SHA-2 Acceleration Meeting the Needs of Emerging Applications: A Comparative Survey <s> A. BLOCKCHAINS <s> Large-scale peer-to-peer systems face security threats from faulty or hostile remote computing elements. To resist these threats, many such systems employ redundancy. However, if a single faulty entity can present multiple identities, it can control a substantial fraction of the system, thereby undermining this redundancy. One approach to preventing these "Sybil attacks" is to have a trusted agency certify identities. This paper shows that, without a logically centralized authority, Sybil attacks are always possible except under extreme and unrealistic assumptions of resource parity and coordination among entities. <s> BIB001 </s> SHA-2 Acceleration Meeting the Needs of Emerging Applications: A Comparative Survey <s> A. BLOCKCHAINS <s> Recently, the Bitcoin cryptocurrency has been an international sensation. This paper tells the story of Bitcoin hardware: how a group of early-adopters self-organized and financed the creation of an entire new industry, leading to the development of machines, including ASICs, that had orders of magnitude better performance than what Dell, Intel, NVidia, AMD or Xilinx could provide. We examine this story for clues as to how we can foster greater innovation in the semiconductor industry and enable this phenomenon to occur more broadly for more application areas, spawning a new age of hardware innovation tailored to emerging application domains---an Age of Bespoke Silicon. <s> BIB002 </s> SHA-2 Acceleration Meeting the Needs of Emerging Applications: A Comparative Survey <s> A. BLOCKCHAINS <s> Bitcoin is a “crypto currency”, a decentralized electronic payment scheme based on cryptography. It implements a particular type of peer-to-peer payment system. Bitcoin depends on well-known cryptographic standards such as SHA-256. In this paper we revisit the cryptographic process which allows one to make money by producing new bitcoins. We reformulate this problem as a specific sort of Constrained Input Small Output (CISO) hashing problem and reduce the problem to a pure block cipher problem, cf. Fig. 1. We estimate the speed of this process and we show that the amortized cost of this process is less than it seems and it depends on a certain cryptographic constant which is estimated to be at most 1.89. These optimizations enable bitcoin miners to save countless millions of dollars per year in electricity bills. <s> BIB003 </s> SHA-2 Acceleration Meeting the Needs of Emerging Applications: A Comparative Survey <s> A. BLOCKCHAINS <s> Bitcoin is a digital cryptocurrency that has generated considerable public interest, including both booms in value and busts of exchanges dealing in Bitcoins. One of the fundamental concepts of Bitcoin is that work, called mining, must be done in checking all monetary transactions, which in turn creates Bitcoins as a reward. In this paper we look at the energy consumption of Bitcoin mining. We consider if and when Bitcoin mining has been profitable compared to the energy cost of performing the mining, and conclude that specialist hardware is usually required to make Bitcoin mining profitable. We also show that the power currently used for Bitcoin mining is comparable to Ireland's electricity consumption. <s> BIB004 </s> SHA-2 Acceleration Meeting the Needs of Emerging Applications: A Comparative Survey <s> A. BLOCKCHAINS <s> Bit coin has emerged as the most successful cryptographic currency in history. Within two years of its quiet launch in 2009, Bit coin grew to comprise billions of dollars of economic value despite only cursory analysis of the system's design. Since then a growing literature has identified hidden-but-important properties of the system, discovered attacks, proposed promising alternatives, and singled out difficult future challenges. Meanwhile a large and vibrant open-source community has proposed and deployed numerous modifications and extensions. We provide the first systematic exposition Bit coin and the many related crypto currencies or 'altcoins.' Drawing from a scattered body of knowledge, we identify three key components of Bit coin's design that can be decoupled. This enables a more insightful analysis of Bit coin's properties and future stability. We map the design space for numerous proposed modifications, providing comparative analyses for alternative consensus mechanisms, currency allocation mechanisms, computational puzzles, and key management tools. We survey anonymity issues in Bit coin and provide an evaluation framework for analyzing a variety of privacy-enhancing proposals. Finally we provide new insights on what we term disinter mediation protocols, which absolve the need for trusted intermediaries in an interesting set of applications. We identify three general disinter mediation strategies and provide a detailed comparison. <s> BIB005 </s> SHA-2 Acceleration Meeting the Needs of Emerging Applications: A Comparative Survey <s> A. BLOCKCHAINS <s> Besides attracting a billion dollar economy, Bitcoin revolutionized the field of digital currencies and influenced many adjacent areas. This also induced significant scientific interest. In this survey, we unroll and structure the manyfold results and research directions. We start by introducing the Bitcoin protocol and its building blocks. From there we continue to explore the design space by discussing existing contributions and results. In the process, we deduce the fundamental structures and insights at the core of the Bitcoin protocol and its applications. As we show and discuss, many key ideas are likewise applicable in various other fields, so that their impact reaches far beyond Bitcoin itself. <s> BIB006 </s> SHA-2 Acceleration Meeting the Needs of Emerging Applications: A Comparative Survey <s> A. BLOCKCHAINS <s> Bitcoin is the most popular cryptocurrency today. A bedrock of the Bitcoin framework is mining, a computation intensive process that is used to verify Bitcoin transactions for profit. We observe that mining is inherently error tolerant due to its embarrassingly parallel and probabilistic nature. We exploit this inherent tolerance to inaccuracy by proposing approximate mining circuits that trade off reliability with area and delay. These circuits can then be operated at Better Than Worst-Case (BTWC) to enable further gains. Our results show that approximation has the potential to increase mining profits by 30%. <s> BIB007 </s> SHA-2 Acceleration Meeting the Needs of Emerging Applications: A Comparative Survey <s> A. BLOCKCHAINS <s> Bitcoin "miners" are electromagnetic alchemists, effectively turning megawatt-hours of electricity into the world's fastest-growing currency. Their intensive computational activity cryptographically secures the virtual currency, approves transactions, and, in the process, creates new