Lisa Morhaim
email: lisa.morhaim@u-paris2.fr.

Blockchain and cryptocurrencies technologies and network structures: applications, implications and beyond

Keywords: Blockchain, Cryptocurrency, Technologies, Network structures, Applications, Implications, Economics, Law, Geography, Humanities, Interdisciplinary research

Blockchain technology is bringing together concepts and operations from several fields, including computing, communications networks, cryptography, and has broad implications and consequences thus encompassing a wide variety of domains and issues, including Network Science, computer science, economics, law, geography, etc. The aim of the paper is to provide a synthetic sketch of issues raised by the development of Blockchains and Cryptocurrencies, these issues are mainly presented through the link between on one hand the technological aspects, i.e. involved technologies and networks structures, and on the other hand the issues raised from applications to implications. We believe the link is a two-sided one. The goal is that it may contribute facilitating bridges between research areas.

Introduction

Blockchain technology is bringing together concepts and operations from several fields, including computing, communications networks, cryptography, and artificial intelligence (Swan[547]). Additionnally, the separation between economics' analysis, law analysis, etc can not be quite pertinent as they often mix. The Blockchain technology has broad implications and consequences thus encompassing a wide variety of domains and issues. Network Science is a deeply interdisciplinary rooted field. Keeping in that tradition, this paper proposes some paths to think about the Blockchain revolution and analyze its technologies and structures, applications and implications in a deeply interdisciplinary way. The objective is mainly twice: to give a most possible synthetic panorama of issues raised by the Blockchain technologies and network structures both for researchers working on a specific Blockchain research area and for researchers working and thinking on the tools in one or some of the specific domain(s) that are in the scope of the paper (which includes besides Network Science, economics, but also computer science, law, geography, political science, etc) and we hope it will easy and enhance interdisciplinary researches. As the paper is intended to easy bridges between area researches, it has been conceived somehow self-contained and synthetic as possible. The aim of the paper is to provide a synthetic sketch of issues raised by the development of Blockchains and Cryptocurrencies. These issues are mainly presented through the link between on one hand the technological aspects (involved technologies and networks structures) and on the other hand the issues raised in Economics, Law, etc, from applications to implications and beyond. We believe the link is a two-sided one. The goal is to contribute facilitating bridges between research areas and to give a first introduction to these links and issues. It refers to many existing good surveys and on-going research. The panorama have been thought from the issues they raise and discuss. Given the fast rythm at which new articles and analysis are provided, it is becoming impossible to cover exhaustively the literature on Blockchain, cryptocurrencies and related fields. Choices have been made in order to provide a quite wide range of questions and issues that are being currently discussed while easying interdisciplinary research. Network Science is rooted as an interdisciplinary field using and providing mathematical, physical, statistical as well as biological, engineering and computer science tools. As the Blockchain technology field is spreading, it is becoming clearer and clearer that Network Science can deeply fruitfully provide and develop tools at the interaction with some other various disciplines, as Economics, Law, Geography, History, Anthropology, Sociology, Political Science, etc....The aim of this paper is to give insights on what such an experience is already being done while providing some motivation and will for future research, mainly through a few chosen examples and studies. The main remarkable feature of blockchain technology is that it has been thought so that the users trust the system without no longer having to trust the partner or an intermediary and so that it solves the double-spending 1 issue. Cryptocurrency 2 . As reported by the ECB-European Central Bank [47,[START_REF]Virtual currency schemes a further analysis[END_REF], Virtual Currency Schemes (VCS) are diverse, ECB distinguishing closed, unidirectional, and bi-directional VCS while underlying that the most common approach distinguishes centralised and decentralised VCS. Decentralised bi-directional VCS (the vast majority of all VCS) can differ from various standpoints. 4 The virtual currency ecosystem involves new categories of actors not before present in the payments 1 i.e. spending the same unit more than once. 2 Cryptocurrencies date from Chaum 1983[136] and many developments have followed (see [START_REF] Rosenberg | Handbook of financial cryptography and security[END_REF]). Haber Stornetta 1990 [START_REF] Haber | How to time-stamp a digital document[END_REF], refering to Diffie Hellman [START_REF] Diffie | New directions in cryptography[END_REF]'s asymmetric (i.e. public-key) cryptography 3 (see also RSA [START_REF] Ronald L Rivest | A method for obtaining digital signatures and public-key cryptosystems[END_REF], Merckle [START_REF] Ralph C Merkle | Secure communications over insecure channels[END_REF], Bayer Haber Stornetta[59]), first described the concept of a blockchain. 4 ECB [47,[START_REF]Virtual currency schemes a further analysis[END_REF]. They can differ from their validating systems (i.e. the methods used for validating the transactions made and securing the network), the algorithms involved (i.e. the mathematical procedure for calculating and processing data), their (total) supply of coins, a functional perspective (i.e. extra features available on the network).

environment. 5 Since Nakamoto's seminal paper [START_REF] Nakamoto | Bitcoin: A peer-to-peer electronic cash system[END_REF] on Bitcoin, the Blockchain technology is currently intensively studied in the scientific community. As Swan [START_REF] Swan | Blockchain: Blueprint for a new economy[END_REF] underlines: Bitcoin terminology can be confusing because the word Bitcoin is used to simultaneously denote three different things. First, Bitcoin refers to the underlying blockchain technology platform. Second, Bitcoin is used to mean the protocol that runs over the underlying blockchain technology to describe how assets are transferred on the blockchain. Third, Bitcoin denotes a digital currency, Bitcoin, the first and largest of the cryptocurrencies. Blockchain and cryptocurrencies: definitions, technologies and specificities A blockchain is the combination of several technologies and characteristics: distributed database over a P2P network, public-key cryptography (including eventually digital signature) and eventually consensus mechanisms (see Narayanan Clark [START_REF] Narayanan | Bitcoin's academic pedigree[END_REF]). Narayanan Clark [START_REF] Narayanan | Bitcoin's academic pedigree[END_REF] show that, in 2008 when Nakamoto [START_REF] Nakamoto | Bitcoin: A peer-to-peer electronic cash system[END_REF]'s paper on Bitcoin was published, nearly all of the technical components of bitcoin originated in the academic literature of the 1980s and '90s. 6 . For a discussion on public blockchain versus private (and semi-private) blockchain see Guegan [START_REF] Guegan | Public blockchain versus private blockhain[END_REF]. A cryptographic hash function h is firstly a hash function i.e. one that maps a bit string x (of arbitrary length) to a short unique value h(x) (a short bit string of fixed length) such that computing h(x) knowing x is easy. Given a hash function h, a collision is a couple (x, x ) such that x = x and h(x) = h(x ). A cryptographic hash function h is collision resistant, i.e. it is infeasible 7 to find a collision. It is a one-way function: finding x from its hash value h(x) is infeasible. It is expected to satisfy the avalanche effect: a small change in x must lead to a large change in h(x). 8 Public-key (or asymmetric) cryptography is a cryptographic system that involves the use of two keys, a public-key that may be disseminated widely 9 by the owner and a private key known only to the owner (and that must remain private to achieve efffective security). The key used to encrypt the message cannot be used to decrypt it, and the message encrypted using one key can only be decrypted with the other key. It can ensure confidentiality, the message (data) being encrypted by the sender with the recipient's public key and decrypted by the recipient with the recipient's private key. It can ensure authentication and data integrity through digital signatures, the message being encrypted by the sender with her/his own private key and decrypted by anyone with the sender's public key. Combining public-key cryptography and hash functions allows to ensure both authentication and confidentiality efficiently. A blockchain is a distributed ledger (i.e. a distributed database allowing to record and share data across multiple data stores, the ledgers) with a linked list of blocks using hash pointers (i.e. pointers to where some information is stored, together with a cryptographic hash of the information), such that additions to the database are done through the procedure 5 These are (ECB [47,[START_REF]Virtual currency schemes a further analysis[END_REF]): inventors (known or unknown individuals or organisations that create a virtual currency and develop the technical part of its network, issuers (that are able to generate units of the virtual currency), miners (persons, sometimes working as a group, who voluntarily make computer processing available in order to validate a set of transactions (a block) made with a decentralised VCS and add this to the payment ledger (a blockchain)), processing service providers (facilitating the transfer of units from one user to another, these services being part of the activity performed by the miners in decentralised VCS), users, wallet providers (offering a digital wallet to users for storing their virtual currency cryptographic keys and transaction authentication codes, online or offline wallets, although users can also set up and maintain a wallet themselves without making use of a wallet provider), exchanges offer trading services (quoting exchange rates by which the exchange will buy/sell virtual currency against the main currencies), trading platforms (that function as marketplaces) and various other actors not specific to the VCS environment (merchants, payment facilitators, software developers, computer hardware manufacturers (building specific equipment for mining) and ATM-Automated Teller Machine manufacturers). 6 See also Sherman [START_REF] Sherman | On the origins and variations of blockchain technologies[END_REF] 7 meaning here that no process, not even one subject to arbitrary faults, can find a collision (Cachin Guerraoui Rodrigues [START_REF] Cachin | Introduction to reliable and secure distributed programming[END_REF]). In particular, it does not mean that no collision exists. This can also be expressed in terms of "easy/not easy" and is clearly related to algorithmic complexity issues (see Katz et al.[317,[START_REF] Katz | Introduction to modern cryptography[END_REF], Stallings [START_REF] Stallings | Cryptography and network security: principles and practice[END_REF]).

8 h being clearly not continuous nor invertible. 9 Each user will thus have a collection of public keys of the other users

• transactions are grouped with other transactions to form a block

• the network nodes determine collectively if the block is valide through a validation algorithm called a consensus mechanism

• as an example, in the PoW consensus mechanism, a puzzle that needs time and computing power has to be solved. The miner who first solves the puzzle sends the solution to the other nodes of the network (who can easily check it and validate the transactions in the block), and is rewarded for his contribution to the network by finding the puzzle solution.

• once a block (each block containing the transactions, a hash of its own, a hash of the previous block, timestamp) is validated, it is added to the database and the blockchain is updated accross the network.

Do you need a blockchain? Blockchain is not advantageous for every situation. On the way to construct indicators for comparing Blockchains. A decision-model. A vademecum on Blockchain for identifying when, which and how. Framework propositions for practitioners and decision-tree. On DLT characteristics. On misconceptions. Insights to select a protocol.. As noted in Swan [START_REF] Swan | Blockchain: Blueprint for a new economy[END_REF]: the Blockchain is not for every situation despite the many interesting potential uses of blockchain technology, one of the most important skills in the developing industry is to see where it is and is not appropriate to use cryptocurrency and blockchain models (Swan [START_REF] Swan | Blockchain: Blueprint for a new economy[END_REF]). So, firstly, do you need a Blockchain ? (see Wust [START_REF] Wüst | Do you need a blockchain?[END_REF]) or what blockchain alternative do you need ? (see Koens [START_REF] Koens | What blockchain alternative do you need? In Data Privacy Management[END_REF]). Criteria are being developed. Guegan Henot [START_REF] Guégan | A probative value for authentication use case blockchain[END_REF] analyse from different aspects why a company (in banking or insurance system, and industry) interested to develop its business with a public blockchain decides that a blockchain protocol is more legitimate than another one for the business it wants to develop looking at the legal (in case of dispute) points of view and introduce the notion of probative or evidential value associated to a blockchain in order to provide to the entrepreneurs an intrinsic value characterizing the blockchain he/she wants to use to develop his/her business. By quantifying the revenues a 51% attack can create for the miners, a corresponding cost is provided for each blockchain. Betzwieser 2019 [START_REF] Betzwieser | A decision model for the implementation of blockchain solutions[END_REF] propose a decision model for the implementation of Blockchain solutions. Belotti et al. [START_REF] Belotti | A vademecum on blockchain technologies: When, which and how[END_REF] provide a vademecum on Blockchain technologies, drawing a picture to answer to when (when there are actual advantages in using blockchain instead of any other traditional solution, such as centralized databases), which (which kind of blockchain better meets usecase requirements) and how (how to use it). De 2019 [START_REF] Maria | Towards a comprehensive blockchain architecture continuum[END_REF] propose a framework of blockchain models to help practitioners understanding and potentially implement Blockchain-based solutions based.

Mulligan [START_REF] Mulligan | Blockchain beyond the hype: A practical framework for business leaders[END_REF] propose a framework for practitioners (including a decision-tree). Kannengiesser et al. [START_REF] Kannengießer | Mind the gap: Tradeoffs between distributed ledger technology characteristics[END_REF] present a comprehensive set of 49 DLT characteristics synthesized from the literature on DLT, which have been found relevant to consider when developing viable applications on DLT. Conte [START_REF] Conte De Leon | Blockchain: properties and misconceptions[END_REF]'s purpose is to clarify current and widespread misconceptions about the properties of blockchain technologies. Shahaab [START_REF] Shahaab | Applicability and appropriateness of distributed ledgers consensus protocols in public and private sectors: A systematic review[END_REF] have listed consensus protocols against basic features and sector preference in a tabular format to facilitate selection. They argue that no protocol is a silver bullet, therefore should be selected carefully, considering the sector requirements and environment.

Applicability. An applicability framework. A taxonomy of Blockchain applications. Risius and Sohrer [START_REF] Risius | A blockchain research framework[END_REF] provide a framework to understand where and how blockchain technology is effectively applicable and where it has mentionable practical effects. Labazova [START_REF] Lavazova | From hype to reality: A taxonomy of blockchain applications[END_REF] gives a taxonomy of blockchain applications.

Layers Some analysis of Blockchain through layers.

A blockchain can be analyzed through its layers (see Singhal et al. [START_REF] Singhal | Beginning Blockchain: A Beginner's Guide to Building Blockchain Solutions[END_REF]): application layer (i.e. the layer where the desired functionalities are coded and made an application out of it for the end users), execution layer (i.e. the layer where the executions of instructions ordered by the application layer take place on all the nodes in a blockchain network, the instructions being simple instructions or a set of multiple instructions in the form of a smart contract), semantic layer (the rules of the system can be defined in this layer, such as data models and structures and how the blocks are linked with each other), propagation layer (i.e. the peer-to-peer communication layer that allows the nodes to discover each other), consensus layer (i.e. the layer getting all the nodes to agree on one consistent state of the ledger). See also Casino [START_REF] Casino | A systematic literature review of blockchain-based applications: current status, classification and open issues[END_REF]. Glaser Hawlitschek Notheisen in [START_REF] Horst | Business Transformation Through Blockchain, Two Volumes[END_REF] (volume 1 chapter 4) investigate the blockchain as a platform and present technical layers of the system as well as institutional characteristics and governance implications, followed by a discussion of the role of trust in blockchain systems.

Digital disruption Thinking the Blockchain revolution within innovations (and digital) disruption Theories of disruptive innovations and managerial implications have been explored and developed since the 1990's. Moller [START_REF] Møller | Characterizing digital disruption in the general theory of disruptive innovation[END_REF] on characterizing digital disruption in the theory of disruptive innovation. See also Lessig[353,[START_REF] Lessig | Code: And other laws of cyberspace[END_REF], Wu [START_REF] Wu | When code isn't law[END_REF], De Filippi Hassan [START_REF] De | Blockchain technology as a regulatory technology: From code is law to law is code[END_REF], De Filippi Wright [START_REF] De | Blockchain and the law: The rule of code[END_REF], Olleros [START_REF] Xavier | Research handbook on digital transformations[END_REF].

