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# -*- coding: utf-8 -*-
# crypto.py
# Copyright (C) 2013,2014 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/>.
"""
Cryptographic utilities for Soledad.
"""
import os
import binascii
import hmac
import hashlib
from pycryptopp.cipher.aes import AES
from pycryptopp.cipher.xsalsa20 import XSalsa20
from leap.soledad.common import (
soledad_assert,
soledad_assert_type,
)
MAC_KEY_LENGTH = 64
class EncryptionMethods(object):
"""
Representation of encryption methods that can be used.
"""
AES_256_CTR = 'aes-256-ctr'
XSALSA20 = 'xsalsa20'
class UnknownEncryptionMethod(Exception):
"""
Raised when trying to encrypt/decrypt with unknown method.
"""
pass
class NoSymmetricSecret(Exception):
"""
Raised when trying to get a hashed passphrase.
"""
def encrypt_sym(data, key, method):
"""
Encrypt C{data} using a {password}.
Currently, the only encryption methods supported are AES-256 in CTR
mode and XSalsa20.
: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)
"""
soledad_assert_type(key, str)
soledad_assert(
len(key) == 32, # 32 x 8 = 256 bits.
'Wrong key size: %s bits (must be 256 bits long).' %
(len(key) * 8))
iv = None
# AES-256 in CTR mode
if method == EncryptionMethods.AES_256_CTR:
iv = os.urandom(16)
ciphertext = AES(key=key, iv=iv).process(data)
# XSalsa20
elif method == EncryptionMethods.XSALSA20:
iv = os.urandom(24)
ciphertext = XSalsa20(key=key, iv=iv).process(data)
else:
# raise if method is unknown
raise UnknownEncryptionMethod('Unkwnown method: %s' % method)
return binascii.b2a_base64(iv), ciphertext
def decrypt_sym(data, key, method, **kwargs):
"""
Decrypt data using symmetric secret.
Currently, the only encryption method supported is AES-256 CTR mode.
:param data: The data to be decrypted.
: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: dict
:return: The decrypted data.
:rtype: str
"""
soledad_assert_type(key, str)
# assert params
soledad_assert(
len(key) == 32, # 32 x 8 = 256 bits.
'Wrong key size: %s (must be 256 bits long).' % len(key))
soledad_assert(
'iv' in kwargs,
'%s needs an initial value.' % method)
# AES-256 in CTR mode
if method == EncryptionMethods.AES_256_CTR:
return AES(
key=key, iv=binascii.a2b_base64(kwargs['iv'])).process(data)
elif method == EncryptionMethods.XSALSA20:
return XSalsa20(
key=key, iv=binascii.a2b_base64(kwargs['iv'])).process(data)
# raise if method is unknown
raise UnknownEncryptionMethod('Unkwnown method: %s' % method)
def doc_mac_key(doc_id, secret):
"""
Generate a key for calculating a MAC for a document whose id is
C{doc_id}.
The key is derived using HMAC having sha256 as underlying hash
function. The key used for HMAC is the first MAC_KEY_LENGTH characters
of Soledad's storage secret. The HMAC message is C{doc_id}.
:param doc_id: The id of the document.
:type doc_id: str
:param secret: soledad secret storage
:type secret: Soledad.storage_secret
:return: The key.
:rtype: str
:raise NoSymmetricSecret: if no symmetric secret was supplied.
"""
if secret is None:
raise NoSymmetricSecret()
return hmac.new(
secret[:MAC_KEY_LENGTH],
doc_id,
hashlib.sha256).digest()
class SoledadCrypto(object):
"""
General cryptographic functionality.
"""
def __init__(self, soledad):
"""
Initialize the crypto object.
:param soledad: A Soledad instance for key lookup.
:type soledad: leap.soledad.Soledad
"""
self._soledad = soledad
def encrypt_sym(self, data, key,
method=EncryptionMethods.AES_256_CTR):
return encrypt_sym(data, key, method)
def decrypt_sym(self, data, key,
method=EncryptionMethods.AES_256_CTR, **kwargs):
return decrypt_sym(data, key, method, **kwargs)
def doc_mac_key(self, doc_id, secret):
return doc_mac_key(doc_id, self.secret)
def doc_passphrase(self, doc_id):
"""
Generate a passphrase for symmetric encryption of document's contents.
The password is derived using HMAC having sha256 as underlying hash
function. The key used for HMAC are the first
C{soledad.REMOTE_STORAGE_SECRET_KENGTH} bytes of Soledad's storage
secret stripped from the first MAC_KEY_LENGTH characters. The HMAC
message is C{doc_id}.
:param doc_id: The id of the document that will be encrypted using
this passphrase.
:type doc_id: str
:return: The passphrase.
:rtype: str
:raise NoSymmetricSecret: if no symmetric secret was supplied.
"""
if self.secret is None:
raise NoSymmetricSecret()
return hmac.new(
self.secret[
MAC_KEY_LENGTH:
self._soledad.REMOTE_STORAGE_SECRET_LENGTH],
doc_id,
hashlib.sha256).digest()
#
# secret setters/getters
#
def _get_secret(self):
return self._soledad.storage_secret
secret = property(
_get_secret, doc='The secret used for symmetric encryption')
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