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Elastic-Tweak: A Framework for Short Tweak Tweakable Block Cipher
Get PDFTweakable block cipher (TBC), a stronger notion than standard
block ciphers, has wide-scale applications in symmetric-key schemes. At a high level, it provides flexibility in design and (possibly) better security bounds. In multi-keyed applications, a TBC with short tweak values can be used to replace multiple keys. However, the existing TBC construction frameworks, including TWEAKEY and XEX, are designed for general purpose tweak sizes. Specifically, they are not optimized for short tweaks, which might render them inefficient for certain resource constrained applications. So a dedicated paradigm to construct short-tweak TBCs (tBC) is highly desirable. In this paper, as a first contribution, we present a dedicated framework, called the Elastic-Tweak framework (ET in short), to convert any reasonably secure SPN block cipher into a secure tBC. We apply the ET framework on GIFT and AES to construct efficient tBCs, named TweGIFT and TweAES. These short-tweak TBCs have already been employed in recent NIST lightweight competition candidates, LOTUS-LOCUS and ESTATE. As our second contribution, we show some concrete applications of ET-based tBCs, which are better than their block cipher counterparts in terms of key size, state size, number of block cipher calls, and short message processing. Some notable applications include, Twe-FCBC (reduces the key size of FCBC and gives better security than CMAC), Twe-LightMAC Plus (better rate than LightMAC Plus), Twe-CLOC, and Twe-SILC (reduces the number of block cipher calls and simplifies the design of CLOC and SILC)
Laconic Private Set Intersection and Applications
No full textConsider a server with a large set S of strings {????1,????2…,????????} that would like to publish a small hash h of its set S such that any client with a string y can send the server a short message allowing it to learn y if ????∈???? and nothing otherwise. In this work, we study this problem of two-round private set intersection (PSI) with low (asymptotically optimal) communication cost, or what we call laconic private set intersection (ℓ PSI) and its extensions. This problem is inspired by the recent general frameworks for laconic cryptography [Cho et al. CRYPTO 2017, Quach et al. FOCS’18].
We start by showing the first feasibility result for realizing ℓ PSI based on the CDH assumption, or LWE with polynomial noise-to-modulus ratio. However, these feasibility results use expensive non-black-box cryptographic techniques leading to significant inefficiency. Next, with the goal of avoiding these inefficient techniques, we give a construction of ℓ PSI schemes making only black-box use of cryptographic functions. Our construction is secure against semi-honest receivers, malicious senders and reusable in the sense that the receiver’s message can be reused across any number of executions of the protocol. The scheme is secure under the ????-hiding, decisional composite residuosity and subgroup decision assumptions.
Finally, we show natural applications of ℓ PSI to realizing a semantically-secure encryption scheme that supports detection of encrypted messages belonging to a set of “illegal” messages (e.g., an illegal video) circulating online. Over the past few years, significant effort has gone into realizing laconic cryptographic protocols. Nonetheless, our work provides the first black-box constructions of such protocols for a natural application setting
Runtime Enforcement of Hyperproperties
Get PDFAn enforcement mechanism monitors a reactive system for
undesired behavior at runtime and corrects the system’s output in case it violates the given specification. In this paper, we study the enforcement problem for hyperproperties, i.e., properties that relate multiple computation traces to each other. We elaborate the notion of sound and transparent enforcement mechanisms for hyperproperties in two trace
input models: 1) the parallel trace input model, where the number of traces is known a-priori and all traces are produced and processed in parallel and 2) the sequential trace input model, where traces are processed sequentially and no a-priori bound on the number of traces is known. For both models, we study enforcement algorithms for specifications given as formulas in universally quantified HyperLTL, a temporal
logic for hyperproperties. For the parallel model, we describe an enforcement mechanism based on parity games. For the sequential model, we show that enforcement is in general undecidable and present algorithms for reasonable simplifications of the problem (partial guarantees or the
restriction to safety properties). Furthermore, we report on experimental results of our prototype implementation for the parallel model