On previous and existing surveys Books Many books on Blockchain have been published. See Narayanan et al. 2016 [START_REF] Narayanan | Bitcoin and cryptocurrency technologies: a comprehensive introduction[END_REF], Tapscott [START_REF] Tapscott | Blockchain revolution: how the technology behind bitcoin is changing money, business, and the world[END_REF], Casey [START_REF] Michael | The Truth Machine: The Blockchain and the Future of Everything[END_REF], Burniske [START_REF] Burniske | Cryptoassets: The Innovative Investor's Guide to Bitcoin and Beyond[END_REF], Swan [START_REF] Swan | Blockchain: Blueprint for a new economy[END_REF], Ammous 2018 [START_REF] Ammous | The bitcoin standard: the decentralized alternative to central banking[END_REF],Campbell-Verduyn [START_REF] Campbell-Verduyn | Bitcoin, crypto-coins, and global anti-money laundering governance[END_REF], Treiblmaier Beck [START_REF] Horst | Business Transformation Through Blockchain, Two Volumes[END_REF], etc. On Blockchain economics: see Tasca 2016 [START_REF] Tasca | Banking beyond banks and money[END_REF], Swan [START_REF] Swan | Blockchain Economics: Implications Of Distributed Ledgers-Markets, Communications Networks, And Algorithmic Reality[END_REF] and the references herein, and Blockchain and the law: see De Filippi Wright [START_REF] De | Blockchain and the law: The rule of code[END_REF]. For a technical survey, see Tschorsch [START_REF] Tschorsch | Bitcoin and beyond: A technical survey on decentralized digital currencies[END_REF]. Refer to see Tasca et al. [START_REF] Tasca | A taxonomy of blockchain technologies: Principles of identification and classification[END_REF] and Casino Dasaklis Patsakis [START_REF] Casino | A systematic literature review of blockchain-based applications: current status, classification and open issues[END_REF] for general surveys. See also [START_REF] Lu | Blockchain: A survey on functions, applications and open issues[END_REF][START_REF] Yaga | Blockchain technology overview[END_REF][START_REF] Xu | A systematic review of blockchain[END_REF][START_REF] Ali | Blockchain and the future of the internet: A comprehensive review[END_REF]. Sejfuli 2018 [START_REF] Sejfuli-Ramadani | Blockchain: General overview of the architecture, security and reliability[END_REF] provide a synthetic and general overview of the Architecture, Security and Reliability of blockchain. Belotti et al. [START_REF] Belotti | A vademecum on blockchain technologies: When, which and how[END_REF] provide a vademecum on Blockchain technologies. Bonneau et al. [START_REF] Bonneau | Research perspectives and challenges for bitcoin and cryptocurrencies[END_REF] provide a systematic exposition of the second generation of cryptocurrencies, including Bitcoin and altcoins. Hardle [START_REF] Wolfgang K Härdle | Understanding cryptocurrencies[END_REF] provide some insights into the mechanics of cryptocurrencies, describing summary statistics and focusing on potential future research avenues in financial economics. See also Kumar Smith [START_REF] Smith | Crypto-currencies-an introduction to not-so-funny moneys[END_REF].

Surveys
Singh [START_REF] Awadhesh | Bitcoin?upsides, downsides and bone of contention?a deep dive[END_REF] perform a literature review on Bitcoin and its upsides, downside and divergent views from previous studies. Holub 2018 [START_REF] Holub | Bitcoin research across disciplines[END_REF] surveys on Bitcoin research across discplines. Wang et al.2019 [START_REF] Wang | A survey on consensus mechanisms and mining strategy management in blockchain networks[END_REF] survey on consensus mechanisms and mining strategy management. Yang 2019 [START_REF] Yang | A survey on blockchain-based internet service architecture: Requirements, challenges, trends and future[END_REF] provides a survey on Blockchain-based internet service architecture (requirements, challenges, trends and future). Bosamia [START_REF] Bosamia | Current trends and future implementation possibilities of the merkel tree[END_REF] discusses the Merkle tree concept with its advantages and disadvantages and its implementations. Dasgupta et al. [START_REF] Dasgupta | A survey of blockchain from security perspective[END_REF] and Kolokotronis [START_REF] Kolokotronis | Secured by blockchain: Safeguarding internet of things devices[END_REF] survey on blockchain from security perspective. See also Taylor [START_REF] Paul J Taylor | A systematic literature review of blockchain cyber security[END_REF]. Conti [START_REF] Conti | A survey on security and privacy issues of bitcoin[END_REF] on privacy. On Blockchain applications, see Schedlbauer Wagner [START_REF] Schedlbauer | Blockchain beyond digital currencies-a structured literature review on blockchain applications[END_REF] for a literature review, Joude[302] for a recent survey on applications usage in different domains survey. For an overview Platforms based on Distributed Ledger Technology see Schoenhals et al. [START_REF] Schoenhals | Overview of licensing platforms based on distributed ledger technology[END_REF]. Collomb [START_REF] Collomb | Blockchain/distributed ledger technology (dlt): What impact on the financial sector?[END_REF] survey on implications on the financial sector. See also Zhao Meng [START_REF] Zhao | Research on innovation and development of blockchain technology in financial field[END_REF]. Li [START_REF] Li | Initial coin offerings: Current research and future directions[END_REF] for a recent discussion on ICO current research and future directions. On Fintech see Kavuri 2019 [START_REF] Savio | Fintech and the future of financial services: What are the research gaps?[END_REF]. On RegTech see Johansson et al. [START_REF] Johansson | Regtech-a necessary tool to keep up with compliance and regulatory changes[END_REF]. For a literature review on use of Blockchain in governance: Razzaq et al. [START_REF] Razzaq | Use of blockchain in governance: A systematic[END_REF]. Wang [START_REF] Wang | A summary of research on blockchain in the field of intellectual property[END_REF] for a recent summary of research on Blockchain in the field of Intellectual property. On Blockchain economics, see among many Catalini Gans [START_REF] Catalini | Some simple economics of the blockchain[END_REF] Davidson et al. [START_REF] Davidson | Economics of blockchain[END_REF], Abadi Brunnermeier[1], Davidson et al. [START_REF] Davidson | Economics of blockchain[END_REF], Halaburda [START_REF] Halaburda | Blockchain revolution without the blockchain[END_REF] and Qin [START_REF] Qin | Economic issues in bitcoin mining and blockchain research[END_REF] on economic issues in bitcoin mining and blockchain research. Liu [START_REF] Liu | A survey on applications of game theory in blockchain[END_REF] provides a survey on applications of game theory in Blockchain. Benson [START_REF] Benson | Implications of adopting blockchain technology on international sales transactions[END_REF] on implications of adopting Blockchain technology on international sales transactions. For a survey on Blockchain issues and the law, we refer to Filippi Wright [START_REF] De | Blockchain and the law: The rule of code[END_REF] and Marmoz [START_REF] Franck | Marmoz[END_REF], Berg et al. [START_REF] Berg | Blockchains and constitutional catallaxy[END_REF], see also Ostbye [START_REF] Østbye | Who is liable if a public cryptocurrency protocol fails? Available at[END_REF] on liability issue if a public cryptocurrency protocol fails. De Filippi Wright [START_REF] Wright | Decentralized blockchain technology and the rise of lex cryptographia[END_REF] on the widespread deployment of Blockchains will lead to expansion of a new subset of law, which they term Lex Cryptographia.

Organization of the paper. Section 1 introduces the aims, definitions, literature and frameworks.

Section 2 provides a brief sketch of some of the many Blockchain applications. Section 3 describes the technologies, specificities, network structures, implications and related issues of Blockchains and Cryptocurrencies. Section 4 provides some insights on a broader scope. Section 5 concludes.

Applications a brief sketch

For a systematic literature review of Blockchain-based applications refer to Casino [START_REF] Casino | A systematic literature review of blockchain-based applications: current status, classification and open issues[END_REF] [START_REF] Horst | Business Transformation Through Blockchain, Two Volumes[END_REF]) on identifying industries and use cases that may benefit from adopting blockchain when it comes to crowdfunding and showing how crowdfunding and initial coin offerings differ and how the latter is reshaping the former, Cervhiello [START_REF] Cerchiello | Ico success drivers: A textual and statistical analysis[END_REF] for statistical approach to detect characteristics of ICO significantly related to fraudulent behaviors, Holoweiko 2018 [START_REF] Holoweiko | What is an ico? defining a security on the blockchain[END_REF] on ico security, Garratt gar-ratt2019entrepreneurial examines how financing a start-up through an ICO changes the incentives of an entrepreneur relative to debt and venture capital financing: depending on market characteristics, an ICO can result in a better or worse alignment of the interests of the entrepreneur and the investors compared with conventional modes of financing), Humanitarian aid, Shared Economy (see Huckle [START_REF] Huckle | Internet of things, blockchain and shared economy applications[END_REF] (volume 1 chapter 3 in [START_REF] Horst | Business Transformation Through Blockchain, Two Volumes[END_REF]) providing a technology adoption perspective on the Blockchain-Based decentralized business models in the sharing economy and apply agent-based modeling to explore the circumstances under which a decentralized sharing economy business model might achieve widespread adoption), Management and governance (DAO, dApps, Howell 2019 [START_REF] Howell | Governance of smart contracts in blockchain institutions[END_REF], Young 2018 [START_REF] Young | Changing governance models by applying blockchain computing[END_REF]), Supply Chain (see [START_REF] Vyas | Blockchain and the Supply Chain: Concepts, Strategies and Practical Applications[END_REF]), Supply Chain Finance (see [278]), Marketing and Adertising uses.

In Law areas (see references in Bolotaeva [START_REF] Os Bolotaeva | The legal nature of cryptocurrency[END_REF], Filippi Hassan [START_REF] De | Blockchain and the law: The rule of code[END_REF], De Filippi [START_REF] De | Blockchain and the law: The rule of code[END_REF], one can insist on Smart Contracts (SCs) (see Bakos Halaburda 2019[46], Howell 2019 [START_REF] Howell | Governance of smart contracts in blockchain institutions[END_REF], see Alharby Moorsel [START_REF] Alharby | Blockchain-based smart contracts: A systematic mapping study[END_REF], see also [START_REF] Bistarelli | Analysis of ethereum smart contracts and opcodes[END_REF][START_REF] He | Characterizing code clones in the ethereum smart contract ecosystem[END_REF][START_REF] Di | Mayflies, breeders, and busy bees in ethereum: Smart contracts over time[END_REF], Meneghetti [START_REF] Meneghetti | A survey on efficient parallelization of blockchain-based smart contracts[END_REF], senopra [START_REF] Le | Senopra: Reconciling data privacy and utility via attested smart contract execution[END_REF], [START_REF] Ning | Keeping time-release secrets through smart contracts[END_REF], see Dargaye [START_REF] Dargaye | Pluralize: a trustworthy framework for high-level smart contract-draft[END_REF] 10 , Tonelli [START_REF] Tonelli | Smart contracts software metrics: a first study[END_REF], Casino [START_REF] Casino | A systematic literature review of blockchain-based applications: current status, classification and open issues[END_REF],

Marchesi Tonnelli [START_REF] Pinna | A massive analysis of ethereum smart contracts empirical study and code metrics[END_REF], Krishnan [START_REF] Krishnan | Validating smart contract execution across a heterogeneous collection: A proposal[END_REF] on smart contract and interoperability, O'Shields [START_REF] Shields | Smart contracts: Legal agreements for the blockchain[END_REF] and Westerkamp [START_REF] Westerkamp | Verifiable smart contract portability[END_REF]), Multisignature: Smart Complex Contracts, LegalTech (see Corrales Fenwick Haapio [START_REF] Corrales | Legal Tech, Smart Contracts and Blockchain[END_REF]), Regulation (see Smith [START_REF] Smith | The life-cycle and character of crypto-assets: A framework for regulation and investor protection[END_REF] for a framework, Melo [START_REF] Jr | How blockchains can help legal metrology[END_REF], Baidoo [START_REF] Edwin | Regulatory effects on traditional financial systems versus blockchain and emerging financial systems[END_REF]), Dispute resolution (Raymond 2014 [START_REF] Anjanette | Trusting strangers: Dispute resolution in the crowd[END_REF]), Crowdsourcing and Court system (Ast [START_REF] Ast | The crowdjury, a crowdsourced justice system for the collaboration era[END_REF], Li 2018 [START_REF] Li | Crowdbc: A blockchain-based decentralized framework for crowdsourcing[END_REF]).

Beside Economics and Law, many other applications are being developed: Archives (on decentralized scientific publications, see Tenorio 2019 [START_REF] Tenorio-Fornés | Towards a decentralized process for scientific publication and peer review using blockchain and ipfs[END_REF] and on medical see Coghill [START_REF] Jeffrey | Blockchain and its implications for libraries[END_REF]), Health (see Burniske 2016[592], Sachin et al. (volume 2 chapter 5 in [START_REF] Horst | Business Transformation Through Blockchain, Two Volumes[END_REF]) presenting a mobile healthcare system for personal health data collection, sharing, and collaboration between individuals and healthcare providers, as well as insurance companies, Genestier [START_REF] Genestier | Blockchains et smart contracts: des perspectives pour l?internet des objets (iot) et pour l?esanté[END_REF], review [START_REF] Kuo | Blockchain distributed ledger technologies for biomedical and health care applications[END_REF][START_REF] William | Blockchain technology for healthcare: facilitating the transition to patient-driven interoperability[END_REF][START_REF] Drosatos | Blockchain applications in the biomedical domain: a scoping review[END_REF][START_REF] Haider | A review on the role of blockchain technology in the healthcare domain[END_REF][START_REF] Khezr | Blockchain technology in healthcare: A comprehensive review and directions for future research[END_REF][START_REF] Faeq | An adaptive biomedical data managing scheme based on the blockchain technique[END_REF][START_REF] Kombe | A review on healthcare information systems and consensus protocols in blockchain technology[END_REF]), Agriculture, Food traceability, Energy (see Strucker et al.(volume 2 chapter 2 in Treiblmaier Beck 2019 [START_REF] Horst | Business Transformation Through Blockchain, Two Volumes[END_REF]) having a close look at the energy sector and present some ideas on how blockchain might potentially impact this sector in the not-so-far-off future, Peter [START_REF] Viktor | Blockchain meets energy: digital solutions for a decentralized and decarbonized sector[END_REF]), Politics (see De Filippi Loveluck[168], Berg [START_REF] Berg | Byzantine political economy. Available at SSRN[END_REF], Martinez [START_REF] Luis | The ?tokenization? of the eparticipation in public governance: An opportunity to hack democracy[END_REF] argues on Blockchain solution in eDemocracy platforms, Grontas [START_REF] Grontas | Blockchain, consensus, and cryptography in electronic voting[END_REF] on electronic voting, Dhillon Grammateia Riley [START_REF] Dhillon | Introduction to voting and the blockchain: some open questions for economists[END_REF] on voting questions for economists, Elsden [START_REF] Elsden | Making the blockchain civic[END_REF]), Education (see Chen [START_REF] Chen | Exploring blockchain technology and its potential applications for education[END_REF], Sommer [START_REF] Sommer | Request for comments: Proposal of a blockchain for the automatic management and acceptance of student achievements[END_REF], Palavinel [START_REF] Palanivel | Blockchain architecture to higher education systems[END_REF]), Post-Disaster Recovery (see Nawari Ravindran [START_REF] Nawari | Blockchain and building information modeling (bim): Review and applications in post-disaster recovery[END_REF], Demir [START_REF] Demir | Utility blockchain for transparent disaster recovery[END_REF]), Smart cities (see Kitchin [START_REF] Kitchin | Making sense of smart cities: addressing present shortcomings[END_REF], Speed [START_REF] Speed | Blockchain city: Economic, social and cognitive ledgers[END_REF], Ramos 2019 [START_REF] Felipe | Privacy and data protection concerns regarding the use of blockchains in smart cities[END_REF]), Prediction markets, Blockchain gaming (see Min [START_REF] Min | Blockchain games: A survey[END_REF], and Min [START_REF] Min | A security case study for blockchain games[END_REF] on security of blockchain games).

