Blockchain Papers

Vadim Lyubashevsky, Gregor Seiler

When constructing practical zero-knowledge proofs based on the hardness of the Ring-LWE or the Ring-SIS problems over polynomial rings \(\mathbb {Z}_p[X]/(X^n+1)\), it is often necessary that the challenges come from a set \(\mathcal {C}\) that satisfies three properties: the set should be large (around \(2^{256}\)), the elements in it should have small norms, and all the non-zero elements in the difference set \(\mathcal {C}-\mathcal {C}\) should be invertible. The first two properties are straightforward to satisfy, while the third one requires us to make efficiency compromises. We can either work over rings where the polynomial \(X^n+1\) only splits into two irreducible factors modulo p, which makes the speed of the multiplication operation in the ring sub-optimal; or we can limit our challenge set to polynomials of smaller degree, which requires them to have (much) larger norms.

Jonathan Bootle, Andrea Cerulli, Essam Ghadafi, Jens Groth · 6 authors

No abstract is available for this record.

Pablo Lamela Seijas, Simon Thompson, Darryl McAdams

We give an overview of the scripting languages used in existing cryptocurrencies, and in particular we review in some detail the scripting languages of Bitcoin, Nxt and Ethereum, in the context of a high-level overview of Distributed Ledger Technology and cryptocurrencies. We survey different approaches, and give an overview of critiques of existing languages. We also cover technologies that might be used to underpin extensions and innovations in scripting and contracts, including technologies for verification, such as zero knowledge proofs, proof-carrying code and static analysis, as well as approaches to making systems more efficient, e.g. Merkelized Abstract Syntax Trees.

