def decrypt(self, ciphertext):
"""
Decrypts the given ciphertext with the DES cipher.
Note that every operation done is lazy, returning generators rather than lists or tuples
to save memory.
Example:
>>> cipher = DesCipher(123456)
>>> cipher.decrypt('Òh*&BU¢¸')
'messageX'
"""
# Pad the bitstream to be evenly divisible by 64 bit chunks. Randomly choose between 0 and 1
bitstream = lazy_pad(TextBitstream(ciphertext), 64, pad_values=[0, 1])
# Chunk the bitstream into 64 bit chunks --> a tuple (L, R) of 32 bit bitstrings.
chunker = DesChunker(bitstream, 32)
# Run each chunk through an initial permutation.
permuter = self.initial_permuter(chunker)
# Lazily decrypt chunk after chunk.
decrypter = self.decrypt_chunks(permuter)
# Unrun each chunk through the initial permutation.
permuter = self.inverse_initial_permuter(decrypter)
# Now convert the above generator into a string and return it.
return DesChunker.chunks_to_string(permuter)
def chunker(m, chunk_size):
"""
Chunker implementation. Converts the message to a series of numbers.
"""
for c in nslice(lazy_pad(m, chunk_size, string.ascii_lowercase),
chunk_size):
yield BaseRsaCipher.str2num(''.join(c))
def chunker(bitstream, chunk_size):
"""
Chunker implementation. Will pad the given bitstream with 0s if it is not evenly
divisible by 2*chunk_size.
"""
for chunk in nslice(lazy_pad(bitstream, 2 * chunk_size),
2 * chunk_size):
yield chunk[:chunk_size], chunk[chunk_size:]
def decrypt(self, ciphertext):
"""
Decrypts the given ciphertext with the DES cipher.
Example:
>>> cipher = ToyDesCipher(0b001001101)
>>> cipher.decrypt('=Í"¨\\x88¸\\x7fßX\\x185\\x0f')
'thisisatestx'
"""
# Pad the ciphertext to ensure that there is the right number of bits in the ciphertext
ciphertext = lazy_pad(ciphertext, 3, string.printable)
# Convert the ciphertext to a bitstream.
bitstream = TextBitstream(ciphertext)
# Chunk the bitstream into 12 bit chunks --> a tuple (L, R) of 6 bit bitstrings.
chunker = DesChunker(bitstream, 6)
# Lazily decrypt chunk after chunk
decrypter = self.decrypt_chunks(chunker)
# Now convert the above generator into a string and return it.
return DesChunker.chunks_to_string(decrypter)
def encrypt(self, message):
"""
Encrypts the given message with the DES cipher.
Example:
>>> cipher = ToyDesCipher(0b001001101)
>>> cipher.encrypt('thisisatestx')
'=Í"¨\\x88¸\\x7fßX\\x185\\x0f'
"""
# Pad the message to ensure that there is the right number of bits in the message
message = lazy_pad(message, 3, string.printable)
# Convert the message to a bitstream.
bitstream = TextBitstream(message)
# Chunk the bitstream into 12 bit chunks --> a tuple (L, R) of 6 bit bitstrings.
chunker = DesChunker(bitstream, 6)
# Lazily encrypt chunk after chunk.
encrypter = self.encrypt_chunks(chunker)
# Now convert the above generator into a string and return it.
return DesChunker.chunks_to_string(encrypter)