Literatura científica selecionada sobre o tema "Message adversary"

In this paper, we consider authentication codes where the adversary has access to a verification oracle. We formally study two attack games: offline attack and online attack. In an offline impersonation attack with verification query of order i, the adversary launches its attack through two stages. In the first stage — the query stage — the adversary can adaptively choose i distinct messages to query the verification oracle. The verification oracle will answer whether these queried messages are valid or invalid under the secret encoding rule agreed by the transmitter and the receiver. In the later stage — the spoofing stage — the adversary creates a fraudulent message which is different from all its queried messages and sends this message to the receiver. The adversary wins if the receiver accepts the fraudulent message as a valid message. In an online impersonation attack with verification query of order i, the adversary has i + 1 chances to query the verification oracle and wins as soon as one of the queries is a valid message. We make use of strategy trees, which allow optimal strategies in both attack games to be identified, to establish a number of relationships between the value of the two games. This allows us to formally prove a relationship between the value of the game when the adversary has i queries, and the one in which he does not have any. The relationship, though widely believed to be true, was only recently proved for computationally secure systems. Our result complements this latter work for the information theoretic setting.

We study the information-theoretic model of stegosystem with an active adversary, where unlike a passive adversary he can not only read but also write. The legitimate sender as well as the adversary can embed or not a message in the sending data. The receiver’s first task is to decide whether the communication is a covertext, data with no hidden message, or a stegotext, modified data with a hidden secret message. In case of stegotext, the receiver’s second task is to decide whether the message was sent by a legitimate sender or from an adversary. For this purpose an authenticated encryption from the legitimate sender is considered. In this paper we suggest two-stage statistical hypothesis testing approach from the receivers point of view. We propose the logarithmically asymptotically optimal testing for this model. As a result the functional dependence of reliabilities of the first and second kind of errors in both stages is constructed. A comparison of overall error probabilities with the situation of one stage hypotheses testing is discussed and the behaviour of functional dependences of reliabilities are illustrated.

The paper is devoted to the analysis of the unforgeability property of the Chaum - Pedersen blind signature scheme in case an adversary is able to initiate parallel sessions of the signature generation protocol. It is shown that the scheme does not ensure strong unforgeability, i.e., it allows to create the forgeries for “old” messages that were legitimately signed. An analysis of the weak unforgeability property (the adversary’s task is to create a forgery for a new message) is also conducted. Using the reduction method, we obtain a security bound on the weak unforgeability property in the algebraic group model and random oracle model. This estimation identifies the base problems whose complexity underpins the scheme security.

An authentication protocol is a procedure by which a sender tries to convey n bits of information, which we call an input message, to a receiver. An adversary controls the network over which the sender and the receiver talk and may change any message before it reaches its destination. This paper deals with the simple scenario where two parties, Alice and Bob, communicate and want to assure that the message received by Bob is the one sent by Alice. Unconditional cryptographic security cannot be generated simply from scratch, but must be based on some given primitive to start with. In this paper, we introduce a message authentication protocol with unconditional cryptographic security. More precisely, we give protocols using a weakly secret key allowing for the exchange of authenticated messages.

We consider the problem of constructing an unconditionally secure cipher with a short key for the case where the probability distribution of encrypted messages is unknown. Note that unconditional security means that an adversary with no computational constraints can only obtain a negligible amount of information (“leakage”) about an encrypted message (without knowing the key). Here, we consider the case of a priori (partially) unknown message source statistics. More specifically, the message source probability distribution belongs to a given family of distributions. We propose an unconditionally secure cipher for this case. As an example, one can consider constructing a single cipher for texts written in any of the languages of the European Union. That is, the message to be encrypted could be written in any of these languages.

Linear network coding can achieve the network capacity in the single source multicast case. For the single source multicast network with wiretap adversary, the paper of Cai and Yeung constructs an information-secure linear coding which tightly achieves the transmitting rate upper bound , where is the capacity of the network and is the maximum number of edges the adversary can wiretap. The current paper considers the cryptographic security for the messages in the random linear network coding setting. The indistinguishability under chosen-message-attack (or CMA-Security) from probabilistic polynomial-time (PPT) wiretap adversary is defined. With a pseudorandom generator against linear cryptanalysis, an end-to-end protocol is constructed for multicast network using random linear network coding. When the adversary wiretap less than edges, the protocol is CMA-Secure and attains transmitting rate approaching the network’s capacity from below, asymptotically in the expanding ratio (i.e., length of output string/length of input string) of the pseudorandom generator. Compared with secret-key based scheme, no secret is needed by the receiver nodes, which means the key managing issues for dynamic networks would never come up.

