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Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
New Ways to Garble Circuits
No full textThesis (Ph.D.)--University of Washington, 2025A garbling scheme transforms a circuit C into a garbled circuit C-hat, along with a pair of short keys (k^(i)_0 , k^(i)_1) for each input bit x[i], such that the program, garbled program and input keys (C, C-hat, {k^(i)_x[i]}) can be used to recover the output z = C(x) while revealing nothing else about the input x. A main objective in the research of garbling schemes is reducing the size of the garbling material (C-hat, {k^(i)_x[i]}). On the one hand, theoretical schemes using the heavy tools of attribute-based encryption (ABE) and fully homomorphic encryption (FHE), or indistinguishable obfuscation (iO) can achieve constant size, independent of |C|. On the other hand, practically oriented schemes using only symmetric key cryptography all have sizes Ω(λ · |C|). Motivated by the gap in between, this thesis explores new ways of leveraging light-weight techniques from public-key cryptography to construct communication efficient garbling schemes. In particular, our explorations are centered around two primitives, linearly homomorphic encryption (LHE) and homomorphic secret sharing (HSS). In Part I, we apply LHE techniques to construct communication efficient garbling schemes that specialize for arithmetic operation gates over a modulus R or bounded integers. We define the (succinctness) rate of such schemes to be the per-gate garbling size normalized by log R or the range of bounded integers. Our results include:• rate-O(1) arithmetic garbling over bounded integers, and
• rate-O(λ_DCR) mixed garbling over Z_R and Boolean gates for any modulus R.
In Part II, we apply HSS techniques to construct communication efficient Boolean garbling schemes. Our results lead to a unified framework for garbling arbitrary Boolean gates (as truth tables) with 1-bit per output wire in garbling size. Consequences of this framework include:
• standard Boolean garbling with 1-bit per gate;
• rate-O(1) arithmetic garbling over Z_R for any modulus R.
All of the mentioned results were achieved for the first time without using FHE or iO
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Transforming Pseudorandomness and Non-malleability with Minimal Overheads
Get PDFIn this thesis, we investigate the cost of transforming “weaker” or “less-structured” variants of a cryptographic primitive into a “stronger” or “more structured” variant of the same primitive. We conduct the study via the lens of two fundamental security properties:Pseudrandomness is critical to almost all of cryptography, and pseudorandom functions (PRFs) and pseudorandom permutations (PRPs) are powerful primitives enabling simple solutions for fundamental problems in secret-key cryptography. Their existence from general assumptions (e.g., one-way functions) is well-studied. But here we investigate new ways of building them with the goal of efficiency and achieving stronger security. First, we consider building PRFs from non-adaptive PRFs (naPRFs), i.e., PRFs which are secure only against distinguishers issuing all of their queries at once. Known constructions either make calls to an underlying naPRF or incur an undesirable super-polynomial loss in security. We provide the first evidence for this state of affairs by showing that a large class of one-call constructions cannot be proved to be a secure PRF under a black-box reduction to the (polynomial-time) naPRF security of the underlying function. Second, we revisit the question of transforming PRFs to PRPs which are used to reason about the security of block-ciphers when the underlying key is kept secret. However, in practice block-ciphers are also used in settings where the key is known to the adversary. To address this disparity, we introduce the first, plausible extensions of pseudorandomness to the known-key setting and provide secure constructions of PRPs which make two calls to an underlying appropriate PRF. This matches the complexity of PRF to PRP transformations in the secret-key setting.Non-malleability captures security of cryptographic protocols against man-in-the-middle attacks and non-malleable commitments (NMC) are paragon examples of non-malleable protocols. Resolving the round complexity of NMC, a fundamental measure of cost, has remained a fascinating open question and barriers to achieving two-round (and non-interactive) solutions from polynomial-time assumptions were proved in 2013. We provide the first constructions of two-round and non-interactive NMC under sub-exponential time well-studied assumptions, crucially exploiting the synergy between different axes of hardness to circumvent the above impossibility. At heart, our result presents a round-preserving transformation (i.e., incurring no overhead in number of rounds) from NMC on -bit identities to -bits where the length of identities is a measure of a protocol's “non-malleability”. Previous such amplifications incurred additive blow-up in the round-complexity
Linear-Time Accumulation Schemes
No full textProof-carrying data (PCD) is a powerful cryptographic primitive for computational integrity in a distributed setting. State-of-the-art constructions of PCD are based on accumulation schemes (and, closely related, folding schemes). We present WARP, the first accumulation scheme with linear prover time and logarithmic verifier time. Our scheme is hash-based (secure in the random oracle model), plausibly post-quantum secure, and supports unbounded accumulation depth. We achieve our result by constructing an interactive oracle reduction of proximity that works with any linear code over a sufficiently large field. We take a novel approach by constructing a straightline extractor that relies on erasure correction, rather than error-tolerant decoding like prior extractors. Along the way, we introduce a variant of straightline round-by-round knowledge soundness that is compatible with our extraction strategy.COMPSE
