diff --git a/tests/telethon/crypto/test_rsa.py b/tests/telethon/crypto/test_rsa.py
new file mode 100644
index 00000000..a1a949d2
--- /dev/null
+++ b/tests/telethon/crypto/test_rsa.py
@@ -0,0 +1,37 @@
+"""
+tests for telethon.crypto.rsa
+"""
+import pytest
+
+from telethon.crypto import rsa
+
+@pytest.fixture
+def server_key_fp():
+    """factory to return a key, old if so chosen"""
+    def _server_key_fp(old: bool):
+        for fp, data in rsa._server_keys.items():
+            _, old_key = data
+            if old_key == old:
+                return fp
+
+    return _server_key_fp
+
+def test_encryption_inv_key():
+    """test for #1324"""
+    assert rsa.encrypt("invalid", b"testdata") is None
+
+def test_encryption_old_key(server_key_fp):
+    """test for #1324"""
+    assert rsa.encrypt(server_key_fp(old=True), b"testdata") is None
+
+def test_encryption_allowed_old_key(server_key_fp):
+    data = rsa.encrypt(server_key_fp(old=True), b"testdata", use_old=True)
+    # we can't verify the data is actually valid because we don't have
+    # the decryption keys
+    assert data is not None and len(data) == 256
+
+def test_encryption_current_key(server_key_fp):
+    data = rsa.encrypt(server_key_fp(old=False), b"testdata")
+    # we can't verify the data is actually valid because we don't have
+    # the decryption keys
+    assert data is not None and len(data) == 256