A Review on the Use of Blockchain for the Internet of Things

In the paper

“some reports [1] predict that IoT devices will grow to 26 billions by 2020, which are 30 times the estimated number of devices deployed in 2009 and is far more than the 7.3 billion smartphones, tablets and PCs that are expected to be in use by 2020.”

What the sources say

• Not checked yetcites [1] [1] Gartner. Report: 'Forecast: The Internet of Things, Worldwide, 2013'. Nov. 2013. -

In the paper

“For instance, in [69] it is presented a traceability application that makes use of IoT sensors and blockchain technology to verify data integrity and public accessibility to temperature records in the pharmaceutical supply chain.”

What the sources say

• Not checked yetcites [69] [69] Bocek, T., Rodrigues, B. B., Strasser, T., Stiller, B. 'Blockchains everywhere - a use-case of blockchains in the pharma supply-chain', in Proceedings of the IFIP/IEEE Symposium on Integrated Network and Service Management (IM), Lisbon, Portugal, 8-12 May 2017. -

In the paper

“The need of this feature is not enough to justify the use of a blockchain: there also has to be at least a lack of trust in the entity that manages the distributed computing system.”

In the paper

“some forecasts [2] anticipate a fourfold growth in Machine-to-Machine (M2M) connections in the next years (from 780 million in 2016 to 3.3 billion by 2021)”

What the sources say

• Not checked yetcites [2] [2] Cisco Systems. White paper: Cisco Visual Networking Index: Global Mobile Data Traffic Forecast Update, 2016-2021. March 2017. -

In the paper

“The experiments measure the average time to reach a consensus and it can be observed how it grows as the number of peers increases.”

What the sources say

• Not checked yetcites [77] [77] Sukhwani, H., Martínez, J. M., Chang, X., Trivedi, K. S., Rindos, A. 'Performance Modeling of PBFT Consensus Process for Permissioned Blockchain Network (Hyperledger Fabric)', in Proceedings of the IEEE 36th Symposium on Reliable Distributed Systems (SRDS), Hong Kong, China, 26-29 Sep. 2017. -

In the paper

“In order to optimize them, several authors studied BIoT performance in different scenarios. They analyzed a number of influential aspects, but they mainly focus on the performance of consensus algorithms.”

In the paper

“Among such proposals, decentralized architectures were suggested in the past to create large Peer-to-Peer (P2P) Wireless Sensor Networks (WSNs) [9]-[11]”

What the sources say

• Not checked yetcites [9]-[11]

In the paper

“However, many users still trust blindly certain companies, government agencies or banks, so if there is mutual trust, a blockchain is not required.”

In the paper

“Finally, it should be mentioned that Big Data can be leveraged by blockchain technology (i.e., to ensure its trustworthiness), so some researchers [27] reviewed the main blockchain-based solutions to gather and control massive amounts of data that may be collected from IoT networks.”

What the sources say

• Not checked yetcites [27] [27] Karafiloski, E., Mishev, A., 'Blockchain solutions for big data challenges: A literature review', in Proceedings of the IEEE International Conference on Smart Technologies, Ohrid, Macedonia, 6-8 July 2017. -

In the paper

“Another healthcare BIoT application is detailed in [70], where it is presented the architecture of a blockchain-based platform for clinical trials and precision medicine.”

What the sources say

• Not checked yetcites [70] [70] Shae, Z., Tsai, J. J. P. 'On the Design of a Blockchain Platform for Clinical Trial and Precision Medicine', in Proceedings of the IEEE 37th International Conference on Distributed Computing Systems (ICDCS), Atlanta, United States, 5-8 June 2017. - source

In the paper

“Before delving into the details on how to make use of a blockchain for IoT applications, it must be first emphasized that a blockchain is not always the best solution for every IoT scenario.”

In the paper

“Some IoT applications [43], [44] may need to keep a record of every transaction to maintain traceability, for auditing purposes or because Big Data techniques will be applied later [45], [46]. In these situations, a sidechain may be useful [47].”

What the sources say

• Not checked yetcites [43] [43] Wu, Z., Meng, Z., Gray, J. 'IoT-Based Techniques for Online M2MInteractive Itemized Data Registration and Offline Information Traceability in a Digital Manufacturing System', in IEEE Transactions on Industrial Informatics, vol. 13, no. 5, pp. 2397-2405, Oct. 2017. -
• Not checked yetcites [44] [44] Lomotey, R. K., Pry, J., Sriramoju, S., Kaku, E., Deters, R. 'Wearable IoT Data Architecture', in Proceedings of theIEEE World Congress on Services (SERVICES), Honolulu, United States, 25-30 June 2017. -
• Not checked yetcites [47] [47] Back, A., Corallo, M., Dashjr, L., Friedenbach, M., Maxwell, G., Miller, A., Poelstra, A., Timón, J., Wuille, P. 'Enabling Blockchain Innovations with Pegged Sidechains'. Available online: https://www.blockstream. com/sidechains.pdf (Accessed on 10 April 2018) <!-- image --> IEEEAccess -

In the paper

“As reported by Statista [15], investments by venture capitalists in blockchain start-ups rose from 93 million to 550 million U.S. dollars from 2013 to 2016.”

What the sources say

• Not checked yetcites [15] [15] MarketsandMarkets; Statista estimates. Market for blockchain technology worldwide. Available online: https://www.statista.com/statistics/ 647231/worldwide-blockchain-technology-market-size/ (Accessed on 10 April 2018). -

In the paper

“Blockchain technologies are able to track, coordinate, carry out transactions and store information from a large amount of devices, enabling the creation of applications that require no centralized cloud.”

In the paper

“Distributed systems can also be built on top of clouds, server farms or any form of traditional distributed computing systems [42].”

What the sources say

• Not checked yetcites [42] [42] Datla, D., Chen, X., Tsou, T., Raghunandan, S., Shajedul Hasan, S. M., Reed, J. H., Dietrich, C. B., Bose, T., Fette, B., Kim, J.-H. 'Wireless distributed computing: a survey of research challenges', in IEEE Communications Magazine, vol. 50, no. 1, pp. 144-152, Jan. 2012. - source

In the paper

“Although this solution may work properly nowadays, the expected growth suggests that new paradigms will have to be proposed.”

In the paper

“Traditional databases or Directed Acyclic Graph (DAG) based ledgers [37] may be a better fit for certain IoT applications.”