Traditionally, due to efficiency considerations, when encrypting long messages using an asymmtric cryptosystem, one needs to use a symmetric cryptosystem in addition. To eliminate this requirement, Hwang, Chang, and Hwang introduced an asymmetric cryptosystem for encrypting long messages. However, they did not give any formal proof of the security of this cryptosystem. In this paper, we propose an improved asymmetric cryptosystem for encrypting long messages, which is both efficient and secure. In the aspect of efficiency, our cryptosystem is about twice as fast as the Hwang-Chang-Hwang cryptosystem. In the aspect of security, besides providing an informal analysis, we rigorously show that computing any part of the plaintext message encrypted using our cryptosystem is as hard as breaking the ElGamal cryptosystem, even if all other parts of the message are already known to the adversary.

After critiquing what have become the main axes of political debate in the occupied territories——suicide bombings, armed operations, and reform——the author emphasizes the imperative need for a comprehensive, inclusive resistance strategy. Elaborating upon five major ingredients that must be taken into account when developing a sound strategy——cost to the adversary, cost to Palestinian society, political discourse, a clear message to the adversary, and a clear message to the world——he argues that in the present phase a resistance strategy is not at odds with state building, and that the two should be pursued in tandem.

The efficient message authentication is one of the most effective ways to thwart unauthorized and corrupted messages from being forwarded in wireless sensor networks. For this reason, many message authentication schemes have been developed, based on either symmetric key cryptosystems or parallel cryptosystems. Most of them, however, have the limitations of high complex and communication overhead in addition to lack of scalability and resilience to node compromise attacks. To solve these issues, a polynomial-based scheme was recently introduced. However, this scheme and its extensions all have the weakness of a built-in threshold determined by the degree of the polynomial based scheme: when the number of messages transmitted is larger than this threshold, the adversary can fully recover the polynomial. In this paper, we propose a scalable authentication scheme based on elliptic curve cryptography. While enabling intermediate nodes authentication, our proposed scheme allows any node to transmit an unlimited number of messages without suffering the threshold problem. In addition, our scheme can also provide message source privacy.

The problem of secure message transmission (SMT), due to its importance in both practice and theory, has been studied extensively. Given a communication network in which a sender S and a receiver R are indirectly connected by unreliable and distrusted channels, the aim of SMT is to enable messages to be transmitted from S to R with a reasonably high level of privacy and reliability. SMT must be achieved in the presence of a Byzantine adversary who has unlimited computational power and can corrupt the transmission. In the general adversary model, the adversary is characterized by an adversary structure. We study two different measures of security: perfect (PSMT) and almost perfect (APSMT). Moreover, reliable (but not private) message transmission (RMT) are considered as a specific part of SMT. In this thesis, we study RMT, APSMT and PSMT in two different network settings: point-to-point and multicast. To prepare the study of SMT in these two network settings, we present some ideas and observations on secret sharing schemes (SSSs), generalized linear codes and critical paths. First, we prove that the error-correcting capability of an almost perfect SSS is the same as a perfect SSS. Next, we regard general access structures as linear codes, and introduce some new properties that allow us to construct pseudo-basis for efficient PSMT protocol design. In addition, we define adversary structures over "critical paths", and observe their properties. Having these new developments, the contributions on SMT in the aforementioned two network settings can be presented as follows. The results on SMT in point-to-point networks are obtained in three aspects. First, we show a Guessing Attack on some existing PSMT protocols. This attack is critically important to the design of PSMT protocols in asymmetric networks. Second, we determine necessary and sufficient conditions for different levels of RMT and APSMT. In particular, by applying the result on almost perfect SSS, we show that relaxing the requirement of privacy does not weaken the minimal network connectivity. Our final contribution in the point-to-point model is to give the first ever efficient, constant round PSMT protocols in the general adversary model. These protocols are designed using linear codes and critical paths, and they significantly improve some previous results in terms of communication complexity and round complexity. Regarding SMT in multicast networks, we solve a problem that has been open for over a decade. That is, we show the necessary and sufficient conditions for all levels of SMT in different adversary models. First, we give an Extended Characterization of the network graphs based on our observation on the eavesdropping and separating activities of the adversary. Next, we determine the necessary and sufficient conditions for SMT in the general adversary model with the new Extended Characterization. Finally, we apply the results to the threshold adversary model to completely solve the problem of SMT in general multicast network graphs.