"What's in the box?!": Deflecting Adversarial Attacks by Randomly Deploying Adversarially-Disjoint Models
No full textMachine learning models are now widely deployed in real-world applications. However, the existence of adversarial examples has been long considered a real threat to such models. While numerous defenses aiming to improve the robustness have been proposed, many have been shown ineffective. As these vulnerabilities are still nowhere near being eliminated, we propose an alternative deployment-based defense paradigm that goes beyond the traditional white-box and black-box threat models. Instead of training and deploying a single partially-robust model, one could train a set of same-functionality, yet, adversarially-disjoint models with minimal in-between attack transferability. These models could then be randomly and individually deployed, such that accessing one of them minimally affects the others. Our experiments on CIFAR-10 and a wide range of attacks show that we achieve a significantly lower attack transferability across our disjoint models compared to a baseline of ensemble diversity. In addition, compared to an adversarially trained set, we achieve a higher average robust accuracy while maintaining the accuracy of clean examples
The Complexities of Healing in Secure Group Messaging: Why {Cross-Group} Effects Matter
Get PDFModern secure messaging protocols can offer strong security
guarantees such as Post-Compromise Security (PCS) [18],
which enables participants to heal after compromise. The
core PCS mechanism in protocols like Signal [34] is designed
for pairwise communication, making it inefficient for large
groups, while recently proposed designs for secure group mes-
saging, ART [19], IETF’s MLS Draft-11 [7]/TreeKEM [11],
use group keys derived from tree structures to efficiently pro-
vide PCS to large groups. Until now, research on PCS designs
only considered healing behaviour within a single group.
In this work we provide the first analysis of the healing
behaviour when a user participates in multiple groups. Sur-
prisingly, our analysis reveals that the currently proposed pro-
tocols based on group keys, such as ART and TreeKEM/MLS
Draft-11, provide significantly weaker PCS guarantees than
group protocols based on pairwise PCS channels. In fact,
we show that if new users can be created dynamically, ART,
TreeKEM, and MLS Draft-11 never fully heal authentication.
We map the design space of healing mechanisms, analyz-
ing security and overhead of possible solutions. This leads
us to a promising solution based on (i) global updates that
affect all current and future groups, and (ii) post-compromise
secure signatures. Our solution allows group messaging pro-
tocols such ART and MLS to achieve substantially stronger
PCS guarantees. We provide a security definition for post-
compromise secure signatures and an instantiation
ANYway: Measuring the Amplification DDoS Potential of Domains
Get PDFDDoS attacks threaten Internet security and stability, with attacks reaching the Tbps range. A popular approach involves DNS-based reflection and amplification, a type of attack in which a domain name, known to return a large answer, is queried using spoofed requests. Do the chosen names offer the largest amplification, however, or have we yet to see the full amplification potential? And while operational countermeasures are proposed, chiefly limiting responses to ‘ANY’ queries, up to what point will these countermeasures be effective? In this paper we make three main contributions. First, we propose and validate a scalable method to estimate the amplification potential of a domain name, based on the expected ANY response size. Second, we create estimates for hundreds of millions of domain names and rank them by their amplification potential. By comparing the overall ranking to the set of domains observed in actual attacks in honeypot data, we show whether attackers are using the most-potent domains for their attacks, or if we may expect larger attacks in the future. Finally, we evaluate the effectiveness of blocking ANY queries, as proposed by the IETF, to limit DNS-based DDoS attacks, by estimating the decrease in attack volume when switching from ANY to other query types. Our results show that by blocking ANY, the response size of domains observed in attacks can be reduced by 57%, and the size of most-potent domains decreases by 69%. However, we also show that dropping ANY is not an absolute solution to DNS-based DDoS, as a small but potent portion of domains remain leading to an expected response size of over 2,048 bytes to queries other than ANY
Verifying Accountability for Unbounded Sets of Participants
Get PDFLittle can be achieved in the design of security protocols without trusting at least some participants.
This trust should be justified or, at the very least, subject to examination.