What the sources say

• Not checked yetcites [37] [37] IOTA's official web page. Available online: https://www.iota.org (Accessed on 10 April 2018) -

In the paper

“In addition, to reduce the transaction fees of cryptocurrencies like Bitcoin, the researchers present a singlefee micro-payment protocol that aggregates several small payments into a larger transaction.”

What the sources say

• Not checked yetcites [68] [68] Lundqvist, T., de Blanche, A., Andersson, H. R. H. 'Thing-to-thing electricity micro payments using blockchain technology', in Proceedings <!-- image --> IEEEAccess - of the Global Internet of Things Summit (GIoTS), Geneva, Switzerland, 6-9 June 2017. - source

In the paper

“For example, in [63] it is presented a traceability system for tracking Chinese agri-food supplies. The system is based on the use of Radio Frequency Identification (RFID) and a blockchain, being its aim to enhance food safety and quality, and to reduce losses in logistics.”

What the sources say

• Not checked yetcites [63] [63] Tian, F., 'An agri-food supply chain traceability system for China based on RFID & blockchain technology', in Proceedings of the 13th International Conference on Service Systems and Service Management (ICSSSM), Kunming, China, 24-26 June 2016. -

In the paper

“An example is detailed in [68], where the authors propose a blockchain-based system that allows IoT/IoE devices to pay each other for services without human intervention. In the paper it is described an implementation that shows the potential of the system: a smart cable that connects to a smart socket is able to pay for the electricity consumed.”

What the sources say

• Not checked yetcites [68] [68] Lundqvist, T., de Blanche, A., Andersson, H. R. H. 'Thing-to-thing electricity micro payments using blockchain technology', in Proceedings <!-- image --> IEEEAccess - of the Global Internet of Things Summit (GIoTS), Geneva, Switzerland, 6-9 June 2017. - source

In the paper

“In [28], different blockchain-based industrial applications are reviewed, including their connection to Industrial IoT (IIoT) networks.”

What the sources say

• Not checked yetcites [28] [28] Ahram, T., Sargolzaei, A., Sargolzaei, S., Daniels, J., Amaba, B., 'Blockchain technology innovations', in Proceedings of the IEEE Technology & Engineering Management Conference (TEMSCON), Santa Clara, United States, 8-10 June 2017. -

In the paper

“In fact, Ethereum is characterized by being Turing-complete, which is a mathematical concept that indicates that Ethereum's programming language can be used to simulate any other language.”

In the paper

“since it addresses the current critical challenges for its massive adoption:”

In the paper

“Blockchain technologies can bring many benefits to IoT, but, since they have not been devised explicitly for IoT environments, the different pieces that make them up should be adapted.”

In the paper

“The author points out that, although Bitcoin has been a clear success, its poor scalability makes no sense today, since there are modern cryptocurrency platforms like Ethereum.”

What the sources say

• Not checked yetcites [78] [78] Vukoli´ c, M. 'The Quest for Scalable Blockchain Fabric: Proof-ofWork vs. BFT Replication'. Available online: http://www.vukolic.com/ iNetSec\_2015.pdf (Accessed on 10 April 2018) -

In the paper

“Some authors [19] suggested that blockchain applicability evolution started with Bitcoin (blockchain 1.0), then evolved towards smart contracts (blockchain 2.0) and later moved to justice, efficiency and coordination applications (blockchain 3.0).”

What the sources say

• Not checked yetcites [19] [19] Swan, M. 'Blockchain: blueprint for a new economy'. First Edition, O'Reilly Media, Jan. 2015. -

In the paper

“Some IoT applications may require to perform economic transactions with third parties, but many applications do not. Moreover, economic transactions can still be carried out through traditional payment systems, although they usually imply to pay transaction fees and it is necessary to trust banks or middlemen.”

In the paper

“Many IoT networks collect data that need to be timestamped and stored sequentially. Nonetheless, such needs may be easily fulfilled with traditional databases, especially in cases where security is guaranteed or where attacks are rare.”

In the paper

“Other researchers focused on managing IoT devices through a blockchain [64]. Such researchers proposed a system able to control and configure IoT devices remotely. The system stores public keys in Ethereum while private keys are saved on each IoT device.”

What the sources say

• Not checked yetcites [64] [64] Huh, S., Cho, S., Kim, S., 'Managing IoT devices using blockchain platform', in Proceedings of the 19th International Conference on Advanced Communication Technology (ICACT), Bongpyeong, South Korea, 19-22 Feb. 2017. -

In the paper

“Ethereum is arguably the most popular blockchain-based platform for running smart contracts, although it can actually run other distributed applications and interact with more than one blockchain.”

In the paper

“It is also worth mentioning the work described in [71], which presents a generic smart healthcare system that makes use of IoT devices, cloud and fog computing [72], a blockchain, Tor [73] and message brokers.”

What the sources say

• Not checked yetcites [71] [71] Salahuddin, M. A., Al-Fuqaha, A., Guizani, M., Shuaib, K., Sallabi, F. 'Softwarization of Internet of Things Infrastructure for Secure and Smart Healthcare' in Computer, vol. 50, no. 7, July 2017, pp. 74-79. - source
• Not checked yetcites [72] [72] Dolui, K., Datta, S. K. 'Comparison of edge computing implementations: Fog computing, cloudlet and mobile edge computing', in Proceedings of the Global Internet of Things Summit (GIoTS), Geneva, Switzerland, 6-9 June 2017. - source
• ?Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  cites [73] [73] Tor project official web page. Available online: https://www.torproject. org (Accessed on 10 April 2018) -

In the paper

“In the case of [76] it is proposed a framework that integrates smart devices in a secure way for providing smart city applications.”

What the sources say

• Not checked yetcites [76] [76] Biswas, K., Muthukkumarasamy, V. 'Securing Smart Cities Using Blockchain Technology', in Proceedings of the IEEE 14th International Conference on Smart City, Sydney, Australia, 12-14 Dec. 2016. - source

In the paper

“Therefore, the key contribution of blockchain is that it provides a way to carry out transactions with another person or entity without having to rely on third-parties.”

In the paper

“Furthermore, the market for blockchain technology worldwide is forecast to grow to 2.3 billion U.S. dollars by 2021.”

What the sources say

• Not checked yetcites [15] [15] MarketsandMarkets; Statista estimates. Market for blockchain technology worldwide. Available online: https://www.statista.com/statistics/ 647231/worldwide-blockchain-technology-market-size/ (Accessed on 10 April 2018). -

In the paper

“According to McKinsey &amp; Company, although it is still in a nascent stage, blockchain technology may reach its full potential within the next 4 years based on its current pace of evolution [16].”

