diff --git a/bundles/backup-server/metadata.py b/bundles/backup-server/metadata.py
index 2128622..a495959 100644
--- a/bundles/backup-server/metadata.py
+++ b/bundles/backup-server/metadata.py
@@ -8,7 +8,7 @@ defaults = {
     },
     'users': {
         'backup-receiver': {
-            'authorized_keys': [],
+            'authorized_keys': set(),
         },
     },
     'sudoers': {
@@ -78,12 +78,12 @@ def backup_authorized_keys(metadata):
     return {
         'users': {
             'backup-receiver': {
-                'authorized_keys': [
+                'authorized_keys': {
                     other_node.metadata.get('users/root/pubkey')
                         for other_node in repo.nodes
                         if other_node.has_bundle('backup')
                         and other_node.metadata.get('backup/server') == node.name
-                ],
+                },
             },
         },
     }
diff --git a/bundles/users/metadata.py b/bundles/users/metadata.py
index 124d1e2..f69d407 100644
--- a/bundles/users/metadata.py
+++ b/bundles/users/metadata.py
@@ -18,11 +18,11 @@ def authorized_users(metadata):
 
     for name, config in metadata.get('users').items():
         users[name] = {
-            'authorized_keys': [],
+            'authorized_keys': set(),
         }
         for authorized_user in config.get('authorized_users', []):
             authorized_user_name, authorized_user_node = authorized_user.split('@')
-            users[name]['authorized_keys'].append(
+            users[name]['authorized_keys'].add(
                 repo.get_node(authorized_user_node).metadata.get(f'users/{authorized_user_name}/pubkey')
             )
     return {
@@ -38,7 +38,7 @@ def user_defaults(metadata):
 
     for name, config in metadata.get('users').items():
         users[name] = {
-            'authorized_keys': [],
+            'authorized_keys': set(),
         }
 
         if not 'full_name' in config:
diff --git a/groups/all.py b/groups/all.py
index 14ad117..65e32f9 100644
--- a/groups/all.py
+++ b/groups/all.py
@@ -12,9 +12,9 @@
         'users': {
             'root': {
                 'shell': '/usr/bin/zsh',
-                'authorized_keys': [
+                'authorized_keys': {
                     'ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIEU1l2ijW3ZqzFGZcdWg2ESgTGehdNfBTfafxsjWvWdS mwiegand@macbook',
-                ],
+                },
             },
         },
     }
diff --git a/nodes/htz.mails.py b/nodes/htz.mails.py
index 7b105dc..b884a24 100644
--- a/nodes/htz.mails.py
+++ b/nodes/htz.mails.py
@@ -126,9 +126,9 @@
                 'authorized_users': [
                     'root@home.server',
                 ],
-                'authorized_keys': [
+                'authorized_keys': {
                     'ecdsa-sha2-nistp256 AAAAE2VjZHNhLXNoYTItbmlzdHAyNTYAAAAIbmlzdHAyNTYAAABBBHMKTJLw6Cb+MLt+9JFOkuo2QBpuA8EoTKOFpb3IFQHEq19YLMzOhcErWmzaRfiCnILhnwTQz0njS+n9Qu4aghk= root@mail.sublimity.de'
-                ],
+                },
             },
         },
         'vm': {