Support for traditional OpenSSL and PKCS8 RSA private key serialization

CHANGELOG.rst

@@ -78,6 +78,14 @@ Changelog
   support loading DER encoded public keys.
 * Fixed building against LibreSSL, a compile-time substitute for OpenSSL.
 * FreeBSD 9.2 was removed from the continuous integration system.
+* Added
+  :class:`~cryptography.hazmat.primitives.asymmetric.rsa.RSAPrivateKeyWithSerialization`
+  and deprecated
+  :class:`~cryptography.hazmat.primitives.asymmetric.rsa.RSAPrivateKeyWithNumbers`.
+* Added
+  :meth:`~cryptography.hazmat.primitives.asymmetric.rsa.RSAPrivateKeyWithSerialization.as_bytes`
+  to
+  :class:`~cryptography.hazmat.primitives.asymmetric.rsa.RSAPrivateKeyWithSerialization`.
 
 0.7.2 - 2015-01-16
 ~~~~~~~~~~~~~~~~~~

docs/hazmat/primitives/asymmetric/rsa.rst

@@ -80,6 +80,39 @@ password. If the key is encrypted we can pass a ``bytes`` object as the
 There is also support for :func:`loading public keys in the SSH format
 <cryptography.hazmat.primitives.serialization.load_ssh_public_key>`.
 
+Key serialization
+~~~~~~~~~~~~~~~~~
+
+If you have a key that you've loaded or generated which implements the
+:class:`~cryptography.hazmat.primitives.asymmetric.rsa.RSAPrivateKeyWithSerialization`
+interface you can use
+:meth:`~cryptography.hazmat.primitives.asymmetric.rsa.RSAPrivateKeyWithSerialization.as_bytes`
+to serialize the key.
+
+.. doctest::
+
+    >>> from cryptography.hazmat.primitives import serialization
+    >>> pem = private_key.as_bytes(
+    ...    encoding=serialization.Encoding.PEM,
+    ...    format=serialization.Format.PKCS8,
+    ...    encryption_algorithm=serialization.BestAvailableEncryption(b'mypassword')
+    ... )
+    >>> pem.splitlines()[0]
+    '-----BEGIN ENCRYPTED PRIVATE KEY-----'
+
+It is also possible to serialize without encryption using
+:class:`~cryptography.hazmat.primitives.serialization.NoEncryption`.
+
+.. doctest::
+
+    >>> pem = private_key.as_bytes(
+    ...    encoding=serialization.Encoding.PEM,
+    ...    format=serialization.Format.TraditionalOpenSSL,
+    ...    encryption_algorithm=serialization.NoEncryption()
+    ... )
+    >>> pem.splitlines()[0]
+    '-----BEGIN RSA PRIVATE KEY-----'
+
 Signing
 ~~~~~~~
 
@@ -485,6 +518,43 @@ Key interfaces
             instance.
 
 
+.. class:: RSAPrivateKeyWithSerialization
+
+    .. versionadded:: 0.8
+
+    Extends :class:`RSAPrivateKey`.
+
+    .. method:: private_numbers()
+
+        Create a
+        :class:`~cryptography.hazmat.primitives.asymmetric.rsa.RSAPrivateNumbers`
+        object.
+
+        :returns: An
+            :class:`~cryptography.hazmat.primitives.asymmetric.rsa.RSAPrivateNumbers`
+            instance.
+
+    .. method:: as_bytes(encoding, format, encryption_algorithm)
+
+        Allows serialization of the key to bytes. Encoding (PEM or DER), format
+        (TraditionalOpenSSL or PKCS8) and encryption algorithm (such as
+        :class:`~cryptography.hazmat.primitives.serialization.BestAvailableEncryption`
+        or :class:`~cryptography.hazmat.primitives.serialization.NoEncryption`)
+        are chosen to define the exact serialization.
+
+        :param encoding: A value from the
+            :class:`~cryptography.hazmat.primitives.serialization.Encoding` enum.
+
+        :param format: A value from the
+            :class:`~cryptography.hazmat.primitives.serialization.Format` enum.
+
+        :param encryption_algorithm: An instance of an object conforming to the
+            :class:`~cryptography.hazmat.primitives.serialization.KeySerializationEncryption`
+            interface.
+
+        :return bytes: Serialized key.
+
+
 .. class:: RSAPublicKey
 
     .. versionadded:: 0.2

docs/hazmat/primitives/asymmetric/serialization.rst

@@ -3,7 +3,7 @@
 Key Serialization
 =================
 
-.. currentmodule:: cryptography.hazmat.primitives.serialization
+.. module:: cryptography.hazmat.primitives.serialization
 