What the sources say

• Not checked yetcites [16] [16] Blockchain Technology report to the US Federal Advisory Committee on Insurance. Available online: https://www.treasury.gov/initiatives/fio/ Documents/McKinsey\_FACI\_Blockchain\_in\_Insurance.pdf (Accessed on 10 April 2018). -

In the paper

“but some pieces were missing in relation to privacy and security until the arrival of blockchain technology.”

In the paper

“In addition, as of writing, there are over 1,563 digital coins [17]”

What the sources say

• ?Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  cites [17] [17] Crypto-currency market capitalizations. Available online: https:// coinmarketcap.comhttps://coinmarketcap.com/ (Accessed on 10 April 2018). -

In the paper

“Decentralization. IoT applications demand decentralization when there is not a trusted centralized system.”

In the paper

“In the paper it is suggested to improve PoW performance by mixing it with a BFT protocol.”

What the sources say

• Not checked yetcites [78] [78] Vukoli´ c, M. 'The Quest for Scalable Blockchain Fabric: Proof-ofWork vs. BFT Replication'. Available online: http://www.vukolic.com/ iNetSec\_2015.pdf (Accessed on 10 April 2018) -

In the paper

“The most common public-key based cipher suites are RSAand Elliptic Curve Diffie-Hellman Exchange (ECDHE), which are the ones recommended by the National Institute of Standards and Technology (NIST) [105] for Transport Layer Security (TLS) [106].”

What the sources say

• Not checked yetcites [105] [105] NIST official web page. Available online: https://www.nist.gov (Accessed on 10 April 2018) -
• Not checked yetcites [106] [106] Polk, T., McKay, K., Chokhani, S. 'Guidelines for the Selection and Use of Transport Layer Security (TLS) Implementations', NIST Special Publication 800-52 Revision 1, June 2005. -

In the paper

“Therefore, ADEPT uses Proof-of-Stake (PoS) and PoW, which guarantee network integrity and security, but which do not impose additional limitations.”

What the sources say

• Not checked yetcites [88] [88] IBM, 'ADEPT: An IoT Practitioner Perspective', white paper, 2015. -

In the paper

“Moreover, transactions are verified cryptographically, so when malicious activities from a compromised device are detected, the system can reject its blockchain updates.”

In the paper

“The results obtained by the authors indicate that the architecture reduces delays, increases throughput and it is able to detect real-time attacks on the IoT network.”

What the sources say

• Not checked yetcites [102] [102] Sharma, P. K., Chen, M.-Y., Park, J.-H. 'A Software Defined Fog Node based Distributed Blockchain Cloud Architecture for IoT', IEEE Access, Sep. 2017. -

In the paper

“In addition, it is important to emphasize that if a single IoT device is compromised, it may disrupt the whole network by performing Denial of Service (DoS) attacks [80], eavesdropping private data [81], altering the collected data [82] or misleading other systems [83].”

What the sources say

• Not checked yetcites [80] [80] Anirudh, M., Thileeban, S. A., Nallathambi, D. J. 'Use of honeypots for mitigating DoS attacks targeted on IoT networks', in Proceedings of the International Conference on Computer, Communication and Signal Processing (ICCCSP), Chennai, Indica, 10-11 Jan. 2017. -
• Not checked yetcites [81] [81] Xu, Q., Ren, P., Song, H., Du, Q. 'Security Enhancement for IoT Communications Exposed to Eavesdroppers With Uncertain Locations', in IEEE Access, vol. 4, pp. 2840-2853, June 2016. -
• Not checked yetcites [82] [82] Li, X., Wang, H., Yu, Y., Qian, C. 'An IoT Data Communication Framework for Authenticity and Integrity', in Proceedings of the IEEE/ACM Second International Conference on Internet-of-Things Design and Implementation (IoTDI), Pittsburgh, United States, 18-21 Apr. 2017. -

In the paper

“Such a platform was conceived for secure, scalable and autonomous peer-to-peer IoT telemetry.”

What the sources say

• Not checked yetcites [88] [88] IBM, 'ADEPT: An IoT Practitioner Perspective', white paper, 2015. -

In the paper

“For instance, the method implemented by Bitcoin is inspired by one of the solutions proposed in [125], where each timestamp includes a hash of the previous timestamp, what maintains the order of the transactions (even when the clocks are inaccurate) and makes it difficult to insert fake transactions in the already linked chain.”

What the sources say

• Not checked yetcites [125] [125] Haber, S., Stornetta, W. S. 'How to time-stamp a digital document', in Journal of Cryptology, vol. 3, no. 2, pp. 99-111, Jan. 1991. -

In the paper

“In addition, it is stated that the implementation of the consensus protocols in hardware is probably the most promising way for improving the performance of any consensus method.”

What the sources say

• Not checked yetcites [78] [78] Vukoli´ c, M. 'The Quest for Scalable Blockchain Fabric: Proof-ofWork vs. BFT Replication'. Available online: http://www.vukolic.com/ iNetSec\_2015.pdf (Accessed on 10 April 2018) -

In the paper

“In order to track modifications on the blockchain, transactions have to be both signed and timestamped.”

In the paper

“In addition, timestamping can be distributed, hence avoiding the problem of having a single point of failure. Although such a distributed system is prone to Sybil attacks [126], Bitcoin solves them by linking blocks and using the PoW mechanism.”

What the sources say

• Not checked yetcites [126] [126] Douceur, J. R. 'The Sybil Attack', in Proceedings of the 1st International Workshop on Peer-to-Peer Systems (IPTPS), Cambridge, United States, 7-8 March 2002. -

In the paper

“The authors indicate that the architecture is proposed because is really difficult to host a regular blockchain on traditional resource-constrained IoT devices.”

What the sources say

• Not checked yetcites [95] [95] Samaniego, M., Deters, R. 'Blockchain as a Service for IoT', in Proceedings of the IEEE International Conference onInternet of Things (iThings) and IEEE Green Computing and Communications (GreenCom) and IEEE Cyber, Physical and Social Computing (CPSCom) and IEEE Smart Data (SmartData), Chengdu, China, 15-18 Dec. 2016. -

In the paper

“Traditional schemes rely on having trustworthiness on the server, which signs and timestamps transactions with its own private key. Nonetheless, no one deters the server from signing past transactions.”

In the paper

“A 2048-bit key is the minimum size considered secure, since 768-bit and 1024-bit RSA implementations were broken in 2010 [109], [110].”

