Locally decodable codes (LDCs) are codes that simultaneously provide efficient random access retrieval and high noise resilience by allowing reliable reconstruction of an arbitrary bit of a message by looking at only a small number of randomly chosen codeword bits. Local decodability comes with a certain loss in terms of efficiency – specifically, locally decodable codes require longer codeword lengths than their classical counterparts. Private information retrieval (PIR) schemes are cryptographic protocols designed to safeguard the privacy of database users. They allow clients to retrieve records from public databases while completely hiding the identity of the retrieved records from database owners. In this book the author provides a fresh algebraic look at the theory of locally decodable codes and private information retrieval schemes, obtaining new families of each which have much better parameters than those of previously known constructions, and he also proves limitations of two server PIRs in a restricted setting that covers all currently known schemes. The author's related thesis won the ACM Dissertation Award in 2007, and this book includes some expanded sections and proofs, and notes on recent developments.

Brief informal introductions to coding techniques developed for the storage, retrieval, and transmission of large amounts of data.

This book constitutes the refereed proceedings of the 13th International Conference on Cryptology and Network Security, CANS 2014, held in Heraklion, Creete, Greece, in October 2014. The 25 revised full papers presented together with the abstracts of 3 invited talks were carefully reviewed and selected from 86 submissions. The papers cover topics of interest such as encryption; cryptanalysis; malware analysis; and privacy and identification systems as well as various types of network protocol design and analysis work.

Cloud computing has brought great benefits in cost and flexibility for provisioning services. The greatest challenge of cloud computing remains however the question of security. The current standard tools in access control mechanisms and cryptography can only partly solve the security challenges of cloud infrastructures. In the recent years of research in security and cryptography, novel mechanisms, protocols and algorithms have emerged that offer new ways to create secure services atop cloud infrastructures. This report provides introductions to a selection of security mechanisms that were part of the "Cloud Security Mechanisms" seminar in summer term 2013 at HPI.

This volume contains the papers presented at the 13th International Wo- shop on Approximation Algorithms for Combinatorial Optimization Problems (APPROX 2010) and the 14th International Workshop on Randomization and Computation (RANDOM 2010), which took place concurrently in Universitat Politècnica de Catalunya (UPC) Barcelona, Spain, during September 1-3, 2010. APPROX focuses on algorithmic and complexity issues surrounding the dev- opment of e?cient approximate solutions to computationally di?cult problems, and was the 13th in the series after Aalborg (1998), Berkeley (1999), Sa- brücken (2000), Berkeley (2001), Rome (2002), Princeton (2003), Cambridge (2004), Berkeley (2005), Barcelona (2006), Princeton (2007), Boston (2008) and Berkeley (2009). RANDOM is concerned with applications of randomness to computational and combinatorial problems, and was the 14th workshop in the - ries following Bologna (1997), Barcelona (1998), Berkeley (1999), Geneva (2000), Berkeley (2001), Harvard (2002), Princeton (2003), Cambridge (2004), Berkeley (2005), Barcelona (2006), Princeton (2007), Boston (2008), and Berkeley (2009).

The Internet and the World Wide Web (WWW) play an increasingly imp- tant role in our today's activities. More and more we use the Web to buy goods and to inform ourselves about cultural, political, economical, medical, and scienti?c developments. For example, accessing?ight schedules, me- cal data, or retrieving stock information become common practice in today's world. Many people assume that there is no one who "watches" them when accessing this data. However, sensitive userswho accesselectronic shops(e-shops) might have observedthat this assumptionoften isnot true. In many cases, E-shopstrack the users'"accessbehavior"when browsingthe Web pagesof the e-shopthus deriving "accesspatterns" for individual shoppers. Therefore, this knowledge on access behavior and access patters allows the system to tailor access to Webpagesforthatusertohis/herspeci?cneedsinthefuture. Thistrackingof usersmightbeconsideredharmlessand"acceptable"inmanycases. However, in cases when this information is used to harm a person - for example about the person's health problems - or to violate his/her privacy (for example?nding out about his/her?nancial situation), he/she would like to be sure that such tracking is impossible to protect the user's rights

Property Testing is the study of super-fast (randomized) algorithms for approximate decision making. These algorithms are given direct access to items of a huge data set, and determine, whether this data set has some predetermined (global) property or is far from having this property. Remarkably, this approximate decision is made by accessing a small portion of the data set. This state-of-the-art survey presents a collection of extended abstracts and surveys of leading researchers in property testing and related areas; it reflects the program of a mini-workshop on property testing that took place in January 2010 at the Institute for Computer Science (ITCS), Tsinghua University, Beijing, China. The volume contains two editor's introductions, 10 survey papers and 18 extended abstracts.

This book presents a collection of 36 pieces of scientific work in the areas of complexity theory and foundations of cryptography: 20 research contributions, 13 survey articles, and 3 programmatic and reflective viewpoint statements. These so far formally unpublished pieces were written by Oded Goldreich, some in collaboration with other scientists. The articles included in this book essentially reflect the topical scope of the scientific career of Oded Goldreich now spanning three decades. In particular the topics dealt with include average-case complexity, complexity of approximation, derandomization, expander graphs, hashing functions, locally testable codes, machines that take advice, NP-completeness, one-way functions, probabilistically checkable proofs, proofs of knowledge, property testing, pseudorandomness, randomness extractors, sampling, trapdoor permutations, zero-knowledge, and non-iterative zero-knowledge. All in all, this potpourri of studies in complexity and cryptography constitutes a most valuable contribution to the field of theoretical computer science centered around the personal achievements and views of one of its outstanding representatives.

We propose a network-type scheme of private information retrieval, presented as a modification of the conventional setup, where the user is replaced with two users, the user-sender and the user-receiver. As a result of communication, the user-receiver becomes informed about the bit located at a certain position of the database, owned by the servers. Each server receives a query from the user-sender that contains information about the position in a hidden form and the server cannot disclose this position. On the basis of the query and the database, each server forms the replica, which is then transmitted to the user-receiver. By combining replicas, the user-receiver decodes the retrieved bit. We present a simple algebraic scheme where the communication complexity and the computational complexity are expressed as functions of the logarithm of the database size. The approaches allow extensions to the one-server scheme, the multi-scheme with noisy replicas of a fixed number of servers, and the authentication of a certain fragment of the database.

This book collates the key security and privacy concerns faced by individuals and organizations who use various social networking sites. This includes activities such as connecting with friends, colleagues, and family; sharing and posting information; managing audio, video, and photos; and all other aspects of using social media sites both professionally and personally. In the setting of the Internet of Things (IoT) that can connect millions of devices at any one time, the security of such actions is paramount. Securing Social Networks in Cyberspace discusses user privacy and trust, location privacy, protecting children, managing multimedia content, cyberbullying, and much more. Current state-of-the-art defense mechanisms that can bring long-term solutions to tackling these threats are considered in the book. This book can be used as a reference for an easy understanding of complex cybersecurity issues in social networking platforms and services. It is beneficial for academicians and graduate-level researchers. General readers may find it beneficial in protecting their social-media-related profiles.