Cette thèse se penche sur les systèmes distribués tolérants les pannes, et s'intéresse plus particulièrement au problème de la diffusion fiable dans des environnements asynchrones sujets à des défaillances hybrides. Elle introduit un nouveau modèle de calcul combinant des défaillances byzantines de processus avec un adversaire de messages. Elle définit ensuite l'abstraction de Diffusion Fiable Byzantine Tolérante aux Adversaires de Messages (MBRB) et prouve sa condition de résilience optimale. Elle propose enfin trois algorithmes clés pour réaliser cette abstraction : un algorithme MBRB simple basé sur les signatures, une nouvelle primitive appelée k2l-cast pour des implémentations MBRB sans cryptographie, et un algorithme MBRB basé sur les codes correcteurs d'erreurs optimisant la complexité de communication. Ces contributions font progresser la compréhension des systèmes distribués tolérants les pannes, et participent aux fondations nécessaires à la conception d'algorithmes répartis résilients et efficaces, avec des applications dans les infrastructures critiques, les systèmes financiers et les technologies blockchain
This thesis explores fault-tolerant distributed systems. It focuses more specifically on implementing reliable broadcast in asynchronous environments prone to hybrid failures. We introduce a novel computing model combining Byzantine process failures with a message adversary. We then define the Message-Adversary-tolerant Byzantine Reliable Broadcast (MBRB) abstraction and prove its optimal resilience condition. We present three key algorithms implementing this abstraction: a simple signature-based MBRB algorithm, a new primitive called k2l-cast for cryptography-free MBRB implementations, and an erasure-coding-based MBRB algorithm optimizing communication complexity. These contributions advance the understanding of fault-tolerant distributed systems and provide a foundation for designing resilient and efficient distributed algorithms, with applications in critical infrastructures, financial systems, and blockchain technologies

This chapter examines the hip-hop community's relationship with Obama. The hip-hop community was generally supportive of Obama as the first prospective black president and an imagined emblem of hope and change, while Obama acknowledged the phenomenal power of hip-hop and admitted that he is a fan of distinguished contemporary artists in the genre. Adversely, hip-hop is highly skeptical and critical of government, and Obama has voiced disdain for the negative content and misogynist messages in hip-hop music. Now that Obama is elected, how will this anomalous relationship impact the collective posture of the hip-hop community? How will he communicate and approach the hip-hop community? Will the presence of Obama and his positive messages make the typical outlier of drug dealer passé and make it cool to be informed, articulate, and befittingly ambitious?

In this commentary Lindsay Wilson shows the book of Job to be a coherent literary work that addresses this question: Is it possible for humans to have genuine faith in God regardless of their circumstances? Wilson argues that Job's bold, sometimes questioning cries to God are portrayed as legitimate expressions of trust for a righteous person in adversity. Through critical exegesis of the text, Wilson focuses on the message of Job and its implications for practical ministry, examining such key issues as suffering, justice, lament, and faith. He also touches on various pertinent topics in Christian ethics, including individual character, wealth, suicide, and the environment. In a final section Wilson offers guidance on using Job as a resource book for pastoral care and prayer, and he discusses how to teach and preach from the book of Job.

AbstractIntangible culture is at the very heart of development in Africa. Greetings and salutations are therapeutic, as considerable energy is invested into greetings and questions about an individual’s welfare. Dress carries a message from the person wearing it, as it demonstrates the state of the mind of the person. Music features prominently at every stage of the life of the individual: there is music when a woman conceives, music at the birth of a child, music at wedding and music at death and funeral celebrations. The Convention for the Safeguarding of the Intangible Cultural Heritage was an answer to the prayers of Africans for the protection and preservation of the important and yet intangible cultural heritage with immense impact on the individual, community and people in general. Embraced with enthusiasm, the convention dominated discourse was well received. Urbanization, competition with the tangible cultural heritage, poverty and sometimes differences between political leaders and policy makers have adversely affected the performance of Africans in the implementation of the 2003 Convention, as demonstrated in this paper.