Technologies, network structures and specificities

Technical aspects and specificities and related issues involved in applications and implications reveal that advantages of Blockchain can sometimes also be their main limitations.

3.1 Distributed system, peer-to-peer (P2P) network, decentralization and immutability 3.1.1 Distributed system, peer-to-peer (P2P) network and Blockchain

Distributed system. Processes cooperate? Distributed computing community. Theoretical aspects of Blockchains.

Blockchain protocols are solving a classical distributed computing problem. When a program encompasses multiple processes (a process representing a computer, a processor in a computer, etc), the fundamental problem is having all the processes cooperate on a common task. Important issues then arise as the tolerance to uncertainty and adversarial influence in a distributed system, which may arise from network delays, faults, or even malicious attacks (Cachin Guerraoui Rodrigues [START_REF] Cachin | Introduction to reliable and secure distributed programming[END_REF]).

There is growing work on the line of recent distributed computing11 community efforts dedicated to the theoretical aspects of blockchains (see [START_REF] Anceaume | Distributed ledger register: From safe to atomic[END_REF][START_REF] Potop-Butucaru | Are blockchains a challenge for distributed computing? available at[END_REF][START_REF] Guerraoui | Si la blockchain est la solution, quel est le problème ?[END_REF]). Anceaume et al. [START_REF] Anceaume | Blockchain abstract data type[END_REF] is the first paper specifying blockchains as a composition of abstract data types all together with a hierarchy of consistency criteria that formally characterizes the histories admissible for distributed programs that use them. Anceaume et al. [START_REF] Anceaume | Bitcoin a distributed shared register[END_REF] introduce the Distributed Register, a register that mimics the behaviour of the Bitcoin ledger, the aim being to provide formal guarantees on the coherent evolution of Bitcoin. 12 Rauchs et al. [START_REF] Rauchs | Distributed ledger technology systems: a conceptual framework[END_REF] establish a conceptual framework and terminology that can be applied across DLT systems and to distinguish these newer technologies from traditional databases and other systems, providing a multidimensional tool for examining and comparing existing DLT systems and their traits and features, it also can serve when examining new DLT systems proposals. Siris et al. [START_REF] Vasilios | Interledger approaches[END_REF] discusses on the interledger approach: blockchains and more generally distributed ledger technologies(DLTs)' shortcomings becoming more apparent, a relatively recent approach to address their performance, scalability, privacy, and other problems are to use multiple different DLTs instead of relying on just one. Daniel Burkhardt et al. (volume 2 chapter 4 in [START_REF] Horst | Business Transformation Through Blockchain, Two Volumes[END_REF]) argue that distributed ledgers will enable new opportunities to replace existing components on all layers of industrial IT architecture.

The main examples of distributed systems without blockchains are distributed systems based on Directed Acyclic Graph (DAG). Instead of a chain, such distributed systems use a Directed Acyclic Graph (DAG) 13 as decentralized structure. Examples of such cryptocurrencies are Iota (based on the DAG called Tangle), Hashgraph, and Nano. There are other distributed systems without blockchains, for example Corda [START_REF] Hearn | A distributed ledger[END_REF][START_REF] Gendal Brown | Corda: an introduction. R3 CEV[END_REF][START_REF] Gendal | The corda platform: An introduction[END_REF] used to treat financial legal agreements could look like a firms' consortium blockchain but uses of a concept of change of states and transactions in place of chain of blocks.

Decentralization

Distributed system and organization. New forms of organization. Institutional cryptoeconomics. Dynamics. Organizational economics Resnick [START_REF] Resnick | Decentralized modeling and decentralized thinking[END_REF] discusses how computer-modeling activities can help people move beyond the centralized mindset, helping them gain new insights into (and appreciation for) the workings of decentralized systems. Blockchain can be thought of as an institutional innovation. Berg [START_REF] Berg | Outsourcing vertical integration: Distributed ledgers and the v-form organisation[END_REF] introduces the V-form organisation, a new form of firm organisation where vertical integration is outsourced to a decentralised distributed ledger (a blockchain), and rely on the coordination of a (trusted) third party.

Allen [START_REF] Darcy We Allen | Blockchain and supply chains: V-form organisations, value redistributions, de-commoditisation and quality proxies[END_REF] apply institutional cryptoeconomics to the information problems in global trade, model incentives under which blockchain-based supply chain infrastructure will be built, and make predictions about the future of supply chains, arguing blockchain will change the patterns and dynamics of how, where and what we trade through four main reasons. Berg [START_REF] Berg | Capitalism after satoshi: Blockchains, dehierarchicalisation, innovation policy, and the regulatory state[END_REF] study the institutional economic dynamics of a wide-spread blockchain technology adoption, examining the structural economic effects of this institutional innovation as disintermediation in markets, dehierarchicalisation of organisations, and growing private provision of economic infrastructure for exchange, contracting and coordination. Schneider [START_REF] Schneider | Decentralization: an incomplete ambition[END_REF] discusses the very concept of decentralization, arguing that to be a reliable concept, it should come with high standards of specificity. Takagi [START_REF] Takagi | Does blockchain decentralize everything: An insight from organizational economics[END_REF] study the economic mechanisms behind blockchain-enabled decentralisation from the viewpoint of organizational economics.

Decentralization analysis and networks. Consensus Network Topology. How to quantify decentralization. Decentralization metrics. Decentralization function. Mining pools and endogenous fees. See Tasca et al. [START_REF] Tasca | A taxonomy of blockchain technologies: Principles of identification and classification[END_REF]: Consensus Network Topology describes the type of interconnection between the nodes and the type of information flow between them for transaction and/or for the purpose of validation. Consensus Network Topology is linked to the level of (de)centralisation in the validation process, lthough it is not the only determinant as other factors influence it (like the reward mechanism) (see Bonneau et al. [START_REF] Bonneau | Sok: Research perspectives and challenges for bitcoin and cryptocurrencies[END_REF]). Gencer et al. [START_REF] Adem Efe Gencer | Decentralization in bitcoin and ethereum networks[END_REF] study decentralization metrics in Bitcoin and Ethereum networks, adapting Internet measurement techniques. Kwon et al. [START_REF] Kwon | Impossibility of full decentralization in permissionless blockchains[END_REF] define (m, ε, δ)-decentralization, a state satisfying that there are at least m participants running a node, and the ratio between the total resource power of nodes run by the richest and the δ-th percentile participants is less than or equal to 1 + ε. So that when δ = ε = 0 and m is large enough, (m, ε, δ)-decentralization is full decentralization. Kwon et al. [START_REF] Kwon | Impossibility of full decentralization in permissionless blockchains[END_REF] study decentralization in PoW-based, proof-of-stake (PoS)-based and delegated proof-of-stake (DPoS)-based coins by the means of studying (m, ε, δ)-decentralization. Stifter [START_REF] Stifter | Echoes of the past: Recovering blockchain metrics from merged mining[END_REF] shows an example of data mining applied to the analysis of the blockchain network. Bodo [START_REF] Bodó | The Logics of Technology Decentralization: the Case of Distributed Ledger Technologies[END_REF] analyzes decentralization related to distributed ledger technologies (DLTs), its extent, its mode, the systems which it can refer to as the products of particular economic, political, social dynamics around and within these techno-social systems. Chu Wang [START_REF] Chu | The curses of blockchain decentralization[END_REF] explore the trade-off decentralization-scalability, decentralization being quantified by the decentralization level they define within the paper. Cong et al. [START_REF] William | Decentralized mining in centralized pools[END_REF] study the centralization and decentralization forces in the creation and competition of mining pools.

Dapps (decentralized applications), DAOs (decentralized autonomous organizations), DACs (decentralized autonomous corporations) and DASs (decentralized autonomous societies) See Raval [START_REF] Raval | Decentralized applications: harnessing Bitcoin's blockchain technology[END_REF] for more details on Decentralized Applications. Hsieh [START_REF] Hsieh | Bitcoin and the rise of decentralized autonomous organizations[END_REF] analyse Bitcoin as an example to shed light on how a DAO works in the cryptocurrency industry.

Some limitations about decentralization. Centralization-decentralization tension. Is decentralization always positive. On the role of the Law.

Swan [START_REF] Swan | Blockchain: Blueprint for a new economy[END_REF] already notes that "There is a mix of forces both toward centralization and decentralization operating in the blockchain industry". Hsieh et al. [START_REF] Hsieh | The internal and external governance of blockchain-based organizations: Evidence from cryptocurrencies[END_REF] provide a statistical analysis whose results may seem paradoxical: they find that decentralization at the blockchain level affects returns positively as one would expect, since the promise of blockchain is decentralization as a way to create value but also find that decentralization at both the protocol and organizational levels affects returns negatively. Neitz [START_REF] Benedetto | The influencers: Facebook's libra, public blockchains, and the ethical considerations of centralization[END_REF] provide a discussion on Blockchain, decentralization issues and the role of the Law.

Record-keeping and immutability

Immutability. Irrevocability. Mutability challenges and solutions. Legal or non-legal reasons for local erasure. Propositions. Rgpd.

As immutability (if realized) is also irrevocability: there is ongoing research on solving this conflict, among which Politou et al. [START_REF] Politou | Blockchain mutability: Challenges and proposed solutions[END_REF]'s survey on mutability challenges, Ateniese et al. [START_REF] Ateniese | Redactable blockchain-or-rewriting history in bitcoin and friends[END_REF] who give a framework that makes it possible to re-write and/or compress the content of any number of blocks in decentralized services exploiting the blockchaintechnology, Kuhn [START_REF] Kuhn | A data structure for integrity protection with erasure capability[END_REF] proposing a data structure for integrity protection with erasure capability, Florian [START_REF] Florian | Erasing data from blockchain nodes[END_REF] providing a discussion of legal and non-legal reasons for local erasure and proposing an approach enabling nodes to erase data while continuing to store and validate most of the blockchain, and on Blockchains and Rgpd see Pagallo et al. [START_REF] Pagallo | Chronicle of a clash foretold: Blockchains and the gdpr's right to erasure[END_REF], Jussila [START_REF] Jussila | Reconciling the conflict between the ?immutability?of public and permissionless blockchain technology and the right to erasure under article 17 of the general data protection regulation[END_REF].

3.2 Asynchrony, consensus and mining

Asynchrony

Coordination. Asynchrony. Double-spending. Is consensus necessary? Coordinating the actions of processes is crucial for virtually all distributed applications, especially in asynchronous systems (Aspnes [START_REF] Aspnes | Combining shared-coin algorithms[END_REF]). As discussed in Guerraoui [START_REF] Rachid | At2: Asynchronous trustworthy transfers[END_REF]: there seems to be a common belief that consensus is necessary for solving the double-spending problem, whether it is for a permissionless or a permissioned environment, the typical solution uses consensus to build a totally ordered ledger of submitted transfers. Guerraoui [START_REF] Rachid | At2: Asynchronous trustworthy transfers[END_REF] show, by introducing AT2 (Asynchronous Trustworthy Transfers) a class of consensusless algorithms, that this common belief is false: consensus is not needed to implement a decentralized asset transfer system.

Consensus mechanisms

A consensus mechanism can be thought as a mechanism to confirm a person's innocence or to discourage him/her to act wrong. The incentives to act not wrong are quite different concepts through computer science, economic or law lenses.

Unifying scheme. Lack of a general framework. Building bridges. Consensus mechanisms. Guerraoui et al. [START_REF] Guerraoui | Blockchain protocols: The adversary is in the details[END_REF] provide a unifying scheme that captures at a high level the behavior of any blockchain protocol, discussing which variation opens which vulnerability breach. Garay Kiayias [START_REF] Juan | Sok: A consensus taxonomy in the blockchain era[END_REF] in a consensus taxonomy give a roadmap for studying the consensus problem under its many guises, classifying the way it operates in the various settings and highlighting the exciting new applications that have emerged in the blockchain era. Rigorous formalization of specific blockchain protocols and their properties can be found in Badertscher et al. [START_REF] Badertscher | Bitcoin as a transaction ledger: A composable treatment[END_REF], Pass et al. [START_REF] Pass | Analysis of the blockchain protocol in asynchronous networks[END_REF], Garay et al. [START_REF] Garay | The bitcoin backbone protocol: Analysis and applications[END_REF]. The blockchain community does not have well-established theoretical foundations for consensus algorithms although Sorensen [START_REF] Sorensen | Establishing standards for consensus on blockchains[END_REF] establishes a framework intended for academic and industrial blockchain researchers as a foundation for the theory of consensus. See Cachin Vukolić [START_REF] Cachin | Blockchain consensus protocols in the wild[END_REF], Cachin [START_REF] Cachin | Blockchain, cryptography, and consensus[END_REF]. Xiao et al. [START_REF] Xiao | A survey of distributed consensus protocols for blockchain networks[END_REF] for a recent survey of distributed consensus protocols for Blockchain networks. Ehmke Blum Gruhn [START_REF] Ehmke | Properties of decentralized consensus technology-why not every blockchain is a blockchain[END_REF] study properties of decentralized donsensus technology ("why not every Blockchain is a Blockchain"). See Amoussou [START_REF] Amoussou-Guenou | Blockchains basées sur du consensus répété[END_REF] on blockchains based on repeated consensus. Shahaab [START_REF] Shahaab | Applicability and appropriateness of distributed ledgers consensus protocols in public and private sectors: A systematic review[END_REF] review 66 known consensus protocols and classify them into philosophical and architectural categories, they argue that advancement of consensus protocols in recent years has enabled distributed ledger technologies (DLTs) to find its application and value in sectors beyond cryptocurrencies. see Wang [START_REF] Wang | A survey on consensus mechanisms and mining strategy management in blockchain networks[END_REF] for a survey on consensus mechanisms and mining strategy management in blockchains. See Azouvi Hicks Murdoch[40] for a discussion on the role of incentives in consensus mechanisms and Hicks Murdoch [START_REF] Hicks | Transparency enhancing technologies to make security protocols work for humans[END_REF]. See also Azouvi Hicks[39] for a discussion on game-theoretic tools. Consensus algorithms are numerous, and some are being created, among which: Proof of Authority (PoA), Proof of Work (PoW) (see Saleh [START_REF] Saleh | Volatility and welfare in a crypto economy[END_REF] for economic impact analysis, see also Szalachowski [START_REF] Szalachowski | Strongchain: Transparent and collaborative proof-of-work consensus[END_REF]), Proof of Stake (PoS) (see Nguyen [START_REF] Cong T Nguyen | Proof-of-stake consensus mechanisms for future blockchain networks: Fundamentals, applications and opportunities[END_REF],Barinov [START_REF] Barinov | Posdao: Proof of stake decentralized autonomous organization[END_REF]), Hybrid PoW/PoS, Delegated Proof of Stake (DPoS) Proof of Brain, Proof of Retrievability (PoR), Proof of Importance (PoI), Byzantine Generals Problem and Practical Byzantine Fault Tolerance (PBFT) (see for instance Amoussou et al [START_REF] Amoussou-Guenou | Rationals vs byzantines in consensus-based blockchains[END_REF] modelling the Byzantine-consensus based blockchains as a committee coordination game), Proof of Burn (also examined in Saleh [START_REF] Saleh | Volatility and welfare in a crypto economy[END_REF] for economic impact), Proof of Activity, Proof of Capacity, proof of storage, Proof of Elapsed Time (PoET), Simplified Byzantine Fault Tolerance (SBFT), Proof of concept, DAG, Committe selection, RAFT consensus (see Huang [START_REF] Huang | Performance analysis of the raft consensus algorithm for private blockchains[END_REF]), Chan et al. 2019 [START_REF] Chan | Consensus through herding[END_REF] propose a State Machine Replication (SMR) protocol (i.e. consensus protocol) inspired by a social phenomenon called herding, where people tend to make choices considered as the social norm. Partially synchronous protocols are being developed see Ranchal-Pedrosa Gramoli [START_REF] Ranchal | Platypus: a partially synchronous offchain protocol for blockchains[END_REF] that develops latypus, a partially synchronous offchain protocol for blockchains, etc

