55 Search Results for "Stanford, David A."

Document
DOI: 10.4230/LIPIcs.ESA.2024.35
On Finding Longest Palindromic Subsequences Using Longest Common Subsequences

Authors: Gerth Stølting Brodal, Rolf Fagerberg, and Casper Moldrup Rysgaard

Published in: LIPIcs, Volume 308, 32nd Annual European Symposium on Algorithms (ESA 2024)

Abstract
Two standard textbook problems illustrating dynamic programming are to find the longest common subsequence (LCS) between two strings and to find the longest palindromic subsequence (LPS) of a single string. A popular claim is that the longest palindromic subsequence in a string can be computed as the longest common subsequence between the string and the reversed string. We prove that the correctness of this claim depends on how the longest common subsequence is computed. In particular, we prove that the classical dynamic programming solution by Wagner and Fischer [JACM 1974] for finding an LCS in fact does find an LPS, while a slightly different LCS backtracking strategy makes the algorithm fail to always report a palindrome.
Cite as

Gerth Stølting Brodal, Rolf Fagerberg, and Casper Moldrup Rysgaard. On Finding Longest Palindromic Subsequences Using Longest Common Subsequences. In 32nd Annual European Symposium on Algorithms (ESA 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 308, pp. 35:1-35:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{brodal_et_al:LIPIcs.ESA.2024.35,
  author =	{Brodal, Gerth St{\o}lting and Fagerberg, Rolf and Rysgaard, Casper Moldrup},
  title =	{{On Finding Longest Palindromic Subsequences Using Longest Common Subsequences}},
  booktitle =	{32nd Annual European Symposium on Algorithms (ESA 2024)},
  pages =	{35:1--35:16},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-338-6},
  ISSN =	{1868-8969},
  year =	{2024},
  volume =	{308},
  editor =	{Chan, Timothy and Fischer, Johannes and Iacono, John and Herman, Grzegorz},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ESA.2024.35},
  URN =		{urn:nbn:de:0030-drops-211068},
  doi =		{10.4230/LIPIcs.ESA.2024.35},
  annote =	{Keywords: Palindromic subsequence, longest common subsequence, dynamic programming}
}
Document
DOI: 10.4230/LIPIcs.ESA.2024.61
Practical Expander Decomposition

Authors: Lars Gottesbüren, Nikos Parotsidis, and Maximilian Probst Gutenberg

Published in: LIPIcs, Volume 308, 32nd Annual European Symposium on Algorithms (ESA 2024)

Abstract
The expander decomposition of a graph decomposes the set of vertices into clusters such that the induced subgraph of each cluster is a subgraph with high conductance, and there is only a small number of inter-cluster edges. Expander decompositions are at the forefront of recent theoretical developments in the area of efficient graph algorithms and act as a central component in several state-of-the-art graph algorithms for fundamental problems like maximum flow, min-cost flow, Gomory-Hu trees, global min-cut, and more. Despite this crucial role and the existence of theoretically efficient expander decomposition algorithms, little is known on their behavior in practice. In this paper we explore the engineering design space in implementations for computing expander decompositions. We base our implementation on the near-linear time algorithm of Saranurak and Wang [SODA'19], and enhance it with practical optimizations that accelerate its running time in practice and at the same time preserve the theoretical runtime and approximation guarantees. We evaluate our algorithm on real-world graphs with up to tens of millions of edges. We demonstrate significant speedups of up to two orders of magnitude over the only prior implementation. To the best of our knowledge, our implementation is the first to compute expander decompositions at this scale within reasonable time.
Cite as

Lars Gottesbüren, Nikos Parotsidis, and Maximilian Probst Gutenberg. Practical Expander Decomposition. In 32nd Annual European Symposium on Algorithms (ESA 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 308, pp. 61:1-61:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{gottesburen_et_al:LIPIcs.ESA.2024.61,
  author =	{Gottesb\"{u}ren, Lars and Parotsidis, Nikos and Gutenberg, Maximilian Probst},
  title =	{{Practical Expander Decomposition}},
  booktitle =	{32nd Annual European Symposium on Algorithms (ESA 2024)},
  pages =	{61:1--61:17},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-338-6},
  ISSN =	{1868-8969},
  year =	{2024},
  volume =	{308},
  editor =	{Chan, Timothy and Fischer, Johannes and Iacono, John and Herman, Grzegorz},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ESA.2024.61},
  URN =		{urn:nbn:de:0030-drops-211323},
  doi =		{10.4230/LIPIcs.ESA.2024.61},
  annote =	{Keywords: Expander Decomposition, Clustering, Graph Algorithms}
}
Document
DOI: 10.4230/LIPIcs.ESA.2024.88
Improved Space-Efficient Approximate Nearest Neighbor Search Using Function Inversion

