def test_put_bitstream_copy_self(self):
"""
Test using the put_bitstream_copy method with the same BitStream object
as origin and destination.
"""
bitstream = BitStream()
# Generate a random string of bits, ie: ('0' | '1')*
num_bits = 50
bits = ""
for i in range(0, num_bits):
bits += random.choice(
('0', '1')) # inefficient, but ok for a test.
# Put those bits in the BitStream...
bitstream.put_bit_dump_string(bits)
# ... copy the bitstream into itself at any point:
bitstream.seek(random.randint(0, 50))
bitstream.put_bitstream_copy(bitstream)
# Check that the bitstream was unchanged by the previous operation:
# (overwriting data with the same data is the same as doing nothing,
# except that the current position is changed to the end of the stream)
self.assertEquals(bitstream.get_length(), num_bits)
self.assertEquals(bitstream.get_current_pos(), num_bits)
bitstream.seek(0)
read_bits = bitstream.get_bit_dump_string(bitstream.get_length())
self.assertEqual(read_bits, bits)
def test_put_bitstream_copy_self(self):
"""
Test using the put_bitstream_copy method with the same BitStream object
as origin and destination.
"""
bitstream = BitStream()
# Generate a random string of bits, ie: ('0' | '1')*
num_bits = 50
bits = ""
for i in range(0,num_bits):
bits += random.choice(('0','1')) # inefficient, but ok for a test.
# Put those bits in the BitStream...
bitstream.put_bit_dump_string(bits)
# ... copy the bitstream into itself at any point:
bitstream.seek(random.randint(0,50))
bitstream.put_bitstream_copy(bitstream)
# Check that the bitstream was unchanged by the previous operation:
# (overwriting data with the same data is the same as doing nothing,
# except that the current position is changed to the end of the stream)
self.assertEquals(bitstream.get_length(),num_bits)
self.assertEquals(bitstream.get_current_pos(),num_bits)
bitstream.seek(0)
read_bits = bitstream.get_bit_dump_string(bitstream.get_length())
self.assertEqual(read_bits, bits)
def test_put_bitstream_copy(self):
"""
Test the basic functionality of the put_bitstream_copy method.
"""
bitstream1 = BitStream()
bitstream1.put_string("This is bitstream1")
bitstream2 = BitStream()
bitstream2.put_string("This is bitstream2")
bitstream3 = BitStream()
# bitstream3 remains empty
bitstream4 = BitStream()
bitstream4.put_string("This is bitstream4")
# copy the full contents of bitstream2 to the end of bitstream1
bitstream2.seek(0)
bitstream1.put_bitstream_copy(bitstream2)
self.assertEquals(bitstream2.get_current_pos(),
bitstream2.get_length())
# check the contents of bitstream1
bitstream1.seek(0)
self.assertEquals(bitstream1.get_string(bitstream1.get_length()),
"This is bitstream1This is bitstream2")
# copy the full contents of bitstream3 (aka. nothing) to the end of
# bitstream4
bitstream3.seek(0)
bitstream4.put_bitstream_copy(bitstream3)
# check the contents of bitstream4
bitstream4.seek(0)
self.assertEquals(bitstream4.get_string(bitstream4.get_length()),
"This is bitstream4")
# copy the contents of bitstream4 from the position 8 onwards
bitstream4.seek(8 * 8)
bitstream1.put_bitstream_copy(bitstream4)
self.assertEquals(bitstream4.get_current_pos(),
bitstream4.get_length())
# check the contents of bitstream1
bitstream1.seek(0)
self.assertEquals(bitstream1.get_string(bitstream1.get_length()),
"This is bitstream1This is bitstream2bitstream4")
def test_put_bitstream_copy(self):
"""
Test the basic functionality of the put_bitstream_copy method.
"""
bitstream1 = BitStream()
bitstream1.put_string("This is bitstream1")
bitstream2 = BitStream()
bitstream2.put_string("This is bitstream2")
bitstream3 = BitStream()
# bitstream3 remains empty
bitstream4 = BitStream()
bitstream4.put_string("This is bitstream4")
# copy the full contents of bitstream2 to the end of bitstream1
bitstream2.seek(0)
bitstream1.put_bitstream_copy(bitstream2)
self.assertEquals(bitstream2.get_current_pos(), bitstream2.get_length())
# check the contents of bitstream1
bitstream1.seek(0)
self.assertEquals(bitstream1.get_string(bitstream1.get_length()),
"This is bitstream1This is bitstream2")
# copy the full contents of bitstream3 (aka. nothing) to the end of
# bitstream4
bitstream3.seek(0)
bitstream4.put_bitstream_copy(bitstream3)
# check the contents of bitstream4
bitstream4.seek(0)
self.assertEquals(bitstream4.get_string(bitstream4.get_length()),
"This is bitstream4")
# copy the contents of bitstream4 from the position 8 onwards
bitstream4.seek(8*8)
bitstream1.put_bitstream_copy(bitstream4)
self.assertEquals(bitstream4.get_current_pos(), bitstream4.get_length())
# check the contents of bitstream1
bitstream1.seek(0)
self.assertEquals(bitstream1.get_string(bitstream1.get_length()),
"This is bitstream1This is bitstream2bitstream4")
def encrypt_bitstream(self, bitstream, pad_to=None, task_monitor=None):
"""
Encrypts the given bitstream into a ciphertext object.
