2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/32220We present a protocol for verification of ``no such entry'' replies from databases. We introduce a new cryptographic primitive as the underlying structure, the keyed hash tree, which is an extension of Merkle's hash tree. We compare our scheme to Buldas et al.'s Undeniable Attesters and Micali et al.'s Zero Knowledge Sets.16 pagesCryptography and SecurityDatabasesE.2; H.2.0text