Authors: Samuel McCauley

Published in: LIPIcs, Volume 308, 32nd Annual European Symposium on Algorithms (ESA 2024)

Abstract
Approximate nearest neighbor search (ANN) data structures have widespread applications in machine learning, computational biology, and text processing. The goal of ANN is to preprocess a set S so that, given a query q, we can find a point y whose distance from q approximates the smallest distance from q to any point in S. For most distance functions, the best-known ANN bounds for high-dimensional point sets are obtained using techniques based on locality-sensitive hashing (LSH). Unfortunately, space efficiency is a major challenge for LSH-based data structures. Classic LSH techniques require a very large amount of space, oftentimes polynomial in |S|. A long line of work has developed intricate techniques to reduce this space usage, but these techniques suffer from downsides: they must be hand tailored to each specific LSH, are often complicated, and their space reduction comes at the cost of significantly increased query times. In this paper we explore a new way to improve the space efficiency of LSH using function inversion techniques, originally developed in (Fiat and Naor 2000). We begin by describing how function inversion can be used to improve LSH data structures. This gives a fairly simple, black box method to reduce LSH space usage. Then, we give a data structure that leverages function inversion to improve the query time of the best known near-linear space data structure for approximate nearest neighbor search under Euclidean distance: the ALRW data structure of (Andoni, Laarhoven, Razenshteyn, and Waingarten 2017). ALRW was previously shown to be optimal among "list-of-points" data structures for both Euclidean and Manhattan ANN; thus, in addition to giving improved bounds, our results imply that list-of-points data structures are not optimal for Euclidean or Manhattan ANN .
Cite as

Samuel McCauley. Improved Space-Efficient Approximate Nearest Neighbor Search Using Function Inversion. In 32nd Annual European Symposium on Algorithms (ESA 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 308, pp. 88:1-88:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{mccauley:LIPIcs.ESA.2024.88,
  author =	{McCauley, Samuel},
  title =	{{Improved Space-Efficient Approximate Nearest Neighbor Search Using Function Inversion}},
  booktitle =	{32nd Annual European Symposium on Algorithms (ESA 2024)},
  pages =	{88:1--88:19},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-338-6},
  ISSN =	{1868-8969},
  year =	{2024},
  volume =	{308},
  editor =	{Chan, Timothy and Fischer, Johannes and Iacono, John and Herman, Grzegorz},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ESA.2024.88},
  URN =		{urn:nbn:de:0030-drops-211590},
  doi =		{10.4230/LIPIcs.ESA.2024.88},
  annote =	{Keywords: similarity search, locality-sensitive hashing, randomized algorithms, data structures, space efficiency, function inversion}
}
Document
DOI: 10.4230/LIPIcs.ESA.2024.97
Engineering Edge Orientation Algorithms

Authors: Henrik Reinstädtler, Christian Schulz, and Bora Uçar

Published in: LIPIcs, Volume 308, 32nd Annual European Symposium on Algorithms (ESA 2024)

Abstract
Given an undirected graph G, the edge orientation problem asks for assigning a direction to each edge to convert G into a directed graph. The aim is to minimize the maximum out-degree of a vertex in the resulting directed graph. This problem, which is solvable in polynomial time, arises in many applications. An ongoing challenge in edge orientation algorithms is their scalability, particularly in handling large-scale networks with millions or billions of edges efficiently. We propose a novel algorithmic framework based on finding and manipulating simple paths to face this challenge. Our framework is based on an existing algorithm and allows many algorithmic choices. By carefully exploring these choices and engineering the underlying algorithms, we obtain an implementation which is more efficient and scalable than the current state-of-the-art. Our experiments demonstrate significant performance improvements compared to state-of-the-art solvers. On average our algorithm is 6.59 times faster when compared to the state-of-the-art.
Cite as

Henrik Reinstädtler, Christian Schulz, and Bora Uçar. Engineering Edge Orientation Algorithms. In 32nd Annual European Symposium on Algorithms (ESA 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 308, pp. 97:1-97:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{reinstadtler_et_al:LIPIcs.ESA.2024.97,
  author =	{Reinst\"{a}dtler, Henrik and Schulz, Christian and U\c{c}ar, Bora},
  title =	{{Engineering Edge Orientation Algorithms}},
  booktitle =	{32nd Annual European Symposium on Algorithms (ESA 2024)},
  pages =	{97:1--97:18},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-338-6},
  ISSN =	{1868-8969},
  year =	{2024},
  volume =	{308},
  editor =	{Chan, Timothy and Fischer, Johannes and Iacono, John and Herman, Grzegorz},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ESA.2024.97},
  URN =		{urn:nbn:de:0030-drops-211682},
  doi =		{10.4230/LIPIcs.ESA.2024.97},
  annote =	{Keywords: edge orientation, pseudoarboricity, graph algorithms}
}
Document
RANDOM
DOI: 10.4230/LIPIcs.APPROX/RANDOM.2024.53
When Do Low-Rate Concatenated Codes Approach The Gilbert-Varshamov Bound?

