python_Twofish.py

from .blockcipher import *
from .pytwofish import Twofish

def new(key,mode=MODE_ECB,IV=None,counter=None,segment_size=None):
    """Create a new cipher object

    Wrapper for pure python implementation pytwofish.py

        key = raw string containing the key
            -> when using XTS mode: the key should be a tuple containing the 2 keys needed
        mode = python_Twofish.MODE_ECB/CBC/CFB/OFB/CTR/XTS/CMAC, default is ECB
            -> for every mode, except ECB and CTR, it is important to construct a seperate cipher for encryption and decryption
        IV = IV as a raw string, default is "all zero" IV
            -> needed for CBC, CFB and OFB mode
        counter = counter object (CryptoPlus.Util.util.Counter)
            -> only needed for CTR mode
            -> use a seperate counter object for the cipher and decipher: the counter is updated directly, not a copy
                see CTR example further on in the docstring
        segment_size = amount of bits to use from the keystream in each chain part
            -> supported values: multiple of 8 between 8 and the blocksize
               of the cipher (only per byte access possible), default is 8
            -> only needed for CFB mode

    EXAMPLES:
    **********
    IMPORTING:
    -----------
    >>> import codecs
    >>> from CryptoPlus.Cipher import python_Twofish

    EXAMPLE:
    ----------
    http://www.schneier.com/code/ecb_ival.txt -> test vector I=5

    >>> cipher = python_Twofish.new(codecs.decode('019F9809DE1711858FAAC3A3BA20FBC3', 'hex'))
    >>> codecs.encode(cipher.encrypt(codecs.decode('6363977DE839486297E661C6C9D668EB', 'hex')), 'hex').upper()
    b'816D5BD0FAE35342BF2A7412C246F752'
    >>> codecs.encode(cipher.decrypt(codecs.decode(_, 'hex')), 'hex').upper()
    b'6363977DE839486297E661C6C9D668EB'
    """
    return python_Twofish(key,mode,IV,counter,segment_size)

class python_Twofish(BlockCipher):
    def __init__(self,key,mode,IV,counter,segment_size):
        if len(key) not in (16,24,32) and type(key) is not tuple:
                raise ValueError("Key should be 128, 192 or 256 bits")
        cipher_module = Twofish
        self.blocksize = 16
        BlockCipher.__init__(self,key,mode,IV,counter,cipher_module,segment_size)

def _test():
    import doctest
    doctest.testmod()

if __name__ == "__main__":
    _test()