Mining and mining pools, fees, costs, incentives and strategies

Pooled mining reward systems. Mining strategy. Incentives. Fees. Bitcoin pooled mining reward systems have been analyzed by Rosenfeld [START_REF] Rosenfeld | Analysis of bitcoin pooled mining reward systems[END_REF], describing various scoring systems used to calculate rewards of participants in Bitcoin pooled mining, explaining problems each were designed to solve and analyzing their respective advantages and disadvantages. Wang et al. [START_REF] Wang | A survey on consensus mechanisms and mining strategy management in blockchain networks[END_REF] survey on consensus mechanisms and mining strategy management. One can refer to Zhu et al. [START_REF] Zhu | A survey: Reward distribution mechanisms and withholding attacks in bitcoin pool mining[END_REF] for a (quite modelized) survey on reward distribution mechanisms and withholding attacks in Bitcoin pool mining. Romiti [START_REF] Romiti | A deep dive into bitcoin mining pools: An empirical analysis of mining shares[END_REF] provide an empirical analysis of Bitcoin mining shares, analyzing mining reward distribution within three of the four largest Bitcoin mining pools and examine their cross-pool economic relationships, their results (in line with previous research) suggesting centralization tendencies in large mining pools and cryptocurrencies in general. Chatzigiannis [START_REF] Chatzigiannis | Diversification across mining pools: Optimal mining strategies under pow[END_REF] present a mining portfolio model, miners optimally distributing their computational power over multiple pools and PoW cryptocurrencies taking into account their risk aversion levels, while Wang Tang [START_REF] Wang | Pool strategies selection in pow-based blockchain networks: Game-theoretic analysis[END_REF] model the pool mining process as a two-stage game, and Kitti 2018 [START_REF] Kitti | Allocating rights to mine blocks[END_REF] on allocating rights for mining as a contest. Eyal Sirer [START_REF] Eyal | Majority is not enough: Bitcoin mining is vulnerable[END_REF] showed that the Bitcoin network is vulnerable even if only a small portion of the hashing power is used to cheat ("selfish mining strategy") and that unless certain assumptions are made, selfish mining may be feasible for any group size of colluding miners. The Bitcoin mining protocol is not incentive-compatible, as they present an attack with which colluding miners obtain a revenue larger than their fair share. They propose a practical modification to the Bitcoin protocol that protects Bitcoin in the general case that prohibits selfish mining by pools that command less than 1/4 of the resources. Selfish mining have been generalized (algorithm to find ε-optimal strategies in [START_REF] Sapirshtein | Optimal selfish mining strategies in bitcoin[END_REF], stubborn mining in [START_REF] Nayak | Stubborn mining: Generalizing selfish mining and combining with an eclipse attack[END_REF], multiple selfish miners in [START_REF] Leelavimolsilp | On the preliminary investigation of selfish mining strategy with multiple selfish miners[END_REF], etc) and Grunspan Pérez-Marco [START_REF] Grunspan | On profitability of selfish mining[END_REF][START_REF] Grunspan | On profitability of trailing mining[END_REF][START_REF] Grunspan | On profitability of stubborn mining[END_REF] have recently proposed a profitability model for repetition games, finding that in the bitcoin network, no strategy is more profitable than the honest strategy before a difficulty adjustment, so selfish mining can only become profitable afterwards, and thus being an attack on the difficulty adjustment algorithm. Falk et al. [START_REF] Brett | Token-curated registries[END_REF] study blockchain-based platforms that have implemented token weighted aggregation to incentivize efficient and effective information crowdsourcing from their users in a decentralized way (these systems aggregate information through user votes, where the final action of the system is determined based on the weighted average of the users votes, and each users vote is weighted according to his token holdings within the system) and provide economic analysis including on wether token weighting encourages or discourages truthful voting and how accurate is the resulting crowdsourced information. Brown-Cohen et al. [START_REF] Brown-Cohen | Formal barriers to longest-chain proof-of-stake protocols[END_REF] focus on incentive-driven deviations (any participant will deviate if doing so yields higher revenue) instead of adversarial corruption (an adversary may take over a signifcant fraction of the network, but the remaining players follow the protocol), obtaining several formal barriers to designing incentivecompatible proof-of-stake cryptocurrencies (that don't apply to proof-of-work). Liu [START_REF] Liu | Research on token incentive mechanism of open source project-take block chain project as an example[END_REF] provides a viewpoint on research on token incentive mechanism of open source project taking Blockchain project as an example. Prat Walter [START_REF] Prat | An equilibrium model of the market for bitcoin mining[END_REF] propose an equilibrium model of the market for Bitcoin mining, refer also to their paper for the main related literature. Zamyatin et al. [START_REF] Zamyatin | Swimming with fishes and sharks: Beneath the surface of queue-based ethereum mining pools[END_REF] formulate a model of the dynamics of a queuebased reward distribution scheme in a popular Ethereum mining pool and develop a corresponding simulation. Bissias et al. [START_REF] Bissias | Greedy but cautious: Conditions for miner convergence to resource allocation equilibrium[END_REF] find that there exists a resource allocation equilibrium between any two blockchains, which is essentially driven by the fiat value of reward that each chain offers in return for providing security and that this equilibrium is singular and always achieved provided that block producers behave in a greedy, but cautious fashion while the opposite is true when they are overly greedy: resource allocation oscillates in extremes between the two chains. Bissias et al. [START_REF] Bissias | Using economic risk to model miner hash rate allocation in cryptocurrencies[END_REF] present an economic model that leverages Modern Portfolio Theory to predict a miners allocation over time using price data and inferred risk tolerance. Shanaev et al. [START_REF] Shanaev | The marginal cost of mining, metcalfe's law and cryptocurrency value formation: Causal inferences from the instrumental variable approach. Metcalfe's Law and Cryptocurrency Value Formation: Causal Inferences from the Instrumental Variable Approach[END_REF] test theories of cryptocurrency pricing (causal inferences from the instrumental variable approach on the marginal cost of mining, Metcalfe's law and cryptocurrency value formation). Hinzen [START_REF] Franz J Hinzen | Proof-of-work?s latency dilemma and a permissioned alternative[END_REF] provides discussion on Proof-of-Work's latency dilemma and a permissioned alternative.

3.3 Cryptography, identity, anonymity and pseudonymity, privacy and security

Blockchain cryptography

Bonneau Miller [START_REF] Bonneau | Fawkescoin: A cryptocurrency without public-key cryptography (transcript of discussion)[END_REF] discusses on cryptocurrency without public-key cryptography and provide a comparison with Bitcoin, having economic implications (in particular it could involve thinking and distributing fees differently). Wang et al. [START_REF] Wang | Cryptographic primitives in blockchains[END_REF] survey cryptographic primitives of 30 principal cryprocurrencies. Raikwar [START_REF] Raikwar | Sok of used cryptography in blockchain[END_REF] beside reviewing and systematizing the cryptographic concepts already used in blockchain, give a list of cryptographic concepts which have not yet been applied but have big potentials to improve the current blockchain solutions and include possible references of these cryptographic concepts in the blockchain domain.They postulate 18 challenging problems that cryptographers interested in blockchain can work on.

Identity, anonymity and pseudonimity, and privacy

For a fundamental paper, refer to (previous to blockchain) Sweeney [START_REF] Sweeney | k-anonymity: A model for protecting privacy[END_REF] and for a discussion on an algorithmic introduction to anonymity in asynchronous systems , see Raynal [START_REF] Raynal | Anonymity in distributed read/write systems: an introductory survey[END_REF], distinguishing process-anonymity and memory-anonymity. See also Herrera-Joancomart Jordi [START_REF] Herrera-Joancomartí | Research and challenges on bitcoin anonymity[END_REF], Fabian [START_REF] Fabian | Anonymity in bitcoin?-the users? perspective[END_REF],

ShenTu [START_REF] Shentu | Research on anonymization and de-anonymization in the bitcoin system[END_REF], fanti [START_REF] Fanti | Anonymity properties of the bitcoin p2p network[END_REF]. While studying Bitcoin, Moser Bohme [START_REF] Möser | Anonymous alone? measuring bitcoin?s second-generation anonymization techniques[END_REF] surveys and compares transaction anonymization techniques. Moser [START_REF] Moser | Anonymity of bitcoin transactions[END_REF] argues that as all transactions in the network are stored publicly in the blockchain, allowing anyone to inspect and analyze them, the system does not provide real anonymity but pseudonymity. Community detection tools have been used in Cazabet et al. [START_REF] Remy | Tracking bitcoin users activity using community detection on a network of weak signals[END_REF] to argue that studying the Bitcoin transaction network, such tools can be used to re-identify multiple addresses belonging to a same user. Dunphy et al. [START_REF] Dunphy | Decentralizing digital identity: Open challenges for distributed ledgers[END_REF] review open questions and challenges for distributed ledgers on decentralizing digital identity. Lesavre 2019 [START_REF] Lesavre | A taxonomic approach to understanding emerging blockchain identity management systems[END_REF] propose a taxonomic approach to understanding emerging Blockchain identity management systems. Borgonovo [START_REF] Borgonovo | Privacy and money: It matters[END_REF][START_REF] Borgonovo | Cryptocurrencies, central bank digital cash, traditional money: does privacy matter? Technical report[END_REF] on Privacy. Bushager [START_REF] Bushager | Bitcoin security and privacy: A study of users experiences[END_REF] provide a study of users experiences of bitcoin security and privacy.

Security

For a survey see Conti [START_REF] Conti | A survey on security and privacy issues of bitcoin[END_REF]. See also Saad et al. [START_REF] Saad | Exploring the attack surface of blockchain: A systematic overview[END_REF] developing defense strategies in theor overview on attacks in Blockchains, Chen [START_REF] Chen | A survey on ethereum systems security: Vulnerabilities, attacks and defenses[END_REF] on ethereum. For a recent survey on blockchain from security perspective see Dasgupta 2019 [START_REF] Dasgupta | A survey of blockchain from security perspective[END_REF]. Bushager [START_REF] Bushager | Bitcoin security and privacy: A study of users experiences[END_REF] provide a study of users experiences of bitcoin security and privacy. Manuskin et al. [START_REF] Manuskin | Ostraka: Secure blockchain scaling by node sharding[END_REF] introduce Ostraka, a blockchain node architecture that scales linearly with the available resources, i.e. to secure Blockchain scaling by node Sharding. see also network analysis. On ico security, see Holoweiko 2018 [START_REF] Holoweiko | What is an ico? defining a security on the blockchain[END_REF]. In order to lay down the foundation of a common body of knowledge, Zhang Preneel [START_REF] Zhang | Lay down the common metrics: Evaluating proof-of-work consensus protocols? security[END_REF] introduce a multimetric evaluation framework to quantitatively analyze PoW protocols chain quality and attack resistance. See also Azouvi [START_REF] Azouvi | Sok: Tools for game theoretic models of security for cryptocurrencies[END_REF] for SoK tools for game theoretic models of security for cryptocurrencies.

Data Security and Privacy

Two-sided issue: issues one side on Data Security and Privacy when using Blockchains and another side on using Blockchain technology for Data Security and Privacy. Truong 2019 [START_REF] Nguyen Binh Truong | Gdpr-compliant personal data management: A blockchain-based solution[END_REF] propose a Blockchain-based Solution for GDPR-Compliant Personal Data Management. On Blockchain for data provenance Tosh 2017 [START_REF] Deepak K Tosh | Consensus protocols for blockchain-based data provenance: Challenges and opportunities[END_REF]. See Clementi 2019 [START_REF] Dehez Clementi | When air traffic management meets blockchain technology: a blockchain-based concept for securing the sharing of flight data[END_REF] for an example on securing the sharing of Flight Data. On privacy issues when using Blockchains in Smart Cities, see Ramos et al. [START_REF] Felipe | Privacy and data protection concerns regarding the use of blockchains in smart cities[END_REF]. Wang [START_REF] Wang | A blockchain based privacy-preserving incentive mechanism in crowdsensing applications[END_REF] describe a blockchain based privacy-preserving incentive mechanism in crowdsensing applications. See also Daneshgar[160], Alsayed [START_REF] Alsayed Kassem | Dns-idm: A blockchain identity management system to secure personal data sharing in a network[END_REF] and in Casino [START_REF] Casino | A systematic literature review of blockchain-based applications: current status, classification and open issues[END_REF] the section on Data management and privacy and security solutions.

Platforms, architecture and design

Blockchain-based platforms. Blockchain as a platform. Architecture. Design. Scalability. Velocity.

On platforms based on distributed ledger technology see Schoenhals [START_REF] Schoenhals | Overview of licensing platforms based on distributed ledger technology[END_REF] for an overview, on Blockchain as a platform Glaser [START_REF] Glaser | Blockchain as a platform[END_REF], Sarkintudu 2018 [START_REF] Shehu | Taxonomy development of blockchain platforms: Information systems perspectives[END_REF] for a taxonomy of blockchain platforms. See also De Filippi [START_REF] De | Blockchain technology: toward a decentralized governance of digital platforms?[END_REF]. Constantinides [START_REF] Constantinides | Introduction?platforms and infrastructures in the digital age[END_REF] have edited research to discuss platforms and infrastructures concomitantly. Glaser et al. (volume 1 chapter 4 in [START_REF] Horst | Business Transformation Through Blockchain, Two Volumes[END_REF]) investigate the blockchain as a platform and present technical layers of the system as well as institutional characteristics and governance implications, followed by a discussion of the role of trust in blockchain systems. On scalability see Szabociteszabo2017money, Jiao [START_REF] Jiao | Bicomp: A bilayer scalable nakamoto consensus protocol[END_REF]. Dang et al. [START_REF] Dang | Chain of trust: Can trusted hardware help scaling blockchains[END_REF] study the use and effectiveness of trusted hardware on scaling distributed consensus protocols. Duffie [START_REF] Duffie | Digital currencies and fast payment systems: Disruption is coming[END_REF] examine monetary policy implications and business strategy concerns related to the introduction of digital currencies and faster payment systems. Lei [START_REF] Lei | A secure key management scheme for heterogeneous secure vehicular communication systems[END_REF] prove that the blockchain concept helps to shorten the key transfer time.

