X448 support (#4580)

* x448 support

This work was originally authored by derwolfe

* update docs to have a more useful derived key length

* error if key is not a valid length in from_public_bytes

* one more

* switch to using evp_pkey_keygen_gc for x448 keygen

* review feedback

* switch to using evp_pkey_derive

* nit fix

1 files changed, 127 insertions, 0 deletions

diff --git a/tests/hazmat/primitives/test_x448.py b/tests/hazmat/primitives/test_x448.py
new file mode 100644
index 00000000..71b25341
--- /dev/null
+++ b/tests/hazmat/primitives/test_x448.py
@@ -0,0 +1,127 @@
+# 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
+
+import binascii
+import os
+
+import pytest
+
+from cryptography.exceptions import _Reasons
+from cryptography.hazmat.backends.interfaces import DHBackend
+from cryptography.hazmat.primitives.asymmetric.x448 import (
+    X448PrivateKey, X448PublicKey
+)
+
+from ...utils import (
+    load_nist_vectors, load_vectors_from_file, raises_unsupported_algorithm
+)
+
+
+@pytest.mark.supported(
+    only_if=lambda backend: not backend.x448_supported(),
+    skip_message="Requires OpenSSL without X448 support"
+)
+@pytest.mark.requires_backend_interface(interface=DHBackend)
+def test_x448_unsupported(backend):
+    with raises_unsupported_algorithm(_Reasons.UNSUPPORTED_EXCHANGE_ALGORITHM):
+        X448PublicKey.from_public_bytes(b"0" * 32)
+
+    with raises_unsupported_algorithm(_Reasons.UNSUPPORTED_EXCHANGE_ALGORITHM):
+        X448PrivateKey.generate()
+
+
+@pytest.mark.supported(
+    only_if=lambda backend: backend.x448_supported(),
+    skip_message="Requires OpenSSL with X448 support"
+)
+@pytest.mark.requires_backend_interface(interface=DHBackend)
+class TestX448Exchange(object):
+    @pytest.mark.parametrize(
+        "vector",
+        load_vectors_from_file(
+            os.path.join("asymmetric", "X448", "rfc7748.txt"),
+            load_nist_vectors
+        )
+    )
+    def test_rfc7748(self, vector, backend):
+        private = binascii.unhexlify(vector["input_scalar"])
+        public = binascii.unhexlify(vector["input_u"])
+        shared_key = binascii.unhexlify(vector["output_u"])
+        private_key = X448PrivateKey._from_private_bytes(private)
+        public_key = X448PublicKey.from_public_bytes(public)
+        computed_shared_key = private_key.exchange(public_key)
+        assert computed_shared_key == shared_key
+
+    def test_rfc7748_1000_iteration(self, backend):
+        old_private = private = public = binascii.unhexlify(
+            b"05000000000000000000000000000000000000000000000000000000"
+            b"00000000000000000000000000000000000000000000000000000000"
+        )
+        shared_key = binascii.unhexlify(
+            b"aa3b4749d55b9daf1e5b00288826c467274ce3ebbdd5c17b975e09d4"
+            b"af6c67cf10d087202db88286e2b79fceea3ec353ef54faa26e219f38"
+        )
+        private_key = X448PrivateKey._from_private_bytes(private)
+        public_key = X448PublicKey.from_public_bytes(public)
+        for _ in range(1000):
+            computed_shared_key = private_key.exchange(public_key)
+            private_key = X448PrivateKey._from_private_bytes(
+                computed_shared_key
+            )
+            public_key = X448PublicKey.from_public_bytes(old_private)
+            old_private = computed_shared_key
+
+        assert computed_shared_key == shared_key
+
+    # These vectors are also from RFC 7748
+    # https://tools.ietf.org/html/rfc7748#section-6.2
+    @pytest.mark.parametrize(
+        ("private_bytes", "public_bytes"),
+        [
+            (
+                binascii.unhexlify(
+                    b"9a8f4925d1519f5775cf46b04b5800d4ee9ee8bae8bc5565d498c28d"
+                    b"d9c9baf574a9419744897391006382a6f127ab1d9ac2d8c0a598726b"
+                ),
+                binascii.unhexlify(
+                    b"9b08f7cc31b7e3e67d22d5aea121074a273bd2b83de09c63faa73d2c"
+                    b"22c5d9bbc836647241d953d40c5b12da88120d53177f80e532c41fa0"
+                )
+            ),
+            (
+                binascii.unhexlify(
+                    b"1c306a7ac2a0e2e0990b294470cba339e6453772b075811d8fad0d1d"
+                    b"6927c120bb5ee8972b0d3e21374c9c921b09d1b0366f10b65173992d"
+                ),
+                binascii.unhexlify(
+                    b"3eb7a829b0cd20f5bcfc0b599b6feccf6da4627107bdb0d4f345b430"
+                    b"27d8b972fc3e34fb4232a13ca706dcb57aec3dae07bdc1c67bf33609"
+                )
+            )
+        ]
+    )
+    def test_public_bytes(self, private_bytes, public_bytes, backend):
+        private_key = X448PrivateKey._from_private_bytes(private_bytes)
+        assert private_key.public_key().public_bytes() == public_bytes
+        public_key = X448PublicKey.from_public_bytes(public_bytes)
+        assert public_key.public_bytes() == public_bytes
+
+    def test_generate(self, backend):
+        key = X448PrivateKey.generate()
+        assert key
+        assert key.public_key()
+
+    def test_invalid_type_exchange(self, backend):
+        key = X448PrivateKey.generate()
+        with pytest.raises(TypeError):
+            key.exchange(object())
+
+    def test_invalid_length_from_public_bytes(self, backend):
+        with pytest.raises(ValueError):
+            X448PublicKey.from_public_bytes(b"a" * 55)
+
+        with pytest.raises(ValueError):
+            X448PublicKey.from_public_bytes(b"a" * 57)