New Frontiers of Attribute-Based Encryption via a General Paradigm and More
No full textThesis (Ph.D.)--University of Washington, 2025Attribute-based encryption (ABE) is an advanced form of public-key encryption incorporating fine-grained access control. In such a system, keys and ciphertexts are associated with attributes and policies , respectively, and decryption is conditioned on satisfying . Designing ABE schemes is challenging and its objectives include expressiveness, succinctness, efficiency, achieving strong security, and relying on minimal assumptions. This dissertation pushes the frontiers of ABE in terms of these objectives separately and jointly and studies the interaction among them. In the first part, we propose a general paradigm that greatly simplifies the task of constructing ABE schemes. It reasonably distributes the complexities into constituents, making each ingredient and the overall scheme easier to understand, reason about, and potentially improve. It is also versatile and powerful. The benefits are demonstrated by four different instantiations, which achieve various ABE schemes with improved objectives and are related to each other by replacements of ingredients. In the second part, we push the frontiers of ABE outside the paradigm. In one chapter, we resolve a long-standing open problem of constructing depth-unbounded ABE from lattices. In the other, we present the first systematic study of the upper/lower bounds of ABE succinctness and efficiency, showing inherent trade-offs among the objectives and constructing a few Pareto-optimal schemes
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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Memory-Hard Functions: When Theory Meets Practice
Get PDFMemory-hard functions (MHFs) is a class of hash functions whose fast evaluation requires the heavy use of memory, and an evaluation that spends less memory has to incur a much larger time penalty. Memory-hardness is particularly useful in the setting of password hashing and cryptocurrencies, as memory cost is platform-independent and efficient special-purpose hardware for brute-forcing attacks becomes much harder to be built. Since its first proposal by Colin Percival in 2009, many memory-hard hash heuristics were proposed, and the notion/design of MHFs has received a considerable amount of theoretical scrutiny as well. However, a large gap still exists when theory meets practice. On the one hand, most of the practical schemes are only heuristics without formal analysis, and attacks do exist for some of them; on the other hand, theoretical analyses are usually based on unrealistic assumptions: they consider MHFs as modes of operation of some underlying hash function H, modeled as a random oracle. Unfortunately, in practice, this is never the case as H is usually a heuristic design built from simpler primitives.This dissertation makes progress in addressing both of the problems. Our main contributions are threefold. First, we prove that a widely-used MHF candidate, called scrypt, is provably and optimally memory-hard, thus shedding light on the confidence of its wide application. Second, we model simple cryptographic tools (e.g. AES) as the underlying ideal primitives and present a generic and provably-secure MHF construction from hard-to-pebble graphs. The resulting scheme significantly decreases the efficiency gap between legitimate users and ASICs-equipped attackers. Finally, given the practice demands for H to have large outputs (to increase memory hardness without changing the description size of MHFs), we go back to the framework of constructing MHFs from H (with large output). Different from previous work, we take finer-granularity of the hash function H into account and provide the first provably secure design of H from simpler primitives (e.g. fixed-key AES)
New Ways to Garble Circuits
Get PDFThesis (Ph.D.)--University of Washington, 2025A garbling scheme transforms a circuit C into a garbled circuit C-hat, along with a pair of short keys (k^(i)_0 , k^(i)_1) for each input bit x[i], such that the program, garbled program and input keys (C, C-hat, {k^(i)_x[i]}) can be used to recover the output z = C(x) while revealing nothing else about the input x. A main objective in the research of garbling schemes is reducing the size of the garbling material (C-hat, {k^(i)_x[i]}). On the one hand, theoretical schemes using the heavy tools of attribute-based encryption (ABE) and fully homomorphic encryption (FHE), or indistinguishable obfuscation (iO) can achieve constant size, independent of |C|. On the other hand, practically oriented schemes using only symmetric key cryptography all have sizes Ω(λ · |C|). Motivated by the gap in between, this thesis explores new ways of leveraging light-weight techniques from public-key cryptography to construct communication efficient garbling schemes. In particular, our explorations are centered around two primitives, linearly homomorphic encryption (LHE) and homomorphic secret sharing (HSS). In Part I, we apply LHE techniques to construct communication efficient garbling schemes that specialize for arithmetic operation gates over a modulus R or bounded integers. We define the (succinctness) rate of such schemes to be the per-gate garbling size normalized by log R or the range of bounded integers. Our results include:• rate-O(1) arithmetic garbling over bounded integers, and
• rate-O(λ_DCR) mixed garbling over Z_R and Boolean gates for any modulus R.
In Part II, we apply HSS techniques to construct communication efficient Boolean garbling schemes. Our results lead to a unified framework for garbling arbitrary Boolean gates (as truth tables) with 1-bit per output wire in garbling size. Consequences of this framework include:
• standard Boolean garbling with 1-bit per gate;
• rate-O(1) arithmetic garbling over Z_R for any modulus R.
All of the mentioned results were achieved for the first time without using FHE or iO
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