diff --git a/cryptography/hazmat/primitives/hmac.py b/cryptography/hazmat/primitives/hmac.py
index 4da0cc3..0277086 100644
--- a/cryptography/hazmat/primitives/hmac.py
+++ b/cryptography/hazmat/primitives/hmac.py
@@ -17,43 +17,35 @@
 
 import six
 
+from cryptography.hazmat.primitives import interfaces
 
+
+@interfaces.register(interfaces.HashContext)
 class HMAC(object):
-    def __init__(self, key, msg=None, digestmod=None, ctx=None, backend=None):
+    def __init__(self, key, algorithm, ctx=None, backend=None):
         super(HMAC, self).__init__()
+        self.algorithm = algorithm
+
         if backend is None:
             from cryptography.hazmat.bindings import _default_backend
             backend = _default_backend
 
-        if digestmod is None:
-            raise TypeError("digestmod is a required argument")
-
         self._backend = backend
-        self.digestmod = digestmod
-        self.key = key
+        self._key = key
         if ctx is None:
-            self._ctx = self._backend.hmacs.create_ctx(key, self.digestmod)
+            self._ctx = self._backend.hmacs.create_ctx(key, self.algorithm)
         else:
             self._ctx = ctx
 
-        if msg is not None:
-            self.update(msg)
-
     def update(self, msg):
         if isinstance(msg, six.text_type):
             raise TypeError("Unicode-objects must be encoded before hashing")
         self._backend.hmacs.update_ctx(self._ctx, msg)
 
     def copy(self):
-        return self.__class__(self.key, digestmod=self.digestmod,
-                              backend=self._backend, ctx=self._copy_ctx())
+        return self.__class__(self._key, self.algorithm, backend=self._backend,
+                              ctx=self._backend.hmacs.copy_ctx(self._ctx))
 
-    def digest(self):
-        return self._backend.hmacs.finalize_ctx(self._copy_ctx(),
-                                                self.digestmod.digest_size)
-
-    def hexdigest(self):
-        return str(binascii.hexlify(self.digest()).decode("ascii"))
-
-    def _copy_ctx(self):
-        return self._backend.hmacs.copy_ctx(self._ctx)
+    def finalize(self):
+        return self._backend.hmacs.finalize_ctx(self._ctx,
+                                                self.algorithm.digest_size)
diff --git a/tests/hazmat/primitives/test_hmac.py b/tests/hazmat/primitives/test_hmac.py
index 42726a7..4390902 100644
--- a/tests/hazmat/primitives/test_hmac.py
+++ b/tests/hazmat/primitives/test_hmac.py
@@ -32,26 +32,15 @@
     )
 
     def test_hmac_reject_unicode(self, backend):
-        h = hmac.HMAC(key=b"mykey", digestmod=hashes.SHA1, backend=backend)
+        h = hmac.HMAC(b"mykey", hashes.SHA1, backend=backend)
         with pytest.raises(TypeError):
             h.update(six.u("\u00FC"))
 
-    def test_base_hash_hexdigest_string_type(self, backend):
-        h = hmac.HMAC(key=b"mykey", digestmod=hashes.SHA1, backend=backend,
-                      msg=b"")
-        assert isinstance(h.hexdigest(), str)
-
-    def test_hmac_no_digestmod(self):
-        with pytest.raises(TypeError):
-            hmac.HMAC(key=b"shortkey")
-
-
-class TestCopyHMAC(object):
     def test_copy_backend_object(self):
         pretend_hmac = pretend.stub(copy_ctx=lambda a: True)
         pretend_backend = pretend.stub(hmacs=pretend_hmac)
         pretend_ctx = pretend.stub()
-        h = hmac.HMAC(b"key", digestmod=hashes.SHA1, backend=pretend_backend,
+        h = hmac.HMAC(b"key", hashes.SHA1, backend=pretend_backend,
                       ctx=pretend_ctx)
         assert h._backend is pretend_backend
         assert h.copy()._backend is pretend_backend
diff --git a/tests/hazmat/primitives/utils.py b/tests/hazmat/primitives/utils.py
index efc5fbf..1dfad6e 100644
--- a/tests/hazmat/primitives/utils.py
+++ b/tests/hazmat/primitives/utils.py
@@ -129,7 +129,7 @@
     assert m.finalize() == binascii.unhexlify(md.lower().encode("ascii"))
 
 
-def generate_hmac_test(param_loader, path, file_names, digestmod,
+def generate_hmac_test(param_loader, path, file_names, algorithm,
                        only_if=None, skip_message=None):
     def test_hmac(self):
         for backend in _ALL_BACKENDS:
@@ -138,7 +138,7 @@
                     yield (
                         hmac_test,
                         backend,
-                        digestmod,
+                        algorithm,
                         params,
                         only_if,
                         skip_message
@@ -146,18 +146,15 @@
     return test_hmac
 
 
-def hmac_test(backend, digestmod, params, only_if, skip_message):
+def hmac_test(backend, algorithm, params, only_if, skip_message):
     if only_if is not None and not only_if(backend):
         pytest.skip(skip_message)
     msg = params[0]
     md = params[1]
     key = params[2]
-    h = hmac.HMAC(binascii.unhexlify(key), digestmod=digestmod)
+    h = hmac.HMAC(binascii.unhexlify(key), algorithm)
     h.update(binascii.unhexlify(msg))
-    assert h.hexdigest() == md
-    digest = hmac.HMAC(binascii.unhexlify(key), digestmod=digestmod,
-                       msg=binascii.unhexlify(msg)).hexdigest()
-    assert digest == md
+    assert h.finalize() == binascii.unhexlify(md)
 
 
 def generate_base_hmac_test(hash_cls, only_if=None, skip_message=None):
@@ -173,11 +170,11 @@
     return test_base_hmac
 
 
-def base_hmac_test(backend, digestmod, only_if, skip_message):
+def base_hmac_test(backend, algorithm, only_if, skip_message):
     if only_if is not None and not only_if(backend):
         pytest.skip(skip_message)
     key = b"ab"
-    h = hmac.HMAC(binascii.unhexlify(key), digestmod=digestmod)
+    h = hmac.HMAC(binascii.unhexlify(key), algorithm)
     h_copy = h.copy()
     assert h != h_copy
     assert h._ctx != h_copy._ctx