 .. testsetup::
 
@@ -75,7 +75,7 @@ methods.
     .. doctest::
 
         >>> from cryptography.hazmat.backends import default_backend
-        >>> from cryptography.hazmat.primitives.asymmetric import dsa, rsa
+        >>> from cryptography.hazmat.primitives.asymmetric import rsa
         >>> from cryptography.hazmat.primitives.serialization import load_pem_private_key
         >>> key = load_pem_private_key(pem_data, password=None, backend=default_backend())
         >>> if isinstance(key, rsa.RSAPrivateKey):
@@ -282,3 +282,64 @@ DSA keys look almost identical but begin with ``ssh-dss`` rather than
 
     :raises cryptography.exceptions.UnsupportedAlgorithm: If the serialized
         key is of a type that is not supported.
+
+Serialization Formats
+~~~~~~~~~~~~~~~~~~~~~
+
+.. class:: Format
+
+    .. versionadded:: 0.8
+
+    An enumeration for key formats.
+
+    .. attribute:: TraditionalOpenSSL
+
+        Frequently known as PKCS#1 format. Still a widely used format, but
+        generally considered legacy.
+
+    .. attribute:: PKCS8
+
+        A more modern format for serializing keys which allows for better
+        encryption. Choose this unless you have explicit legacy compatibility
+        requirements.
+
+Serialization Encodings
+~~~~~~~~~~~~~~~~~~~~~~~
+
+.. class:: Encoding
+
+    .. versionadded:: 0.8
+
+    An enumeration for encoding types.
+
+    .. attribute:: PEM
+
+        For PEM format. This is a base64 format with delimiters.
+
+    .. attribute:: DER
+
+        For DER format. This is a binary format.
+
+
+Serialization Encryption Types
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. class:: KeySerializationEncryption
+
+    Objects with this interface are usable as encryption types with methods
+    like
+    :meth:`~cryptography.hazmat.primitives.asymmetric.rsa.RSAPrivateKeyWithSerialization.as_bytes`.
+    All other classes in this section represent the available choices for
+    encryption and have this interface.
+
+.. class:: BestAvailableEncryption(password)
+
+    Encrypt using the best available encryption for a given key's backend.
+    This is a curated encryption choice and the algorithm may change over
+    time.
+
+    :param bytes password: The password to use for encryption.
+
+.. class:: NoEncryption
+
+    Do not encrypt.

docs/spelling_wordlist.txt

@@ -44,6 +44,8 @@ pseudorandom
 pyOpenSSL
 Schneier
 scrypt
+Serializers
+serializer
 Solaris
 Tanja
 testability

src/cryptography/hazmat/backends/openssl/rsa.py

@@ -17,8 +17,13 @@
 from cryptography.hazmat.primitives.asymmetric.padding import (
     AsymmetricPadding, MGF1, OAEP, PKCS1v15, PSS
 )
-from cryptography.hazmat.primitives.interfaces import (
-    RSAPrivateKeyWithNumbers, RSAPublicKeyWithNumbers
+from cryptography.hazmat.primitives.asymmetric.rsa import (
+    RSAPrivateKeyWithNumbers, RSAPrivateKeyWithSerialization,
+    RSAPublicKeyWithNumbers
+)
+from cryptography.hazmat.primitives.serialization import (
+    BestAvailableEncryption, Encoding, Format, KeySerializationEncryption,
+    NoEncryption
 )
 
 
@@ -507,6 +512,7 @@ def _verify_pss(self, evp_md):
 
 
 @utils.register_interface(RSAPrivateKeyWithNumbers)
+@utils.register_interface(RSAPrivateKeyWithSerialization)
 class _RSAPrivateKey(object):
     def __init__(self, backend, rsa_cdata):
         self._backend = backend
@@ -559,6 +565,62 @@ def private_numbers(self):
             )
         )
 
