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# -*- coding: utf-8 -*-
# crypto.py
# Copyright (C) 2013 LEAP
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program. If not, see <http://www.gnu.org/licenses/>.
from Crypto.Cipher import AES
from Crypto.Random import random
from Crypto.Util import Counter
from leap.common.check import leap_assert, leap_assert_type
#
# encryption methods
#
class EncryptionMethods(object):
"""
Representation of encryption methods that can be used.
"""
AES_256_CTR = 'aes-256-ctr'
class UnknownEncryptionMethod(Exception):
"""
Raised when trying to encrypt/decrypt with unknown method.
"""
pass
#
# encrypt/decrypt functions
#
# In the future, we might want to implement other encryption schemes and
# possibly factor out the actual encryption/decryption routines of the
# following functions to specific classes, while not changing the API.
def encrypt_sym(data, key, method=EncryptionMethods.AES_256_CTR):
"""
Encrypt C{data} with C{key}, using C{method} encryption method.
@param data: The data to be encrypted.
@type data: str
@param key: The key used to encrypt C{data} (must be 256 bits long).
@type key: str
@param method: The encryption method to use.
@type method: str
@return: A tuple with the initial value and the encrypted data.
@rtype: (long, str)
"""
leap_assert_type(key, str)
# AES-256 in CTR mode
if method == EncryptionMethods.AES_256_CTR:
leap_assert(
len(key) == 32, # 32 x 8 = 256 bits.
'Wrong key size: %s bits (must be 256 bits long).' % (len(key)*8))
iv = random.getrandbits(256)
ctr = Counter.new(128, initial_value=iv)
cipher = AES.new(key=key, mode=AES.MODE_CTR, counter=ctr)
return iv, cipher.encrypt(data)
# raise if method is unknown
raise UnknownEncryptionMethod('Unkwnown method: %s' % method)
def decrypt_sym(data, key, method=EncryptionMethods.AES_256_CTR, **kwargs):
"""
Decrypt C{data} with C{key} using C{method} encryption method.
@param data: The data to be decrypted with prepended IV.
@type data: str
@param key: The key used to decrypt C{data} (must be 256 bits long).
@type key: str
@param method: The encryption method to use.
@type method: str
@param kwargs: Other parameters specific to each encryption method.
@type kwargs: long
@return: The decrypted data.
@rtype: str
"""
leap_assert_type(key, str)
# AES-256 in CTR mode
if method == EncryptionMethods.AES_256_CTR:
# assert params
leap_assert(
len(key) == 32, # 32 x 8 = 256 bits.
'Wrong key size: %s (must be 256 bits long).' % len(key))
leap_assert(
'iv' in kwargs,
'AES-256-CTR needs an initial value given as.')
ctr = Counter.new(128, initial_value=kwargs['iv'])
cipher = AES.new(key, AES.MODE_CTR, counter=ctr)
return cipher.decrypt(data)
# raise if method is unknown
raise UnknownEncryptionMethod('Unkwnown method: %s' % method)
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