Authors: Dean Doron, Jonathan Mosheiff, and Mary Wootters

Published in: LIPIcs, Volume 317, Approximation, Randomization, and Combinatorial Optimization. Algorithms and Techniques (APPROX/RANDOM 2024)

Abstract
The Gilbert-Varshamov (GV) bound is a classical existential result in coding theory. It implies that a random linear binary code of rate ε² has relative distance at least 1/2 - O(ε) with high probability. However, it is a major challenge to construct explicit codes with similar parameters. One hope to derandomize the Gilbert-Varshamov construction is with code concatenation: We begin with a (hopefully explicit) outer code 𝒞_out over a large alphabet, and concatenate that with a small binary random linear code 𝒞_in. It is known that when we use independent small codes for each coordinate, then the result lies on the GV bound with high probability, but this still uses a lot of randomness. In this paper, we consider the question of whether code concatenation with a single random linear inner code 𝒞_in can lie on the GV bound; and if so what conditions on 𝒞_out are sufficient for this. We show that first, there do exist linear outer codes 𝒞_out that are "good" for concatenation in this sense (in fact, most linear codes codes are good). We also provide two sufficient conditions for 𝒞_out, so that if 𝒞_out satisfies these, 𝒞_out∘𝒞_in will likely lie on the GV bound. We hope that these conditions may inspire future work towards constructing explicit codes 𝒞_out.
Cite as

Dean Doron, Jonathan Mosheiff, and Mary Wootters. When Do Low-Rate Concatenated Codes Approach The Gilbert-Varshamov Bound?. In Approximation, Randomization, and Combinatorial Optimization. Algorithms and Techniques (APPROX/RANDOM 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 317, pp. 53:1-53:12, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{doron_et_al:LIPIcs.APPROX/RANDOM.2024.53,
  author =	{Doron, Dean and Mosheiff, Jonathan and Wootters, Mary},
  title =	{{When Do Low-Rate Concatenated Codes Approach The Gilbert-Varshamov Bound?}},
  booktitle =	{Approximation, Randomization, and Combinatorial Optimization. Algorithms and Techniques (APPROX/RANDOM 2024)},
  pages =	{53:1--53:12},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-348-5},
  ISSN =	{1868-8969},
  year =	{2024},
  volume =	{317},
  editor =	{Kumar, Amit and Ron-Zewi, Noga},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.APPROX/RANDOM.2024.53},
  URN =		{urn:nbn:de:0030-drops-210467},
  doi =		{10.4230/LIPIcs.APPROX/RANDOM.2024.53},
  annote =	{Keywords: Error-correcting codes, Concatenated codes, Derandomization, Gilbert-Varshamov bound}
}
Document
DOI: 10.4230/LIPIcs.AFT.2024.3
CFT-Forensics: High-Performance Byzantine Accountability for Crash Fault Tolerant Protocols

Authors: Weizhao Tang, Peiyao Sheng, Ronghao Ni, Pronoy Roy, Xuechao Wang, Giulia Fanti, and Pramod Viswanath

Published in: LIPIcs, Volume 316, 6th Conference on Advances in Financial Technologies (AFT 2024)

Abstract
Crash fault tolerant (CFT) consensus algorithms are commonly used in scenarios where system components are trusted - e.g., enterprise settings and government infrastructure. However, CFT consensus can be broken by even a single corrupt node. A desirable property in the face of such potential Byzantine faults is accountability: if a corrupt node breaks the protocol and affects consensus safety, it should be possible to identify the culpable components with cryptographic integrity from the node states. Today, the best-known protocol for providing accountability to CFT protocols is called PeerReview; it essentially records a signed transcript of all messages sent during the CFT protocol. Because PeerReview is agnostic to the underlying CFT protocol, it incurs high communication and storage overhead. We propose CFT-Forensics, an accountability framework for CFT protocols. We show that for a special family of forensics-compliant CFT protocols (which includes widely-used CFT protocols like Raft and multi-Paxos), CFT-Forensics gives provable accountability guarantees. Under realistic deployment settings, we show theoretically that CFT-Forensics operates at a fraction of the cost of PeerReview. We subsequently instantiate CFT-Forensics for Raft, and implement Raft-Forensics as an extension to the popular nuRaft library. In extensive experiments, we demonstrate that Raft-Forensics adds low overhead to vanilla Raft. With 256 byte messages, Raft-Forensics achieves a peak throughput 87.8% of vanilla Raft at 46% higher latency (+44 ms). We finally integrate Raft-Forensics into the open-source central bank digital currency OpenCBDC, and show that in wide-area network experiments, Raft-Forensics achieves 97.8% of the throughput of Raft, with 14.5% higher latency (+326 ms).
Cite as

