipher(key, iv, alg)
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cmsg = iv + cipher.encrypt(msg)
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if b64enc:
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return b64encode(cmsg)
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else:
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return cmsg
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def decrypt(key, msg, iv=None, padding="PKCS#7", b64dec=True):
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"""
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:param key: The encryption key
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:param iv: init vector
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:param msg: Base64 encoded message to be decrypted
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:return: The decrypted message
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"""
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if b64dec:
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data = b64decode(msg)
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else:
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data = msg
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_iv = data[:AES.block_size]
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if iv:
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assert iv == _iv
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cipher, iv = build_cipher(key, iv)
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res = cipher.decrypt(data)[AES.block_size:]
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if padding in ["PKCS#5", "PKCS#7"]:
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res = res[:-ord(res[-1])]
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return res
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if __name__ == "__main__":
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key_ = "1234523451234545" # 16 byte key
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# Iff padded the message doesn't have to be multiple of 16 in length
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msg_ = "ToBeOrNotTobe W.S."
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iv_ = os.urandom(16)
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encrypted_msg = encrypt(key_, msg_, iv_)
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txt = decrypt(key_, encrypted_msg, iv_)
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assert txt == msg_
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encrypted_msg = encrypt(key_, msg_, 0)
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txt = decrypt(key_, encrypted_msg, 0)
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assert txt == msg_
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