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#!/usr/bin/python
# Authors:
# Ade Lee <alee@redhat.com>
#
# 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; version 2 of the License.
#
# 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, write to the Free Software Foundation, Inc.,
# 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
#
# Copyright (C) 2013 Red Hat, Inc.
# All rights reserved.
#
"""
Module containing crypto classes.
"""
import abc
import exceptions
import nss.nss as nss
import os
import shutil
import subprocess
import tempfile
class CryptoProvider(object):
"""
Abstract class containing methods to do cryptographic operations.
"""
__metaclass__ = abc.ABCMeta
def __init__(self):
""" Constructor """
pass
@abc.abstractmethod
def initialize(self):
""" Initialization code """
pass
@staticmethod
@abc.abstractmethod
def generate_nonce_iv(mechanism):
""" Create a random initialization vector """
pass
@abc.abstractmethod
def generate_symmetric_key(self, mechanism=None, size=0):
""" Generate and return a symmetric key """
pass
@abc.abstractmethod
def generate_session_key(self):
""" Generate a session key to be used for wrapping data to the DRM
This must return a 3DES 168 bit key """
pass
@abc.abstractmethod
def symmetric_wrap(self, data, wrapping_key, mechanism=None, nonce_iv=None):
""" encrypt data using a symmetric key (wrapping key)"""
pass
@abc.abstractmethod
def symmetric_unwrap(self, data, wrapping_key, mechanism=None,
nonce_iv=None):
""" decrypt data originally encrypted with symmetric key (wrapping key)
We expect the data and nonce_iv values to be base64 encoded.
The mechanism is the type of key used to do the wrapping. It defaults
to a 56 bit DES3 key.
"""
pass
@abc.abstractmethod
def asymmetric_wrap(self, data, wrapping_cert, mechanism=None):
""" encrypt a symmetric key with the public key of a transport cert.
The mechanism is the type of symmetric key, which defaults to a 56 bit
DES3 key.
"""
pass
#abc.abstractmethod
def get_cert(self, cert_nick):
""" Get the certificate for the specified cert_nick. """
pass
class NSSCryptoProvider(CryptoProvider):
"""
Class that defines NSS implementation of CryptoProvider.
Requires an NSS database to have been set up and initialized.
Note that all inputs and outputs are unencoded.
"""
@staticmethod
def setup_database(db_dir, password=None, over_write=False, password_file=None):
""" Create an NSS database """
if os.path.exists(db_dir):
if not over_write:
raise exceptions.IOError("Directory already exists.")
if os.path.isdir(db_dir):
shutil.rmtree(db_dir)
else:
os.remove(db_dir)
os.makedirs(db_dir)
try:
if password:
(f, password_file) = tempfile.mkstemp()
os.write(f, password)
os.close(f)
command = ['certutil', '-N', '-d', db_dir, '-f', password_file]
subprocess.check_call(command)
finally:
if password and password_file:
os.remove(password_file)
def __init__(self, certdb_dir, certdb_password=None, password_file=None):
""" Initialize nss and nss related parameters
This method expects a NSS database to have already been created at
certdb_dir with password certdb_password.
