fix: make it impossible to overwrite default key

Replacing default key
when a profile is already part of
verified groups results in
`[The message was sent with non-verified encryption. See 'Info' for more details]`
messages for other users.

It is still possible
to import the default key before
Delta Chat generates the key.

deltachat-rpc-client/tests/test_key_transfer.py

@@ -0,0 +1,50 @@
+import pytest
+
+from deltachat_rpc_client import EventType
+from deltachat_rpc_client.rpc import JsonRpcError
+
+
+def wait_for_autocrypt_setup_message(account):
+    while True:
+        event = account.wait_for_event()
+        if event.kind == EventType.MSGS_CHANGED and event.msg_id != 0:
+            msg_id = event.msg_id
+            msg = account.get_message_by_id(msg_id)
+            if msg.get_snapshot().is_setupmessage:
+                return msg
+
+
+def test_autocrypt_setup_message_key_transfer(acfactory):
+    alice1 = acfactory.get_online_account()
+
+    alice2 = acfactory.get_unconfigured_account()
+    alice2.set_config("addr", alice1.get_config("addr"))
+    alice2.set_config("mail_pw", alice1.get_config("mail_pw"))
+    alice2.configure()
+
+    setup_code = alice1.initiate_autocrypt_key_transfer()
+    msg = wait_for_autocrypt_setup_message(alice2)
+
+    # Test that entering wrong code returns an error.
+    with pytest.raises(JsonRpcError):
+        msg.continue_autocrypt_key_transfer("7037-0673-6287-3013-4095-7956-5617-6806-6756")
+
+    msg.continue_autocrypt_key_transfer(setup_code)
+
+
+def test_ac_setup_message_twice(acfactory):
+    alice1 = acfactory.get_online_account()
+    alice2 = acfactory.get_unconfigured_account()
+    alice2.set_config("addr", alice1.get_config("addr"))
+    alice2.set_config("mail_pw", alice1.get_config("mail_pw"))
+    alice2.configure()
+
+    # Send the first Autocrypt Setup Message and ignore it.
+    _setup_code = alice1.initiate_autocrypt_key_transfer()
+    wait_for_autocrypt_setup_message(alice2)
+
+    # Send the second Autocrypt Setup Message and import it.
+    setup_code = alice1.initiate_autocrypt_key_transfer()
+    msg = wait_for_autocrypt_setup_message(alice2)
+
+    msg.continue_autocrypt_key_transfer(setup_code)