Tammy Wahpeconiah

How is God in the world? Is He, according to Christian theology, both transcendent and immanent? In other words, is He distant and separate from the world and humanity while at the same time working within both? Or, did He create the universe and then remove Himself from it? Are we able to comprehend certain aspects of God through our understanding of the order and beauty of the universe? Or, do humans seek a God who is no longer interested? Many science fiction writers have asked and responded to such questions including Ted Chiang in his collection, Stories of Your Life and Others. Several of his stories deal directly with these questions and we can read them as a critique of faith, religion, belief, and the nature of God. Chiang questions whether God has a role in our lives, what that role may look like, and the ability of religion to provide meaning. Furthermore, these stories are apocalyptic in nature, especially if we think of apocalypse as revelation, the Greek definition. Frederick Krueziger further defines apocalypse as “an unfolding; hence a revelation through unfolding” (5). Such unfolding always takes place within a story; thus, we must consider the inherent connection between apocalypse and story. As Krueziger says, “Apocalypse as story first of all reveals story as that which shapes our search for meaning” (5). The revelation, the unfolding, therefore is the story itself as well as what the story means. We can read Chiang's stories as apocalyptic because they reveal our disillusionment with our world and our inability to find meaning in religion alone. For Krueziger, science fiction as apocalypse illustrates our disillusionment with “the failure of the promise of technology and science to deliver the world from poverty, ignorance, disease, war, famine, plague, and death. &”(6). Although I agree that many science fiction works address these particular disillusionments, Chiang's stories, I would argue, have a certain similarity to the apocalyptic writings of John. People disappointed at the failure of the Second Coming to occur during their lifetime lost faith in the promise of God. John's writings deal with crises of both history and faith. Thus, Chiang's stories are similar to John's writings in that they deal with the disillusionment and failure of faith and religion. Before discussing the stories, it may behoove us to consider the definitions of faith, religion, and belief. Although we may feel we know what these words mean, and may even think they are synonymous, the distinctions among them are of importance to this essay. As John Bishop states, “& at its most general, ‘faith’ means the same as ‘trust‘.” Greg Popcak defines faith more narrowly, asserting that faith “is merely the innate drive to search for meaning, purpose and significance.” Religion, at its most basic, can be defined as a specific form of human activity as a means of achieving spiritual or material improvement. However, this form of human activity is often cultural because it is a system of behaviors and praxes uniting a community. Belief, according to Eric Schwitzgebel, refers “to the attitude we have, roughly, whenever we take something to be the case or regard it as true.” Interestingly, many define faith as belief without proof. Although many use these three terms interchangeably, Chiang employs them in specific ways in his stories. In the “Tower of Babylon,” Chiang uses the biblical story of the tower of Babel as his premise. His focus is not on God's creation of various languages as punishment for defying Him, but on humanity's desire “to see what lay beyond [the earth's] borders, all the rest of Yahweh's creation” (5-6). This story juxtaposes science with faith and religion as the Babylonians are building the tower so they can break into the vault of heaven. They desire knowledge about their world, but also desire knowledge about God, believing that the tower will enable them “to ascend to see the works of Yahweh” while allowing Yahweh to “descend to see the works of man” (6). In this story, Ted Chiang combines the above definitions of religion as a “search for meaning, purpose and significance” as well as the desire for material and spiritual improvement (Popcak). The envisaged structure is simple: Earth was seen as being situated in the middle of a great volume of water, with water both above and below Earth. A great dome was thought to be set above Earth (like an inverted glass bowl), maintaining the water above Earth in its place. Earth was pictured as resting on foundations that go down into the deep. These foundations secured the stability of the land as something that is not floating on the water and so could not be tossed about by wind and wave. The waters surrounding Earth were thought to have been gathered together in their place. The stars, sun, moon, and planets moved in their allotted paths across the great dome above Earth, with their movements defining the months, seasons, and year. (60) Chiang brilliantly describes the geocentric worldview through the protagonist of the story, Hillalum, who is an Elamite miner contracted to dig into the vault of heaven. He, along with other Elamite miners, spends four months climbing to the top of the tower. Along the way, he discovers how his world and his universe functions. He comes to know that night is “the shadow of the earth itself, cast against the sky” (“Tower” 11). He and the others reach a point on the tower where they see “storms from above and from below” and where people “[harvest] crops from the air” (14). After climbing a number of weeks, the miners find themselves “at precisely the same level as the moon when it passed; they had reached the height of the first of the celestial bodies” (14). When they reach the level of the sun, the intense heat forces them to travel at night. Passing this level, Hillalum finds that the sun shines “upward, which [seems] unnatural to the utmost” (15, emphasis in original). When they are level with the stars, the miners discover that a star has hit the tower, leaving “a knotted mass of black heaven-metal, as large as a man could wrap his arms around” (16). Finally, they reach the vault of heaven itself, “a solid carapace enclosing all the sky (16) that ”[seems] to be made of fine-grained white granite, unmarred and utterly featureless“ (18-19). Hillalum's travels to the top of the tower allows him to discover both the meaning and significance of the physical world, not through religion or faith, but through his own observation. Since, in the geocentric view, the Earth is “situated in the middle of a great volume of water,” the Babylonians and the Elamite miners fear that breaking into the vault of heaven will release another Great Flood (Robishaw 60). They believe Yahweh caused the Great Flood, or the “Deluge,” by releasing “the waters of the Abyss & from the springs of the earth, and & [from] the sluice gates in the vault” (19). Concerned that they may hit one of these reservoirs, the Babylonians enlist Egyptian masons who design a system using large blocks of granite that will “slide down until [they] rest in the recess of the floor” and will completely block any opening (22). Using this design, they are able to safeguard the world from another flood when their worst fear is realized and the miners accidently dig into a reservoir. Hillalum and two others are trapped within the vault, but only Hillalum survives. The rising water forces him upward and the current of water carries him until “the walls [open] out away from him” (25). He awakens in a tunnel, but is able to see light ahead. He comes out of what he discovers is a cave and finds himself in the land of Shinnar, which is south of Babylon. Hillalum's return to earth from the vault of heaven forces him to realize that the world is shaped like a seal cylinder, “wrapped around in some fantastic way so that heaven and earth [touch]” (28). Thus, Hillalum's journey is in itself apocalyptic—as his story unfolds, the world reveals itself through his experience. The scientific worldview Chiang incorporates is fascinating; yet, what is even more fascinating is the way the inhabitants view God and their attempts to connect with Him. The people fear God's displeasure and Hillalum feels uneasy at the thought of breaking open the vault of heaven (4). Standing at the base of the tower even Hillalum's senses rebel, “insisting that nothing should stand so high” (6). He and the others continually wait for a sign from God “to let men know that their venture was approved,” yet God is silent (14). When the star mentioned above first hit the tower, “everyone descended &, waiting for retribution from Yahweh for disturbing the workings of Creation. They waited for months, but no sign came” (16). God never acknowledges their efforts, either blessing or damning them for their attempts. Their overwhelming desire for knowledge of God's workings cause them to give “thanks that they [are] permitted to see so much” while at the same time they “beg forgiveness for their desire to see more” (18). Their reactions show lack of surety regarding their purpose as Yahweh fails to respond. The inhabitants debate how God may perceive their attempts to reach Him. Qurdusa, one of the tower's bricklayers argues that “if the tower were sacrilege, Yahweh would have destroyed it earlier” causing one of the Elamites to counter: “If Yahweh looked upon this venture with such favor there would already be a stairway ready-made for us to use in the vault” (19). Hillalum, however, takes a more Deistic viewpoint, saying, “Yahweh may not punish us, but Yahweh may allow us to bring our judgment upon ourselves” (19). The God in this story creates the world but does not actively intervene. When Hillalum and the others hit a reservoir, he believes “his fate had come at last. Yahweh had not asked men to build the tower or to pierce the vault; the decision to build it belonged to men alone, and they