Trust

The implications of the Blockchain technology could be at very various levels, because it modifies trust and trust is central to many interactions. Trust have been studied across many different disciplines. Thielmann Hilbig [START_REF] Thielmann | Trust: An integrative review from a person-situation perspective[END_REF] provide a review on interpersonal trust among strangers accross many disciplines (including psychology, economics, political science, sociology, law). Tazdait [START_REF] Tazdaït | L'analyse économique de la confiance[END_REF] provides insights for a study of the economic analysis of trust. Note that this must include also issues about trust in technical systems (see Kaindl Svetinovic [START_REF] Kaindl | Avoiding undertrust and overtrust[END_REF] arguing that both undertrust and overtrust need to be avoided). Glaser et al. (volume 1 chapter 4 in [START_REF] Horst | Business Transformation Through Blockchain, Two Volumes[END_REF]) investigate the blockchain as a platform and present technical layers of the system as well as institutional characteristics and governance implications, followed by a discussion of the role of trust in blockchain systems. See also Kim[323] and references herein.Trust, IoT and network analysis see Li [START_REF] Li | Dynamic trustworthiness overlapping community discovery in mobile internet of things[END_REF]. Mistrust see Tariq 2019 [START_REF] Tariq | Never trust bitcoin: Blockchain technology-the misnomer of a'trustless' system[END_REF]. Kaindl Svetinovic [START_REF] Kaindl | Avoiding undertrust and overtrust[END_REF] analyse whether new systems can be trusted by human users through the notions of Undertrust and Overtrust. [START_REF] Günce Keziban Orman | Comparative evaluation of community detection algorithms: a topological approach[END_REF]), are one of the most relevant key features in the study of real-world complex networked systems, let them be considered as static or temporal (see [START_REF] Cazabet | Challenges in community discovery on temporal networks[END_REF]) and has many application areas (see Karatacs [START_REF] Karataş | Application areas of community detection: A review[END_REF]): for a review and discussion on community structure see Cherifi et al. [START_REF] Cherifi | On community structure in complex networks: challenges and opportunities[END_REF]. Moreover, as underlined by Ghalmane et al. [START_REF] Ghalmane | Centrality in complex networks with overlapping community structure[END_REF] identifying influential spreaders in networks is an essential issue: they introduce a framework allowing to redefine all the classical centrality measures (designed for networks without community structure) to non-overlapping modular networks and extend some centrality measures to to networks with overlapping communities, as in real-world networks, nodes usually belong to several communities. This can be completed with many other tools, including core decompositions (see Malliaros 2019 [START_REF] Malliaros | The core decomposition of networks: Theory, algorithms and applications[END_REF]), etc On another hand, maps can be defined as graphical tools that "classify, represent and communicate spatial relations; a concentrated database of information on the location, shape and size of key features of the landscape and the connections between them" (Hodgkiss cited in [528]). In their (beautiful) Atlas of Cyberspace, Dodge Kitchin [START_REF] Dodge | Atlas of cyberspace[END_REF] give insights on the way cyberspace has evolved and provide cyberspace representations (maps, diagrams, etc) while explaining the informations considered, cartography goals and the mapping techniques. They also examine critically such maps in [START_REF] Dodge | Exposing the ?second text?of maps of the net[END_REF]. In Abrams Hall [4] an analysis of mapping as new cartographies of networks and territories is provided while in Dodge Kitchin Perkins [START_REF] Dodge | Rethinking maps: new frontiers in cartographic theory[END_REF] are developed many aspects15 of new mappings. Landscape research (see Hunziker et al. [START_REF] Hunziker | Space and place-two aspects of the human-landscape relationship[END_REF]) is developing tools dealing with the multi-faceted interrelationship between landscape and society, and digital geographies examine the spread of digital devices, platforms, and code as they infiltrate, define, and shape the spaces and experiences of all human and animal life (Gieseking [START_REF] Jack | Digital[END_REF]). See also Hirschkorn [START_REF] Hirschkorn | Nation-state adoption of distributed ledger technology: How blockchain will remake traditional nation-state relationships[END_REF] on Blockchain and traditional Nation-State relationships.

Networks

Historically oriented social network analyses as developed by Padgett Powell [START_REF] John | Organizational invention and elite transformation: The birth of partnership systems in renaissance florence[END_REF][START_REF] John | Organizational invention and elite transformation: The birth of partnership systems in renaissance florence[END_REF] or Ferguson [START_REF] Ferguson | The ascent of money: A financial history of the world[END_REF][START_REF] Ferguson | The square and the tower: networks, hierarchies and the struggle for global power[END_REF] show that the emergence of organizational novelty comes from spillovers accross intertwined mul-tiple networks and hierarchies. This is also the kind of issues that are raised through topological thinking in social sciences and geography (Allen [START_REF] Allen | Three spaces of power: territory, networks, plus a topological twist in the tale of domination and authority[END_REF][START_REF] Allen | Assemblages of state power: topological shifts in the organization of government and politics[END_REF][START_REF] Allen | Topological twists: Power?s shifting geographies[END_REF][START_REF] Allen | Topologies of power: beyond territory and networks[END_REF], Paasi [START_REF] Paasi | Geography, space and the re-emergence of topological thinking[END_REF]. Via a reading of Steven Soderbergh's 2011 film, Contagion, Dixon et al. [START_REF] Deborah | The tactile topologies of contagion[END_REF] provide a rich discussion on such issues, including on topography "versus" topology thinking in geography. By heeding the recent research on topologies published by geographers and social theorists, Bille [START_REF] Billé | Skinworlds: Borders, haptics, topologies[END_REF] intends to contribute to the emerging mathematical turn. For historical, institutional economics and game-theoretic insights on Blockchain, see Berg [START_REF] Berg | What diplomacy in the ancient near east can tell us about blockchain technology[END_REF] who studies similarities between two protocols -diplomacy in the Ancient Near East and blockchain. Meanwhile, Blockchain Networks community structure analysis is being studied (see for example Chen [START_REF] Chen | Distributed community detection over blockchain networks based on structural entropy[END_REF] propose a "distributed community detection method") and dynamic bitcoin transaction visualization patterns are provided (McGinn [START_REF] Mcginn | Visualizing dynamic bitcoin transaction patterns[END_REF]).

While the Blockchain technology is spreading, combining such geographic, landscape research, historically oriented and network science analysis and tools would be deeply fruitful, especially with the emergence of smart cities. [START_REF] Miller | Discovering bitcoin's public topology and influential nodes[END_REF] analyze the measured topology to discover both high-degree nodes and a well connected giant component. Efficient propagation over the Bitcoin backbone does not necessarily result in a transaction being accepted into the block chain. They introduce a decloaking method to find influential nodes in the topology that are well connected to a mining pool. Their results find that in contrast to Bitcoin's idealized vision of spreading mining responsibility to each node, mining pools are prevalent and hidden: roughly 2% of the (influential) nodes represented three quarters of the mining power. Javarone Wright [START_REF] Alberto | From bitcoin to bitcoin cash: a network analysis[END_REF] study the Bitcoin network and the Bitcoin Cash network, analyze their global structure and we try to evaluate if they are provided with a smallworld behavior: their esults suggest that the principle known as fittest-gets-richer, combined with a continuous increasing of connections, might constitute the mechanism leading these networks to reach their current structure. They provide further observations openning the way to new investigations into this direction. Yang Kim[602] examine a few complexity measures of the Bitcoin transaction flow networks and model the joint dynamic relationship between these complexity measures and Bitcoin market variables such as return and volatility. They find that a particular complexity measure of the Bitcoin transaction network flow is significantly correlated with the Bitcoin marketreturn and volatility. More specifically we document that the residual diversity or freedom of Bitcoin network flow scaled by the total system throughput can significantly improve the predictability of Bitcoin market return and volatility. Bovet et al. [START_REF] Bovet | Network-based indicators of bitcoin bubbles[END_REF] by using the complete transaction history from December 5th 2011 to December 23rd 2013, this period including three bubbles experienced by the Bitcoin price and focus on the global and local structural properties of the user network (and their variation in relation to the different period of price surge and decline). Maesa et al. [START_REF] Di | An analysis of the bitcoin users graph: inferring unusual behaviours[END_REF] analyse the topological properties of the Bitcoin transaction graph to obtain insights in the behaviour of the users, in particular outliers in the in-degree distribution of the bitcoin users graph, and argue that some users behaviors are not strictly related to normal economic interaction. Other analyses have been conducted for Bitcoin or for other networks (see [START_REF] Miller | An empirical analysis of linkability in the monero blockchain[END_REF][START_REF] Moreno-Sanchez | Mind your credit: Assessing the health of the ripple credit network[END_REF][START_REF] Di | Data-driven analysis of bitcoin properties: exploiting the users graph[END_REF][START_REF] Chen | Understanding ethereum via graph analysis[END_REF]). Maesa et al. [START_REF] Di | The bow tie structure of the bitcoin users graph[END_REF] analyze the Bitcoin users graph and show by clustering the transaction graph, that the bow tie structure already observed for the graph of the web is augmented, in the Bitcoin users graph with the economical information about the entities involved, and perform a temporal analysis of the evolution of the resulting bow tie structure. Oggier et al. [START_REF] Oggier | Entropic centrality for non-atomic flow networks[END_REF] generalize Tutzauer' entropic centrality notion (that characterizes vertices which are important in the sense that there is a high uncertainty about the destination of an atomic flow starting at them, assuming that at each hop, the flow is equally likely to continue to any unvisited vertex, or to be terminated there notion) to non-atomic flows and show using network graphs derived from Bitcoin transactions that depending on the graph characteristics, the presented entropy based centrality metric can provide a unique perspective not captured by other existing centrality measure, particularly in identifying vertices with relatively low out-degrees which may nevertheless be connected to hub vertices, and thus can have high spread in the network. For a survey on clustering, see Schaeffer [START_REF] Satu | Graph clustering[END_REF]. Oggier et al. [START_REF] Oggier | Entropy-based graph clustering-a simulated annealing approach[END_REF] propose one possible adaptation of the entropy measure Renyi quadratic entropy based measure in the context of graph clustering, exploring how the algorithm performs with subgraphs from the Bitcoin transactions network. Nagarajan [START_REF] Nagarajan | Blockchain single and interval valued neutrosophic graphs[END_REF] discuss on Blockchain single and interval valued neutrosophic graphs proposed and applied in transaction of Bitcoins, as well as degree, total degree, minimum and maximum degree for the proposed graphs, and give comparative analysis with advantages and limitations of different types of Blockchain graphs. Fadhil [START_REF] Fadhil | Bitcoin network measurements for simulation validation and parameterisation[END_REF] provide some measurements briefly describing the Bitcoin networking aspects. Whang Chu Yang [START_REF] Wang | Measurement and analysis of the bitcoin networks: A view from mining pools[END_REF] about the details of mining pool behaviors (e.g., empty blocks, mining revenue and transaction collection strategies) and their effects on the Bitcoin end users (e.g., transaction fees, transaction delay and transaction acceptance rate). Chen [START_REF] Chen | Understanding ethereum via graph analysis[END_REF] conduct a systematic study on Ethereum by leveraging graph analysis to characterize three major activities on Ethereum(money transfer, smart contract creation, and smart contract creation invocation). Fadhil et al.

[443] introduce a proximity-aware extension to the current Bitcoin protocol, named Bitcoin Clustering Based Ping Time protocol (BCBPT). This protocol, that is based on how the clusters are formulated and the nodes define their membership, is to improve the transaction propagation delay in the Bitcoin network. Kieffer et al. [START_REF] Kiffer | Analyzing ethereum's contract topology[END_REF] analyze Ethereums smart contract topology, finding high levels of contract activity (largely independent of price) but low levels of contract diversity: most contracts are direct-or near-copies of other contracts. Park et al. [START_REF] Park | Nodes in the bitcoin network: Comparative measurement study and survey[END_REF] present a comparative measurement study of nodes in the Bitcoin network. Forestier et al. [START_REF] Forestier | Blockclique: scaling blockchains through transaction sharding in a multithreaded block graph[END_REF] addresses the scalability issue by defining an architecture, called the blockclique,that addresses this limitation by sharding transactions in ablock graph with multiple threads. See also [START_REF] Rohrer | Discharged payment channels: Quantifying the lightning network's resilience to topology-based attacks[END_REF][START_REF] István | Topological analysis of bitcoin's lightning network[END_REF]. Rohrer et al. [START_REF] Rohrer | Discharged payment channels: Quantifying the lightning network's resilience to topology-based attacks[END_REF] provides a discussion on a topological based attack.

Fraudulous behaviors

Attacks. Detection.

Tran [START_REF] Tran | A stealthier partitioning attack against bitcoin peer-to-peer network[END_REF] Stealthier Partitioning Attack against Bitcoin. Neudecker Hartenstein[422] provides a systematic approach that brings together known attacks, the requirements, and the design space of the network layer. Note that they include a summary of known network-based attacks on permissionless blockchains at the example of Bitcoin visualized as attack trees. Neudecker [START_REF] Neudecker | Short paper: An empirical analysis of blockchain forks in bitcoin[END_REF] provide also an empirical analysis of Blockchain forks in Bitcoin. Misic et al. 2019 [START_REF] Vojislav B Mišic | On forks and fork characteristics in a bitcoin-like distribution network[END_REF] for a recent paper on forks and fork characteristics in a Bitcoin-like distribution network. Note that Shalini [START_REF] Shalini | A survey on various attacks in bitcoin and cryptocurrency[END_REF] provide a survey on various attacks in Bitcoin and Cryptocurrency, see also Saad et al. [START_REF] Saad | Exploring the attack surface of blockchain: A systematic overview[END_REF] who explore the attack surface of the Blockchain technology and provide a systematic review. Javarone Wright [START_REF] Alberto | Modeling a double-spending detection system for the bitcoin network[END_REF] propose a model for double-spending detection for the Bitcoin network, the idea is detecting the presence of conflicting transactions by means of an 'oracle' that polls a subset of nodes of the Bitcoin network, assuming it to be a complex network. Phetsouvanh et al. [START_REF] Phetsouvanh | Egret: Extortion graph exploration techniques in the bitcoin network[END_REF] propose graph mining techniques to explore the relationships among wallet addresses (pseudonyms for Bitcoin users) suspected to be involved in a given extortion racket, exploiting the anonymity of the Bitcoin network to collect and launder money.

Evolving networks, dynamics

Information propagation. Transaction dynamics. Block dynamics. Contagion. Systemic risks.