What the sources say

• Not checked yetcites [109] [109] Kleinjung, T., Aoki, K., Franke, J., Lenstra, A. K., Thomé, E., Bos, J. W., Gaudry, P., Kruppa, A., Montgomery, P. L., Osvik, D. A., te Riele, H. J. J., Timofeev, A., Zimmermann, P. 'Factorization of a 768-Bit RSA Modulus', in Proceedings of the 30th annual conference on Advances in cryptology, Santa Barbara, United States, 15-19 Aug. 2010. - source
• ?Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  cites [110] [110] Pellegrini, A., Bertacco, V., Austin, T. 'Fault-based attack of RSA authentication', in Proceedings of the Design, Automation & Test in Europe Conference & Exhibition, Dresden, Germany, 8-12 Mar. 2010. -

In the paper

“However, note that in August 2015 the National Security Agency (NSA) recommended stopping the use of Suite B, an ECC-based algorithm, apparently, because of the progress recently made on quantum cryptography [120].”

What the sources say

• Not checked yetcites [120] [120] Koblitz, N., Menezes, A. 'A Riddle Wrapped in an Enigma', in IEEE Security & Privacy, vol 14, no. 6, pp. 34-42, Dec. 2016. -

In the paper

“Fog computing is actually considered a subset of edge computing [72]”

What the sources say

• Not checked yetcites [72] [72] Dolui, K., Datta, S. K. 'Comparison of edge computing implementations: Fog computing, cloudlet and mobile edge computing', in Proceedings of the Global Internet of Things Summit (GIoTS), Geneva, Switzerland, 6-9 June 2017. -

In the paper

“The architecture that supports a blockchain used for IoT applications should have to be adapted to the amount of traffic that such applications usually generate.”

In the paper

“However, note that traditional cloud-centered IoT architectures have certain inherent vulnerabilities [59], being the most relevant the fact that the cloud is a point of failure: if the cloud is down due to cyberattacks, maintenance or software problems, the whole system stops working.”

What the sources say

• Not checked yetcites [59] [59] Kshetri, N. 'Can Blockchain Strengthen the Internet of Things?', in IT Professional, vol. 19, no. 4, pp. 68-72, 2017. -

In the paper

“The obtained results show that, under high transaction loads, the fog system latency response is clearly faster than in a cloud-based system.”

What the sources say

• Not checked yetcites [95] [95] Samaniego, M., Deters, R. 'Blockchain as a Service for IoT', in Proceedings of the IEEE International Conference onInternet of Things (iThings) and IEEE Green Computing and Communications (GreenCom) and IEEE Cyber, Physical and Social Computing (CPSCom) and IEEE Smart Data (SmartData), Chengdu, China, 15-18 Dec. 2016. -

In the paper

“The reduction in overhead is carried out by removing the PoW consensus mechanism, so every block is mined and appended to the blockchain without additional efforts.”

What the sources say

• Not checked yetcites [91] [91] Dorri, A., Kanhere, S. S., Jurdak, R. 'Blockchain in internet of things: Challenges and Solutions'. Available online: https://arxiv.org/abs/1608. 05187 (Accessed on 10 April 2018) -
• Not checked yetcites [92] [92] Dorri, A., Kanhere, S. S., Jurdak, R. 'Towards an Optimized BlockChain for IoT', in Proceedings of the IEEE/ACM Second International Conference on Internet-of-Things Design and Implementation (IoTDI), Pittsburgh, United States, 18-21 Apr. 2017. -

In the paper

“This offloading is key for IoT applications, since it is estimated that if the number of IoT connected devices keeps on growing at the same rate [1], the amount of communications to be handled by a cloud will increase remarkably and, therefore, the cloud network capacity will have to be expanded.”

What the sources say

• Not checked yetcites [1] [1] Gartner. Report: 'Forecast: The Internet of Things, Worldwide, 2013'. Nov. 2013. -

In the paper

“It has already been shown that, when implemented on resource-constrained devices, ECC outperforms RSA in terms of speed [113][115] and power consumption [116]-[119].”

What the sources say

• Not checked yetcites [113]-[115]
• Not checked yetcites [116]-[119]

In the paper

“Tendermint [141] is a consensus algorithm that can host arbitrary application states and can only tolerate up to a 1/3 of failures.”

What the sources say

• Not checked yetcites [141] [141] Kwon, J. 'Tendermint: Consensus without mining (v0.6)'. Available online: https://tendermint.com/static/docs/tendermint.pdf (Accessed on 10 April 2018) -

In the paper

“This has already been an issue in fields like RFID-based transportation card systems, where the stored information (i.e., trips, balance, personal data) is supposedly anonymous, but in practice it may be collected by third parties [164]-[166].”

What the sources say

• Not checked yetcites [164]-[166]

In the paper

“However, this mining process makes the blockchain inefficient in throughput, scalability [78], and in terms of energy consumption, what is not desirable in an IoT network.”

What the sources say

• Not checked yetcites [78] [78] Vukoli´ c, M. 'The Quest for Scalable Blockchain Fabric: Proof-ofWork vs. BFT Replication'. Available online: http://www.vukolic.com/ iNetSec\_2015.pdf (Accessed on 10 April 2018) -

In the paper

“However, note that, in many IoT applications anonymity is not necessary, but the privacy of the transactions is required in certain scenarios when the collected data may allow for monitoring and predicting people behavior or habits.”

In the paper

“However, note that these proofs are not immune to attacks [177]. In fact, like in the case of mixing techniques, they are susceptible to de-anonymization through statistical disclosure attacks, but they improve mixing techniques by avoiding the necessity for a mixing server, which can pose a security or performance bottleneck.”

What the sources say

• Not checked yetcites [177] [177] Peng, K. 'Attack against a batch zero-knowledge proof system', in IET Information Security, vol. 6, no. 1, pp. 1-5, March 2012. -

In the paper

“PoS is a consensus mechanism that requires less computational power than PoW, so it consumes less energy.”

In the paper

“Stellar Consensus Protocol (SCP) is a implementation of a consensus method called Federated Byzantine Agreement (FBA) [137]. It is similar to PBFT but, whilst in PBFT every node queries all the other nodes and waits for the majority to agree, in SCP the nodes only wait for a subset of the participants that they consider important.”

What the sources say

• Not checked yetcites [137] [137] Mazieres, D. 'The stellar consensus protocol: A federated model for internet-level consensus'. Available online: https://www.stellar.org/ papers/stellar-consensus-protocol.pdf (Accessed on 10 April 2018). -

In the paper

“Identity certification may also be a problem in IoT: if an identity provider is responsible for authorizing entities, it can also be able to block them.”