One way to strengthen trustworthiness is to hold parties accountable for their actions, as this provides a strong incentive to refrain from malicious behavior.
This has led to an increased interest in accountability in the design of security protocols.
In this work, we combine the accountability definition of Künnemann et al. with the notion of case tests to extend its applicability to protocols with unbounded sets of participants.
We propose a general construction of verdict functions and a set of verification conditions that achieve soundness and completeness.
Expressing the verification conditions in terms of trace properties allows us to extend Tamarin---a protocol verification tool---with the ability to analyze and verify accountability properties in a highly automated way.
In contrast to prior work, our approach is significantly more flexible and applicable to a wider range of protocols
Causality-Based Game Solving
Get PDFWe present a causality-based algorithm for solving two-player reachability games represented by logical constraints. These games are a useful formalism to model a wide array of problems arising, e.g., in program synthesis. Our technique for solving these games is based on the notion of subgoals, which are slices of the game that the reachability player necessarily needs to pass through in order to reach the goal. We use Craig interpolation to identify these necessary sets of moves and recursively slice the game along these subgoals. Our approach allows us to infer winning strategies that are structured along the subgoals. If the game is won by the reachability player, this is a strategy that progresses through the subgoals towards the final goal; if the game is won by the safety player, it is a permissive strategy that completely avoids a single subgoal. We evaluate our prototype implementation on a range of different games. On multiple benchmark families, our prototype scales dramatically better than previously available tools
Privacy considerations for sharing genomics data
No full textAn increasing amount of attention has been geared towards understanding the privacy risks that arise from sharing genomic data of human origin. Most of these efforts have focused on issues in the context of genomic sequence data, but the popularity of techniques for collecting other types of genome-related data has prompted researchers to investigate privacy concerns in a broader genomic context. In this review, we give an overview of different types of genome-associated data, their individual ways of revealing sensitive information, the motivation to share them as well as established and upcoming methods to minimize information leakage. We further discuss the concise threats that are being posed, who is at risk, and how the risk level compares to potential benefits, all while addressing the topic in the context of modern technology, methodology, and information sharing culture. Additionally, we will discuss the current legal situation regarding the sharing of genomic data in a selection of countries, evaluating the scope of their applicability as well as their limitations. We will finalize this review by evaluating the development that is required in the scientific field in the near future in order to improve and develop privacy-preserving data sharing techniques for the genomic context
“Go eat a bat, Chang!”: On the Emergence of Sinophobic Behavior on Web Communities in the Face of COVID-19
Get PDFThe outbreak of the COVID-19 pandemic has changed our lives in unprecedented ways. In the face of the projected catastrophic consequences, many countries have enacted social distancing measures in an attempt to limit the spread of the virus. Under these conditions, the Web has become an indispensable medium for information acquisition, communication, and entertainment. At the same time, unfortunately, the Web is being exploited for the dissemination of potentially harmful and disturbing content, such as the spread of conspiracy theories and hateful speech towards specific ethnic groups, in particular towards Chinese people since COVID-19 is believed to have originated from China. In this paper, we make a first attempt to study the emergence of Sinophobic behavior on the Web during the outbreak of the COVID-19 pandemic. We collect two large-scale datasets from Twitter and 4chan's Politically Incorrect board (/pol/) over a time period of approximately five months and analyze them to investigate whether there is a rise or important differences with regard to the dissemination of Sinophobic content. We find that COVID-19 indeed drives the rise of Sinophobia on the Web and that the dissemination of Sinophobic content is a cross-platform phenomenon: it exists on fringe Web communities like \dspol, and to a lesser extent on mainstream ones like Twitter. Also, using word embeddings over time, we characterize the evolution and emergence of new Sinophobic slurs on both Twitter and /pol/. Finally, we find interesting differences in the context in which words related to Chinese people are used on the Web before and after the COVID-19 outbreak: on Twitter we observe a shift towards blaming China for the situation, while on /pol/ we find a shift towards using more (and new) Sinophobic slurs