DB forge/utilities polishing (docs) following #3375, #3378
diff --git a/user_guide_src/source/libraries/encryption.rst b/user_guide_src/source/libraries/encryption.rst
index f29ebf4..2d0ee23 100644
--- a/user_guide_src/source/libraries/encryption.rst
+++ b/user_guide_src/source/libraries/encryption.rst
@@ -533,6 +533,7 @@
:param int $length: Optional output length
:param string $info: Optional context/application-specific info
:returns: A pseudo-random key or FALSE on failure
+ :rtype: string
Derives a key from another, presumably weaker key.