In the paper

“Such an approach is valid as long as the administrators of the centralized infrastructure are trusted and while the system remains robust against attacks [185], [186] and internal leaks.”

What the sources say

• Not checked yetcites [185] [185] Jabir, R. M., Khanji, S. I. R., Ahmad, L. A., Alfandi, O., Said, H. 'Analysis of cloud computing attacks and countermeasures', in Proceedings of the 18th International Conference on Advanced Communication Technology (ICACT), Pyeongchang, South Korea, 31 Jan.-3 Feb. 2016. -
• Not checked yetcites [186] [186] Atya, A. O. F., Qian, Z., Krishnamurthy, S. V., Porta, T. L., McDaniel, P., Marvel, L. 'Malicious co-residency on the cloud: Attacks and defense', in Proceedings of the IEEE Conference on Computer Communications, Atlanta, United States, 1-4 May 2017. -

In the paper

“Finally, it is worth noting that private blockchains, which control user access, reduce the probability of Sybil attacks, so they do not require costly mining algorithms and economic incentives are removed.”

In the paper

“In addition, delegates can adjust block size and intervals, and, if they behave dishonestly, they can be substituted easily.”

What the sources say

• Not checked yetcites [130] [130] DPOS description on Bitshares. Available on: http://docs.bitshares.org/ bitshares/dpos.html (Accessed on 10 April 2018) -

In the paper

“In the case of IoT applications, zeroknowledge proofs can be used for authentication or during regular transactions in order to avoid revealing the identity of a user or a device.”

What the sources say

• ?Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  cites [173] [173] Zerocoin official web page. Available online: http://zerocoin.org (Accessed on 10 April 2018). -
• ?Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  cites [174] [174] Zerocash official web page. Available online: http://zerocash-project.org (Accessed on 10 April 2018). -
• ?Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  cites [175] [175] Zcash official web page. Available online: https://z.cash (Accessed on 10 April 2018). -

In the paper

“Moreover, the mixing service has to be trusted, since a malicious mixer may expose users and, in the case of economic transactions, it may end up stealing coins.”

In the paper

“This means that anonymity is not guaranteed and, since all transactions are shared, it is possible for third-parties to analyze such transactions and infer the actual identities of the participants [159], [160].”

What the sources say

• Not checked yetcites [159] [159] Meiklejohn, S., Pomarole, M., Jordan, G., Levchenko, K., McCoy, D., Voelker, G. M., Savage, S. 'A fistful of bitcoins: Characterizing payments among men with no names', Communications of the ACM, vol. 59, no. 4, pp. 86-93, April 2016. -
• Not checked yetcites [160] [160] Möser, M., Böhme, R., Breuker, D. 'An inquiry into money laundering tools in the Bitcoin ecosystem', in Proceedings of the APWG eCrime Researchers Summit, San Francisco, United States, 17-18 Sep. 2013. -

In the paper

“These techniques increase privacy, but they are not perfect, since they may be de-anonymized through statistical disclosure attacks [170].”

What the sources say

• Not checked yetcites [170] [170] Danezis, G., Serjantov, A. 'Statistical Disclosure or Intersection Attacks on Anonymity Systems', in Proceedings of the 6th International Workshop on Information Hiding, Toronto, Canada, 23-25 May, 2004, pp. 293308. -

In the paper

“Thus, BFTRaft enhances the Raft algorithm by making it Byzantine fault tolerant and by increasing its security against diverse threats.”

What the sources say

• Not checked yetcites [138] [138] Copeland, C., Zhong, H. 'Tangaroa: A Byzantine fault tolerant raft', Available online: http://www.scs.stanford.edu/14au-cs244b/labs/ projects/copeland\_zhong.pdf (Accessed on 10 April 2018) -
• Not checked yetcites [139] [139] Ongaro, D., Ousterhout, J. 'In Search of an Understandable Consensus Algorithm', in Proceedings of USENIX Annual Technical Conference, Philadelphia, United States, 19-20 June, 2014. -

In the paper

“Transactions as Proof-of-Stake (TaPoS) [131] is a PoS variant. While in PoS systems only some nodes contribute to the consensus, in TaPoS all nodes that generate transactions contribute to the security of the network.”

What the sources say

• Not checked yetcites [131] [131] Larimer, D. 'Transactions as proof-of-stake'. Available online: https: //bravenewcoin.com/assets/Uploads/TransactionsAsProofOfStake10.pdf (Accessed on 10 April 2018) -

In the paper

“Proof-of-Activity (PoA) consensus algorithms were proposed due to the main limitation of PoS systems based on stake age: it is accumulated even when the node is not connected to the network. Thus, PoA schemes have been proposed to encourage both ownership and activity on the blockchain [132], rewarding stakeholders who participate instead of punishing passive stakeholders.”

What the sources say

• Not checked yetcites [132] [132] Bentov, I., Lee, C., Mizrahi, A., Rosenfeld, M. 'Proof of activity: Extending bitcoin's proof of work via proof of stake', in Proceedings of the <!-- image --> IEEEAccess - 9th Workshop on the Economics of Networks, Systems and Computation, Austin, United States, 16 June 2014. -

In the paper

“PBFT [135] is a consensus algorithm that solves the Byzantine Generals Problem for asynchronous environments.”

What the sources say

• Not checked yetcites [135] [135] Castro, M., Liskov, B. 'Practical Byzantine fault tolerance', in Proceedings of the Third Symposium on Operating Systems Design and Implementation, New Orleans, United States, Feb. 1999. -

In the paper

“According to some researchers [149] these updates can be performed by using a blockchain, which enables IoT devices to spread securely new firmware versions.”

What the sources say

• Not checked yetcites [149] [149] Boudguiga, A., Bouzerna, N., Granboulan, L., Olivereau, A., Quesnel, F., Roger, A., Sirdey, R. 'Towards Better Availability and Accountability for IoT Updates by Means of a Blockchain', in Proceedings of the IEEE European Symposium on Security and Privacy Workshops, Paris, France, 26-28 Apr. 2017. -

In the paper

“CryptoNote is a protocol that makes use of ring signatures and whose transactions cannot be followed through the blockchain in order to determine who performed them.”

What the sources say

• ?Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  cites [180] [180] CryptoNote's official web page. Available online: https://cryptonote.org (Accessed on 10 April 2018). -

In the paper

“In contrast, blockchain technologies are characterized by being decentralized, so, although one node is compromised, the global system should keep on working.”

In the paper

“Assuming the neutrality of the access controller, it is possible to reduce exposure by establishing an independent blockchain with every entity a user is collaborating with.”