Weizhao Tang, Peiyao Sheng, Ronghao Ni, Pronoy Roy, Xuechao Wang, Giulia Fanti, and Pramod Viswanath. CFT-Forensics: High-Performance Byzantine Accountability for Crash Fault Tolerant Protocols. In 6th Conference on Advances in Financial Technologies (AFT 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 316, pp. 3:1-3:25, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{tang_et_al:LIPIcs.AFT.2024.3,
  author =	{Tang, Weizhao and Sheng, Peiyao and Ni, Ronghao and Roy, Pronoy and Wang, Xuechao and Fanti, Giulia and Viswanath, Pramod},
  title =	{{CFT-Forensics: High-Performance Byzantine Accountability for Crash Fault Tolerant Protocols}},
  booktitle =	{6th Conference on Advances in Financial Technologies (AFT 2024)},
  pages =	{3:1--3:25},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-345-4},
  ISSN =	{1868-8969},
  year =	{2024},
  volume =	{316},
  editor =	{B\"{o}hme, Rainer and Kiffer, Lucianna},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.AFT.2024.3},
  URN =		{urn:nbn:de:0030-drops-209399},
  doi =		{10.4230/LIPIcs.AFT.2024.3},
  annote =	{Keywords: CFT Protocols, forensics, blockchain}
}
Document
DOI: 10.4230/LIPIcs.AFT.2024.8
A Circuit Approach to Constructing Blockchains on Blockchains

Authors: Ertem Nusret Tas, David Tse, and Yifei Wang

Published in: LIPIcs, Volume 316, 6th Conference on Advances in Financial Technologies (AFT 2024)

Abstract
Recent years have witnessed an explosion of blockchains, each with an open ledger that anyone can read from and write to. In this multi-chain world, an important question emerges: how can we build a more secure overlay blockchain by reading from and writing to a given set of blockchains? Drawing an analogy with switching circuits, we approach the problem by defining two basic compositional operations between blockchains, serial and triangular compositions, and use these operations as building blocks to construct general overlay blockchains. Under the partially synchronous setting, we have the following results: 1) the serial composition, between two certificate-producing blockchains, yields an overlay blockchain that is safe if at least one of the two underlay blockchains is safe and that is live if both of them are live; 2) the triangular composition between three blockchains, akin to parallel composition of switching circuits, yields an overlay blockchain that is safe if all underlay blockchains are safe and that is live if over half of them are live; 3) repeated composition of these two basic operations can yield all possible tradeoffs of safety and liveness for an overlay blockchain built on an arbitrary number of underlay chains. The results are also extended to the synchronous setting.
Cite as

Ertem Nusret Tas, David Tse, and Yifei Wang. A Circuit Approach to Constructing Blockchains on Blockchains. In 6th Conference on Advances in Financial Technologies (AFT 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 316, pp. 8:1-8:25, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{tas_et_al:LIPIcs.AFT.2024.8,
  author =	{Tas, Ertem Nusret and Tse, David and Wang, Yifei},
  title =	{{A Circuit Approach to Constructing Blockchains on Blockchains}},
  booktitle =	{6th Conference on Advances in Financial Technologies (AFT 2024)},
  pages =	{8:1--8:25},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-345-4},
  ISSN =	{1868-8969},
  year =	{2024},
  volume =	{316},
  editor =	{B\"{o}hme, Rainer and Kiffer, Lucianna},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.AFT.2024.8},
  URN =		{urn:nbn:de:0030-drops-209442},
  doi =		{10.4230/LIPIcs.AFT.2024.8},
  annote =	{Keywords: interchain consensus protocols, serial composition, triangular composition, circuits}
}
Document
DOI: 10.4230/LIPIcs.AFT.2024.15
Privacy Comparison for Bitcoin Light Client Implementations

Authors: Arad Kotzer and Ori Rottenstreich

Published in: LIPIcs, Volume 316, 6th Conference on Advances in Financial Technologies (AFT 2024)

Abstract
Light clients implement a simple solution for Bitcoin’s scalability problem, as they do not store the entire blockchain but only the state of particular addresses of interest. To be able to keep track of the updated state of their addresses, light clients rely on full nodes to provide them with the required information. To do so, they must reveal information about the addresses they are interested in. This paper studies the two most common light client implementations, SPV and Neutrino with regards to their privacy. We define privacy metrics for comparing the privacy of the different implementations. We evaluate and compare the privacy of the implementations over time on real Bitcoin data and discuss the inherent privacy-communication tradeoff. In addition, we propose general techniques to enhance light client privacy in the existing implementations. Finally, we propose a new SPV-based light client model, the aggregation model, evaluate it, and show it can achieve enhanced privacy than in the existing light client implementations.
Cite as