Bubbles

As studied in MarianneVerdier [START_REF] Verdier | La blockchain et l'intermédiation financière[END_REF], the Blockchain obviously questions the power of intermedi-aries on financial information. Decker Wattenhofer [START_REF] Decker | Information propagation in the bitcoin network[END_REF] early studied information propagation in the bitcoin network. For a reference point on information propagation in the Blockchain see Decker Wattenhofer [START_REF] Decker | Information propagation in the bitcoin network[END_REF]. Castells [START_REF] Castells | The rise of the network society[END_REF] on how information/network economy has transformed relationships, particularly social and economic relationships as well as reshaping the labor markets. Akcora 2018 [START_REF] Cuneyt Gurcan Akcora | Bitcoin risk modeling with blockchain graphs[END_REF] model the Bitcoin network with a high fidelity graph (as Blockchain based crypto-currencies expose the entire transaction history to the public) so that it is possible to characterize how the flow of information in the network evolves over time and show this data representation permits a new form of microstructure modeling with the emphasis on the local topological network structure to study the role of users, entities and their interactions in formation and dynamics of crypto-currency investment risk, identifying certain sub-graphs (chainlets) that exhibit predictive influence on Bitcoin price and volatility and characterize the types of chainlets that signify extreme losses. Shahsavari et al. [START_REF] Shahsavari | Performance modeling and analysis of the bitcoin inventory protocol[END_REF] present an analytical model using a random graph network and capture the Bitcoin network behavior and dynamics. Pappalardo et al. [START_REF] Pappalardo | Blockchain inefficiency in the bitcoin peers network[END_REF] investigate both the transaction dynamics and the block dynamics on the Bitcoin network, and find that the Bitcoin system fails in taking accurate record of the transactions with some of them taking months before being recorded in the Blockchain, although this inefficiency is much larger in terms of transaction recording than in terms of volumes exchanged.

Fadhil [START_REF] Fadhil | Bitcoin network measurements for simulation validation and parameterisation[END_REF] analyse how transaction validation is achieved by the transaction propagation round trip and how transaction dissemination throughout the network can lead to inconsistencies in the view of the current transactions ledger by different nodes. We then measure the transaction propagation delay in the real Bitcoin network and how it is affected by the number of nodes and network topology. This measurement enables a precise validation of any simulation model of the Bitcoin network. Large-scale measurements of the real Bitcoin network are performed. Bovet et al. [START_REF] Bovet | Network-based indicators of bitcoin bubbles[END_REF] by using the complete transaction history from December 5th 2011 to December 23rd 2013, this period including three bubbles experienced by the Bitcoin price and beside focussing on the global and local structural properties of the user network and their variation in relation to the different period of price surge and decline. By analysing the temporal variation of the heterogeneity of the connectivity patterns they gain insights on the different mechanisms that take place during bubbles, and find that hubs (i.e., the most connected nodes) had a fundamental role in triggering the burst of the second bubble. Finally, we examine the local topological structures of interactions between users, we discover that the relative frequency of triadic interactions experiences a strong change before, during and after a bubble, and suggest that the importance of the hubs grows during the bubble. These results provide further evidence that the behaviour of the hubs during bubbles significantly increases the systemic risk of the Bitcoin network, and discuss the implications on public policy interventions. See Dixon et al. [START_REF] Francis Dixon | Blockchain analytics for intraday financial risk modeling[END_REF] transaction graph analysis and financial risk. Structure properties and anonymity of the bitcoin transaction graph have been studied (see Ober et al. [START_REF] Ober | Structure and anonymity of the bitcoin transaction graph[END_REF]) See also Lischke Fabian[362], Baumann Fabian Lischke [START_REF] Baumann | Exploring the bitcoin network[END_REF]. See Guo et al. [START_REF] Guo | A dynamic network perspective on the latent group structure of cryptocurrencies[END_REF] for a dynamic network perspective on the latent group structure of cryptocurrencies. Baçao et al. [START_REF] Bação | Information transmission between cryptocurrencies: does bitcoin rule the cryptocurrency world[END_REF] investigates information transmission between cryptocurrencies. Chawla et al. [START_REF] Chawla | Velocity: Scalability improvements in block propagation through rateless erasure coding[END_REF] underline that improving how information is stored and more importantly, how it propagates across the (Blockchain) network, are open research questions and propose a block propagation approach while studying economic incentives and showing the benefits the proposed approach have to rational actors. Papadis et al. [START_REF] Papadis | Stochastic models and wide-area network measurements for blockchain design and analysis[END_REF] develop stochastic network models to capture the Blockchain evolution and dynamics and analyze the impact of the block dissemination delay and hashing power of the member nodes on Blockchain performance in terms of the overall block generation rate and required computational power for launching a successful attack. Misic et al. 2019 [START_REF] Vojislav B Mišic | On forks and fork characteristics in a bitcoin-like distribution network[END_REF] investigate the performance of block propagation in a Bitcoin-like peer-to-peer distribution network and highlight the impact of the Nakamoto consensus protocol on the dynamics of blockchain growth. Li [START_REF] Li | Markov processes in blockchain systems[END_REF] markov processes in the queueing study of blockchain systems. Ben Van Lier (volume 1 chapter 5 in [START_REF] Horst | Business Transformation Through Blockchain, Two Volumes[END_REF]) takes a wider perspective investigating the autonomy and self-organization of cyber-physical systems.

3.7 Multiplex networks, connecting blockchains and interoperability

Connecting blockchains, interledger, sidechains and cross-blockchain Technologies

Towards interoperability, see Buterin [START_REF] Vitalik Buterin | Chain interoperability[END_REF]. Mattila [START_REF] Mattila | Blockchains as a path to a network of systems. An Emerging New Trend of the Digital Platforms in Industry and Society[END_REF] on the need of thinking on the scale of a network of systems. On the blockchain system and the cloud platform being interdependent see [START_REF] Lu | Blockchain: A survey on functions, applications and open issues[END_REF]. See also Robinson[492], Chitra [START_REF] Chitra | Agent-based simulations of blockchain protocols illustrated via kadena's chainweb[END_REF]. interledger encompasses several different approaches that attempt to establish interoperability among different distributed ledgers or blockchains. On Interledger see Thomas Schwartz [START_REF] Thomas | A protocol for interledger payments[END_REF] and Hope-Bailie Thomas [START_REF] Hope-Bailie | Interledger: Creating a standard for payments[END_REF] and refer to [START_REF] Vasilios | Interledger approaches[END_REF] for a recent survey. On sidechain see Back [START_REF] Back | Enabling blockchain innovations with pegged sidechains[END_REF]. On the code diversity issue, see Reibel [START_REF] Reibel | Short paper: An exploration of code diversity in the cryptocurrency landscape[END_REF][START_REF] Reibel | Why is a ravencoin like a tokendesk? an exploration of code diversity in the cryptocurrency landscape[END_REF]. These issues are linked with interoperability issues.

Interoperability

Hardjono et al. [START_REF] Hardjono | Toward an interoperability architecture for blockchain autonomous systems[END_REF] for a recent discussion. Casino [START_REF] Casino | A systematic literature review of blockchain-based applications: current status, classification and open issues[END_REF]: the growth of the number of cryptocurrency could raise interoperability problems due to the heterogeneity of cryptocurrency applications see Tschorsch and Scheuermann, 2016; Haferkorn and Quintana Diaz, 2015) see Casino [START_REF] Casino | A systematic literature review of blockchain-based applications: current status, classification and open issues[END_REF] section on Blockchain adoption and interoperability Interoperability between Blockchains as well as between Blockchains and other technologies are clearly crucial issues and paths to solutions are ongoing. 16Clearly Multiplex networks analysis and methods (see Boccaletti [START_REF] Boccaletti | The structure and dynamics of multilayer networks[END_REF], Bianconi [START_REF] Bianconi | Multilayer Networks: Structure and Function[END_REF], Battiston et al. [START_REF] Battiston | Multiplex and Multilevel Networks[END_REF]) are to provide frameworks for Blockchain analysis and methods. How about for instance the description in Chakraborty [START_REF] Rishi | Managing computation load on a blockchain-based multi-layered internet-of-things network[END_REF]? For competition among networks, one can see for example Iranzo [START_REF] Iranzo | Competition among networks highlights the power of the weak[END_REF] and Fan [START_REF] Fan | Game among interdependent networks: The impact of rationality on system robustness[END_REF] on game theory between networks. Note that Lee [START_REF] Lee | A nash equilibrium based decision-making method for internet of things[END_REF] develops a game theory Nash equilibrium model for IoT. Some blockchains involve studying networks with (even temporary) heterogeneous nodes, such as (maybe temporary) leading nodes, validating nodes (see for instance Belotti et al. [START_REF] Belotti | A vademecum on blockchain technologies: When, which and how[END_REF]).

3.8 Economic analysis, networks and Blockchains: some insights towards new frameworks and models?

Network cryptoeconomics. Decentralized Network Economy. Theory of the firm. Public choice. Taxation. Competition. General equilibrium.

Mainly, the development of Blockchain ecosystems leads both to adapt existing frameworks and models and to depart from them. Clearly economic analysis and network science are to be more more crucially intertwinned (see Garcia et al. [START_REF] Garcia | The digital traces of bubbles: feedback cycles between socio-economic signals in the bitcoin economy[END_REF]). See Swan editor [START_REF] Swan | Blockchain Economics: Implications Of Distributed Ledgers-Markets, Communications Networks, And Algorithmic Reality[END_REF] and early overviews and introductions (see Catalini Gans [START_REF] Catalini | Some simple economics of the blockchain[END_REF] Davidson et al. [START_REF] Davidson | Economics of blockchain[END_REF] 17 , Abadi Brunnermeier [START_REF] Abadi | Blockchain economics[END_REF]). Caliskan [START_REF] Caliskan | Data money: The socio-technical infrastructure of cryptocurrency blockchains[END_REF] question the framework of economic and social models analysis adapted to Blockchain development.

Pagnotta Buraschi [START_REF] Pagnotta | An equilibrium valuation of bitcoin and decentralized network assets[END_REF] consider a new type of production economy "a decentralized financial network (DN)". They formalize such a Decentralized Networks economy and address the valuation of bitcoins and other blockchain tokens. An identifying property of these assets is that contributors to the DN trust (miners) receive units of the same asset used by consumers of DN services, and then the overall production (hashrate) and the bitcoin price are jointly determined. They characterize the demand for bitcoins and the supply of hashrate, show that the equilibrium price is obtained by solving a fixed-point problem and study its determinants. Meunier [START_REF] Meunier | Bitcoin, distributed ledgers and the theory of the firm[END_REF] discusses Bitcoin, Distributed Ledgers and the Theory of the Firm. How about General equilibrium? (see empirical study Aoyagi 2019 [START_REF] Aoyagi | The empirical analysis of bitcoin market in the general equilibrium framework[END_REF] and He [START_REF] He | Proof-of-work blockchain network and its viability as a payment system[END_REF] constructing a general equilibrium model of PoW protocol based blockchain network).

As we have already seen, Institutional economics is clearly greatly concerned (Berg et al. [START_REF] Berg | Institutional discovery and competition in the evolution of blockchain technology[END_REF][START_REF] Berg | Blockchains and constitutional catallaxy[END_REF]). Allen et al. [START_REF] Darcy We Allen | The economics of cryptodemocracy[END_REF] analyze democracy as an economic problem of choice constrained by transaction costs and information costs. Society must choose between competing institutional frameworks for the conduct of voting and elections, these decisions being constrained by the technologies and institutions available. As Blockchains are a governance technology, it could be applied to the voting and electoral process to form a crypto-democracy. Analysed through the Institutional Possibility Frontier framework, they propose that blockchain lowers disorder and dictatorship costs of the voting and electoral process (Allen et al. [START_REF] Darcy We Allen | The economics of cryptodemocracy[END_REF]). How about Public choice? (Oguro[433], Berg [START_REF] Berg | Crypto public choice[END_REF]), taxation issues (Houben et al. [START_REF] Houben | Cryptocurrencies and blockchain: Legal context and implications for financial crime, money laundering and tax evasion[END_REF], Ahmad [START_REF] Ahmad | Secure and transparent audit logs with blockaudit[END_REF]). On Auditing, see Abreu [START_REF] Abreu | Blockchain technology in the auditing environment[END_REF], Piemntel 2019 [START_REF] Pimentel | Systemizing the challenges of auditing blockchain-based assets[END_REF] and the report [START_REF] Bible | Blockchain technology and its potential impact on the audit and assurance profession[END_REF].

On how generally (i.e. not specifically by blockchains) smart connected products are transforming competition, see Porter [START_REF] Michael | How smart, connected products are transforming competition[END_REF]. On how generally (i.e. not specifically by blockchains) Breidbach [START_REF] Breidbach | Operating without operations: how is technology changing the role of the firm[END_REF] technology is transforming the role of the firm. Pilkington [START_REF] Pilkington | Bitcoin through the lenses of complexity theory: Some non-orthodox implications for economic theorizing[END_REF] while analyzing Bitcoin through the lenses of complexity theory, argue that rationality, equilibrium and self-interest, the Bitcoin phenomenon would cast light on the emergence of non-intuitive macroeconomic results derived from numerous micro-interactions involving groundbreaking technology, and argues how knowledge fields, such as monetary policy and banking regulation have been shaken by Bitcoin, while articulating a reflection on the new geography of money and finance. How about Game theory? (see Biais et al. [START_REF] Biais | The blockchain folk theorem[END_REF] on the Blockchain folk theorem, mean-field game theory in Barreiro et al. [START_REF] Barreiro | Blockchain token economics: A mean-field-type game perspective[END_REF], [START_REF] Azouvi | Sok: Tools for game theoretic models of security for cryptocurrencies[END_REF] for SoKtools for game theoretic models of security for cryptocurrencies, Amoussou et al. [START_REF] Amoussou-Guenou | Rationals vs byzantines in consensus-based blockchains[END_REF] modelize the Byzantine-consensus based blockchains as a committee coordination game, Wang Tang [START_REF] Wang | Pool strategies selection in pow-based blockchain networks: Game-theoretic analysis[END_REF] for a game-theoretic analysis of pool strategies selection in PoW-based Blockchain Networks, Jaag [START_REF] Beccuti | The bitcoin mining game: On the optimality of honesty in proof-of-work consensus mechanism[END_REF] on the bitcoin mining game, Liu [START_REF] Liu | A survey on applications of game theory in blockchain[END_REF] for a recent survey on applications of game theory in Blockchain, etc).

