diff --git a/inbox/automatic-trust-transfer.xml b/inbox/automatic-trust-transfer.xml
index b71ab63b..ee5f4ebb 100644
--- a/inbox/automatic-trust-transfer.xml
+++ b/inbox/automatic-trust-transfer.xml
@@ -121,6 +121,10 @@
 			<dt>Automatic key authentication</dt>
 			<dd>Key authentication without user interaction (e.g., ATT)</dd>
 		</di>
+		<di>
+			<dt>Mutual key authentication</dt>
+			<dd>Key authentication in which two devices authenticate the key of each other</dd>
+		</di>
 		<di>
 			<dt>Trust message</dt>
 			<dd>