+    def as_bytes(self, encoding, format, encryption_algorithm):
+        if not isinstance(encoding, Encoding):
+            raise TypeError("encoding must be an item from the Encoding enum")
+
+        if not isinstance(format, Format):
+            raise TypeError("format must be an item from the Format enum")
+
+        # This is a temporary check until we land DER serialization.
+        if encoding is not Encoding.PEM:
+            raise ValueError("Only PEM encoding is supported by this backend")
+
+        if format is Format.PKCS8:
+            write_bio = self._backend._lib.PEM_write_bio_PKCS8PrivateKey
+            key = self._evp_pkey
+        elif format is Format.TraditionalOpenSSL:
+            write_bio = self._backend._lib.PEM_write_bio_RSAPrivateKey
+            key = self._rsa_cdata
+
+        if not isinstance(encryption_algorithm, KeySerializationEncryption):
+            raise TypeError(
+                "Encryption algorithm must be a KeySerializationEncryption "
+                "instance"
+            )
+
+        if isinstance(encryption_algorithm, NoEncryption):
+            password = b""
+            passlen = 0
+            evp_cipher = self._backend._ffi.NULL
+        elif isinstance(encryption_algorithm, BestAvailableEncryption):
+            # This is a curated value that we will update over time.
+            evp_cipher = self._backend._lib.EVP_get_cipherbyname(
+                b"aes-256-cbc"
+            )
+            password = encryption_algorithm.password
+            passlen = len(password)
+            if passlen > 1023:
+                raise ValueError(
+                    "Passwords longer than 1023 bytes are not supported by "
+                    "this backend"
+                )
+        else:
+            raise ValueError("Unsupported encryption type")
+
+        bio = self._backend._create_mem_bio()
+        res = write_bio(
+            bio,
+            key,
+            evp_cipher,
+            password,
+            passlen,
+            self._backend._ffi.NULL,
+            self._backend._ffi.NULL
+        )
+        assert res == 1
+        return self._backend._read_mem_bio(bio)
+
 
 @utils.register_interface(RSAPublicKeyWithNumbers)
 class _RSAPublicKey(object):

src/cryptography/hazmat/primitives/asymmetric/rsa.py

@@ -42,13 +42,30 @@ def public_key(self):
 
 
 @six.add_metaclass(abc.ABCMeta)
-class RSAPrivateKeyWithNumbers(RSAPrivateKey):
+class RSAPrivateKeyWithSerialization(RSAPrivateKey):
     @abc.abstractmethod
     def private_numbers(self):
         """
         Returns an RSAPrivateNumbers.
         """
 
+    @abc.abstractmethod
+    def as_bytes(self, encoding, format, encryption_algorithm):
+        """
+        Returns the key serialized as bytes.
+        """
+
+
+RSAPrivateKeyWithNumbers = utils.deprecated(
+    RSAPrivateKeyWithSerialization,
+    __name__,
+    (
+        "The RSAPrivateKeyWithNumbers interface has been renamed to "
+        "RSAPrivateKeyWithSerialization"
+    ),
+    utils.DeprecatedIn08
+)
+
 
 @six.add_metaclass(abc.ABCMeta)
 class RSAPublicKey(object):

src/cryptography/hazmat/primitives/interfaces/__init__.py

@@ -289,11 +289,12 @@
 )
 
 RSAPrivateKeyWithNumbers = utils.deprecated(
-    rsa.RSAPrivateKeyWithNumbers,
+    rsa.RSAPrivateKeyWithSerialization,
     __name__,
     (
         "The RSAPrivateKeyWithNumbers interface has moved to the "
-        "cryptography.hazmat.primitives.asymmetric.rsa module"
+        "cryptography.hazmat.primitives.asymmetric.rsa module and has been "
+        "renamed RSAPrivateKeyWithSerialization"
     ),
     utils.DeprecatedIn08
 )

src/cryptography/hazmat/primitives/serialization.py

@@ -4,11 +4,14 @@
 
 from __future__ import absolute_import, division, print_function
 
+import abc
 import base64
 import struct
+from enum import Enum
 
 import six
 
+from cryptography import utils
 from cryptography.exceptions import UnsupportedAlgorithm
 from cryptography.hazmat.primitives.asymmetric import dsa, ec, rsa
 
@@ -164,3 +167,32 @@ def _int_from_bytes(data, byteorder, signed=False):
             data = data[4:]
 
         return result
+
+
+class Encoding(Enum):
+    PEM = "PEM"
+    DER = "DER"
+
+
+class Format(Enum):
+    PKCS8 = "PKCS8"
+    TraditionalOpenSSL = "TraditionalOpenSSL"
+
+
+@six.add_metaclass(abc.ABCMeta)
+class KeySerializationEncryption(object):
+    pass
+
+
+@utils.register_interface(KeySerializationEncryption)
+class BestAvailableEncryption(object):
+    def __init__(self, password):
+        if not isinstance(password, bytes) or len(password) == 0:
+            raise ValueError("Password must be 1 or more bytes.")
+
+        self.password = password
+
+
+@utils.register_interface(KeySerializationEncryption)
+class NoEncryption(object):
+    pass