Arguments:
bitstream::BitStream-- A stream of bits to encrypt
(see BitStream utility class).
pad_to::int -- Minimum size (in bytes) of the resulting
ciphertext. Data will be padded before
encryption to match this size.
task_monitor::TaskMonitor -- A task monitor for this task.
Returns:
ciphertext:Ciphertext -- A ciphertext object encapsulating the
encrypted data.
"""
random = StrongRandom()
## PART 1
# First, format the bitstream as per Ciphertext.py Note 001,
# previous to encryption.
# [size (64 bits) | message (size bits) | padding (X bits) ]
##
formated_bitstream = BitStream()
# The first 64 encode the size of the actual data in bits
SIZE_BLOCK_LENGTH = 64
size_in_bits = bitstream.get_length()
if(size_in_bits >= 2**SIZE_BLOCK_LENGTH):
raise ValueError("The size of the bitstream to encrypt is larger " \
"than 16 Exabits. The current format for " \
"PloneVote ciphertext only allows encrypting a " \
"maximum of 16 Exabits of information.")
formated_bitstream.put_num(size_in_bits, SIZE_BLOCK_LENGTH)
# We then copy the contents of the original bitstream
bitstream.seek(0)
formated_bitstream.put_bitstream_copy(bitstream)
# Finally, we append random data until we reach the desired pad_to
# length
unpadded_length = formated_bitstream.get_length()
if(pad_to != None and (pad_to * 8) > unpadded_length):
full_length = pad_to * 8
else:
full_length = unpadded_length
padding_left = full_length - unpadded_length
while(padding_left > 1024):
padding_bits = random.randint(1, 2**1024)
formated_bitstream.put_num(padding_bits,1024)
padding_left -= 1024
if(padding_left > 0):
padding_bits = random.randint(1, 2**padding_left)
formated_bitstream.put_num(padding_bits, padding_left)
padding_left = 0
## PART 2
# We encrypt the formated bitsteam using ElGamal into a Ciphertext
# object.
# See "Handbook of Applied Cryptography" Algorithm 8.18
##
# block_size is the size of each block of bits to encrypt
# since we can only encrypt messages in [0, p - 1]
# we should use (nbits - 1) as the block size, where
# 2**(nbits - 1) < p < 2**nbits
block_size = self.cryptosystem.get_nbits() - 1
prime = self.cryptosystem.get_prime()
generator = self.cryptosystem.get_generator()
# We pull data from the bitstream one block at a time and encrypt it
formated_bitstream.seek(0)
ciphertext = \
Ciphertext(self.cryptosystem.get_nbits(), self.get_fingerprint())
plaintext_bits_left = formated_bitstream.get_length()
# Check if we have a task monitor and register with it
if(task_monitor != None):
# We will do two tick()s per block to encrypt: one for generating
# the gamma component of the ciphertext block and another for the
# delta component (those are the two time intensive steps,
# because of exponentiation).
ticks = math.ceil((1.0 * plaintext_bits_left) / block_size) * 2
encrypt_task_mon = \
task_monitor.new_subtask("Encrypt data", expected_ticks = ticks)
while(plaintext_bits_left > 0):
# get next block (message, m, etc) to encrypt
if(plaintext_bits_left >= block_size):
block = formated_bitstream.get_num(block_size)
plaintext_bits_left -= block_size
else:
block = formated_bitstream.get_num(plaintext_bits_left)
# Encrypt as if the stream was filled with random data past its
# end, this avoids introducing a 0's gap during decryption to
# bitstream
displacement = block_size - plaintext_bits_left
block = block << displacement
padding = random.randint(0, 2**displacement - 1)
assert (padding / 2**displacement == 0), \
"padding should be at most displacement bits long"
block = block | padding
plaintext_bits_left = 0
# Select a random integer k, 1 <= k <= p − 2
k = random.randint(1, prime - 2)
# Compute gamma and delta
gamma = pow(generator, k, prime)
if(task_monitor != None): encrypt_task_mon.tick()
delta = (block * pow(self._key, k, prime)) % prime
if(task_monitor != None): encrypt_task_mon.tick()
# Add this encrypted data portion to the ciphertext object
ciphertext.append(gamma, delta)
# return the ciphertext object
return ciphertext
def encrypt_bitstream(self, bitstream, pad_to=None, task_monitor=None):
"""
Encrypts the given bitstream into a ciphertext object.