Arad Kotzer and Ori Rottenstreich. Privacy Comparison for Bitcoin Light Client Implementations. In 6th Conference on Advances in Financial Technologies (AFT 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 316, pp. 15:1-15:23, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{kotzer_et_al:LIPIcs.AFT.2024.15,
  author =	{Kotzer, Arad and Rottenstreich, Ori},
  title =	{{Privacy Comparison for Bitcoin Light Client Implementations}},
  booktitle =	{6th Conference on Advances in Financial Technologies (AFT 2024)},
  pages =	{15:1--15:23},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-345-4},
  ISSN =	{1868-8969},
  year =	{2024},
  volume =	{316},
  editor =	{B\"{o}hme, Rainer and Kiffer, Lucianna},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.AFT.2024.15},
  URN =		{urn:nbn:de:0030-drops-209510},
  doi =		{10.4230/LIPIcs.AFT.2024.15},
  annote =	{Keywords: Blockchain, Privacy, Light Clients, Bloom filter}
}
Document
DOI: 10.4230/LIPIcs.AFT.2024.30
Profitable Manipulations of Cryptographic Self-Selection Are Statistically Detectable

Authors: Linda Cai, Jingyi Liu, S. Matthew Weinberg, and Chenghan Zhou

Published in: LIPIcs, Volume 316, 6th Conference on Advances in Financial Technologies (AFT 2024)

Abstract
Cryptographic Self-Selection is a common primitive underlying leader-selection for Proof-of-Stake blockchain protocols. The concept was first popularized in Algorand [Jing Chen and Silvio Micali, 2019], who also observed that the protocol might be manipulable. [Matheus V. X. Ferreira et al., 2022] provide a concrete manipulation that is strictly profitable for a staker of any size (and also prove upper bounds on the gains from manipulation). Separately, [Maryam Bahrani and S. Matthew Weinberg, 2024; Aviv Yaish et al., 2023] initiate the study of undetectable profitable manipulations of consensus protocols with a focus on the seminal Selfish Mining strategy [Eyal and Sirer, 2014] for Bitcoin’s Proof-of-Work longest-chain protocol. They design a Selfish Mining variant that, for sufficiently large miners, is strictly profitable yet also indistinguishable to an onlooker from routine latency (that is, a sufficiently large profit-maximizing miner could use their strategy to strictly profit over being honest in a way that still appears to the rest of the network as though everyone is honest but experiencing mildly higher latency. This avoids any risk of negatively impacting the value of the underlying cryptocurrency due to attack detection). We investigate the detectability of profitable manipulations of the canonical cryptographic self-selection leader selection protocol introduced in [Jing Chen and Silvio Micali, 2019] and studied in [Matheus V. X. Ferreira et al., 2022], and establish that for any player with α < (3-√5)/2 ≈ 0.38 fraction of the total stake, every strictly profitable manipulation is statistically detectable. Specifically, we consider an onlooker who sees only the random seed of each round (and does not need to see any other broadcasts by any other players). We show that the distribution of the sequence of random seeds when any player is profitably manipulating the protocol is inconsistent with any distribution that could arise by honest stakers being offline or timing out (for a natural stylized model of honest timeouts).
Cite as

Linda Cai, Jingyi Liu, S. Matthew Weinberg, and Chenghan Zhou. Profitable Manipulations of Cryptographic Self-Selection Are Statistically Detectable. In 6th Conference on Advances in Financial Technologies (AFT 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 316, pp. 30:1-30:23, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{cai_et_al:LIPIcs.AFT.2024.30,
  author =	{Cai, Linda and Liu, Jingyi and Weinberg, S. Matthew and Zhou, Chenghan},
  title =	{{Profitable Manipulations of Cryptographic Self-Selection Are Statistically Detectable}},
  booktitle =	{6th Conference on Advances in Financial Technologies (AFT 2024)},
  pages =	{30:1--30:23},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-345-4},
  ISSN =	{1868-8969},
  year =	{2024},
  volume =	{316},
  editor =	{B\"{o}hme, Rainer and Kiffer, Lucianna},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.AFT.2024.30},
  URN =		{urn:nbn:de:0030-drops-209660},
  doi =		{10.4230/LIPIcs.AFT.2024.30},
  annote =	{Keywords: Blockchain, Cryptocurrency, Proof-of-Stake, Strategic Mining, Statistical Detection}
}
Document
DOI: 10.4230/LIPIcs.ECOOP.2024.14
The Performance Effects of Virtual-Machine Instruction Pointer Updates

