create a wrapper for libsodium to access functions needed for protocol version4

Author: purificant

paseto/crypto/libsodium_wrapper.py

@@ -0,0 +1,30 @@
+"""This module accesses libsodium via ctypes."""
+
+import ctypes
+import ctypes.util
+
+_library = ctypes.util.find_library("sodium") or ctypes.util.find_library("libsodium")
+if _library is None:
+    raise ValueError("Could not find libsodium")
+_sodium = ctypes.cdll.LoadLibrary(_library)
+
+
+def crypto_stream_xchacha20_xor(message: bytes, nonce: bytes, key: bytes) -> bytes:
+    """Gives access to libsodium function of the same name."""
+
+    if len(nonce) != _sodium.crypto_stream_xchacha20_noncebytes():
+        raise ValueError("incorrect nonce size")
+    if len(key) != _sodium.crypto_stream_xchacha20_keybytes():
+        raise ValueError("incorrect key size")
+
+    message_length: ctypes.c_longlong = ctypes.c_longlong(len(message))
+
+    ciphertext = ctypes.create_string_buffer(len(message))
+
+    exit_code = _sodium.crypto_stream_xchacha20_xor(
+        ciphertext, message, message_length, nonce, key
+    )
+    if exit_code != 0:
+        raise ValueError
+
+    return ciphertext.raw

tests/crypto/test_libsodium_wrapper.py

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+"""This module contains tests for libsodium wrapper."""
+
+import ctypes.util
+from unittest.mock import MagicMock, patch
+
+import pytest
+
+from paseto.crypto import libsodium_wrapper
+
+
+def test_key_size() -> None:
+    """Test exception when nonce size is incorrect."""
+    with pytest.raises(ValueError, match="key"):
+        libsodium_wrapper.crypto_stream_xchacha20_xor(b"", b"0" * 24, b"")
+
+
+def test_nonce_size() -> None:
+    """Test exception when key size is incorrect."""
+    with pytest.raises(ValueError, match="nonce"):
+        libsodium_wrapper.crypto_stream_xchacha20_xor(b"", b"", b"0" * 32)
+
+
+@patch.object(ctypes.util, "find_library")
+def test_no_libsodium(mock: MagicMock) -> None:
+    """Test that exception is raised when libsodium can is not found."""
+    mock.return_value = None
+    with pytest.raises(ValueError):
+        import importlib
+
+        import paseto.crypto.libsodium_wrapper
+
+        importlib.reload(paseto.crypto.libsodium_wrapper)
+
+
+@patch.object(libsodium_wrapper._sodium, "crypto_stream_xchacha20_xor")
+def test_non_zero_exit_code(mock: MagicMock) -> None:
+    mock.return_value = 1
+    with pytest.raises(ValueError):
+        libsodium_wrapper.crypto_stream_xchacha20_xor(b"", b"0" * 24, b"0" * 32)