AbstractGay neighborhoods, like all neighborhoods, are in a state of continual change. The relevance of gay neighborhoods—originally formed to promote segregation of individuals who identify as sexual minorities—is lately challenged by advances in technology, experiences with pandemics, shifts in generational opinion and social values, increasing acceptance of LGBTQ+ individuals, and (in certain places) increased rights and protections for LGBTQ+ individuals. This confluence of change has created for many people anxiety related to the belief that gay neighborhoods may be dissolving or even disappearing altogether. Seeking to address these concerns, this opening chapter of the book The Life and Afterlife of Gay Neighborhoods: Renaissance and Resurgence presents eight important takeaway messages distilled from the chapters in this volume that, taken together, provide an in-depth overview of the formation, maturation, current challenges, and future prospects of LGBTQ+ spaces in urban environments. Findings suggest that shifts in patterns of residence, socialization, and entertainment for LGBTQ+ residents and visitors across metropolitan space have resulted in certain gay neighborhoods becoming less gay while other neighborhoods become more gay. In this time of social change, economic inequities, public health crises, and technological evolution, gay neighborhoods provide a culturally and historically significant template for communities in confronting adversity, fear, and discrimination. At this point in their maturity, gay neighborhoods have reached a plateau in their evolution; from here we pause to consider the current state of gay neighborhoods—and trajectories that might describe their future form—as we contemplate the importance of gay neighborhoods in the ongoing advancement of LGBTQ+ people everywhere. We conclude by observing that while gayborhoods have experienced a certain level of de-gaying, the trend toward viewing gayborhoods as inclusive and gay-friendly places de-emphasizes the self-segregation aspects of gayborhoods that were important to their initial formation; consequently, while gay neighborhoods may become less gay, other neighborhoods may also become more gay.

To deal with active attacks in public key encryptions, the notion of security against an adaptive chosen ciphertext attack has been defined by Researchers. If an adversary can inject messages into a network, these messages may be ciphertexts, and the adversary may be able to extract partial information about the corresponding cleartexts through its interaction with parties in the network. The Security against chosen ciphertext attack is defined using an “decryption oracle.” Given an encryption of a message the “ciphertext” we want to guarantee that the adversary cannot obtain any partial information about the message. A method of securing Public Key Cryptosystems using hash functions is described in this chapter.

Abstract Through word and deed, leaders can arguably bolster their credibility to act, that is, their apparent capacity and willingness to meet potential challenges. Chapter 4 asserts, however, that both words and deeds involve risks that are frequently downplayed or ignored. Verbal and physical commitments each offer distinct benefits. Words allow a sender to convey messages quickly to deflect potential challenges. But deeds also hold advantages over words beyond the deficiencies of articulating a commitment. By acting, a person or other entity can strengthen its message in various ways that link adversary transgressions to specific retaliatory actions. Despite their relative advantages and disadvantages, commitments made through word or deed, are potentially ineffective and even counterproductive. Policymakers might reduce these accompanying risks with ambiguous commitments, though they arguably bring risks of their own.

Abstract One or more myths about a god or hero killing a dragon or other reptilian adversary, usually just called ‘snake, serpent’, is found in a vast number of cultures around the world; it may be a quasi-universal. We cannot speak of an exclusively Indo-European dragon; our task rather is to sort out the Indo-European modalities of the myth as a verbal message and to underline the peculiarities which characterize the Indo-European version and which allow us to assert that it existed.

Ransomware attacks are a devastatingly severe class of cyber-attacks capable of crippling an organization through disrupting operations or egregious financial demands. A number of solutions have been proposed to decrease the risk of ransomware infection or detect ransomware once a system has been infected. However, these proposed solutions do not address the root of the problem: identifying the adversary that created them. This study takes steps towards identifying an adversary by utilizing linguistic analysis of ransomware messages to ascertain the adversary’s language of origin. Our proposed method begins by using existing ransomware messages. We isolate commonly used phrases by analyzing a number of notable ransomware attacks: CryptoLocker, Locky, Petya, Ryuk, WannaCry, Cerber, GandCrab, SamSam, Bad Rabbit, and TeslaCrypt. Afterwards, we translate these phrases from English to another language and then back to English using Google Translate and calculate the Levenshtein Distance between the two English phrases. Next, we identify the languages that have a Levenshtein Distance greater than 0 for these phrases due to differences in how parts of speech are implemented in the respective languages. Finally, we analyze new ransomware messages and rank the languages from easiest to most difficult to distinguish.

