A vast body of theoretical research has focused either on overly simplistic models of parallel computation, notably the PRAM, or overly specific models that have few representatives in the real world. Both kinds of models encourage exploitation of formal loopholes, rather than rewarding development of techniques that yield performance across a range of current and future parallel machines. This paper offers a new parallel machine model, called LogP, that reflects the critical technology trends underlying parallel computers. it is intended to serve as a basis for developing fast, portable parallel algorithms and to offer guidelines to machine designers. Such a model must strike a balance between detail and simplicity in order to reveal important bottlenecks without making analysis of interesting problems intractable. The model is based on four parameters that specify abstractly the computing bandwidth, the communication bandwidth, the communication delay, and the efficiency of coupling communication and computation. Portable parallel algorithms typically adapt to the machine configuration, in terms of these parameters. The utility of the model is demonstrated through examples that are implemented on the CM-5.

/pdf/logp-towards-a-realistic-model-of-parallel-computation-2hpmqi5j0f.pdf

LogP: towards a realistic model of parallel computation

/pdf/sequencing-and-scheduling-algorithms-and-complexity-lnutyrr3kz.pdf

Sequencing and scheduling: algorithms and complexity

Computational geometry

On the complexity of fixed-priority scheduling of periodic, real-time tasks

Storage outsourcing is a rising trend which prompts a number of interesting security issues, many of which have been extensively investigated in the past. However, Provable Data Possession (PDP) is a topic that has only recently appeared in the research literature. The main issue is how to frequently, efficiently and securely verify that a storage server is faithfully storing its client's (potentially very large) outsourced data. The storage server is assumed to be untrusted in terms of both security and reliability. (In other words, it might maliciously or accidentally erase hosted data; it might also relegate it to slow or off-line storage.) The problem is exacerbated by the client being a small computing device with limited resources. Prior work has addressed this problem using either public key cryptography or requiring the client to outsource its data in encrypted form.In this paper, we construct a highly efficient and provably secure PDP technique based entirely on symmetric key cryptography, while not requiring any bulk encryption. Also, in contrast with its predecessors, our PDP technique allows outsourcing of dynamic data, i.e, it efficiently supports operations, such as block modification, deletion and append.

http://sprout.ics.uci.edu/pubs/a9-ateniese.pdf

Scalable and efficient provable data possession

Integrity critical databases, such as financial data used in high-value decisions, are frequently published over the Internet. Publishers of such data must satisfy the integrity, authenticity, and non-repudiation requirements of clients. Providing this protection over public networks is costly.

/pdf/authentic-third-party-data-publication-1884viub3r.pdf

Authentic Third-party Data Publication

Query answers from on-line databases can easily be corrupted by hackers or malicious database publishers. Thus it is important to provide mechanisms which allow clients to trust the results from on-line queries. Authentic publication allows untrusted publishers to answer securely queries from clients on behalf of trusted off-line data owners. Publishers validate answers using hard-to-forge verification objects VOs), which clients can check efficiently. This approach provides greater scalability, by making it easy to add more publishers, and better security, since on-line publishers do not need to be trusted.To make authentic publication attractive, it is important for the VOs to be small, efficient to compute, and efficient to verify. This has lead researchers to develop independently several different schemes for efficient VO computation based on specific data structures. Our goal is to develop a unifying framework for these disparate results, leading to a generalized security result. In this paper we characterize a broad class of data structures which we call Search DAGs, and we develop a generalized algorithm for the construction of VOs for Search DAGs. We prove that the VOs thus constructed are secure, and that they are efficient to compute and verify. We demonstrate how this approach easily captures existing work on simple structures such as binary trees, multi-dimensional range trees, tries, and skip lists. Once these are shown to be Search DAGs, the requisite security and efficiency results immediately follow from our general theorems. Going further, we also use Search DAGs to produce and prove the security of authenticated versions of two complex data models for efficient multi-dimensional range searches. This allows efficient VOs to be computed (size O(log N + T)) for typical one- and two-dimensional range queries, where the query answer is of size T and the database is of size N. We also show I/O-efficient schemes to construct the VOs. For a system with disk blocks of size B, we answer one-dimensional and three-sided range queries and compute the VOs with O(logB N + T/B) I/O operations using linear size data structures.

A General Model for Authenticated Data Structures

Integrity critical databases, such as financial information used in high-value decisions, are frequently published over the Internet. Publishers of such data must satisfy the integrity, authenticity, and nonrepudiation requirements of clients. Providing this protection over public data networks is an expensive proposition. This is, in part, due to the difficulty of building and running secure systems. In practice, large systems can not be verified to be secure and are frequently penetrated. The negative consequences of a system intrusion at the publisher can be severe. The problem is further complicated by data and server replication to satisfy availability and scalability requirements.To our knowledge this work is the first of its kind to give general approaches for reducing the trust required of publishers of large databases. To do this, we separate the roles of data owner and data publisher. With a few digital signatures on the part of the owner and no trust required of a publisher, we give techniques based on Merkle hash trees that publishers can use to provide authenticity and nonrepudiation of the answer to database queries posed by a client. This is done without requiring a key to be held in an on-line system, thus reducing the impact of system penetrations. By reducing the trust required of the publisher, our solution is a step towards the publication of large databases in a scalable manner.

/pdf/authentic-data-publication-over-the-internet-4f26dp3rtp.pdf

Authentic data publication over the internet

Scheduling periodically occurring tasks on multiple processors

We present new design and analysis techniques for the synthesis of parallel multiplier circuits that have smaller predicted delay than the best current multipliers. V.G. Oklobdzija et al. (1996) suggested a new approach, the Three-Dimensional Method (TDM), for Partial Product Reduction Tree (PPRT) design that produces multipliers that outperform the current best designs. The goal of TDM is to produce a minimum delay PPRT using full adders. This is done by carefully modeling the relationship of the output delays to the input delays in an adder and, then, interconnecting the adders in a globally optimal way. Oklobdzija et al. suggested a good heuristic for finding the optimal PPRT, but no proofs about the performance of this heuristic were given. We provide a formal characterization of optimal PPRT circuits and prove a number of properties about them. For the problem of summing a set of input bits within the minimum delay, we present an algorithm that produces a minimum delay circuit in time linear in the size of the inputs. Our techniques allow us to prove tight lower bounds on multiplier circuit delays. These results are combined to create a program that finds optimal TDM multiplier designs. Using this program, we can show that, while the heuristic used by Oklobdzija et al. does not always find the optimal TDM circuit, it performs very well in terms of overall PPRT circuit delay. However, our search algorithms find better PPRT circuits for reducing the delay of the entire multiplier.

/pdf/optimal-circuits-for-parallel-multipliers-3jtrpslmyo.pdf

Charles U. Martel

Papers

Authentic Third-party Data Publication

A General Model for Authenticated Data Structures

Authentic data publication over the internet

Scheduling periodically occurring tasks on multiple processors

Optimal circuits for parallel multipliers