would die in this endeavor just as they did in any of their earthbound tasks. Their righteousness could not save them from the consequences of their actions” (24). In this world, the focus is on the choices one makes and the consequences one must pay for those choices. Yes, God exists, but He does not intervene in human lives, nor does He care if they are virtuous or sinful, or if they worship or ignore Him. It was clear now why Yahweh had not struck down the tower, had not punished men for wishing to reach beyond the bounds set for them: for the longest journey would merely return them to the place whence they'd come. Centuries of their labor would not reveal to them any more of Creation than they already knew. Yet through their endeavor, men would glimpse the unimaginable artistry of Yahweh's work, in seeing how ingeniously the world had been constructed. By this construction, Yahweh's work was indicated, and Yahweh's work was concealed. Thus men would know their place. (28). Hillalum comes to understand that faith does not provide meaning or significance to his life. He glimpses “the unimaginable artistry” of the world through human endeavor, not through worship or religious ritual. As Alan Gregory states, while all “apocalyptic texts reveal human life in its precarious contingency,” apocalyptic “science fiction finds the contingency of life before immanent powers” (161). The inhabitants of this world find “a sense of wonder at the complexity of creation” that comes from their own exploration of the world (Smith). Yahweh does not open their minds or increase their understanding of their world and their place in it, only an individual's desire for knowledge does so. Chiang's story is apocalyptic in that it is the story itself that reveals our search for meaning. We do not need religion to achieve spiritual or material improvement; what we need is our continuing desire to discover and understand the physical world. The “Tower of Babylon” is a story illustrating the existence of God through the reasoning and observation of its characters, but not by supernatural manifestations. Such is not the case in “Hell Is the Absence of God.” In the world of the story, the idea of faith as belief without proof is not an issue. Angels make frequent appearances and inhabitants witness the dead ascending into Heaven or descending into Hell. Hell itself becomes visible on occasion, allowing the living to see a place very similar to their world as going to Hell means “permanent exile from God, no more and no less” (“Hell” 208). Angelic manifestations can lead to miracles but can also lead to indiscriminate death and birth defects because of the destructive power of their visitations. Furthermore, anyone caught in “Heaven's light,” which appears “only when an angel [enters] or [leaves] the mortal plain,” go to Heaven, even if they are wicked or evil (226). The protagonist of the story, Neil Fisk, believes in God (as do all in this world since there is no question of God's existence), but he does not love God. Neil in the believing that were of unfolding, or without from Neil is of either or about God, he to go to Hell people like Hell was where when exile from God no fear for Neil as it means without His however, is a that Neil since many of such as he in “the for God that he had love of God had to the then it did make The together even view of God and Neil would have reached the point where he was to However, he is not that is one of during a from the angel is by glass when the of the of the in which was see to Heaven, and while Neil have seen death as a he becomes of He to be with and the only way to achieve this is for Neil to to love God. However, he finds himself in a had been the blessing of his and God had he was to love for it? For it was like a love as a for his he have but was a he He a of those who the but is by the that he should his role as one of God's those who have a to Neil is to his and make with God to find a way to love God, Neil finds a when a and while of the of his an and his was seen ascending to Heaven, to the of his Neil to a one of those who go to where either or the mortal When the angel Neil attempts to him but his into a However, a of light that “the light to Neil all the he should love As he now God an beyond what humans can for one he that he will go to Heaven since of him to Hell In is and he has a he than was when he was but his only is to love God. & He his being to Hell was not a of he he there was no for it, no His love for God, the us, “is the nature of In “Hell Is the Absence of Chiang brilliantly a of those who a religious that God those who love Him. Chiang forces the to with a why would a God on the Chiang believes this “is one of the of and with the that in the this story as of an world in which the is a directly the of the religious that miracles are always I do not agree that it is just the religious who believe miracles are always I do agree that many who would define themselves as religious have such In the world of the story, supernatural can have both and on However, we see on these have no at a witness to the angel believes God has a purpose for him and for “an with the to provide him However, does not either or He Neil death and to which to a of God's people that they can no more in the than in the mortal while them to worship God, just not a one God or not to have no on whether one in heaven or the is to question the of religious faith. In many “Hell Is the Absence of is a on In the world of the story, the inhabitants know God there is no or in to believe or not to The or is situated in the love one has or does not have for God. one God and to then one However, if one God and to as does Neil Fisk, then one is no in this world as one God to the argues that is us to take a religious belief and make it a and by so he forces us to think about ways religion can be so and in our Many of us feel certain as either a blessing or a from God, yet of us would feel a birth for as one or the Chiang us into a world where the inhabitants do not have such a world where is not God is not God is not (“Hell” This God is the God for those who do not see religion as a means of achieving any of spiritual improvement. Chiang the and the of God's We never know why God Neil to Hell and to “Hell Is the Absence of is an apocalyptic story that reveals a of faith, the disillusionment of those who no longer believe in the promise of God to the The disillusionment of faith those who do not see God as a way of their belief as Eric defines it, something we regard as what when one that something return to what if one can that God does not what when the one to it is the one for religious belief In by and what when the seek and find to the questions surrounding religious belief. understanding of and the universe on of the of For “is the of the the and the As a & is and of being & think and the of is to think and the has always with a of discovers this when is a and the understanding of the universe However, to a that is and discovers “a that any number with any other that any two are which of in the same sense of that has world to this but this sense of to that the of is nor with apocalypse reveals that can no longer provide meaning or structure to life and attempts understanding of himself and the universe on his that a of his allows him to a who “the between and and he finds his in his ability to in similar as to world, in the other and the other to world is to discover he has no for was it was something he In he feels more than a sense of to a when faith and religion no longer provide structure and meaning, both and their when they discover that what they have always as the of themselves and their world can no longer be Chiang's structure of by further to the of of faith. The story is out in with the of the which only two and The first is one through and a the other two are on either or a in and we can read one as a for faith and belief. For in the us that two The first one in that that may be but are & His that a of the of is just such a it be by any means using the of In other words, and proof are not the same we can know certain to be while not the ability to they are Such is one of the definitions of belief without proof. Chiang us with an look at what when what we believe meaning the is and the proof not from the but from As the that this is to a that there was no God. just it, but it for a For was something and is “the one who that it is not the same discovers his ability to his belief that meaning his understanding of the does not to for feel He feels as that has the of something he which is why the of the story is However, this this feels for than and their faith and both do so through their and Ted Chiang's apocalyptic stories are on our own search for meaning. Many science fiction writers often consider religion may however, creates and where religion and faith are while at the same time to the As the stories we our own disillusionment and many of us, the in the “Tower of Babylon” are to themselves whether they in knowledge or and Hillalum's and understanding of the world reveals to him that meaning is in scientific not or faith. Fisk, on the other in a world where proof of God is a yet he comes to know that God and may question why God, like the God in “Hell is the Absence of the and the without or In by religion for and “the to of the universe as yet, they find their universe not only but Chiang's story to those belief structure has intense and search for meaning them not to a and but only them further into As with all science Ted Chiang's stories reveal more of our than our reveals to We are not to God's role in our his stories us to question our own Chiang's apocalyptic is out of our own disillusionment that is on the world, but on the promise of God & which has and for some 11). these stories do not us or lead us and Ted Chiang's apocalypse reveals and that meaning and come out of death of

