Offline Authentication of Untrusted Storage

Abstract

We extend the offline memory correctness checking scheme presented by Blum et. al [BEG+91], by using incremental cryptography, to detect attacks by an active adversary. We also introduce a hybrid o_ine-online checking scheme designed for untrusted storages in file systems and databases. Previous work [GSC+02] [FKM00] [MVS00] describe systems in which Merkle trees are used to verify the authenticity of data stored on untrusted storage. The Merkle trees [Mer79] are used to check, after each operation, whether the storage performed correctly. The offline and hybrid checkers are designed for checking sequences of operations on an untrusted storage and, in the common case, require only a constant overhead on the number of accesses to the storage, as compared to the logarithmic overhead incurred by online Merkle tree schemes