Authors: M. Anton Ertl and Bernd Paysan

Published in: LIPIcs, Volume 313, 38th European Conference on Object-Oriented Programming (ECOOP 2024)

Abstract
How much performance do VM instruction-pointer (IP) updates cost and how much benefit do we get from optimizing them away? Two decades ago it had little effect on the hardware of the day, but on recent hardware the dependence chain of IP updates can become the critical path on processors with out-of-order execution. In particular, this happens if the VM instructions are light-weight and the application programs are loop-dominated. The present work presents several ways of reducing or eliminating the dependence chains from IP updates, either by breaking the dependence chains with the loop optimization or by reducing the number of IP updates (the c and ci optimizations) or their latency (the b optimization). Some benchmarks see speedups from these optimizations by factors > 2 on most recent cores, while other benchmarks and older cores see more modest results, often in the speedup ranges 1.1-1.3.
Cite as

M. Anton Ertl and Bernd Paysan. The Performance Effects of Virtual-Machine Instruction Pointer Updates. In 38th European Conference on Object-Oriented Programming (ECOOP 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 313, pp. 14:1-14:26, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{ertl_et_al:LIPIcs.ECOOP.2024.14,
  author =	{Ertl, M. Anton and Paysan, Bernd},
  title =	{{The Performance Effects of Virtual-Machine Instruction Pointer Updates}},
  booktitle =	{38th European Conference on Object-Oriented Programming (ECOOP 2024)},
  pages =	{14:1--14:26},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-341-6},
  ISSN =	{1868-8969},
  year =	{2024},
  volume =	{313},
  editor =	{Aldrich, Jonathan and Salvaneschi, Guido},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ECOOP.2024.14},
  URN =		{urn:nbn:de:0030-drops-208634},
  doi =		{10.4230/LIPIcs.ECOOP.2024.14},
  annote =	{Keywords: virtual machine, interpreter, out-of-order execution}
}
Document
DOI: 10.4230/LIPIcs.COSIT.2024.3
Can You Sketch in 3D? Exploring Perceived Feasibility and Use Cases of 3D Sketch Mapping

Authors: Kevin Gonyop Kim, Tiffany C.K. Kwok, Sailin Zhong, Peter Kiefer, and Martin Raubal

Published in: LIPIcs, Volume 315, 16th International Conference on Spatial Information Theory (COSIT 2024)

Abstract
Sketch mapping is a research technique that has been widely used to study what people think about the spatial layout of an environment. One of the limitations of the current practice of sketch mapping is that the interface (a pen on paper or digital tablets) forces people to draw on 2D surfaces even when the information to be represented is 3D. For the purpose of studying the 3D aspect of spatial understanding, the recent advancements in extended reality (XR) technologies including virtual reality, augmented reality, and mixed reality are interesting as they provide novel ways to create 3D sketches. In this paper, we investigate how the concept of 3D sketch mapping using XR is perceived by users and explore its potential feasibility and use cases. For this, we conducted semi-structured interviews with 27 participants from three domains: aviation, architecture, and wayfinding. Our findings show that the concept is well-perceived as an intuitive way to externalize the 3D aspect of spatial information, and it has the potential to be a research tool for human cognition research as well as a practical tool that can provide added value in different professional activities.
Cite as

Kevin Gonyop Kim, Tiffany C.K. Kwok, Sailin Zhong, Peter Kiefer, and Martin Raubal. Can You Sketch in 3D? Exploring Perceived Feasibility and Use Cases of 3D Sketch Mapping. In 16th International Conference on Spatial Information Theory (COSIT 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 315, pp. 3:1-3:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{kim_et_al:LIPIcs.COSIT.2024.3,
  author =	{Kim, Kevin Gonyop and Kwok, Tiffany C.K. and Zhong, Sailin and Kiefer, Peter and Raubal, Martin},
  title =	{{Can You Sketch in 3D? Exploring Perceived Feasibility and Use Cases of 3D Sketch Mapping}},
  booktitle =	{16th International Conference on Spatial Information Theory (COSIT 2024)},
  pages =	{3:1--3:17},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-330-0},
  ISSN =	{1868-8969},
  year =	{2024},
  volume =	{315},
  editor =	{Adams, Benjamin and Griffin, Amy L. and Scheider, Simon and McKenzie, Grant},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.COSIT.2024.3},
  URN =		{urn:nbn:de:0030-drops-208186},
  doi =		{10.4230/LIPIcs.COSIT.2024.3},
  annote =	{Keywords: Sketch maps, spatial understanding, 3D sketching, extended reality, use cases, interviews}
}
Document
DOI: 10.4230/LIPIcs.ITP.2024.9
Verifying Peephole Rewriting in SSA Compiler IRs

