An unguessable ID that designates some resource is called a (crypto) capability. Capabilities are quite different from access control lists (ACLs). In an ACL

An unguessable ID that designates some resource is called a (crypto) capability. Capabilities are quite different from access control lists (ACLs). In an ACL system, the list of authorized principals is attached to the resource. Thus, sharing access to a resource requires updating the resource. For instance, if Alice creates a document and wants to share it with Bob, then Bob needs an account and Alice needs to add Bob to the document's ACL. In a capability system, the capabilities designate the resource and sharing the resource is as simple as copying the capability. In fact, Bob can also share the document (without copying it first) with Carol. In an ACL system, Bob would not typically have permission to update the ACL. For more information about capabilities, start with, for instance, the e-rights wiki at http://erights.org/elib/capability/index.html http://erights.org/elib/capability/index.html .