def re_decrypt(data=None,
re_enc_length=const.RE_ENC_LENGTH,
seed=None,
key=None,
iv=None,
init_val=None,
debug=0):
"""
Re-decrypt data using the given parameters.
:param data: data to re-decrypt
:param re_enc_length: number of re-encrypted bytes
:param seed: seed that randomly selected re-encrypted bytes
:param key: symmetric key to decrypt randomly selected bytes
:param iv: initialisation vector for the symmetric decryption
:param init_val: initial value (ONLY FOR CTR MODE)
:param debug: if 1, prints will be shown during execution; default 0, no prints are shown
:return: re-decrypted data
"""
# Check if data is set
if data is None:
logging.error('re_decrypt data exception')
# if debug: # ONLY USE FOR DEBUG
# print('EXCEPTION in re_decrypt data')
raise Exception
# Check if key is set
if key is None:
logging.error('re_decrypt key exception')
if debug: # ONLY USE FOR DEBUG
print('EXCEPTION in re_decrypt key')
raise Exception
# Check if iv is set
if iv is None:
logging.error('re_decrypt iv exception')
if debug: # ONLY USE FOR DEBUG
print('EXCEPTION in re_decrypt iv')
raise Exception
# Check if the number of bytes to re-encrypt is lesser than the data length
if re_enc_length < len(data): # Apply punctured encryption
return remove_punctured_enc(data, re_enc_length, seed, key, iv,
init_val, debug)
else: # Re-encryption of the whole data
sym_cipher = sym.get_cipher(AES.MODE_CTR, init_val, None, key, iv)
return sym.decrypt(sym_cipher, data, debug)
def remove_punctured_enc(data,
re_enc_length,
seed,
key,
iv,
init_val,
debug=0):
"""
Remove punctured encryption to the given data: 're_enc_length' bytes are randomly selected using the seed and
symmetrically decrypted using the given key and iv.
:param data: data to re-decrypt
:param re_enc_length: number of re-encrypted bytes
:param seed: seed that randomly selected re-encrypted bytes
:param key: symmetric key to decrypt randomly selected bytes
:param iv: initialisation vector for the symmetric decryption
:param debug: if 1, prints will be shown during execution; default 0, no prints are shown
:return: re-decrypted data
"""
# Get random re-encrypted bytes to decrypt
bytes_to_re_dec, re_dec_indexes = get_bytes_to_re_enc(
data, re_enc_length, seed, debug)
if debug: # ONLY USE FOR DEBUG
print('BYTES TO RE-DECRYPT = (%d) %s' %
(len(bytes_to_re_dec), bytes_to_re_dec))
print('INDEX TO RE-DECRYPT = (%d) %s' %
(len(re_dec_indexes), re_dec_indexes))
# Decrypt re-encrypted data bytes
sym_cipher = sym.get_cipher(AES.MODE_CTR, init_val, None, key, iv)
re_dec_bytes = sym.decrypt(sym_cipher, bytes_to_re_dec, debug)
if debug: # ONLY USE FOR DEBUG
print('RE-DECRYPTED BYTES = (%s) (%d) %s' %
(type(re_dec_bytes), len(re_dec_bytes), re_dec_bytes))
# Replace bytes with re-decrypted ones in data
return replace_bytes(data, re_dec_bytes, re_dec_indexes, debug)
def _decode(self, full_path, chunk_num, offset, sym_cipher, re_enc_args):
"""
Remove AONT and encryption from the given chunk and write the result on the temporary file
:param chunk_num: number of file chunk to anti-transform and decrypt
:param offset: position where the result must be written
:param sym_cipher: symmetric cipher
"""
if self.enc_fp.closed:
self.enc_fp = open(full_path, 'rb+')
self.enc_fp.seek(0, os.SEEK_END)
file_size = self.enc_fp.tell()
if file_size <= chunk_num * self.meta['random_size']:
return
# Move file pointer
self.enc_fp.seek(chunk_num * self.meta['chunk_size'])
# Read file chunk
chunk = self.enc_fp.read(self.meta['chunk_size'])
# If applied, remove all re-encryption operations
if self.debug:
print("Remove re-encryptions from file chunk")
re_enc_ops_num = len(self.meta['re_encs'])
re_enc_init_val = self._get_cipher_initial_value(
int(chunk_num) * self.meta['chunk_size'])
if re_enc_ops_num > 0:
for i in range(re_enc_ops_num):
index = re_enc_ops_num - 1 - i
# Add other params to re-encryption params
re_enc_args[index]['init_val'] = re_enc_init_val
# Remove re-encryption
chunk = re_enc.remove_re_enc(chunk, re_enc_args[index],
self.debug)
if self.debug:
print("DE-RE-ENCRYPTED CHUNK = (%d) %s" %
(len(chunk), chunk))
print("Re-encryption successfully removed")
if self.debug:
print("Re-encryptions successfully removed")
if self.debug:
print("Remove AONT from encrypted file chunk")
# Get AONT anti-transformation parameters
aont_args = self._create_aont_anti_transf_params(len(chunk))
# Anti-transform file chunk
chunk = aont.anti_transform(chunk, aont_args, self.debug)
if self.debug:
print("ANTI-TRANSFORMED CHUNK = (%d) %s" % (len(chunk), chunk))
print("AONT successfully removed")
# Decrypt the anti-transformed file chunk with the sym key and write it on the temporary file
x = sym.decrypt(sym_cipher, chunk, self.debug)
# x = chunk
if self.debug:
print("got chunk in _decode: ", x)
# Write anti-transformed decrypted chunk on the temporary file at its proper position
if self.debug:
print("writing on temp file at position", offset, "byte ", x)
self.temp_fp.seek(offset)
self.temp_fp.write(x)
# Reset both file pointers
self.enc_fp.seek(0)
self.temp_fp.seek(0)