In the paper

“Delegated Proof-of-Stake (DPoS) [130] is similar to PoS, but stakeholders instead of being the ones generating and validating blocks, they select certain delegates to do it. Since less nodes are involved in block validation, transactions are performed faster than with other schemes.”

What the sources say

• Not checked yetcites [130] [130] DPOS description on Bitshares. Available on: http://docs.bitshares.org/ bitshares/dpos.html (Accessed on 10 April 2018) -

In the paper

“The issue is even more problematic when adding a blockchain, since transactions are shared among peers, what in certain fields like industry or financial systems, allows for monitoring the activity of competitors.”

In the paper

“Sieve [140] is a consensus algorithm proposed by IBM Research that has already been implemented for Hyperledger-Fabric. Its objective is to run nondeterministic smart contracts on a permissioned blockchain that makes use of BFT replication.”

What the sources say

• Not checked yetcites [140] [140] Cachin, C., Schubert, S., Vukoli´ c, M. 'Non-determinism in Byzantine fault-tolerant replication', in Proceedings of the International Conference on Principles of Distributed Systems (OPODIS 2016), Madrid, Spain, 1316 Dec. 2016. -

In the paper

“Privacy is even more complex in IoT environments, since IoT devices can reveal private user data that could be stored in a blockchain whose privacy requirements differ from one country to another [161].”

What the sources say

• Not checked yetcites [161] [161] Fabiano, N. 'The Internet of Things ecosystem: The blockchain and privacy issues. The challenge for a global privacy standard', in Proceedings of the International Conference on Internet of Things for the Global Community (IoTGC), Funchal, Portugal, 10-13 July 2017, pp. 1-7. -

In the paper

“Bitcoin-NG [142] implements a variant of the Bitcoin consensus algorithm aimed at improving scalability, throughput and latency. The developers performed experiments with 1,000 nodes and concluded that BitcoinNG scales optimally, only limited by the bandwidth of the nodes and the latency related to the propagation time of the network.”

What the sources say

• Not checked yetcites [142] [142] Eyal, I., Gencer, A. E., Sirer, E. G., Van Renesse, R. 'Bitcoin-NG: A Scalable Blockchain Protocol', in Proceedings of the 13th USENIX Symposium on Networked Systems Design and Implementation, Santa Clara, United States, 16-18 Mar. 2016. -

In the paper

“For example, in the case of Bitcoin, block creation times follow a Poisson distribution with a 10-minute mean [18], although, for avoiding double-spend, merchants are recommended to wait for about an hour, since five or six blocks usually need to be added to the chain before the transaction is confirmed.”

What the sources say

• Not checked yetcites [18] [18] Nakamoto, S. 'Bitcoin: A Peer-to-Peer Electronic Cash System'. Available online: https://bitcoin.org/bitcoin.pdf (Accessed on 10 April 2018) -

In the paper

“Another interesting example is Primecoin [198], whose PoW mechanism looks for chains of prime numbers.”

What the sources say

• Not checked yetcites [198] [198] Primecoin's official web page. Available online: http://www.primecoin. org (Accessed on 10 April 2018) -

In the paper

“The most feared attack is a 51-percent attack (also called majority attack), where a single miner can control the whole blockchain and perform transactions at wish.”

In the paper

“PoS systems require users to show a legitimate interest in a specific service by allocating certain amount of memory or disk.”

In the paper

“For example, in the case of Bitcoin, block creation times follow a Poisson distribution with a 10-minute mean [18], although, for avoiding double-spend, merchants are recommended to wait for about an hour, since five or six blocks usually need to be added to the chain before the transaction is confirmed.”

What the sources say

• Not checked yetcites [18] [18] Nakamoto, S. 'Bitcoin: A Peer-to-Peer Electronic Cash System'. Available online: https://bitcoin.org/bitcoin.pdf (Accessed on 10 April 2018) -

In the paper

“For instance, VISA network (VisaNet) can handle up to 24,000 transactions per second [207].”

What the sources say

• Not checked yetcites [207] [207] VISA claims about the number of transactions handled by VisaNet. Available online: https://usa.visa.com/run-your-business/ small-business-tools/retail.html (Accessed on 10 April 2018) -

In the paper

“The third characteristic of security is availability, but it is actually the most straightforward to be fulfilled by blockchains, since they are conceived by design to be distributed systems, what allows them to keep on working even when some nodes are under attack.”

In the paper

“Obviously, this kind of attack also affects data integrity.”

In the paper

“To reduce the number of updates, mini-blokchains [201] may allow IoT nodes to interact directly with a blockchain, since they only keep the latest transactions and lower the computational requirements of a full node.”

What the sources say

• Not checked yetcites [201] [201] Bruce, J. D. 'The Mini-Blockchain Scheme'. Available online: https://www.weusecoins.com/assets/pdf/library/The\ %20Mini-Blockchain\%20Scheme.pdf (Accessed on 10 April 2018) -

In the paper

“Therefore, although many information sources indicate that blockchains are a permanent storage for data that cannot be altered, it is actually not true in practice for preserving integrity in very exceptional cases.”

In the paper

“Other consensus methods have been proposed to reduce energy consumption respect to PoW, like Proof-of-Stake or Practical Byzantine Fault Tolerance (both described in Section IV-D).”

In the paper

“In IoT applications, data integrity is also essential and it is usually provided by third-parties.”

In the paper

“Some initiatives based on blockchains, like Gridcoin [197], reward volunteer scientific research computing with coins (although, as a consensus algorithm, Gridcoin uses PoS).”

What the sources say

• Not checked yetcites [197] [197] Gridcoin's official web page. Available online: http://gridcoin.us (Accessed on 10 April 2018) -

In the paper

“Thus, a massive infrastructure like the one involved in IoT could also be harnessed to solve problems while making use of a blockchain.”

In the paper

“Other hashing algorithms have been suggested, like Blake-256 [204], and some blockchains are able to make use of different hashing algorithms (e.g., Myriad [205]), but further analyses should be carried out on the performance and optimization of modern hash functions to be used on IoT devices.”

What the sources say

• Not checked yetcites [204] [204] Aumasson, J.-P., Henzen, L., Meier, W., Phan, R. C.-W. 'SHA-3 Proposal BLAKE,submission to NIST'. Available online: http://131002.net/blake/ (accesed on 10 April 2018) -
• Not checked yetcites [205] [205] Myriad. Available online: http://myriadcoin.org (Accessed on 10 April 2018) -

In the paper

“Proof-of-Space (PoS) (also known as Proof-of-Capacity (PoC)) has also been suggested as a greener alternative to PoW [199].”

