To solve this problem KeyKOS provides sense keys to nodes. A sense key is weaker than a fetch key. A sense key appears to the holder as a fetch key except that any key delivered to the holder as a result of an invocation of a sense key is the sensory version of the key being fetched.
The sensory version of a node, sense, or fetch key to node N is the sense key to node N. The sensory version of a segment key is a segment key without authority to invoke a segment keeper. The sensory version of a page key is the read-only key to the same page.
If K is a number key or a key to one of the following objects then the sensory version of K is K:
The important thing about a sense key is that it conveys no authority to influence a structure. The holder of the sense key can browse through the structure but is unable to affect it, nor may a non-sensory key be obtained using a sense key. If the structure holds page keys (a common situation) then those pages will be available for reading but not writing.