Authors: Siddharth Bhat, Alex Keizer, Chris Hughes, Andrés Goens, and Tobias Grosser

Published in: LIPIcs, Volume 309, 15th International Conference on Interactive Theorem Proving (ITP 2024)

Abstract
There is an increasing need for domain-specific reasoning in modern compilers. This has fueled the use of tailored intermediate representations (IRs) based on static single assignment (SSA), like in the MLIR compiler framework. Interactive theorem provers (ITPs) provide strong guarantees for the end-to-end verification of compilers (e.g., CompCert). However, modern compilers and their IRs evolve at a rate that makes proof engineering alongside them prohibitively expensive. Nevertheless, well-scoped push-button automated verification tools such as the Alive peephole verifier for LLVM-IR gained recognition in domains where SMT solvers offer efficient (semi) decision procedures. In this paper, we aim to combine the convenience of automation with the versatility of ITPs for verifying peephole rewrites across domain-specific IRs. We formalize a core calculus for SSA-based IRs that is generic over the IR and covers so-called regions (nested scoping used by many domain-specific IRs in the MLIR ecosystem). Our mechanization in the Lean proof assistant provides a user-friendly frontend for translating MLIR syntax into our calculus. We provide scaffolding for defining and verifying peephole rewrites, offering tactics to eliminate the abstraction overhead of our SSA calculus. We prove correctness theorems about peephole rewriting, as well as two classical program transformations. To evaluate our framework, we consider three use cases from the MLIR ecosystem that cover different levels of abstractions: (1) bitvector rewrites from LLVM, (2) structured control flow, and (3) fully homomorphic encryption. We envision that our mechanization provides a foundation for formally verified rewrites on new domain-specific IRs.
Cite as

Siddharth Bhat, Alex Keizer, Chris Hughes, Andrés Goens, and Tobias Grosser. Verifying Peephole Rewriting in SSA Compiler IRs. In 15th International Conference on Interactive Theorem Proving (ITP 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 309, pp. 9:1-9:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{bhat_et_al:LIPIcs.ITP.2024.9,
  author =	{Bhat, Siddharth and Keizer, Alex and Hughes, Chris and Goens, Andr\'{e}s and Grosser, Tobias},
  title =	{{Verifying Peephole Rewriting in SSA Compiler IRs}},
  booktitle =	{15th International Conference on Interactive Theorem Proving (ITP 2024)},
  pages =	{9:1--9:20},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-337-9},
  ISSN =	{1868-8969},
  year =	{2024},
  volume =	{309},
  editor =	{Bertot, Yves and Kutsia, Temur and Norrish, Michael},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ITP.2024.9},
  URN =		{urn:nbn:de:0030-drops-207372},
  doi =		{10.4230/LIPIcs.ITP.2024.9},
  annote =	{Keywords: compilers, semantics, mechanization, MLIR, SSA, regions, peephole rewrites}
}
Document
DOI: 10.4230/LIPIcs.CONCUR.2024.6
Causally Deterministic Markov Decision Processes

Authors: S. Akshay, Tobias Meggendorfer, and P. S. Thiagarajan

Published in: LIPIcs, Volume 311, 35th International Conference on Concurrency Theory (CONCUR 2024)

Abstract
Probabilistic systems are often modeled using factored versions of Markov decision processes (MDPs), where the states are composed out of the local states of components and each transition involves only a small subset of the components. Concurrency arises naturally in such systems. Our goal is to exploit concurrency when analyzing factored MDPs (FMDPs). To do so, we first formulate FMDPs in a way that aids this goal and port several notions from concurrency theory to the probabilistic setting of MDPs. In particular, we provide a concurrent semantics for FMDPs based on the classical notion of event structures, thereby cleanly separating causality, concurrency, and conflicts that arise from stochastic choices. We further identify the subclass of causally deterministic FMDPs (CMDPs), where non-determinism arises solely due to concurrency. Using our event structure semantics, we show that in CMDPs, local reachability properties can be computed using a "greedy" strategy. Finally, we implement our ideas in a prototype and apply it to four models, confirming the potential for substantial improvements over state-of-the-art methods.
Cite as

S. Akshay, Tobias Meggendorfer, and P. S. Thiagarajan. Causally Deterministic Markov Decision Processes. In 35th International Conference on Concurrency Theory (CONCUR 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 311, pp. 6:1-6:22, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{akshay_et_al:LIPIcs.CONCUR.2024.6,
  author =	{Akshay, S. and Meggendorfer, Tobias and Thiagarajan, P. S.},
  title =	{{Causally Deterministic Markov Decision Processes}},
  booktitle =	{35th International Conference on Concurrency Theory (CONCUR 2024)},
  pages =	{6:1--6:22},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-339-3},
  ISSN =	{1868-8969},
  year =	{2024},
  volume =	{311},
  editor =	{Majumdar, Rupak and Silva, Alexandra},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CONCUR.2024.6},
  URN =		{urn:nbn:de:0030-drops-207781},
  doi =		{10.4230/LIPIcs.CONCUR.2024.6},
  annote =	{Keywords: MDPs, distribution, causal determinism}
}
Document
DOI: 10.4230/LIPIcs.CONCUR.2024.40
A PSPACE Algorithm for Almost-Sure Rabin Objectives in Multi-Environment MDPs