G. Kalpana, P. V. Kumar, R. V. Krishnaiah

Cloud was visualized as the authentic elucidation for rising storage space and service expenditure for Information Technology Applications. Outsourcing the data to cloud storage servers ease the client accountability by facilitating stumpy cost, secure, locality independent platforms and scalable resources. With the proliferation of cloud technologies, outsourced data is scrolling among the nodes, client unaware of storage location and no longer have possession of data. Data privacy and integrity are formidable concerns for data owners. So, verification of data integrity is vital. Thus, an efficient auditing scheme is required to guarantee data possessor so as to assure them data safety and accuracy. In this paper, we propose zero knowledge proof interactive system for data integrity verification on cloud. Our method strengthened by using Homomorphic encryption tags, generated on encrypted data with zero knowledge to the interactive members. We consider TPA (Third Party Auditor) as audit agent inside the cloud on behalf of client to reduce the communication cost. The scheme drastically reduces input and output costs by generating the probabilistic proof of possession using sampling sets of data blocks from the server. Client maintains meta data of file for verification, which reduces huge communication cost on network. Our theoretical analysis and experimental results show the efficiency of the scheme for integrity proofs.

Yasser Shoukry, Konstantinos Gatsis, Amr Alanwar, George J. Pappas · 7 authors

We consider a problem where multiple agents participate in solving a quadratic optimization problem subject to linear inequality constraints in a privacy-preserving manner. Several variables of the objective function as well as the constraints are privacy-sensitive and are known to different agents. We propose a privacy-preserving protocol based on partially homomorphic encryption where each agent encrypts its own information before sending it to an untrusted cloud computing infrastructure. To find the optimal solution the cloud applies a gradient descent algorithm on the encrypted data without the ability to decrypt it. The privacy of the proposed protocol against coalitions of colluding agents is analyzed using the cryptography notion of zero knowledge proofs.

D. Ragav Prasanth, N SANDEEP, TALLURU CHAITANYA

Provable data possession (PDP) is a technique for ensuring the integrity of data in storage outsourcing. In this paper, we address the construction of an efficient PDP scheme for distributed cloud storage to support the scalability of service and data migration, in which we consider the existence of multiple cloud service providers to cooperatively store and maintain the clients' data. We present a cooperative PDP (CPDP) scheme based on homomorphic verifiable response and hash index hierarchy. We prove the security of our scheme based on multi-prover zero-knowledge proof system, which can satisfy completeness, knowledge soundness, and zero-knowledge properties. In addition, we also propose a fuzzy clustering system for analyzing the high dimensional Data bases in cloud Environments. This paper proposes novel effective fuzzy soft clustering systems with the combination of possibilistic c-means.

Geunil Park, Bumryong Kim, Moon-Seog Jun

No abstract is available for this record.

Ariel Segall

This appendix describes the following topics: symmetric cryptography; public key cryptography; key derivation functions; hashes; nonces; and zero-knowledge proofs. Inspec keywords: public key cryptography Other keywords: nonces; symmetric cryptography; zero-knowledge proofs; cryptographic concepts; hashes; key derivation functions; public key cryptography Subjects: Cryptography; Cryptography theory

Anton Jan van Zonneveld, Ton J. Rabelink, Roel Bijkerk

No abstract is available for this record.

Xu Zhang, Mi Wen, Kejie Lu, Jingsheng Lei

No abstract is available for this record.

Hasini Gunasinghe, Elisa Bertino

Unlinkability and accountability are conflicting yet critical requirements that need to be addressed in order to preserve users' privacy as well as to protect service providers in today identity ecosystems. In this paper we present a pseudonymous identity management system in which users can carry out unlinkable on-line transactions without having to disclose their actual identity information in plain text to the service providers. At the same time, the service providers have strong assurance about the authenticity of the transactions. In our approach, users' identity is cryptographically encoded in pseudonymous identity tokens. % issued by trusted identity providers. Our system includes a lightweight policy language which enables users and service providers to express their requirements pertaining to pseudonymous identity verification and a suite of protocols based on zero-knowledge-proofs which enables the fulfillment of these requirements. We have implemented a prototype of the proposed system and carried out a security and performance analysis.

Lexus Jun Hong Sim, Shu Qin Ren, Sye Loong Keoh, Khin Mi Mi Aung

There is a significant increase in the amount of data breaches in corporate servers in the cloud environments. This includes username and password compromise in the cloud and account hijacking, thus leading to severe vulnerabilities of the cloud service provisioning. Traditional authentication schemes rely on the users to use their credentials to gain access to cloud service. However once the credential is compromised, the attacker will gain access to the cloud service easily. This paper proposes a novel scheme that does not require the user to present his credentials, and yet is able to prove ownership of access to the cloud service using a variant of zero-knowledge proof. A challenge-response protocol is devised to authenticate the user, requiring the user to compute a one-time pad (OTP) to authenticate himself to the server without revealing password to the server. A prototype has been implemented to facilitate the authentication of the user when accessing Dropbox, and the experiment results showed that the overhead incurred is insignificant.