bitcoins for the miners, as payment. And it does another thing, too: It uses an absolutely stunning amount of power. The ever-expanding racks of processors used by miners already consume as much electricity as a small city. It's a problem that experts say is bad and getting worse. "The concern that people continue to debate is, where does this end?" says Michael Reed, head of blockchain technology for Intel. The Bitcoin leech sucking on the world's power grids has been held in check, so far, by rapid gains in the energy efficiency of mining hardware. But energy and blockchain analysts are worried about the possibility of a perfect storm: Those efficiency gains are slowing while bitcoin value is rising fast-and its potential transaction growth is immense. <s> BIB008 </s> SHA-2 Acceleration Meeting the Needs of Emerging Applications: A Comparative Survey <s> A. BLOCKCHAINS <s> Abstract Internet of Things (IoT) is one of the promising technologies that has attracted a lot of attention in both industrial and academic fields these years. It aims to integrate seamlessly both physical and digital worlds in one single ecosystem that makes up a new intelligent era of Internet. This technology offers a huge business value for organizations and provides opportunities for many existing applications such as energy, healthcare and other sectors. However, as new emergent technology, IoT suffers from several security issues which are most challenging than those from other fields regarding its complex environment and resources-constrained IoT devices. A lot of researches have been initiated in order to provide efficient security solutions in IoT, particularly to address resources constraints and scalability issues. Furthermore, some technologies related to networking and cryptocurrency fields such as Software Defined Networking (SDN) and Blockchain are revolutionizing the world of the Internet of Things thanks to their efficiency and scalability. In this paper, we provide a comprehensive top down survey of the most recent proposed security and privacy solutions in IoT. We discuss particularly the benefits that new approaches such as blockchain and Software Defined Networking can bring to the security and the privacy in IoT in terms of flexibility and scalability. Finally, we give a general classification of existing solutions and comparison based on important parameters. <s> BIB009
The blockchain technology employs hash functions to ensure the integrity of a distributed ledger. In essence, a blockchain is a distributed database growing in time within a peer-topeer network. Transactions are grouped into blocks, which are concatenated by including the hash of the last block into the header of the next block. New blocks are added to the blockchain by running a distributed consensus algorithm, ensuring a consistent view of the database. Once the block sequence is agreed upon, the collision resistance property of the hash functions implies that it is infeasible to modify a transaction without being detected, since any change in the block would result in a different hash. A critical role in ensuring the integrity of the distributed database is played by the distributed consensus algorithm. In fact, if attackers are able to subvert the consensus protocol, they may force the network to agree on their own version of the blockchain, with a content of their own choice. Specifically, consensus protocols running on peer-to-peer networks must avoid Sybil attacks BIB001 , i.e. attacks based on the capability of the attacker to present multiple identities, gaining an apparent majority which can drive the consensus. The Bitcoin cryptocurrency  , which has introduced the blockchain technology, bases its own distributed consensus protocol on SHA-256. It avoids Sybil attacks by forcing peers to perform a computationally-intensive task in order to participate in the consensus algorithm BIB006 , BIB009 . The Bitcoin consensus protocol is also called Nakamoto consensus BIB005 . It mandates that a new block can be added to the network only if its hash, computed by applying twice the SHA-256 hash function, is below a specific threshold, called target. To this end, the header contains a nonce which can be changed by peers in order to alter the hash value of the block. The Nakamoto consensus relies on the one-way property of SHA-256: were the SHA-256 function to be invertible, it would be possible to compute the value of the nonce leading to the required hash value by simply inverting the SHA-256 function BIB009 . Instead, a brute-force approach is required, with minor possible improvements stemming from details of the Nakamoto consensus protocol BIB003 , BIB007 . The first node in the network capable of finding a new valid block announces it to the network, and gets the reward associated to the block, which consists of the sum of the fees of the transaction included in the new block, plus a pre-defined quantity of newly mined coins, hence the name ''mining'' given to the process. The increased interest in the Bitcoin cryptocurrency, especially during the speculative bubble of late 2017 and early 2018, during which the value of a Bitcoin almost topped 20 000 $, has made the mining process extremely competitive, paving the way for an entire industry of dedicated miner accelerators  , BIB002 with extremely high demands on the underlying SHA-256 circuitry. Not only must such circuits be fast enough to compete profitably within the peer-to-peer network, but they must also be power efficient, in order not to have energy costs exceed mining revenues BIB004 ,  . But, even more importantly, the success of Bitcoin has raised interest in the potential of the underlying blockchain technology and its applications beyond digital cryptocurrencies. In fact, investigating new blockchain applications is currently a flourishing research and development field BIB009 . The Bitcoin blockchain itself is rather limited in its applications, mainly because of its transaction script language which is by design Turing-incomplete BIB006 . Furthermore, the Nakamoto consensus protocol has raised criticism for the large amount of energy it dissipates in a computation yielding no actual result BIB008 . Therefore, several alternative blockchains have been proposed, and most of them have been implemented. However, only a few of these alternatives are actually completely independent blockchains, or altchains, the best known of which being Ethereum  . On the contrary, most of the so-called second-generation blockchains actually rely on the Bitcoin blockchain itself in some way, mainly in order to avoid destructive attacks from the powerful network of Bitcoin miners BIB005 . This means that the Bitcoin blockchain, with its reliance on hardware implementations of the SHA-256 algorithm, is today fundamental for the blockchain industry as a whole.