Arguments:
bitstream::BitStream-- A stream of bits to encrypt
(see BitStream utility class).
pad_to::int -- Minimum size (in bytes) of the resulting
ciphertext. Data will be padded before
encryption to match this size.
task_monitor::TaskMonitor -- A task monitor for this task.
Returns:
ciphertext:Ciphertext -- A ciphertext object encapsulating the
encrypted data.
"""
random = StrongRandom()
## PART 1
# First, format the bitstream as per Ciphertext.py Note 001,
# previous to encryption.
# [size (64 bits) | message (size bits) | padding (X bits) ]
##
formated_bitstream = BitStream()
# The first 64 encode the size of the actual data in bits
SIZE_BLOCK_LENGTH = 64
size_in_bits = bitstream.get_length()
if(size_in_bits >= 2**SIZE_BLOCK_LENGTH):
raise ValueError("The size of the bitstream to encrypt is larger " \
"than 16 Exabits. The current format for " \
"PloneVote ciphertext only allows encrypting a " \
"maximum of 16 Exabits of information.")
formated_bitstream.put_num(size_in_bits, SIZE_BLOCK_LENGTH)
# We then copy the contents of the original bitstream
bitstream.seek(0)
formated_bitstream.put_bitstream_copy(bitstream)
# Finally, we append random data until we reach the desired pad_to
# length
unpadded_length = formated_bitstream.get_length()
if(pad_to != None and (pad_to * 8) > unpadded_length):
full_length = pad_to * 8
else:
full_length = unpadded_length
padding_left = full_length - unpadded_length
while(padding_left > 1024):
padding_bits = random.randint(1, 2**1024)
formated_bitstream.put_num(padding_bits,1024)
padding_left -= 1024
if(padding_left > 0):
padding_bits = random.randint(1, 2**padding_left)
formated_bitstream.put_num(padding_bits, padding_left)
padding_left = 0
## PART 2
# We encrypt the formated bitsteam using ElGamal into a Ciphertext
# object.
# See "Handbook of Applied Cryptography" Algorithm 8.18
##
# block_size is the size of each block of bits to encrypt
# since we can only encrypt messages in [0, p - 1]
# we should use (nbits - 1) as the block size, where
# 2**(nbits - 1) < p < 2**nbits
block_size = self.cryptosystem.get_nbits() - 1
prime = self.cryptosystem.get_prime()
generator = self.cryptosystem.get_generator()
# We pull data from the bitstream one block at a time and encrypt it
formated_bitstream.seek(0)
ciphertext = \
Ciphertext(self.cryptosystem.get_nbits(), self.get_fingerprint())
plaintext_bits_left = formated_bitstream.get_length()
# Check if we have a task monitor and register with it
if(task_monitor != None):
# We will do two tick()s per block to encrypt: one for generating
# the gamma component of the ciphertext block and another for the
# delta component (those are the two time intensive steps,
# because of exponentiation).
ticks = math.ceil((1.0 * plaintext_bits_left) / block_size) * 2
encrypt_task_mon = \
task_monitor.new_subtask("Encrypt data", expected_ticks = ticks)
while(plaintext_bits_left > 0):
# get next block (message, m, etc) to encrypt
if(plaintext_bits_left >= block_size):
block = formated_bitstream.get_num(block_size)
plaintext_bits_left -= block_size
else:
block = formated_bitstream.get_num(plaintext_bits_left)
# Encrypt as if the stream was filled with random data past its
# end, this avoids introducing a 0's gap during decryption to
# bitstream
displacement = block_size - plaintext_bits_left
block = block << displacement
padding = random.randint(0, 2**displacement - 1)
assert (padding // 2**displacement == 0), \
"padding should be at most displacement bits long"
block = block | padding
plaintext_bits_left = 0
# Select a random integer k, 1 <= k <= p − 2
k = random.randint(1, prime - 2)
# Compute gamma and delta
gamma = pow(generator, k, prime)
if(task_monitor != None): encrypt_task_mon.tick()
delta = (block * pow(self._key, k, prime)) % prime
if(task_monitor != None): encrypt_task_mon.tick()
# Add this encrypted data portion to the ciphertext object
ciphertext.append(gamma, delta)
# return the ciphertext object
return ciphertext