What the sources say

• Not checked yetcites [199] [199] Dziembowski, S., Faust, S., Kolmogorov, V., Pietrzak, K. 'Proofs of Space', in Proceedings of the 35th Annual Cryptology Conference on Advances in Cryptology, Santa Barbara, United States, 16-20 Aug. 2015, pp. 585-605. -

In the paper

“This mechanism has already been implemented by cryptocurrencies like Burst-coin [200].”

What the sources say

• Not checked yetcites [200] [200] Burst-coin official web page. Available online: https://www.burst-coin. org (Accessed on 10 April 2018) -

In the paper

“In terms of hashing algorithms, SHA-256 is the reference due to being the one used by Bitcoin, but new algorithms like Scrypt [202] or X11 [203] are faster and thus can reduce mining energy consumption.”

What the sources say

• Not checked yetcites [202] [202] Original Scrypt function for Tarsnap. Available online: http://www. tarsnap.com/scrypt.html (Accessed on 10 April 2018) -
• Not checked yetcites [203] [203] X11 official documentation for Dash. Available online: https://dashpay. atlassian.net/wiki/spaces/DOC/pages/1146918/X11 (Accessed on 10 April 2018) -

In the paper

“Specifically, Google's Certificate Transparency [189] provides a framework for monitoring and auditing SSL certificates in almost real time.”

What the sources say

• Not checked yetcites [189] [189] Google's Certificate Transparency official web page. Available online: https://www.certificate-transparency.org (Accessed on 10 April 2018). -

In the paper

“To avoid such a dependence, in [190] it is proposed a data integrity service framework for cloud-based IoT applications that makes use of blockchain technology, thus eliminating the need for trusting such third-parties.”

What the sources say

• Not checked yetcites [190] [190] Liu, B., Yu, X. L., Chen, S., Xu, X., Zhu, L. 'Blockchain Based Data Integrity Service Framework for IoT Data', in Proceedings of the IEEE International Conference on Web Services, Honolulu, United States, 2530 June 2017. -

In the paper

“In relation to the consensus latency, it can be stated that the complexity of the consensus process is more important in terms of latency than individual hashing, but different blockchains, like the one that supports Litecoin [34], have opted for using scrypt, a hashing algorithm that is slightly faster than SHA-256.”

What the sources say

• Not checked yetcites [34] [34] Litecoin official web page. Available online: https://litecoin.com (Accessed on 10 April 2018) -

In the paper

“Regarding mining, some authors suggested that the power consumed by proofs of work could be used for something useful while providing at the same time the required PoW [196].”

What the sources say

• Not checked yetcites [196] [196] Ball, M., Rosen, A., Sabin, M., Vasudevan, P. N. 'Proofs of Useful Work'. Available online: https://eprint.iacr.org/2017/203.pdf (Accessed on 10 April 2018) -

In the paper

“For instance, Bitcoin's blockchain has a theoretical maximum of 7 transactions per second [78], although it can be increased by processing larger blocks or by modifying certain aspects of the node behavior when accepting transactions [206].”

What the sources say

• Not checked yetcites [78] [78] Vukoli´ c, M. 'The Quest for Scalable Blockchain Fabric: Proof-ofWork vs. BFT Replication'. Available online: http://www.vukolic.com/ iNetSec\_2015.pdf (Accessed on 10 April 2018) -
• Not checked yetcites [206] [206] Courtois, N. T., Emirdag, P., Nagy, D. A. 'Could Bitcoin transactions be 100x faster?', in Proceedings of the11th International Conference on Security and Cryptography (SECRYPT), Vienna, Austria, 28-30 Aug. 2014. -

In the paper

“P2P communications require edge devices that have to be powered on continuously, which could lead to waste energy [191], [192].”

What the sources say

• Not checked yetcites [191] [191] Zhou, Z., Xie, M., Zhu, T., Xu, W., Yi, P., Huang, Z., Zhang, Q., Xiao, S. 'EEP2P: An energy-efficient and economy-efficient P2P network protocol', in Proceedings of the International Green Computing Conference, Dallas, United States, 3-5 Nov. 2014. - source
• Not checked yetcites [192] [192] Sharifi, L., Rameshan, N., Freitag, F., Veiga, L. 'Energy Efficiency Dilemma: P2P-cloud vs. Datacenter', in Proceedings of the IEEE 6th International Conference on Cloud Computing Technology and Science, Singapore, Singapore, 15-18 Dec. 2014. - source

In the paper

“An interesting initiative related to this topic is CONIKS [187], a key management system created to liberate users from encryption key management.”

What the sources say

• Not checked yetcites [187] [187] CONIKS official web page. Available online: https://coniks.cs.princeton. edu (Accessed on 10 April 2018). -

In the paper

“In relation to P2P communications, they are essential for a blockchain to communicate peers and distribute blocks, so the more updates a blockchain receives, the more energy consumption is dedicated to communications.”

In the paper

“Some researchers proposed energy efficient protocols for P2P networks [193]-[195], but the issue still has to be studied further for the specific case of IoT networks.”

What the sources say

• Not checked yetcites [193]-[195]

In the paper

“The solution uses a distributed system based on Merkle hash trees that allows third-parties to audit and verify whether a certificate is valid.”

What the sources say

• Not checked yetcites [189] [189] Google's Certificate Transparency official web page. Available online: https://www.certificate-transparency.org (Accessed on 10 April 2018). -

In the paper

“In this situation, data are available, but the availability for performing transactions can be blocked by the attacker that controls the blockchain.”

In the paper

“IoT deployments may require a blockchain network able to manage large amounts of transactions per time unit. This is a limitation in certain networks.”

In the paper

“For an individual user, the key for maintaining confidentiality is a good management of his/her private keys, since it is what an attacker needs in conjunction with the public key to impersonate someone or steal something from him/her.”

In the paper

“Such a kind of blockchain introduces the use of an account tree, which stores the current state of every user of the blockchain. Thus, only the most recent transaction has to be stored on the blockchain together with the account tree. Therefore, the blockchain only grows when new users are added to the blockchain.”

What the sources say

• ?Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  cites [183] [183] França, B. F. 'Homomorphic Mini-blockchain Scheme', April 2015. Available online: http://cryptonite.info/files/HMBC.pdf (Accessed on 10 April 2018) -
• ?Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  cites [201] [201] Bruce, J. D. 'The Mini-Blockchain Scheme'. Available online: https://www.weusecoins.com/assets/pdf/library/The\ %20Mini-Blockchain\%20Scheme.pdf (Accessed on 10 April 2018) -

In the paper

“Blockchains can be forked for administrative or versioning purposes. Once a blockchain is forked, it is not easy to carry out transactions between both chains.”