3.9 Cryptocurrency and banking

Money

Money and programmable money. Is Bitcoin a Money? See Elsden 2019 [START_REF] Elsden | Recipes for programmable money[END_REF] on programmable money. See also Kubat 2015[336] ,Ammous [START_REF] Ammous | Can cryptocurrencies fulfil the functions of money?[END_REF], Dai Sidiropoulos and al. [START_REF] Dai | Le bitcoin est-il une monnaie?[END_REF]. Guegan [START_REF] Guegan | The digital world: I-bitcoin: from history to real live[END_REF] argues Bitcoin is not a currency from a monetary point of view. "The circulation of Bitcoin is slow and quantity is limited, so from an economical point of view, Bitcoin is not adaptated to the demand for money, cannot help to revive the economy (credit), nor to control inflation. In the case of the purchase of a property, the transactions cannot be canceled, even if the property is not delivered. It can make the exchanges difficult. One can encounter difficulty in converting Bitcoins into Euros (for instance) (no guarantee of convertibility of the currency by the public authorities). The circulation speed is low: only 4% of the bitcoins in circulation are weekly used. This is more like a casino economy, and since there is currently no regulation, no central bank ensures the stability of the value". Milkau Bott [START_REF] Milkau | Digital currencies and the concept of money as a social agreement[END_REF] discuss on Digital currencies and the concept of money as a social agreement. Grym [START_REF] Grym | The great illusion of digital currencies[END_REF] argue cryptocurrencies are not money. See also Guegan[249]. Kuikka [START_REF] Kuikka | Can cryptocurrency come to fulfil the functions of money? an evaluation of cryptocurrency as a global currency[END_REF] discusses if cryptocurrency can come to fulfill the functions of money and evaluates cryptocurrency as a global currency. [START_REF] Tobias | The Rise of Digital Money[END_REF] the rise of digital money. Lutz [START_REF] Lutz | Coexistence of cryptocurrencies and central bank issued fiat currencies, a systematic literature review[END_REF] on Currency Competition. For a recent paper on central bank digital currency see Belke et al. [START_REF] Belke | From cash to central bank digital currencies and cryptocurrencies: A balancing act between modernity and monetary stability[END_REF]. Belke et al. [START_REF] Belke | From cash to central bank digital currencies and cryptocurrencies: A balancing act between modernity and monetary stability[END_REF] discusses the main questions to the ongoing debate on central banking and cryptocurrencies: major characteristics of todays payments systems, pros and cons of still having (partially) tangible means of payment, might cryptocurrencies (and underlying blockchain technology) might somehow contribute to establishing a more modern, secure and stable payments system, etc. Arjalies [START_REF] Arjaliès | ?at the very beginning, there?s this dream.?the role of utopia in the workings of local and cryptocurrencies[END_REF] on alternative finance. see Glaser [START_REF] Glaser | Pervasive decentralisation of digital infrastructures: a framework for blockchain enabled system and use case analysis[END_REF] for a link between blockchain and free banking. See also Hayek [START_REF] Friedrich | Denationalisation of money: The argument refined[END_REF], see White [START_REF] Lawrence | Why didn't hayek favor laissez faire in banking?[END_REF] Williamson [START_REF] Williamson | Central bank digital currency: Welfare and policy implications[END_REF] discusses the welfare and policy implications of Central Bank Digital Currency. See also Berg [START_REF] Berg | Institutional discovery and competition in the evolution of blockchain technology[END_REF].

Markets

Impact on markets

Distributed ledger. Desintermediation. Data markets. Accounting.

See Zamani [START_REF] Efpraxia | With a little help from the miners: distributed ledger technology and market disintermediation[END_REF] on distributed ledger technology and market disintermediation. On personal data markets, one can refer to Spiekermann 2015 [START_REF] Spiekermann | The challenges of personal data markets and privacy[END_REF]. On the GDPR and data markets Politou 2018 [START_REF] Politou | Forgetting personal data and revoking consent under the gdpr: Challenges and proposed solutions[END_REF] "While the principles encompassed by the GDPR were mostly welcomed, two of them, namely the right to withdraw consent and the right to be forgotten, caused prolonged controversy among privacy scholars, human rights advocates and business world due to their pivotal impact on the way personal data would be handled under the new legal provisions and the drastic consequences of enforcing these new requirements in the era of big data and internet of things. In this work, we firstly review all controversies around the new stringent definitions of consent revocation and the right to be forgotten in reference to their implementation impact on privacy and personal data protection, and secondly, we evaluate existing methods, architectures and state-of-the-art technologies in terms of fulfilling the technical practicalities for the implementation and effective integration of the new requirements into current computing infrastructures. The latter allow us to argue that such enforcement is indeed feasible provided that implementation guidelines and low-level business specifications are put in place in a clear and cross-platform manner in order to cater for all possible exceptions and complexities." Molina et al. 2019 [START_REF] Molina | A conceptual marketplace model for iot generated personal data[END_REF] develop a decentralized conceptual marketplace model for IoT generated personal data, thinking personal data as a marketplace product and a marketplace model in which such a product could be effectively bought and sold without compromising the privacy of the data subject. Foy 2019 [START_REF] Foy | Financial accounting classification of cryptocurrency[END_REF] provides a financial accounting classification of cryptocurrency. See also Melse 2018 [START_REF] Melse | Accounting in three dimensions: a case for momentum revisited[END_REF], Karajovic 2019 [START_REF] Karajovic | Thinking outside the block: Projected phases of blockchain integration in the accounting industry[END_REF].

Financial risk, cryptocurrency markets

Can the transaction graph analysis provide warning insights on financial losses? how can Blockchain Economic Network theory contribute to the analysis of systemic risk? what about the study of cryptocurrency markets? how to conduct potfolio analysis and asset pricing? Swan (volume 1 chapter 1 in [START_REF] Horst | Business Transformation Through Blockchain, Two Volumes[END_REF]) develops insights on Blockchain Economic Network theory and discusses how the widespread adoption of blockchain technology might contribute to solving a larger class of economic problems related to systemic risk. For a broad recent discussion on this issue, see Swan [START_REF] Swan | Blockchain economic networks: Economic network theory?systemic risk and blockchain technology[END_REF]. Refer also to Battiston Caldarelli [START_REF] Battiston | Systemic risk in financial networks[END_REF]. Dixon et al. [START_REF] Francis Dixon | Blockchain analytics for intraday financial risk modeling[END_REF] ask in which extent the transaction graph can serve as an early-warning indicator for large financial losses and demonstrate the impact of extreme transaction graph activity on the intraday volatility of the Bitcoin prices series. Specifcally, they identify certain sub-graphs ('chainlets') that exhibit predictive influence on Bitcoin price and volatility and characterize the types of chainlets that signify extreme losses. Using bars ranging from 15 minutes up to a day, they fit GARCH models with and without the extreme chainlets and show that the former exhibit superior Value-at-Risk backtesting performance (Dixon et al. [START_REF] Francis Dixon | Blockchain analytics for intraday financial risk modeling[END_REF]).

Ferreira [START_REF] Ferreira | Contagion effect in cryptocurrency market[END_REF] study the contagion effect in cryptocurrency market. For a survey on efficiency and profitable trading opportunities in cryptocurrency markets Kyriazis [START_REF] Nikolaos | A survey on efficiency and profitable trading opportunities in cryptocurrency markets[END_REF] cf do you need a blockchain. See also Bielinsky et al. [START_REF] Bielinsky | Complex network precursors of crashes and critical events in the cryptocurrency market[END_REF] complex network analysis. Antonakakis [START_REF] Antonakakis | Cryptocurrency market contagion: market uncertainty, market complexity, and dynamic portfolios[END_REF] on cryptocurrency market contagion: market uncertainty, market complexity, and dynamic portfolios. Caporale [START_REF] Guglielmo | Persistence in the cryptocurrency market[END_REF] on the persistence in the cryptocurrency market. Gkillas [START_REF] Gkillas | Extreme correlation in cryptocurrency markets[END_REF] argue for extreme correlation in cryptocurrency markets. Luu [START_REF] Luu | Spillover risks on cryptocurrency markets: A look from var-svar granger causality and student?st copulas[END_REF] on spillover risks on cryptocurrency markets through VAR-SVAR Granger causality and Studentst copulas. Nakavachara [START_REF] Voraprapa Nakavachara | Should all blockchain-based digital assets be classified under the same asset class? Available at[END_REF] on Blockchain-based digital assets classification. On an equilibrium valuation of bitcoin and decentralized network assets: Pagnotta [START_REF] Pagnotta | An equilibrium valuation of bitcoin and decentralized network assets[END_REF]. Bartolucci[54] discusses a model of the optimal selection of crypto assets. Stix [START_REF] Stix | Ownership and purchase intention of crypto-assets-survey results[END_REF] on a survey on Ownership and purchase intention of crypto-assets. See also Antipova [START_REF] Antipova | Building and testing global investment portfolios using alternative asset classes[END_REF]. There are recent papers contributing to the literature on portfolio management and estimation risk. Platanakis [START_REF] Platanakis | Portfolio management with cryptocurrencies: The role of estimation risk[END_REF] compare different portfolio construction methods using cryptocurrencies. and study the performance of nave diversification, Markowitz diversification and the advanced BlackLitterman model with VBCs that controls for estimation errors in a portfolio of cryptocurrencies. See also Platanakis [START_REF] Platanakis | Optimal vs naïve diversification in cryptocurrencies[END_REF]. On asset pricing, see Liu et al. [START_REF] Liu | Common risk factors in cryptocurrency[END_REF]. Rosu Saleh[498] consider a discrete-time infinite-horizon model. Trautman[567] on bitcoin as asset class, Marshall 2019b [START_REF] Ben R Marshall | Bitcoin liquidity. Nuttawat[END_REF]. Liu [START_REF] Liu | Risks and returns of cryptocurrency[END_REF] on risks and returns of cryptocurrency. See also Guadamuz Marsden [START_REF] Guadamuz | Blockchains and bitcoin: Regulatory responses to cryptocurrencies[END_REF] and Girasa18 [START_REF] Girasa | Regulation of Cryptocurrencies and Blockchain Technologies: National and International Perspectives[END_REF].

Law

For a survey on Blockchain issues and the law, we refer to Filippi Wright [START_REF] De | Blockchain and the law: The rule of code[END_REF] and Berg et al. [START_REF] Berg | Blockchains and constitutional catallaxy[END_REF], see also Ostbye [START_REF] Østbye | Who is liable if a public cryptocurrency protocol fails? Available at[END_REF] on liability issue if a public cryptocurrency protocol fails. De Filippi Wright [START_REF] Wright | Decentralized blockchain technology and the rise of lex cryptographia[END_REF] on the widespread deployment of Blockchains will lead to expansion of a new subset of law, which they term Lex Cryptographia. See also Mccallum[385] and Bolotaeva [START_REF] Os Bolotaeva | The legal nature of cryptocurrency[END_REF], Lessig [START_REF] Lessig | Code is law[END_REF][START_REF] Lessig | Code: And other laws of cyberspace[END_REF], Wu [START_REF] Wu | When code isn't law[END_REF] and link between blockchain and lessig see Filippi Hassan [START_REF] De | Blockchain and the law: The rule of code[END_REF], De Filippi [START_REF] De | Blockchain and the law: The rule of code[END_REF]. On regulating Blockchain and Cryptocurrencies, see also Shanaev et al. [START_REF] Shanaev | Taming the blockchain beast? regulatory implications for the cryptocurrency market[END_REF], Hazar [START_REF] Boydaş | The importance of regulations on cryptocurrency transactions[END_REF]. Scholl Bolivar [START_REF] Hans | Regulation as both enabler of technology use and global competitive tool: The gibraltar case[END_REF] analyse the case of Gibraltar not only as the first jurisdiction worldwide to regulate general DLT provision, but as well as using the regulation as a competitive tool and a means for creating new public value. Nabilou [START_REF] Nabilou | How to regulate bitcoin? decentralized regulation for a decentralized cryptocurrency[END_REF][START_REF] Nabilou | Central banks and regulation of cryptocurrencies[END_REF]. See Johansson 2019 [START_REF] Johansson | Regtech-a necessary tool to keep up with compliance and regulatory changes[END_REF] on RegTechs. On GDPR and Blockchains, Truong 2019 [START_REF] Nguyen Binh Truong | Gdpr-compliant personal data management: A blockchain-based solution[END_REF] propose a Blockchain-based Solution for GDPR-Compliant Personal Data Management.

On the right to withdraw consent and the right to be forgotten, see

Beyond 4.1 Risks

Numerous risks and challenges have been mentioned throughout the previous sections. It is crucial to take into account each of but also the interplay dynamics/intertwinned risks of the human element, information systems, and communication networks. There are many definitions and conceptions of risks, and this issue (Blockchain and Cryptocurrency) is clearly deeply multi-faceted, and clearly all domains are concerned there. We give some of the related issues. For example, houy [START_REF] Houy | It will cost you nothing to'kill'a proof-of-stake crypto-currency[END_REF] argues that killing a proof of stake can be done at no cost.

The storage and obsolescence (obsolescence of platform implementations) can also be an issues.

Østbye [START_REF] Østbye | Model risk in cryptocurrency governance reliability assessments[END_REF] "As the role of cryptocurrencies in the economy increases, such model risk is likely to be a concern for regulators. The regulatory implications of model risk are also discussed in this paper." See also Østbye [START_REF] Østbye | Collusion risk and responsibility in public cryptocurrency protocol development[END_REF]. Matzutt et al. [START_REF] Matzutt | A quantitative analysis of the impact of arbitrary blockchain content on bitcoin[END_REF] provide a systematic analysis of the benefits and threats of arbitrary blockchain content, as blockchains irrevocably recording arbitrary data which does not come without risk for users as each participant has to locally replicate the complete blockchain, particularly including potentially harmful content. See Zetzsche [START_REF] Dirk A Zetzsche | The distributed liability of distributed ledgers: Legal risks of blockchain[END_REF] on legal risks of blockchains.

Bielinsky Soloviev [START_REF] Bielinsky | Complex network precursors of crashes and critical events in the cryptocurrency market[END_REF] on indicators based on complex network structure. Soloviev [START_REF] Soloviev | Methods of nonlinear dynamics and the construction of cryptocurrency crisis phenomena precursors[END_REF] Methods of nonlinear dynamics and the construction of cryptocurrency crisis phenomena precursors. See Chia [START_REF] Chia | Rethinking blockchain security: Position paper[END_REF] on cascading failures in blockchains. Goldfeder et al. [START_REF] Goldfeder | When the cookie meets the blockchain: Privacy risks of web payments via cryptocurrencies[END_REF] on cookie and the blockchain, and ODair [START_REF] Marcus | Risks of adoption[END_REF] on risks of adoption.

Adoption, digital divide, digital culture and education

Digital divide. How Blockchain can bridge the gap. Factors in Bitcoin acceptance. Quirquincho. Network structure. Computational thinking. Computer thinking.

Swan [START_REF] Swan | Blockchain: Blueprint for a new economy[END_REF] notes that the term digital divide has typically referred to the gap between those who have access to certain technologies and those who do not. Hooks [START_REF] Hooks | The mesh economy: How blockchain and alternative networks can bridge the digital divide and facilitate economic inclusion[END_REF] discusses on how Blockchain and alternative networks can bridge the digital divide and facilitate economic inclusion. Parino et al. [START_REF] Parino | Analysis of the bitcoin blockchain: socio-economic factors behind the adoption[END_REF] propose to characterize the adoption of the Bitcoin blockchain by country, underlying the fact that while the Bitcoin blockchain attracts a lot of attention, it remains difficult to investigate where this attention comes from, due to the pseudo-anonymity of the system, and consequently to appreciate its social impact. As emphasized in Abraham [3], numerous factors play roles in influencing Bitcoin penetration and acceptance, both at country and individual level, such as trust, perceived risk, security threat, perceived benefit, perceived ease of use, as well as macrotechnological and socioeconomic factors. Stix 2019 [START_REF] Stix | Ownership and purchase intention of crypto-assets-survey results[END_REF] finds that among Austrian households, ownership and purchase intention of crypto-assets are strongly affected by profit expectations and by beliefs that crypto-assets offer advantages for payments -most adopters or potential adopters hold both beliefs. Perceptions of high volatility or the risk of fraud and online theft dampen the demand for crypto-assets. Presthus 2017 [START_REF] Presthus | Motivations and barriers for end-user adoption of bitcoin as digital currency[END_REF] provide an analysis of motivations and barriers for end-user adoption of bitcoin as digital currency. Mendoza 2018 [START_REF] Mendoza | Social commerce as a driver to enhance trust and intention to use cryptocurrencies for electronic payments[END_REF] study social commerce as a driver to enhance trust and intention to use cryptocurrencies for electronic payments. Studies through network analysis deep tools on adoption and diffusion of blockchain and cryptocurrency related assets are to be conducted (see for example [START_REF] Zhang | The construction and simulation of internet financial product diffusion model based on complex network and consumer decisionmaking mechanism[END_REF]).