Dawei Li, Jianwei Liu, Weiran Liu

Space Information Network (SIN) plays an important role in civil and national defense field, and it is highly emphasized by governments. Data transmitted and processed in SIN is massive and dynamic, which is collected by entities in the space. However, with the widely development of SIN, data security in storage and communication is facing a great challenge, and network-based attacks would leak top-secret information, which may lead to social unrest or even threatening national security. Members in SIN like the satellites, spacecrafts and aircrafts normally transmit data in clusters divided according to their function, mission and position, and each member has a superior in the upper layer. Thus we propose a secure and anonymous data transmission system for cluster organised Space Information Network in this paper to improve the security in SIN. Members in this system transmit data in clusters, and there is a cluster head managing all its cluster members. The public key is a meaningful string like the receiver's identity, which is convenient for senders to check the correctness. To reduce the burden of a single public key generator (PKG), private key can be generated from the superior in the upper layer. In addition, messages transmitted in this system are anonymous, while in consideration of non-repudiation, a cluster head can trace the message sender if there are disputes occurring, thus the malicious cluster member will be eliminated by the cluster head. Finally, zero-knowledge proof systems are used to ensure that the ciphertext is generated legally. This system is proved in a full version paper, which is semantic secure, anonymous and traceable, with a perfectly zero-knowledge proof, and its efficient performance shows that it can be applied in SIN.

Tao Jiang, Xiaofeng Chen, Qianhong Wu, Jianfeng Ma · 6 authors

Cross-client data deduplication has been widely used to eliminate redundant storage overhead in cloud storage system. Recently, Abadi et al. introduced the primitive of MLE2 with nice security properties for secure and efficient data deduplication. However, besides the computationally expensive noninteractive zero-knowledge proofs, their fully randomized scheme (R-MLE2) requires the inefficient equality-testing algorithm to identify all duplicate ciphertexts. Thus, an interesting challenging problem is how to reduce the overhead of R-MLE2 and propose an efficient construction for R-MLE2. In this paper, we introduce a new primitive called μR-MLE2, which gives a partial positive answer for this challenging problem. We propose two schemes: static scheme and dynamic scheme, where the latter one allows tree adjustment by increasing some computation cost. Our main trick is to use the interactive protocol based on static or dynamic decision trees. The advantage gained from it is, by interacting with clients, the server will reduce the time complexity of deduplication equality test from linear time to efficient logarithmic time over the whole data items in the database. The security analysis and the performance evaluation show that our schemes are Path-PRV-CDA2 secure and achieve several orders of magnitude higher performance for data equality test than R-MLE2 scheme when the number of data items is relatively large.

Zhenfeng Zhang, Kang Yang, Xuexian Hu, Yuchen Wang

Anonymous authentication allows one to authenticate herself without revealing her identity, and becomes an important technique for constructing privacy-preserving Internet connections. Anonymous password authentication is highly desirable as it enables a client to authenticate herself by a human-memorable password while preserving her privacy. In this paper, we introduce a novel approach for designing anonymous password-authenticated key exchange (APAKE) protocols using algebraic message authentication codes (MACs), where an algebraic MAC wrapped by a password is used by a client for anonymous authentication, and a server issues algebraic MACs to clients and acts as the verifier of login protocols. Our APAKE construction is secure provided that the algebraic MAC is strongly existentially unforgeable under random message and chosen verification queries attack (suf-rmva), weak pseudorandom and tag-randomization simulatable, and has simulation-sound extractable non-interactive zero-knowledge proofs (SE-NIZKs). To design practical APAKE protocols, we instantiate an algebraic MAC based on the q-SDH assumption which satisfies all the required properties, and construct credential presentation algorithms for the MAC which have optimal efficiency for a randomize-then-prove paradigm. Based on the algebraic MAC, we instantiate a highly practical APAKE protocol and denote it by APAKE, which is much more efficient than the mechanisms specified by ISO/IEC 20009-4. An efficient revocation mechanism for APAKE is also proposed.

Roman Matzutt, Oliver Hohlfeld, Martin Henze, Robin Rawiel · 6 authors

As transaction fees skyrocket today, blockchains become increasingly expensive, hurting their adoption in broader applications. This work tackles the saving of transaction fees for economic blockchain applications. The key insight is that other than the existing "default'' mode to execute application logic fully on-chain, i.e., in smart contracts, and in fine granularity, i.e., user request per transaction, there are alternative execution modes with advantages in cost-effectiveness. On Ethereum, we propose a holistic middleware platform supporting flexible and secure transaction executions, including off-chain states and batching of user requests. Furthermore, we propose control-plane schemes to adapt the execution mode to the current workload for optimal runtime cost. We present a case study on the institutional accounts (e.g., coinbase.com) intensively sending Ether on Ethereum blockchains. By collecting real-life transactions, we construct workload benchmarks and show that our work saves 18%\sim 47%18%-47% per invocation than the default baseline while introducing 1.81%\sim 16.59%1.81%-16.59% blocks delay.

Nicole Cusimano, Kevin Burrage, Ian Turner, David Kay

No abstract is available for this record.

