Put differently, "clandestine" means "hidden", while "covert" means "deniable". Deniable encryption allows the sender of an encrypted message to deny sending that message. Sergun supervised the deniable undercover units that America struggled to find an effective response to. Filibuster expeditions have also occasionally been used as cover for government-approved deniable operations. Another application, also described in the original paper, is for deniable signatures.