Authors: Marnix Suilen, Marck van der Vegt, and Sebastian Junges

Published in: LIPIcs, Volume 311, 35th International Conference on Concurrency Theory (CONCUR 2024)

Abstract
Markov Decision Processes (MDPs) model systems with uncertain transition dynamics. Multiple-environment MDPs (MEMDPs) extend MDPs. They intuitively reflect finite sets of MDPs that share the same state and action spaces but differ in the transition dynamics. The key objective in MEMDPs is to find a single strategy that satisfies a given objective in every associated MDP. The main result of this paper is PSPACE-completeness for almost-sure Rabin objectives in MEMDPs. This result clarifies the complexity landscape for MEMDPs and contrasts with results for the more general class of partially observable MDPs (POMDPs), where almost-sure reachability is already EXP-complete, and almost-sure Rabin objectives are undecidable.
Cite as

Marnix Suilen, Marck van der Vegt, and Sebastian Junges. A PSPACE Algorithm for Almost-Sure Rabin Objectives in Multi-Environment MDPs. In 35th International Conference on Concurrency Theory (CONCUR 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 311, pp. 40:1-40:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{suilen_et_al:LIPIcs.CONCUR.2024.40,
  author =	{Suilen, Marnix and van der Vegt, Marck and Junges, Sebastian},
  title =	{{A PSPACE Algorithm for Almost-Sure Rabin Objectives in Multi-Environment MDPs}},
  booktitle =	{35th International Conference on Concurrency Theory (CONCUR 2024)},
  pages =	{40:1--40:17},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-339-3},
  ISSN =	{1868-8969},
  year =	{2024},
  volume =	{311},
  editor =	{Majumdar, Rupak and Silva, Alexandra},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CONCUR.2024.40},
  URN =		{urn:nbn:de:0030-drops-208120},
  doi =		{10.4230/LIPIcs.CONCUR.2024.40},
  annote =	{Keywords: Markov Decision Processes, partial observability, linear-time Objectives}
}
Document
DOI: 10.4230/LIPIcs.MFCS.2024.8
Sublinear Time Shortest Path in Expander Graphs

Authors: Noga Alon, Allan Grønlund, Søren Fuglede Jørgensen, and Kasper Green Larsen

Published in: LIPIcs, Volume 306, 49th International Symposium on Mathematical Foundations of Computer Science (MFCS 2024)

Abstract
Computing a shortest path between two nodes in an undirected unweighted graph is among the most basic algorithmic tasks. Breadth first search solves this problem in linear time, which is clearly also a lower bound in the worst case. However, several works have shown how to solve this problem in sublinear time in expectation when the input graph is drawn from one of several classes of random graphs. In this work, we extend these results by giving sublinear time shortest path (and short path) algorithms for expander graphs. We thus identify a natural deterministic property of a graph (that is satisfied by typical random regular graphs) which suffices for sublinear time shortest paths. The algorithms are very simple, involving only bidirectional breadth first search and short random walks. We also complement our new algorithms by near-matching lower bounds.
Cite as

Noga Alon, Allan Grønlund, Søren Fuglede Jørgensen, and Kasper Green Larsen. Sublinear Time Shortest Path in Expander Graphs. In 49th International Symposium on Mathematical Foundations of Computer Science (MFCS 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 306, pp. 8:1-8:13, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{alon_et_al:LIPIcs.MFCS.2024.8,
  author =	{Alon, Noga and Gr{\o}nlund, Allan and J{\o}rgensen, S{\o}ren Fuglede and Larsen, Kasper Green},
  title =	{{Sublinear Time Shortest Path in Expander Graphs}},
  booktitle =	{49th International Symposium on Mathematical Foundations of Computer Science (MFCS 2024)},
  pages =	{8:1--8:13},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-335-5},
  ISSN =	{1868-8969},
  year =	{2024},
  volume =	{306},
  editor =	{Kr\'{a}lovi\v{c}, Rastislav and Ku\v{c}era, Anton{\'\i}n},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.MFCS.2024.8},
  URN =		{urn:nbn:de:0030-drops-205646},
  doi =		{10.4230/LIPIcs.MFCS.2024.8},
  annote =	{Keywords: Shortest Path, Expanders, Breadth First Search, Graph Algorithms}
}
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