Purpose – Hotel managers meet daily challenges when communicating and conducting hotel business operations. Some challenges can be predicted and prevented, while some are ad hoc and cannot be influenced in advance. To address these challenges and convey messages they use communication. Communication is at the heart of every business and a key success factor. The purpose of this paper is to investigate, analyze, present and map the internal and external challenges that hotel managers face when communicating and managing hotel business, based on a theoretical review of previous research. It aims to identify the importance of the role communication plays in hotel operations and how it contributes to them, and to identify future communication challenges that hotel managers will face in hotel business operations. Methodology – This paper uses the literature review as a research method and focuses on reviewed open sources only and published relevant studies in publications about communication, management and tourism and hospitality industry. Desk research was used to search for and analyse papers. The literature review provides an analytical overview of the latest publications and research on the role of managerial communication and hotel business operations. The search for relevant papers was based on the keywords challenges, communication, management, and hotel business operations, using the citation and bibliographic databases of DOAB, EconLit, Emerald, Google Scholar, SAGE journals, Science Direct, Scopus, Springer, Taylor & Francis, and Web of Science. Findings – Results indicate that maintaining continuous and targeted communication is of crucial importance in ensuring timely and appropriate responses to emerging challenges. At the core of any business, communication is an element that warrants great attention. Poor communication can be counter-productive and adversely affect overall business performance. The paper highlights the primary challenges in communication facing hotel managers. These are: sending the right message to the right audience at the right time; communicating about sustainability; addressing the environmental and social awareness of consumers, financial, political and health crises, information and communication technology development, social networks, climate-related disasters, armed conflicts, and other challenges. Contribution – The contribution of this paper is that it presents an overview of the challenges that hotel managers meet in communicating in hotel business operations and can serve as a basis for further research in this field and improvement of hotel business operations. Challenges that have appeared over the past twenty years have been analyzed and grouped so that hotel managers can learn which challenges often arise in running a hotel business and prepare strategies to overcome the same or similar challenges in their business. By reviewing the literature, the paper determines what is known about this topic and what needs to be further researched. It is recommended that further studies investigate the current challenges facing hotel managers, given the increasingly rapid changes, globalization, computerization and new world crises occurring today.

