python: Add support for the long KDF MAC calculation.

2 files changed, 52 insertions, 0 deletions

diff --git a/python/olm/sas.py b/python/olm/sas.py
index 8574cfd..c12b7bc 100644
--- a/python/olm/sas.py
+++ b/python/olm/sas.py
@@ -220,3 +220,38 @@ class Sas(object):
             )
         )
         return bytes_to_native_str(ffi.unpack(mac_buffer, mac_length))
+
+    @other_pubkey_set
+    def calculate_mac_long_kdf(self, message, extra_info):
+        # type: (str, str) -> str
+        """Generate a message authentication code based on the shared secret.
+
+        This function should not be used unless compatibility with an older
+        non-tagged Olm version is required.
+
+        Args:
+            message (str): The message to produce the authentication code for.
+            extra_info (str): Extra information to mix in when generating the
+                MAC
+
+        Raises OlmSasError on failure.
+
+        """
+        byte_message = to_bytes(message)
+        byte_info = to_bytes(extra_info)
+
+        mac_length = lib.olm_sas_mac_length(self._sas)
+        mac_buffer = ffi.new("char[]", mac_length)
+
+        self._check_error(
+            lib.olm_sas_calculate_mac_long_kdf(
+                self._sas,
+                ffi.from_buffer(byte_message),
+                len(byte_message),
+                ffi.from_buffer(byte_info),
+                len(byte_info),
+                mac_buffer,
+                mac_length
+            )
+        )
+        return bytes_to_native_str(ffi.unpack(mac_buffer, mac_length))
diff --git a/python/tests/sas_test.py b/python/tests/sas_test.py
index 05013b7..9001e67 100644
--- a/python/tests/sas_test.py
+++ b/python/tests/sas_test.py
@@ -80,3 +80,20 @@ class TestClass(object):
         alice_mac = sas_alice.calculate_mac(message, extra_info)
 
         assert alice_mac == expected_mac
+
+    def test_long_mac_generating(self):
+        sas_alice = Sas()
+        sas_bob = Sas()
+
+        with pytest.raises(OlmSasError):
+            sas_alice.calculate_mac_long_kdf(MESSAGE, EXTRA_INFO)
+
+        sas_alice.set_their_pubkey(sas_bob.pubkey)
+        sas_bob.set_their_pubkey(sas_alice.pubkey)
+
+        alice_mac = sas_alice.calculate_mac_long_kdf(MESSAGE, EXTRA_INFO)
+        bob_mac = sas_bob.calculate_mac_long_kdf(MESSAGE, EXTRA_INFO)
+        bob_short_mac = sas_bob.calculate_mac(MESSAGE, EXTRA_INFO)
+
+        assert alice_mac == bob_mac
+        assert alice_mac != bob_short_mac