refactor serialization module into package (#4606)

* refactor serialization into a package so we can add a pkcs12 module

* oops

3 files changed, 35 insertions, 11 deletions

diff --git a/src/cryptography/hazmat/backends/openssl/backend.py b/src/cryptography/hazmat/backends/openssl/backend.py
index c8a46b98..5d73a7e8 100644
--- a/src/cryptography/hazmat/backends/openssl/backend.py
+++ b/src/cryptography/hazmat/backends/openssl/backend.py
@@ -75,6 +75,9 @@ from cryptography.hazmat.primitives.ciphers.modes import (
     CBC, CFB, CFB8, CTR, ECB, GCM, OFB, XTS
 )
 from cryptography.hazmat.primitives.kdf import scrypt
+from cryptography.hazmat.primitives.serialization.base import (
+    _ssh_write_mpint, _ssh_write_string
+)
 from cryptography.x509 import ocsp
 
 
@@ -1795,19 +1798,19 @@ class Backend(object):
         if isinstance(key, rsa.RSAPublicKey):
             public_numbers = key.public_numbers()
             return b"ssh-rsa " + base64.b64encode(
-                serialization._ssh_write_string(b"ssh-rsa") +
-                serialization._ssh_write_mpint(public_numbers.e) +
-                serialization._ssh_write_mpint(public_numbers.n)
+                _ssh_write_string(b"ssh-rsa") +
+                _ssh_write_mpint(public_numbers.e) +
+                _ssh_write_mpint(public_numbers.n)
             )
         elif isinstance(key, dsa.DSAPublicKey):
             public_numbers = key.public_numbers()
             parameter_numbers = public_numbers.parameter_numbers
             return b"ssh-dss " + base64.b64encode(
-                serialization._ssh_write_string(b"ssh-dss") +
-                serialization._ssh_write_mpint(parameter_numbers.p) +
-                serialization._ssh_write_mpint(parameter_numbers.q) +
-                serialization._ssh_write_mpint(parameter_numbers.g) +
-                serialization._ssh_write_mpint(public_numbers.y)
+                _ssh_write_string(b"ssh-dss") +
+                _ssh_write_mpint(parameter_numbers.p) +
+                _ssh_write_mpint(parameter_numbers.q) +
+                _ssh_write_mpint(parameter_numbers.g) +
+                _ssh_write_mpint(public_numbers.y)
             )
         else:
             assert isinstance(key, ec.EllipticCurvePublicKey)
@@ -1824,9 +1827,9 @@ class Backend(object):
                     "supported by the SSH public key format"
                 )
             return b"ecdsa-sha2-" + curve_name + b" " + base64.b64encode(
-                serialization._ssh_write_string(b"ecdsa-sha2-" + curve_name) +
-                serialization._ssh_write_string(curve_name) +
-                serialization._ssh_write_string(public_numbers.encode_point())
+                _ssh_write_string(b"ecdsa-sha2-" + curve_name) +
+                _ssh_write_string(curve_name) +
+                _ssh_write_string(public_numbers.encode_point())
             )
 
     def _parameter_bytes(self, encoding, format, cdata):
diff --git a/src/cryptography/hazmat/primitives/serialization/__init__.py b/src/cryptography/hazmat/primitives/serialization/__init__.py
new file mode 100644
index 00000000..cff775b8
--- /dev/null
+++ b/src/cryptography/hazmat/primitives/serialization/__init__.py
@@ -0,0 +1,21 @@
+# This file is dual licensed under the terms of the Apache License, Version
+# 2.0, and the BSD License. See the LICENSE file in the root of this repository
+# for complete details.
+
+from __future__ import absolute_import, division, print_function
+
+from cryptography.hazmat.primitives.serialization.base import (
+    BestAvailableEncryption, Encoding, KeySerializationEncryption,
+    NoEncryption, ParameterFormat, PrivateFormat, PublicFormat,
+    load_der_parameters, load_der_private_key, load_der_public_key,
+    load_pem_parameters, load_pem_private_key, load_pem_public_key,
+    load_ssh_public_key,
+)
+
+__all__ = [
+    "load_der_parameters", "load_der_private_key", "load_der_public_key",
+    "load_pem_parameters", "load_pem_private_key", "load_pem_public_key",
+    "load_ssh_public_key", "Encoding", "PrivateFormat", "PublicFormat",
+    "ParameterFormat", "KeySerializationEncryption", "BestAvailableEncryption",
+    "NoEncryption",
+]
diff --git a/src/cryptography/hazmat/primitives/serialization.py b/src/cryptography/hazmat/primitives/serialization/base.py
index bd09e6e3..bd09e6e3 100644
--- a/src/cryptography/hazmat/primitives/serialization.py
+++ b/src/cryptography/hazmat/primitives/serialization/base.py