Gina Gallegos-García, Vincenzo Iovino, Alfredo Rial, Peter B. Roenne · 5 authors

In e-voting protocols, cryptographers must balance usability with strong security guarantees, such as privacy and verifiability. In traditional e-voting protocols, privacy is often provided by a trusted authority that learns the votes and computes the tally. Some protocols replace the trusted authority by a set of authorities, and privacy is guaranteed if less than a threshold number of authorities are corrupt. For verifiability, stronger security is demanded. Typically, corrupt authorities that try to fake the tally result must always be detected.To provide verifiability, many e-voting protocols use Non-Interactive Zero-Knowledge proofs (NIZK). Thanks to their non-interactive nature, NIZK allow anybody, including third parties that do not participate in the protocol, to verify the correctness of the tally. Therefore, NIZK can be used to obtain universal verifiability. Additionally, NIZK also improve usability because they allow voters to cast a vote non-interactively.The disadvantage of NIZK is that their security is based on setup assumptions such as the common reference string (CRS) or the random oracle model. The former requires a trusted party to generate a CRS. The latter, though a popular model for secure protocol design, has been shown to be unsound.We address the design of e-voting protocols that provide verifiability without any trust assumptions. We show that Non-Interactive Witness-Indistinguishable proofs can be used for this purpose. Our e-voting protocols are private under the Decision Linear assumption, while perfect individual verifiability, i.e. a fake tally is detected with probability 1, holds unconditionally. Perfect universal verifiability requires a trusted public bulletin board. We remark that our definition of verifiability does not consider eligibility or end-to-end verifiability. First, we present a general construction that supports any tally function. Then, we show how to efficiently instantiate it for specific types of elections through Groth-Sahai proofs.

