Use MultiFernet for encryption

Facilitates key rotation and uses more secure encryption than what
sqlalchemy-utils does.

Fixes #117 and #119.

lemur/certificates/models.py

@@ -13,9 +13,7 @@ from cryptography.hazmat.backends import default_backend
 from sqlalchemy.orm import relationship
 from sqlalchemy import event, Integer, ForeignKey, String, DateTime, PassiveDefault, func, Column, Text, Boolean
 
-from sqlalchemy_utils import EncryptedType
-
-from lemur.utils import get_key
+from lemur.utils import Vault
 from lemur.database import db
 from lemur.plugins.base import plugins
 
@@ -213,7 +211,7 @@ class Certificate(db.Model):
     id = Column(Integer, primary_key=True)
     owner = Column(String(128))
     body = Column(Text())
-    private_key = Column(EncryptedType(String, get_key))
+    private_key = Column(Vault)
     status = Column(String(128))
     deleted = Column(Boolean, index=True)
     name = Column(String(128))

lemur/manage.py

@@ -72,7 +72,7 @@ SECRET_KEY = '{flask_secret_key}'
 
 # You should consider storing these separately from your config
 LEMUR_TOKEN_SECRET = '{secret_token}'
-LEMUR_ENCRYPTION_KEY = '{encryption_key}'
+LEMUR_ENCRYPTION_KEYS = '{encryption_key}'
 
 # this is a list of domains as regexes that only admins can issue
 LEMUR_RESTRICTED_DOMAINS = []
@@ -171,7 +171,9 @@ def generate_settings():
     settings file.
     """
     output = CONFIG_TEMPLATE.format(
-        encryption_key=base64.b64encode(os.urandom(KEY_LENGTH)),
+        # we use Fernet.generate_key to make sure that the key length is
+        # compatible with Fernet
+        encryption_key=Fernet.generate_key(),
         secret_token=base64.b64encode(os.urandom(KEY_LENGTH)),
         flask_secret_key=base64.b64encode(os.urandom(KEY_LENGTH)),
     )

lemur/roles/models.py

@@ -12,9 +12,8 @@
 from sqlalchemy.orm import relationship
 from sqlalchemy import Column, Integer, String, Text, ForeignKey
 
-from sqlalchemy_utils import EncryptedType
 from lemur.database import db
-from lemur.utils import get_key
+from lemur.utils import Vault
 from lemur.models import roles_users
 
 
@@ -23,7 +22,7 @@ class Role(db.Model):
     id = Column(Integer, primary_key=True)
     name = Column(String(128), unique=True)
     username = Column(String(128))
-    password = Column(EncryptedType(String, get_key))
+    password = Column(Vault)
     description = Column(Text)
     authority_id = Column(Integer, ForeignKey('authorities.id'))
     user_id = Column(Integer, ForeignKey('users.id'))

lemur/tests/conf.py

@@ -21,7 +21,7 @@ SECRET_KEY = 'I/dVhOZNSMZMqrFJa5tWli6VQccOGudKerq3eWPMSzQNmHHVhMAQfQ=='
 
 # You should consider storing these separately from your config
 LEMUR_TOKEN_SECRET = 'test'
-LEMUR_ENCRYPTION_KEY = 'jPd2xwxgVGXONqghHNq7/S761sffYSrT3UAgKwgtMxbqa0gmKYCfag=='
+LEMUR_ENCRYPTION_KEYS = 'o61sBLNBSGtAckngtNrfVNd8xy8Hp9LBGDstTbMbqCY='
 
 # this is a list of domains as regexes that only admins can issue
 LEMUR_RESTRICTED_DOMAINS = []

lemur/utils.py

@@ -5,17 +5,93 @@
     :license: Apache, see LICENSE for more details.
 .. moduleauthor:: Kevin Glisson <kglisson@netflix.com>
 """
+import six
 from flask import current_app
+from cryptography.fernet import Fernet, MultiFernet
+import sqlalchemy.types as types
 
 
-def get_key():
+def get_keys():
     """
-    Gets the current encryption key
+    Gets the encryption keys.
+
+    This supports multiple keys to facilitate key rotation. The first
+    key in the list is used to encrypt. Decryption is attempted with
+    each key in succession.
 
     :return:
     """
+
+    # when running lemur create_config, this code needs to work despite
+    # the fact that there is not a current_app with a config at that point
     try:
-        return current_app.config.get('LEMUR_ENCRYPTION_KEY').strip()
-    except RuntimeError:
-        print("No Encryption Key Found")
-        return ''
+        keys = current_app.config.get('LEMUR_ENCRYPTION_KEYS')
+    except:
+        print("no encryption keys")
+        return []
+
+    # this function is expected to return a list of keys, but we want
+    # to let people just specify a single key
+    if not isinstance(keys, list):
+        keys = [keys]
+
+    # make sure there is no accidental whitespace
+    keys = [key.strip() for key in keys]
+
+    return keys
+
+
+class Vault(types.TypeDecorator):
+    """
+    A custom SQLAlchemy column type that transparently handles encryption.
+
+    This uses the MultiFernet from the cryptography package to faciliate
+    key rotation. That class handles encryption and signing.
+
+    Fernet uses AES in CBC mode with 128-bit keys and PKCS7 padding. It
+    uses HMAC-SHA256 for ciphertext authentication. Initialization
+    vectors are generated using os.urandom().
+    """
+
+    # required by SQLAlchemy. defines the underlying column type
+    impl = types.Binary
+
+    def process_bind_param(self, value, dialect):
+        """
+        Encrypt values on the way into the database.
+
+        MultiFernet.encrypt uses the first key in the list.
+        """
+
+        # we assume that the user's keys are already Fernet keys (32 byte
+        # keys that have been base64 encoded).
+        self.keys = [Fernet(key) for key in get_keys()]
+
+        # we only support strings and they should be of type bytes for Fernet
+        if not isinstance(value, six.string_types):
+            return None
+
+        value = bytes(value)
+
+        return MultiFernet(self.keys).encrypt(value)
+
+    def process_result_value(self, value, dialect):
+        """
+        Decrypt values on the way out of the database.
+
+        MultiFernet tries each key until one works.
+        """
+
+        # we assume that the user's keys are already Fernet keys (32 byte
+        # keys that have been base64 encoded).
+        self.keys = [Fernet(key) for key in get_keys()]
+
+        # if the value is not a string we aren't going to try to decrypt
+        # it. this is for the case where the column is null
+        if not isinstance(value, six.string_types):
+            return None
+
+        # TODO this may raise an InvalidToken exception in certain
+        # cases. Should we handle that?
+        # https://cryptography.io/en/latest/fernet/#cryptography.fernet.Fernet.decrypt
+        return MultiFernet(self.keys).decrypt(value)