Digital repositories, either digital preservation systems or archival systems, periodically check the integrity of stored objects to assure users of their correctness. To do so, prior solutions calculate integrity metadata and require the repository to store it alongside the actual data objects. This integrity metadata is essential for regularly verifying the correctness of the stored data objects. To safeguard and detect damage to this metadata, prior solutions rely on widely visible media, that is unaffiliated third parties, to store and provide back digests of the metadata to verify it is intact. However, they do not address recovery of the integrity metadata in case of damage or attack by an adversary. In essence, they do not preserve this metadata. We introduce IntegrityCatalog, a system that collects all integrity related metadata in a single component, and treats them as first class objects, managing both their integrity and their preservation. We introduce a treap-based persistent authenticated dictionary managing arbitrary length key value pairs, which we use to store all integrity metadata, accessible simply by object name. Additionally, IntegrityCatalog is a distributed system that includes a network protocol that manages both corruption detection and preservation of this metadata, using administrator-selected network peers with two possible roles. Verifiers store and offer attestations on digests and have minimal storage requirements, while preservers efficiently synchronize a complete copy of the catalog to assist in recovery in case of a detected catalog compromise on the local system. We describe our prototype implementation of IntegrityCatalog, measure its performance empirically, and demonstrate its effectiveness in real-world situations, with worst measured throughput of approximately 1K insertions per second, and 2K verified search operations per second.
Another alternative for a summary'' function are algebraic formulas that produce signatures @cite_39 @cite_34 @cite_40 . @cite_11 proposed their use for proof of remote data possession when the owner no longer holds the original data. Although potentially faster to calculate than cryptographic hash functions, they also lack the pre-image resistance properties required to be applicable to the long-term digital preservation and archival systems we target.
@cite_40 @cite_34 @cite_11 @cite_39
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The emerging use of the Internet for remote storage and backup has led to the problem of verifying that storage sites in a distributed system indeed store the data; this must often be done in the absence of knowledge of what the data should be. We use m n erasure-correcting coding to safeguard the stored data and use algebraic signatures hash functions with algebraic properties for verification. Our scheme primarily utilizes one such algebraic property: taking a signature of parity gives the same result as taking the parity of the signatures. To make our scheme collusionresistant, we blind data and parity by XORing them with a pseudo-random stream. Our scheme has three advantages over existing techniques. First, it uses only small messages for verification, an attractive property in a P2P setting where the storing peers often only have a small upstream pipe. Second, it allows verification of challenges across random data without the need for the challenger to compare against the original data. Third, it is highly resistant to coordinated attempts to undetectably modify data. These signature techniques are very fast, running at tens to hundreds of megabytes per second. Because of these properties, the use of algebraic signatures will permit the construction of large-scale distributed storage systems in which large amounts of storage can be verified with minimal network bandwidth. Restoration of writing order from a single-stroked handwriting image can be seen as the problem of finding the smoothest path in its graph representation. In this paper, a 3-phase approach to restore a writing order is proposed within the framework of the edge continuity relation (ECR). In the initial, local phase, in order to obtain possible ECRs at an even-degree node, a neural network is used for the node of degree 4 and a theoretical approach is presented for the node of degree higher than 4 by introducing certain reasonable assumptions. In the second phase, we identify double-traced lines by employing maximum weighted matching. This makes it possible to transform the problem of obtaining possible ECRs at odd-degree node to that at even-degree node. In the final, global phase, we find all the candidates of single-stroked paths by depth first search and select the best one by evaluating SLALOM smoothness. Experiments on static images converted from online data in the Unipen database show that our method achieves a restoration rate of 96.0 percent In their seminal work on authentication, Wegman and Carter propose that to authenticate multiple messages, it is sufficient to reuse the same hash function as long as each tag is encrypted with a one-time pad. They argue that because the one-time pad is perfectly hiding, the hash function used remains completely unknown to the adversary. Since their proof is not composable, we revisit it using a composable security framework. It turns out that the above argument is insufficient: if the adversary learns whether a corrupted message was accepted or rejected, information about the hash function is leaked, and after a bounded finite amount of rounds it is completely known. We show however that this leak is very small: Wegman and Carter's protocol is still ( ) -secure, if ( ) -almost strongly universal (_2 ) hash functions are used. This implies that the secret key corresponding to the choice of hash function can be reused in the next round of authentication without any additional error than this ( ) . We also show that if the players have a mild form of synchronization, namely that the receiver knows when a message should be received, the key can be recycled for any arbitrary task, not only new rounds of authentication. Abstract.The efficient retrieval of data items on set-valued attributes is an important research topic that has attracted little attention so far. We studied and modified four index structures (sequential signature files, signature trees, extendible signature hashing, and inverted files) for a fast retrieval of sets with low cardinality. We compared the index structures by implementing them and subjecting them to extensive experiments, investigating the influence of query set size, database size, domain size, and data distribution (synthetic and real). The results of the experiments clearly indicate that inverted files exhibit the best overall behavior of all tested index structures.