Lennard J. Davis

In April 2004, I was invited to speak at a conference on visual culture at the University of California, Berkeley. Speakers were asked to respond to an essay by W. J. T. Mitchell titled, ‘‘Showing Seeing: A Critique of Visual Culture,’’ which offers a series of definitions of the emergent field of visual studies, distinguishing it from the more established disciplines of art history, aesthetics, and media studies. As an admitted outsider to the fieldof visual studies, I chose to comment on the following statement: ‘‘Visual culture entails a meditation on blindness, the invisible, the unseen, the unseeable, and the overlooked’’ (Mitchell, 2002: 170). In my last book, Sight Unseen, I attempted to show blindness through my own experience, and a survey of representationsof blindness in literature and film.At the same time, I wanted to show seeing, to sketch my understanding of vision, drawn from a lifetime of living among the sighted in this visual culture we share. I started from the premise that the average blind CHAPTER 31 person knowsmore about what it means to be sighted than the average sighted person knows aboutwhat itmeans to be blind. The blindgrowup, attend school, and leadadult lives among sighted people. The language we speak, the literature we read, the architecturewe inhabit,were all designedby and for the sighted. If visual studies entails a meditation on blindness, it ismyhopethat itwill avoidsome of the missteps of similar meditations of the past. Specifically, I hope that visual studies can abandon one of the stock characters of the western philosophical tradition-‘‘the Hypothetical Blind Man’’ (Gitter, 2001: 58). The Hypothetical Blind Man-or the Hypothetical as I will call him for the sake of brevity-has long played a useful, though thankless, role as a prop for theories of consciousness. He is the patient subject of endless thought experiments where the experience of the world through four senses can be compared to the experience of the world through five. He is asked to describe his understanding of specific visual phenomena-perspective, reflection, refraction, color, form recognition-as well as visual aids and enhancementsmirrors, lenses, telescopes, microscopes. He is understood to lead a hermit-like existence, so far at themarginsofhis society, that he has never heard this visual terminology before the philosophers bring it up. Part of the emotional baggage he hauls around with him comes from other cultural representations of blindness, such as Oedipus and the many Biblical figures whose sight is withdrawn by the wrathful God of the Old Testament or restored by the redeemer of the New. His primary function is to highlight the importance of sight and to elicit a frisson of awe and pity which promotes gratitude among the sighted theorists for the vision they possess. I will not attempt to survey every appear- ance of the Hypothetical throughout the history of philosophy. It is enough to cite a few of his more memorable performances, and then to suggestwhathappenswhenhe is brought face to facewith actual blind people through their own first-hand, eye-witness accounts. Professor Mitchell alludes to the passages in Descartes’ La Dioptrique where he compares vision to the Hypothetical’s use of sticks to grope his way through space. Descartes’ references to the Hypothetical are confusing and are often conflated by his readers. In one instance, he compares the way the Hypothetical’s stick detects the density and resistance of objects in his path, to the way light acts on objects the eye looks at. In a later passage, Descartes performs a thought experiment, giving the Hypothetical a second stick which he could use to judge the distance between two objects by calculating the angle formed when he touches each object with one of the sticks. Descartes does not explain how the Hypothetical is supposed to make this calculation or how he can avoid running into things while doing so. I doubt that Descartes actually believed that any blind person ever used two sticks in this way. In fact, the image that illustrates his discussion shows the Hypothetical’s dog sound asleep on the ground, indicating that theHypothetical is goingnowhere. Even so, Descartes’ description of the way a blind person uses one stick reflects a basic misunderstanding. He imagines that the blind use the stick to construct a mental image, or its equivalent, of their surroundings, mapping the location of specifically identified objects. In fact, then as now, a stick or cane is a poor tool for this kind ofmental imaging. The stick serves merely to announce the presence of an obstacle, not to determine if it is a rock or a tree root, though there are sound cues-a tap versus a thud-that might help make this distinction. Inmany situations, the cane ismore of an auditory than a tactile tool. It seems that in Descartes’ desire to describe vision as an extension of or hypersensitive form of touch, he recreates the blind man in his own image, where the eyemust correspond to the hand extended by one or perhaps two sticks. The most detailed depiction of the Hypothetical came about in 1693, when William Molyneux wrote his famous letter to JohnLocke.Heproposed a thought experiment where a blind man who had learned to recognize geometric forms such as a cube and a sphere by touch, would have his sight restored through an operation. Would he be able to distinguish the two forms merely by looking at them? The Molyneux question continues to be debated today, even though the history of medicine is full of case studies of actual blind people who have had their sight restored by actual operations. Apparently, Molyneux was married to a blind woman, which has always led me to wonder why he did not pose his hypothetical question about her. Perhaps he knew that others would object that marriage to a philosopher might contaminate the experimental data. There was a risk that the philosopher might prime her answers or otherwise rig the results. Certainly in commentary on actual cases of restored sight, debaters of the Molyneux question are quick to disqualify those who were allowed to cast their eyes upon, for instance the faces of loved ones, before directing their gaze at the sphere and the cube. Denis Diderot’s 1749 ‘‘Letter on the Blind for the Use of Those Who See’’ is generally creditedwithurgingamoreenlightened,and humane attitude toward the blind. His blind man of Puiseaux and Nicholas Saunderson, the English mathematician, were both real rather than hypothetical blind men. As he introduces the man from Puiseaux, Diderot is at pains to supply details of his family history and early life to persuade his reader that this is a real person. Significantly the man from Puiseaux is first encountered helping his young son with his studies, demonstrating both that he is a loving family man, and capable of intellectual activity. But the questions Diderot poses generally fall under the purview of the Hypothetical. Certainly, many of his remarks help support Descartes’ theory relating vision to touch: Diderot praises the blind man’s ability to makephilosophical surmises about vision, but does not have a high opinion of blind people’s capacity for empathy: The phrasing of the question here suggests an afterthought. I imagine Diderot, at his table, conjuring up two men, one pissing, one bleeding. While his visual imagination is practiced inmaking these sorts ofmental images he is less adept at tuning his mind’s ear. He recognizes that for the blood to be spilt at a rate sufficient to create the same sound as the flowing urine, the bleeding man would normally cry out in pain. So he imagines, in effect, a bleedingmute. But he fails to take into account the relative viscosity, not to mention the different odors, of the two fluids. But Diderot cannot think of everything. Now I imagine a blind man wandering onto the scene. My blind man is not quite the one Diderot imagines. For one thing he is a bit preoccupied; the philosophers have dropped by again. They talk at him and over his head, bandying about names that are now familiar to him: Locke, Molyneux, Descartes. They question him about his ability to conceptualize various things: windows, mirrors, telescopes-and he responds with the quaint and winsome answers he knows they have come for. Anything to get rid of them. Distracted as he is, the sound of the bleeding mute’s plashing blood registers on his consciousness. Lacking Diderot’s imagination, however, the thought does not occur to him that this sound emanates from a bleedingmute. His reason opts instead for the explanation that the sound comes from some man relieving his bladder-a farmore commonplace phenomenon, especially in the mean streetswhere theblindman resides. It is not that the blind man has no fellow feeling for the mute. Come to think of it, the mute would make a good companion. He could act as a guide and keep an eye out for marauding philosophers, while the blind man could do all the talking. But the blind man does not have enough information to recognize the mute’s dilemma. The only hope for the bleeding mute is to find some way to attract the blind man’s attention, perhapsby throwing something. But surely, such a massive loss of blood must have affectedhis aim.While theblindman, living as he does at the margins of his society, is accustomed to being spurned by local homeowners and merchants who find his presence unsightly, and so might flee the bleeding mute’s missiles without suspecting that his aid is being solicited. The blindman quickens his pace as best he can. The mute succumbs at last to his mortal wound. And the philosopher shifts to another topic. I am wrong to make fun of Diderot, since his treatment of blindness was at once far more complex and farmore compassionate than that of other philosophers.And it is not as if his low opinion of the blind’s ability to empathize with others’ pain has ceased to contribute to attitudes about blindness. Consider this anecdote from recent history. Some weeks after September 11, 2001, the blind musician Ray Charles was interviewed about his rendition of ‘‘America the Beautiful,’’ which received a good deal of air time during the period of heightened patriotism that followed that event. The interviewer, Jim Gray, commented that Charles should consider himself lucky that his blindness prevented him from viewing the images of the World Trade Center’s collapse, and the Pentagon in flames: ‘‘Was this maybe one time in your life where not having the ability to see was a relief?’’ Like Diderot, the interviewer assumed that true horror can only be evinced through the eyes. Many eyewitness accounts of the event however, were strikingly nonvisual. Many people who were in the vicinity of Ground Zero during and soon after the disaster found it hard to put what they saw into words, in part because visibility in the areawasobscuredby smokeandash, and in part because what they were seeing did not correspond to any visual experience for which they had language. People described instead the sound of falling bodies hitting the ground, the smell of the burning jet fuel, and the particular texture of the ankle deep dust that filled the streets. But for the majority of television viewers, eye-witnesses froma distance, those events are recalled as images, indelible, powerful and eloquent. To many, like the reporter interviewing Ray Charles, it is the images rather than the mere fact of the events that produce the emotional response. The assumption seems to be that because the blind are immune to images they must also be immune to the significance of the events, and therefore must be somehow detached from or indifferent to the nation’s collective horror and grief. It is fortunate for anyone interested in dismantling the image of blindness fostered by the Hypothetical Blind Man, that we have today a great many first-hand accounts of blindness. In recent decades, memoirs, essays, and other texts by actual blind people attempt to loosen the grip the Hypothetical still seems to hold on the sighted imagination. Thanks to work by disability historians, we are also beginning to have older accounts of blindness drawn from archives of institutions and schools for the blind around the world. One such account is a text written in 1825, by a 22year-old blind French woman named The´re`se-Ade`le Husson. Born in Nancy into a petit bourgeois household, Husson became blind at nine months following a bout of smallpox. Her case attracted the attention of the local gentrywho sponsored a convent education for her, and encouraged her to cultivate her interests in literature and music. At the age of 20 she left home for Paris where she hoped to pursue a literary career. Her first text, ‘‘Reflections on the Moral and Physical Condition of the Blind’’ seems to have been written as a part of her petition for aid from theHoˆpitaldesQuinze-Vingts, an institution that provided shelter and financial support to the indigent blind of Paris. For the most part, her text follows the example of comportment and educational manuals of the time, offering advice to parents and caretakers on the correct way to raise a blind child, and to young blind people on their role in It is by and since she from the for the her first-hand experience of blindness her a of that or that of the sighted While it is that convent education would have her to the work of Descartes or Diderot, she some of the same questions to the Hypothetical. It is that the who up her have in For instance, like Diderot’s blind man of Puiseaux, she her of to the sight she at the time of her first her her a of as a or in an attempt to the young Husson the through touch, her in her and even brought in to with the or as a of her attempt to her, Husson In a later discussion of her ability to recognize objects through touch, her seems out of we imagine that she found the object of philosophical by Her on versus objects as well as her and her with the eyes of suggests an that come from question one is also the that such as and visual to which the blind have no and therefore no to use these a to a similar at readers. In her book, The World I she a detailed account of her experience of she her use of the in the was to see a good use of her education to show that the more one knows about language the it is to find that does not have some in sighted or she to her the use of would be to her the ability to at In their two one sighted and one an to put to all the hypothetical the blind before the discussion was If he had we can not only that he and his sighted would have with their but also that about which to use and which of is more who in and an in blind in the the to the discussion to far from the and that the lives of real blind people. For instance, he an from his early before he found an when he was for a as a on a because the assumed that he would not be able to the in the He this as one of of of the sighted people on person has to recognize that sight is not to that the that it would him around with He that vision might him some while viewing a or but that he can what he to about the world from and that this is for his and only different from the of sighted people. He of what I might call that the between the sighted and the blind must be and that vision is a of that these to cite his own early work on and as of his as a He also about the first months of life when his vision was to be might disqualify him as a for the since he might some of a visual from that with a who him that the loss of sight at such an early age would make from that of a person blind. And so the discussion the some about sight that to me to be far from For instance, he that when sighted people are to keep their eyes even for a time, it a kind of To his he that a of is to keep and this can lead to and I that his example is by that blindness with a a blind accustomed to the of sight, might still have similar of and to the or of To his does that some blind are by the people and can the presence of objects even without as of that when he and in a few other in the and to be in a It is not merely that they a experience, but one that is not to as to one of the a is not the experience of texture or form through but an of an and by the as a seems to toward a for a theory of senses where each of the could be into a of which function in with and in to identified at different of that she and In fact, she sound as that the in their while the can through other of their she could by the of her hand a or by the of her these blind have in is an desire to their of blindness as the of the they do not to be or people who have learned to attend to their senses in different I have to my discussion here to by people who became blind early in One of the most of the Hypothetical Blind is that he is always assumed to be both and blind. blindness, today as in the this about of people as in there is are without any visual at It is hard to come by on people who are in part because it only an when the child, or her for the which to occur only when the can that more were blind in the since some of the most of by in the and in the as now, the of blindness occur later in some Some the ability to distinguish light from while others to color, and to some Some people the to or while the vision that through space. And of the or of vision, blind people in the they attend or these theHypothetical is his are quick to anyone with any sight or with even the of a visual In of blindness, only blindness will In a of my Sight Unseen, that I had sight to to be blind He a blind he once knew who that he could not conceptualize a and that he was learned face is to it does not in fact light like an light does not what became of this or even his him only as a of the Hypothetical. he on to the history of the Molyneux If only the blind can speak of blindness with should we make the same on those who talk about there such a thing as a is merely average There are whose than or even can every of the familiar eye as in the case of can the on a toward their at a to many of visual I wonder but can such a of visual visual studies can bring to these is an of the between blindness and It is more to think in of a of in visual as well as a of in of visual or The visual studies in understanding images, who some or even all her sight, will not the ability to images and to her In his ‘‘Showing W. J. T. Mitchell a where or some of visual culture as if to an that has no experience of visual The that some will be at the while others might their with and in all cases their would have if to their visual as it, is in the as it is in the ability to images in all their and into And as we the blindness versus sight I hope we can also abandon the that use the as a for or If the is for others to see what we mean it to what we the in this way seems a to the to the same frisson of awe and It on some to the of blindness as a to which in to among those who and the blind. It also to the among the blind that the only to their is to from

Reza Alimoradi

Recently, by changing security requirements of computer networks, many public key schemes are introduced. One major shortcoming of identity-based cryptosystems is key screw. Certificateless public key cryptosystems were introduced to solve this problem. In this paper, a certificateless, public-key, multiple-key-agreement scheme will be offered which has some significant security properties such as perfect forward secrecy, strong security, and zero-knowledge proof. This scheme produces far more shared hidden keys per session in comparison with many existing schemes. In this paper, the security and the efficiency of the proposed scheme will be compared with some well-known current schemes.

Eli Ben‐Sasson, Alessandro Chiesa, Michael A. Forbes, Ariel Gabizon · 6 authors

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No abstract is available for this record.

John Maurice

No abstract is available for this record.