This paper investigates the Gülen movement’s repertoires of action in order to determine how it differs from traditional Islamic revivalist movements and from the so-called ‘New Social Movements’ in the Western world. Two propositions lead the discussion: First, unlike many Islamic revivalist movements, the Gülen movement shaped its identity against the perceived threat of a trio of enemies, as Nursi named them a century ago – ignorance, disunity, and poverty. This perception of the opposition is crucial to understanding the apolitical mind-set of the Gülen movement’s fol- lowers. Second, unlike the confrontational New Social Movements, the Gülen movement has engaged in ‘moral opposition’, in which the movement’s actors seek to empathise with the adversary by creating (what Bakhtin calls) ‘dialogic’ relationships. ‘Moral opposition’ has enabled the movement to be more alert strategically as well as more productive tactically in solving the everyday practical problems of Muslims in Turkey. A striking example of this ‘moral opposition’ was witnessed in the Merve Kavakci incident in 1999, when the move- ment tried to build bridges between the secular and Islamist camps, while criticising and educating both parties during the post-February 28 period in Turkey. In this way the Gülen movement’s performance of opposition can contribute new theoretical and practical tools for our understanding of social movements. 104 | P a g e Recent works on social movements have criticized the longstanding tradition of classify- ing social movement types as “strategy-oriented” versus “identity-oriented” (Touraine 1981; Cohen 1985; Rucht 1988) and “identity logic of action” versus “instrumentalist logic of ac- tion” (Duyvendak and Giugni 1995) by regarding identities as a key element of a move- ment’s strategic and tactical repertoire (see Bernstein 1997, 2002; Gamson 1997; Polletta 1998a; Polletta and Jasper 2001; Taylor and Van Dyke 2004). Bifurcation of identity ver- sus strategy suggests the idea that some movements target the state and the economy, thus, they are “instrumental” and “strategy-oriented”; whereas some other movements so-called “identity movements” challenge the dominant cultural patterns and codes and are considered “expressive” in content and “identity-oriented.” New social movement theorists argue that identity movements try to gain recognition and respect by employing expressive strategies wherein the movement itself becomes the message (Touraine 1981; Cohen 1985; Melucci 1989, 1996). Criticizing these dualisms, some scholars have shown the possibility of different social movement behaviour under different contextual factors (e.g. Bernstein 1997; Katzenstein 1998). In contrast to new social movement theory, this work on the Gülen movement indi- cates that identity movements are not always expressive in content and do not always follow an identity-oriented approach; instead, identity movements can synchronically be strategic as well as expressive. In her article on strategies and identities in Black Protest movements during the 1960s, Polletta (1994) criticizes the dominant theories of social movements, which a priori assume challengers’ unified common interests. Similarly, Jenkins (1983: 549) refers to the same problem in the literature by stating that “collective interests are assumed to be relatively unproblematic and to exist prior to mobilization.” By the same token, Taylor and Whittier (1992: 104) criticize the longstanding lack of explanation “how structural inequality gets translated into subjective discontent.” The dominant social movement theory approaches such as resource mobilization and political process regard these problems as trivial because of their assumption that identities and framing processes can be the basis for interests and further collective action but cannot change the final social movement outcome. Therefore, for the proponents of the mainstream theories, identities of actors are formed in evolutionary processes wherein social movements consciously frame their goals and produce relevant dis- courses; yet, these questions are not essential to explain why collective behaviour occurs (see McAdam, McCarthy, and Zald 1996). This reductionist view of movement culture has been criticized by a various number of scholars (e.g. Goodwin and Jasper 1999; Polletta 1997, 1999a, 1999b; Eyerman 2002). In fact, the debate over the emphases (interests vis-à-vis identities) is a reflection of the dissent between American and European sociological traditions. As Eyerman and Jamison (1991: 27) note, the American sociologists focused on “the instrumentality of movement strategy formation, that is, on how movement organizations went about trying to achieve their goals,” whereas the European scholars concerned with the identity formation processes that try to explain “how movements produced new historical identities for society.” Although the social movement theorists had recognized the deficiencies within each approach, the attempts to synthesize these two traditions in the literature failed to address the empirical problems and methodological difficulties. While criticizing the mainstream American collective behaviour approaches that treat the collective identities as given, many leading European scholars fell into a similar trap by a 105 | P a g e priori assuming that the collective identities are socio-historical products rather than cog- nitive processes (see, for instance, Touraine 1981). New Social Movement (NSM) theory, which is an offshoot of European tradition, has lately been involved in the debate over “cog- nitive praxis” (Eyerman and Jamison 1991), “signs” (Melucci 1996), “identity as strategy” (Bernstein 1997), protest as “art” (Jasper 1997), “moral performance” (Eyerman 2006), and “storytelling” (Polletta 2006). In general, these new formulations attempt to bring mental structures of social actors and symbolic nature of social action back in the study of collec- tive behaviour. The mental structures of the actors should be considered seriously because they have a potential to change the social movement behaviours, tactics, strategies, timing, alliances and outcomes. The most important failure, I think, in the dominant SM approaches lies behind the fact that they hinder the possibility of the construction of divergent collective identities under the same structures (cf. Polletta 1994: 91). This study investigates on how the Gülen movement differed from other Islamic social move- ments under the same structural factors that were realized by the organized opposition against Islamic activism after the soft coup in 1997. Two propositions shall lead my discussion here: First, unlike many Islamic revivalist movements, the Gülen movement shaped its identity against perceived threat of the triple enemies, what Nursi defined a century ago: ignorance, disunity, and poverty. This perception of the opposition is crucial to grasp non-political men- tal structures of the Gülen movement followers. Second, unlike the confrontational nature of the new social movements, the Gülen movement engaged in a “moral opposition,” in which the movement actors try to empathize with the enemy by creating “dialogic” relationships.