add ChaCha20 support (#3919)

* add ChaCha20 support

* review feedback

* 256 divided by 8 is what again?

* ...

1 files changed, 60 insertions, 0 deletions

diff --git a/tests/hazmat/primitives/test_chacha20.py b/tests/hazmat/primitives/test_chacha20.py
new file mode 100644
index 00000000..16ef97ed
--- /dev/null
+++ b/tests/hazmat/primitives/test_chacha20.py
@@ -0,0 +1,60 @@
+# 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 struct
+
+import pytest
+
+from cryptography.hazmat.backends.interfaces import CipherBackend
+from cryptography.hazmat.primitives.ciphers import Cipher, algorithms
+
+from .utils import _load_all_params
+from ...utils import load_nist_vectors
+
+
+@pytest.mark.supported(
+    only_if=lambda backend: backend.cipher_supported(
+        algorithms.ChaCha20(b"\x00" * 32, b"0" * 16), None
+    ),
+    skip_message="Does not support ChaCha20",
+)
+@pytest.mark.requires_backend_interface(interface=CipherBackend)
+class TestChaCha20(object):
+    @pytest.mark.parametrize(
+        "vector",
+        _load_all_params(
+            os.path.join("ciphers", "ChaCha20"),
+            ["rfc7539.txt"],
+            load_nist_vectors
+        )
+    )
+    def test_vectors(self, vector, backend):
+        key = binascii.unhexlify(vector["key"])
+        nonce = binascii.unhexlify(vector["nonce"])
+        ibc = struct.pack("<i", int(vector["initial_block_counter"]))
+        pt = binascii.unhexlify(vector["plaintext"])
+        encryptor = Cipher(
+            algorithms.ChaCha20(key, ibc + nonce), None, backend
+        ).encryptor()
+        computed_ct = encryptor.update(pt) + encryptor.finalize()
+        assert binascii.hexlify(computed_ct) == vector["ciphertext"]
+
+    def test_key_size(self):
+        chacha = algorithms.ChaCha20(b"0" * 32, b"0" * 16)
+        assert chacha.key_size == 256
+
+    def test_invalid_key_size(self):
+        with pytest.raises(ValueError):
+            algorithms.ChaCha20(b"wrongsize", b"0" * 16)
+
+    def test_invalid_nonce(self):
+        with pytest.raises(ValueError):
+            algorithms.ChaCha20(b"0" * 32, b"0")
+
+        with pytest.raises(TypeError):
+            algorithms.ChaCha20(b"0" * 32, object())