Add hmac (#402)

stdlib/2and3/hmac.pyi

@@ -0,0 +1,36 @@
+# Stubs for hmac
+
+from typing import Any, Callable, Optional, Union, overload
+from types import ModuleType
+import sys
+
+_B = Union[bytes, bytearray]
+
+# TODO more precise type for object of hashlib
+_Hash = Any
+
+if sys.version_info >= (3, 4):
+    def new(key: _B, msg: Optional[_B] = ...,
+            digestmod: Optional[Union[str, Callable[[], _Hash], ModuleType]] = ...) -> HMAC: ...
+else:
+    def new(  # type: ignore
+            key: _B, msg: Optional[_B] = ...,
+            digestmod: Optional[Union[Callable[[], _Hash], ModuleType]] = ...) -> HMAC: ...
+
+class HMAC:
+    if sys.version_info >= (3,):
+        digest_size = ...  # type: int
+    if sys.version_info >= (3, 4):
+        block_size = ...  # type: int
+        name = ...  # type: str
+    def update(self, msg: _B) -> None: ...
+    def digest(self) -> bytes: ...
+    def hexdigest(self) -> str: ...
+    def copy(self) -> HMAC: ...
+
+@overload
+def compare_digest(a: str, b: str) -> bool: ...
+@overload
+def compare_digest(a: bytes, b: bytes) -> bool: ...
+@overload
+def compare_digest(a: bytearray, b: bytearray) -> bool: ...