A primary key may be used for a first attempt by a remote node to decrypt incoming messages from a master. In the event the decrypt attempt fails at the remote node, a secondary key may then be used to attempt to decrypt the message. Initially, the primary and secondary keys may be the same. A field tool, such as a hand-held programming unit operated by a technician at a remote node location, may change the secondary key, but may not cause any change to the primary key. The secondary key may remain so changed until a new primary key is verified and/or authenticated and the secondary key is overwritten with the new primary key. The primary key may only be changed/set by the master via an encrypted request. A technician may not use a field tool to change a primary key.