In the paper

“For instance, authentication across multiple authorities or organizations requires Federated Identity Management (FIM) [209].”

What the sources say

• Not checked yetcites [209] [209] Birrell, E., Schneider, F. B. 'Federated Identity Management Systems: A Privacy-Based Characterization', in IEEE Security & Privacy, vol. 11, no. 5, pp. 36-48, Sept.-Oct. 2013. <!-- image --> TIAGO M. FERNÁNDEZ-CARAMÉS (S'08M'12-SM'15) received his MSc degree and PhD degrees in Computer Science in 2005 and 2011 from University of A Coruña, Spain. Since 2005 he has worked as a researcher and professor for the Department of Computer Engineering of the University of A Coruña inside the Group of Electronic Technology and Communications (GTEC). His current research interests include IoT syste

In the paper

“This can also happen in an IoT scenario, where, for instance, sensor values may be stored in a private blockchain, while financial transactions among nodes that provide services may be supported by Ethereum's or Bitcoin's blockchain.”

In the paper

“However, this approach requires the existence in the IoT hierarchy of certain powerful nodes that would maintain the blockchain for the resource-constrained nodes, what implies a certain degree of data centralization.”

In the paper

“In this ecosystem, blockchain can offer to IoT a platform for distributing trusted information that defy non-collaborative organizational structures.”

In the paper

“In addition, note that the value and security of a blockchain increases with the number of users, also being more difficult to perform the feared 51-percent attacks.”

In the paper

“We can conclude that BIoT is still in its nascent stage, and beyond the earliest BIoT developments and deployments, broader use will require additional technological research advances to address the specific demands, together with the collaboration of organizations and governments.”

In the paper

“Moreover, note that miner adoption rate also influences the capacity of a network to process transactions, so, in a BIoT deployment, the computational power brought by miners should be high enough to handle the transactions received from the IoT devices.”

In the paper

“The adoption of collaborative implementations and the use of international standards for collaborative trust and information protection (i.e., access control, authentication and authorization) will be needed.”

In the paper

“For instance, miners have evolved from simple CPUbased systems, to more sophisticated equipment that harnesses the power of Graphics Processing Units (GPUs), Field-Programmable Gate Arrays (FPGAs) or ApplicationSpecific Integrated Circuits (ASICs) [208].”

What the sources say

• Not checked yetcites [208] [208] Bedford Taylor, M. 'The Evolution of Bitcoin Hardware' in Computer, vol. 50, no. 9, pp. 58-66, 22 Sep. 2017. -

In the paper

“Legal rules have still to be developed to enforce smart contracts and resolve disputes properly.”

In the paper

“Many state-of-the-art approaches that address issues such as trust depend on inter-domain policies and control.”

In the paper

“Thus, higher LoAs will be needed.”

In the paper

“Despite the promising benefits and the brilliant foreseen future of BIoT, there are significant challenges in the development and deployment of existing and planned systems that will need further investigation:”

In the paper

“Blockchains grow periodically as users store their transactions, what derives into larger initial download times and in having to make use of more powerful miners with larger persistent memories.”

In the paper

“This issue could be avoided by using lightweight nodes, which are able to perform transactions on the blockchain, but who do not have to store it.”

In the paper

“We can conclude that, as in any technological innovation, there is no one-size-fits-all solution for a BIoT application.”

In the paper

“The required LoA (from LoA 1 to LoA 4), as defined by the ISO/IEC 29115:2013 standard, is mainly based on risks, on the consequences of an authentication error and/or the misuse of credentials, on the resultant impact, and on their likelihood of occurrence.”

What the sources say

• Not checked yetcites ISO/IEC 29115:2013

In the paper

“These BIoT scenarios face specific technical requirements that differ from implementations involving cryptocurrencies in several aspects like energy efficiency in resource-constrained devices or the need for a specific architecture.”

In the paper

“Nevertheless, the adoption of the paradigm opens a wide area of short- and medium-term potential applications that could disrupt the industry and probably, the economy, as we know it today.”

In the paper

“Governments may demand a strong link between real-world and online identity. Moreover, since IoT transactions can be carried out internationally, it may not be clear who should perform the identification.”

In the paper

“Blockchain infrastructure: it will be needed to create a comprehensive trust framework or infrastructure that can fulfill all the requirements for the use of blockchain in IoT systems.”

In the paper

“For instance, it is possible that some developers fake their blockchain performance in order to attract investors driven by the expected profits.”

In the paper

“In addition, note that transaction and block size have to be scaled according to the bandwidth limitations of IoT networks: many small transactions would increase the energy consumption associated with communications, while a few large ones may involve big payloads that cannot be handled by some IoT devices.”

In the paper

“Regarding the infrastructure, certain elements are required to make the blockchain work properly, including decentralized storage, communication protocols, mining hardware, address management or network administration.”

In the paper

“This issue can happen when the number of conspiring miners are above 51 percent of the total, so small chains and blockchains that delegate their decisions on a subset of miners are susceptible to this kind of boycotts.”

In the paper

“Miners end up deciding which transactions are or are not stored in the blockchain, so they are able to censor certain transactions for economic or ideological reasons.”

In the paper

“Part of these needs are being fulfilled by the industry progressively, creating specific equipment for blockchain applications.”

In the paper

“Moreover, blockchain technologies face design limitations in transaction capacity, in validation protocols or in the implementation of smart contracts.”

In the paper

“We can conclude that BIoT is still in its nascent stage, and beyond the earliest BIoT developments and deployments, broader use will require additional technological research advances to address the specific demands, together with the collaboration of organizations and governments.”

In the paper

“In some cases, the proliferation of blockchains has derived into the necessity of having to deal with several of them at the same time.”

In the paper

“Organizational, governance, regulatory and legal aspects: besides technological challenges, shaping the regulatory environment (i.e., decentralized ownership, international jurisdiction) is one the biggest issues to unlock the potential value of BIoT.”

In the paper

“Complex technical challenges: there are still issues to be addressed regarding the scalability, security, cryptographic development and stability requirements of novel BIoT applications.”

In the paper

“Interoperability and standardization: the adoption of BIoT will require the compromise of all stakeholders in order to achieve full interoperability (i.e., from data to policy interoperability) and integration with legacy systems.”