Apparatus, and an associated method, for communicating a signaling message, such as a message signaling unit, in secure form, even upon a communication path of an untrusted security level. The signaling message is applied to a signal transfer point. An encryption selector selects whether to encrypt the signaling message and, if so, which parts of the message to encrypt. If a portion of the signaling message encrypts the selected portion and causes the signaling message to be communicated upon a communication path to a destination. Once delivered to a trusted signal transfer point, the selected portion of the signaling message is decrypted, and the signaling message is delivered to the ultimate destination.