"""
CryptoProvider.__init__(self)
self.certdb_dir = certdb_dir
if certdb_password:
self.certdb_password = certdb_password
elif password_file:
with open(password_file, 'r') as f:
self.certdb_password = f.readline().strip()
self.nonce_iv = "e4:bb:3b:d3:c3:71:2e:58"
def initialize(self):
"""
Initialize the nss db. Must be done before any crypto operations
"""
nss.nss_init(self.certdb_dir)
def import_cert(self, cert_nick, cert, trust=',,'):
""" Import a certificate into the nss database
"""
# accept both CertData object or cert actual data
if type(cert).__name__ == 'CertData':
content = cert.encoded
else:
content = cert
# certutil -A -d db_dir -n cert_nick -t trust -i cert_file
with tempfile.NamedTemporaryFile() as cert_file:
cert_file.write(content)
cert_file.flush()
command = ['certutil', '-A', '-d', self.certdb_dir,
'-n', cert_nick, '-t', trust,
'-i', cert_file.name]
subprocess.check_call(command)
@staticmethod
def generate_nonce_iv(mechanism=nss.CKM_DES3_CBC_PAD):
""" Create a random initialization vector """
iv_length = nss.get_iv_length(mechanism)
if iv_length > 0:
iv_data = nss.generate_random(iv_length)
return iv_data
else:
return None
@classmethod
def setup_contexts(cls, mechanism, sym_key, nonce_iv):
""" Set up contexts to do wrapping/unwrapping by symmetric keys. """
# Get a PK11 slot based on the cipher
slot = nss.get_best_slot(mechanism)
if sym_key is None:
sym_key = slot.key_gen(mechanism,
None,
slot.get_best_key_length(mechanism))
# If initialization vector was supplied use it, otherwise set it to None
if nonce_iv:
iv_si = nss.SecItem(nonce_iv)
iv_param = nss.param_from_iv(mechanism, iv_si)
else:
iv_data = cls.generate_nonce_iv(mechanism)
if iv_data is not None:
iv_si = nss.SecItem(iv_data)
iv_param = nss.param_from_iv(mechanism, iv_si)
else:
iv_param = None
# Create an encoding context
encoding_ctx = nss.create_context_by_sym_key(mechanism, nss.CKA_ENCRYPT,
sym_key, iv_param)
# Create a decoding context
decoding_ctx = nss.create_context_by_sym_key(mechanism, nss.CKA_DECRYPT,
sym_key, iv_param)
return encoding_ctx, decoding_ctx
def generate_symmetric_key(self, mechanism=nss.CKM_DES3_CBC_PAD, size=0):
""" Returns a symmetric key.
Note that for fixed length keys, this length should be 0. If no length
is provided, then the function will either use 0 (for fixed length keys)
or the maximum available length for that algorithm and the token.
"""
slot = nss.get_best_slot(mechanism)
if size == 0:
size = slot.get_best_key_length(mechanism)
return slot.key_gen(mechanism, None, size)
def generate_session_key(self):
""" Returns a session key to be used when wrapping secrets for the DRM
This will return a 168 bit 3DES key.
"""
return self.generate_symmetric_key(mechanism=nss.CKM_DES3_CBC_PAD)
def symmetric_wrap(self, data, wrapping_key, mechanism=nss.CKM_DES3_CBC_PAD,
nonce_iv=None):
"""
:param data Data to be wrapped
:param wrapping_key Symmetric key to wrap data
Wrap (encrypt) data using the supplied symmetric key
"""
if nonce_iv is None:
nonce_iv = nss.read_hex(self.nonce_iv)
encoding_ctx, _decoding_ctx = self.setup_contexts(mechanism,
wrapping_key,
nonce_iv)
wrapped_data = encoding_ctx.cipher_op(data) +\
encoding_ctx.digest_final()
return wrapped_data
def symmetric_unwrap(self, data, wrapping_key,
mechanism=nss.CKM_DES3_CBC_PAD, nonce_iv=None):
"""
:param data Data to be unwrapped
:param wrapping_key Symmetric key to unwrap data
:param nonce_iv iv data
Unwrap (decrypt) data using the supplied symmetric key
"""
if nonce_iv is None:
nonce_iv = nss.read_hex(self.nonce_iv)
_encoding_ctx, decoding_ctx = self.setup_contexts(mechanism,
wrapping_key,
nonce_iv)
unwrapped_data = decoding_ctx.cipher_op(data) \
+ decoding_ctx.digest_final()
return unwrapped_data
def asymmetric_wrap(self, data, wrapping_cert,
mechanism=nss.CKM_DES3_CBC_PAD):
"""
:param data Data to be wrapped
:param wrapping_cert Public key to wrap data
:param mechanism algorithm of symmetric key to be wrapped
Wrap (encrypt) data using the supplied asymmetric key
"""
public_key = wrapping_cert.subject_public_key_info.public_key
return nss.pub_wrap_sym_key(mechanism, public_key, data)
def get_cert(self, cert_nick):
"""
:param cert_nick Nickname for the certificate to be returned
Searches NSS database and returns SecItem object for this certificate.
"""
return nss.find_cert_from_nickname(cert_nick)
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