Cai 2019 [START_REF] Cai | Identifying multiple peer influences on smart contract adoption in blockchain user network[END_REF] provide evidence that network structure can trigger smart contract adoption (focusing on CryptoKitties adoption in the Ethereum network). Many have conscious of this. As Judmayer et al. (volume 2 in [START_REF] Horst | Business Transformation Through Blockchain, Two Volumes[END_REF]) "Bitcoin show how difficult the fundamentals are to understand for nonexpert users, not to mention the fact that there is still very little awareness or understanding of systems other than cryptocurrencies that rely on the principle of blockchains.", which their Appendix on Blockchain basics contributes helping understanding of the underlying concepts, presenting the basic ideas behind Bitcoins complex components in a way that makes it easy to understand without technological knowledge through using an example of a stone block chain that uses simple analogies that are easy to visualize. See also initiatives as the five volumes comic Las Aventuras de Quirquincho by Castro and Quezada [START_REF] Castro | Las aventuras de Quirquincho. Licencia Creative Commons-Chaucha Ediciones[END_REF], Quirquincho going through diverse adventures that explain basic concepts of the Blockchain. Even if, for usages, knowing the technical very aspects of Blockchain is not needed, digital culture has to be spread, including some basis in Network science tools, as understanding literature and texts wouldn't need to master the technical very aspects of printing but tools developed and needed to understand and read texts with deeper acuity. Wing [START_REF] Wing | Computational thinking[END_REF][START_REF] Wing | Computational thinking and thinking about computing[END_REF] argue that to reading, writing, and arithmetic, we should add computational thinking to every child's analytical ability. See also Atlan et al. [START_REF] Atlan | Apprentissage de la pensée informatique: de la formation des enseignant-e-s à la formation de tou-te-s les citoyen-ne-s[END_REF], Lu [START_REF] James | Thinking about computational thinking[END_REF], Grover [START_REF] Grover | Computational thinking in k-12: A review of the state of the field[END_REF], Yadav [START_REF] Yadav | Introducing computational thinking in education courses[END_REF], Barr [START_REF] Barr | Computational thinking: A digital age skill for everyone[END_REF][START_REF] Barr | Bringing computational thinking to k-12: what is involved and what is the role of the computer science education community?[END_REF], Hambrusch [START_REF] Hambrusch | A multidisciplinary approach towards computational thinking for science majors[END_REF], Henderson [START_REF] Peter B Henderson | Computational thinking[END_REF].

4.3 Quantum computing and Blockchain, Quantum Blockchains, Quantum networks

See Kiktenko et al. [START_REF] Evgeniy O Kiktenko | Quantum-secured blockchain[END_REF]: current blockchain platforms rely on digital signatures, which are vulnerable to attacks by means of quantum computers. Kiktenko et al. [START_REF] Evgeniy O Kiktenko | Quantum-secured blockchain[END_REF] propose a possible solution to the quantum-era blockchain challenge and report an experimental realization of a quantum-safe blockchain platform that utilizes quantum key distribution across an urban fiber network for informationtheoretically secure authentication. See also Fedorov [START_REF] Aleksey K Fedorov | Quantum computers put blockchain security at risk[END_REF], Rodenburg [START_REF] Rodenburg | Blockchain and quantum computing[END_REF], Stewart [START_REF] Stewart | Committing to quantum resistance: a slow defence for bitcoin against a fast quantum computing attack[END_REF], Ikeda [START_REF] Ikeda | Security and privacy of blockchain and quantum computation[END_REF] Sattath [START_REF] Sattath | On the insecurity of quantum bitcoin mining[END_REF], Gao [START_REF] Gao | A secure cryptocurrency scheme based on post-quantum blockchain[END_REF], Jogenfors [START_REF] Jogenfors | Quantum bitcoin: An anonymous and distributed currency secured by the no-cloning theorem of quantum mechanics[END_REF], Yin [START_REF] Yin | An anti-quantum transaction authentication approach in blockchain[END_REF]. On Quantum money see Rajan [START_REF] Rajan | Quantum blockchain using entanglement in time[END_REF], Ingber [START_REF] Ingber | Options on quantum money: Quantum path-integral with serial shocks[END_REF], Ikeda [START_REF] Ikeda | qbitcoin: a peer-to-peer quantum cash system[END_REF], Horodecki [START_REF] Horodecki | Semi-device independent quantum money[END_REF], Ablayev [START_REF] Fm Ablayev | Quantum-assisted blockchain[END_REF], Sun [START_REF] Sun | Quantum-enhanced logic-based blockchain i: Quantum honest-success byzantine agreement and qulogicoin[END_REF], Sun [START_REF] Sun | A simple voting protocol on quantum blockchain[END_REF] (voting protocol), Li [START_REF] Li | A new lattice-based signature scheme in post-quantum blockchain network[END_REF] (post-quantum blockchain networks), Bennet Daryanoosh [START_REF] Adam | Energy efficient mining on a quantum-enabled blockchain using light[END_REF], see also Casino [START_REF] Casino | A systematic literature review of blockchain-based applications: current status, classification and open issues[END_REF] on quantum resilience.

Sustainability and energy consumption

Refer to Casino [START_REF] Casino | A systematic literature review of blockchain-based applications: current status, classification and open issues[END_REF] on sustainability of the blockchain protocol Marcus Dapp (volume 2 chapter 6 in [START_REF] Horst | Business Transformation Through Blockchain, Two Volumes[END_REF]) argue for a new economic approach that has sustainability built into its core design by using cryptoeconomics based on blockchain technology to create incentive systems which encourage sustainable behavior. Leonard Treiblmaier (volume 2 chapter 7 in [START_REF] Horst | Business Transformation Through Blockchain, Two Volumes[END_REF]) question the economic growth paradigm and ask the question whether cryptocurrencies can help to create a more sustainable economy. See also Alvarez-Pereira [START_REF] Alvarez-Pereira | Anticipations of digital sustainability: Self-delusions, disappointments and expectations[END_REF]. For example, alternatives are being looked for (see Amoussou-Guenou [START_REF] Amoussou-Guenou | Correctness and fairness of tendermint-core blockchains[END_REF]).

Conclusion

Towards a categorization and framework for Blockchains. Finding balances. On hierarchies and networks. Interdisciplinary research.

There are many issue-related categorizations, being refined and more and more accurate. However, towards the technical characteristics, specificities and impacts that are particular to the development of Blockchains, the need for building more general frameworks for Blockchain related-issues analysis may arise. As Judmayer et al. (volume 2 chapter 15 in [START_REF] Horst | Business Transformation Through Blockchain, Two Volumes[END_REF]) argue many unsolved problems in terms of finding a balance between performance, scalability, security, decentralization, and anonymity in such systems'. Casino [START_REF] Casino | A systematic literature review of blockchain-based applications: current status, classification and open issues[END_REF] also emphasizes those issues:"All these approaches imply some additional changes in the balance between security, scalability, and decentralisation that blockchains offer by default. Therefore, considerable research effort needs to be undertaken for finding the proper equilibrium". Such balances are to be dealt also through categorizations as provided in Kannengiesser et al. [START_REF] Kannengießer | Mind the gap: Tradeoffs between distributed ledger technology characteristics[END_REF]. As well as other disruptive technologies but also from their specificities, Blockchain and cryptocurrencies'technologies is also an opportunity for reseachers from any areas to reflect on such a disruptive innovation, both from its impact and development observation. It's a good example to study innovation adoption, including observing the anticipating analyses from a multileveled viewpoint. As Cardon [START_REF] Cardon | Culture numérique[END_REF] emphasizes, it is important to have various and interdisciplinary knowledge for living there with agility and prudently, as if we make the digital, the digital also makes us 19 . As digital disruption can be deeply compared with Printing disruption, and we know that it has had many consequences on thinking, religion, organizational power etc (see Eisenstein [START_REF] Elizabeth L Eisenstein | Some conjectures about the impact of printing on western society and thought: A preliminary report[END_REF][START_REF] Elizabeth L Eisenstein | The printing press as an agent of change[END_REF][START_REF] Elizabeth L Eisenstein | The printing revolution in early modern Europe[END_REF][START_REF] Alcorn Baron | Agent of Change: Print Culture Studies after Elizabeth L. Eisenstein[END_REF]), the ongoing Blockchain revolution being part of the digital disruption, it is crucial to develop tools from various and interdisciplinary research for attempts to capture it. What will be the consequences and how will we face them ? While Xu et al. [START_REF] Xu | Architecture for blockchain applications[END_REF] argue that "to achieve the benefits touted from blockchain will require a degree of cooperation among institutions that has not yet been achieved and that could have been achieved with modifications of existing technology", Blamont [START_REF] Blamont | Réseaux! le pari de l'intelligence collective[END_REF] proposes to think about a structure called "Fédération" consisting in establishing a functional link between collaborative communities and established hierarchies, between "exuberance of the crowd" and "rigor of the norm" and Swan underlines that "there is a need for a decentralized ecosystem surrounding the blockchain itself for full-solution operations" ([547], p.19). While transdisciplinary surveys are provided on Blockchain, it becomes clearer and clearer how Network Science can provide tools and analysis making fruitful interdisciplinary researches flourish. It is crucial to take into account each of but also the interplay dynamics/intertwinned analysis of the human elements, information systems, and communication networks.

  General and technical on Blockchain. Cryptocurrencies. Bitcoin. Bitcoin research across disciplines. Consensus and mining strategy. Architecture. Merkle tree. Security. Privacy. Applications. Platforms. Financial sector. ICO. FinTech. RegTech. Governance. Intellectual property. Economics. Game theory. Law.

  3.9.2 Currency pluralism,Central bank digital currency, Currency competition Currency pluralism. Central banking. Central bank digital currency. Currency competition. Free banking. Seang Torre[513] examines in a theoretical setting the properties of two Blockchain consensus protocols (Proof of Work (PoW) and Proof of Stake (PoS)) in the management of a local (or networks of local) complementary currencies. See also Adrian et al. 2019

  Politou 2018[START_REF] Politou | Forgetting personal data and revoking consent under the gdpr: Challenges and proposed solutions[END_REF]. There are many discussion papers on Blockchain technology and the gdpr, see Berberich 2016[START_REF] Berberich | Blockchain technology and the gdpr-how to reconcile privacy and distributed ledgers[END_REF],Salmensuu 2018[503].Buocz 2019[108] on Bitcoin, gdpr and allocating responsibility in distributed networks See Magnier[START_REF] Magnier | The potential impact of blockchains on corporate governance: a survey on shareholders' rights in the digital era. InterEU law east: journal for the international and european law[END_REF] on the potential impact of Blockchains on corporate governance: a survey on shareholders' rights in the digital era, for a literature review on use of Blockchain in governance Razzaq[START_REF] Razzaq | Use of blockchain in governance: A systematic[END_REF], see alsoDavidson et al.[164], De Filippi Hassan[START_REF] Hassan | The expansion of algorithmic governance: From code is law to law is code. Field Actions Science Reports[END_REF].

Dargaye[162] presents a formal logical framework able to extend the execution of blockchain transactions to events coming from external oracles: in many industrial applications smart contracts react to information coming from external sources (sensors, human interfaces, other applications), often called oracles in the blockchain jargon, which amplifies their vulnerability, these events being by essence non-reliable, since transaction execution can be triggered by information whose veracity cannot be established by the blockchain

see Cachin et al.[START_REF] Cachin | Introduction to reliable and secure distributed programming[END_REF], Fokkink[START_REF] Fokkink | Distributed algorithms: an intuitive approach[END_REF][START_REF] Fokkink | Modelling distributed systems[END_REF]

Anceaume et al.[START_REF] Anceaume | Bitcoin a distributed shared register[END_REF] underlines that even though the behaviour of distributed ledgers is similar to abstractions that have been deeply studied for decades in distributed systems no abstraction is sufficiently powerful to capture the distributed ledger behaviour.

i.e. une chaine avec des ramifications

See alsoEstrada[200,[START_REF] Estrada | Network science: complexity in nature and technology[END_REF][START_REF] Estrada | A first course in network theory[END_REF], Konig Battiston[START_REF] Michael | From graph theory to models of economic networks. a tutorial[END_REF], Tasca Tessone[START_REF] Tasca | A taxonomy of blockchain technologies: Principles of identification and classification[END_REF], Newman Watts Barabasi[START_REF] Mark | The structure and dynamics of networks[END_REF].

Noting that "The power of a map lies in how it communicates spatial relations, how the information has been selected, abstracted, generalized and portrayed by the cartographer. Because of this process of creation, no map is an objective, neutral artefact as many subjective decisions are made about what to include, how the map will look, what the map is seeking to communicate" ([START_REF] Dodge | Rethinking maps: new frontiers in cartographic theory[END_REF])

See Koensa[START_REF] Koensa | Assessing interoperability solutions for distributed ledgers extended version[END_REF], Schulte[START_REF] Schulte | Towards blockchain interoperability[END_REF], Koen[START_REF] Koens | Assessing interoperability solutions for distributed ledgers[END_REF], Hardjono[START_REF] Hardjono | Towards a design philosophy for interoperable blockchain systems[END_REF], Brogan[START_REF] Brogan | Authenticating health activity data using distributed ledger technologies[END_REF], Pillai[START_REF] Pillai | Blockchain interoperable digital objects[END_REF], Krishnan[START_REF] Krishnan | Validating smart contract execution across a heterogeneous collection: A proposal[END_REF],[START_REF] Hardjono | Towards a design philosophy for interoperable blockchain systems[END_REF],[483].

Davidson De Filippi Potts[START_REF] Davidson | Economics of blockchain[END_REF] provides some propositions for building analytical frameworks for economics of blockchain (suggests two approaches to economics of blockchain: innovation-centred and governance-centred. Argues that the governance approachbased in new institutional economics and public choice economicsis most promising, because it models blockchain as a new technology for creating spontaneous organizations, i.e. new types of economies).

Note that Girasa has also written more genarally on Cyberlaw. Refer to Girasa[START_REF] Rosario | Cyberlaw: National and International Perspectives[END_REF]

(our translation from French) Cardon: "Il est important de disposer de connaissances variées et interdisciplinaires pour y vivre avec agilité et prudence, car si nous fabriquons le numérique, le numérique nous fabrique aussi"([START_REF] Cardon | Culture numérique[END_REF])