Cryptocurrency Solutions to Enable Micro-payments in Consumer IoT
CCryptocurrency Solutions to EnableMicro-payments in Consumer IoT
Suat Mercan ∗ , Ahmet Kurt ∗ , Enes Erdin † , and Kemal Akkaya ∗∗ Dept. of Elec. and Comp. Engineering, Florida International University, Miami, FL 33174Email: { smercan,akurt005,kakkaya } @fiu.edu † Department of Computer Science, University of Central Arkansas, Conway, AR 72035Email: [email protected]
Abstract —The successful amalgamation of cryptocurrency andconsumer Internet of Things (IoT) devices can pave the wayfor novel applications in machine-to-machine economy. However,the lack of scalability and heavy resource requirements of initialblockchain designs hinders the integration as they prioritizeddecentralization and security. Numerous solutions have beenproposed since the emergence of Bitcoin to achieve this goal. How-ever, none of them seem to dominate and thus it is unclear howconsumer devices will be adapting these approaches. Therefore, inthis paper, we critically review the existing integration approachesand cryptocurrency designs that strive to enable micro-paymentsamong consumer devices. We identify and discuss solutionsunder three main categories; direct integration , payment channelnetwork and new cryptocurrency design . The first approachutilizes a full node to interact with the payment system. Offlinechannel payment is suggested as a second layer solution tosolve the scalability issue and enable instant payment with lowfee. New designs converge to semi-centralized scheme and focuson lightweight consensus protocol that does not require highcomputation power which might mean loosening the initial designchoices in favor of scalability. We evaluate the pros and cons ofeach of these approaches and then point out future researchchallenges. Our goal is to help researchers and practitioners tobetter focus their efforts to facilitate micro-payment adoptions. Index Terms —Cryptocurrency, Internet of Things, Machine-to-machine economy, Micro-transaction
I. I
NTRODUCTION
Internet of Things (IoT) from tiny sensors to autonomouscars are becoming an indispensable part of life. To create abuoyant and effective IoT ecosystem, it is significant to enabledata and service sharing which, in turn, will require makingdevice-to-device payments to the provider for the services suchas parking, vehicle charging, sensor data sale, internet sharing,vending machine among others [1]. Since this ecosystem willbe dependent on financial micro-transactions among digitalobjects/devices, a reliable payment system without humanintervention is desirable for a seamless experience. As IoTevolves over time, cryptocurrency can play a critical roleby serving as digital money in creating such an ecosys-tem. The successful integration of IoT and cryptocurrencytechnologies will foster the revolution by introducing novelconsumer applications such as enhanced shopping experiencefor consumers, automated payment among sensing devices,programmable financial transactions for electric vehicles ordrones, etc. Nevertheless, this brings many new challenges tobe tackled to create an environment that buyers and sellers can perform frictionless transactions in an IoT environment.Most of these challenges stem from the way the current dis-tributed ledger based cryptocurrencies are designed [2]. Theirdesign is not feasible to create a machine-to-machine economyfor enabling micro-payments due to a number of reasons: 1)
Scalability as they have limited performance in number oftransactions they can handle in a second. For instance, thetheoretical maximum throughtput in Bitcoin is calculated to be7 transactions per second which is far lower than what Visa orMasterCard can process; 2)
High transaction fees , which is notattractive for micropayments, and; 3)
Long block confirmationtimes as it takes 10 minutes to approve a block of transactionsfor Bitcoin. In addition, there are other major challenges due tothe limitations of the IoT devices. Despite the heterogeneity,IoT devices are characterized as small lightweight devices,they are mostly resource constrained and most of them arenot be capable of running a full node (e.g., 250 GB storageis required for running a full Bitcoin node). Robust Internetconnection and high computation power are also required toreceive and verify new blocks. Therefore, lightweight solutionsare needed to enable resource-constrained IoT devices toutilize cryptocurrencies. To this end, recent years witnessedseveral efforts from the research community to offer solutionsto this emerging problem. However, there seems to be noconvergence among these solutions to offer a clear path forthe benefit of consumers.Therefore, in this paper, we critically review the solutionsthat aim to integrate IoT with existing cryptocurrencies andvarious designs that claim to be IoT friendly. Our goal is tocome up with a guideline to be able to assess the benefitsand impact of existing solutions. We basically classify theapproaches that we find promising and useful to remedy someof the aforementioned problems into three categories: The firstcategory applies direct integration through a trusted gatewayin order to connect IoT devices to the cryptocurrency network.This does not solve blockchain’s inheriting problems such asscalability but it helps to connect resource constrained IoTdevices to the network. Second category introduced
PaymentChannel Networks (PCN) , known as a second layer solution,which address specifically the scalability issue by allowinginfinite number of off-chain instant transactions among thenodes with minimal fee. Finally, under the third category,new designs are explored among which
Directed Acyclic a r X i v : . [ c s . CR ] F e b onsumerElectronics AutomotiveResourceSharingInternet Service &Product Contentpurchase Healthcare Fig. 1: Machine-to-Machine Economy.
Graph (DAG) has emerged as an alternative structure to theblockchain. It still holds the idea of distributed structure ina different manner which is a web of confirmation, tangle,instead of a single blockchain. After we provide a summaryof these solutions, we make an evaluation of them consideringsome qualitative metrics. We discuss which of them could bemore appropriate depending on the application. Finally, weprovide some future research challenges that need to be tackledfor successful deployment of these approaches.The remainder of this paper is organized as follows: Sec-tion II gives preliminaries. In Section III, we present directintegration approaches while Section IV explains PaymentChannel Network related works. Section V explores variouscryptocurrency proposals traded in the market and Section VIpresents the evaluation. Section VII concludes the paper.II. P
RELIMINARIES
Basics and Applications:
IoT are utilized in many domainsto sense and collect data. In the last few years, they becomestandard consumer electronics like TVs to be used in homesand cities for smart sensing and control. This created use-caseswhere these devices would offer services that can be consumedby other devices in return for cash. For instance, consumerelectronics in a futuristic smart home may shop independently(e.g., a washing machine can order detergent automatically, thefridge may request refill for milk etc.) An electric autonomousvehicle may pay tolls and also sell its LIDAR data to nearbyvehicles. A smart water machine at home can order refills.A drone may sell its video and people may be incentivizedthrough their smart phones to share their resources, such ascomputation power, data, charge, internet which may requirereceiving payments from the providers. As a real use case,RightMesh [3] is using microRaiden cryptocurrency to createa mesh network in which participants pay to others. Most ofthe smart city applications such as electric vehicle charging,sensor data selling will also benefit from this integration. Allthese examples point out to a future where we will witnessmachine-to-machine (M2M) economy as depicted in Fig. 1. In such an economy, the main feature will be decentralization of payments to have a self managed system without relying ortrusting on third parties and dealing with their management.In this sense, cryptocurrencies offer great potential as theyrely on distributed ledger technologies providing decentralizedmanagement of cash without trusting any third parties. Startingwith Bitcoin in 2009, many new cryptocurrencies are currentlyin use that deploy variations of blockchain technologies. Asuccessful integration of IoT and cryptocurrency will enableand boost various innovative applications, which in turn bringconvenience and efficiency in our lives. However, this raisesseveral challenges as detailed next.
Desirable Features for IoT Cryptocurrencies:
An IoTecosystem consisting of many devices interacting with eachother generates tremendous number of transactions, and thusrequires a high throughput. However, most of the cryptocur-rency systems including Bitcoin and Ethereum are not scal-able . Consequently, limited number of transactions and highdemand increase the fee which could be much greater thanactual amount being sent in a micro-payment scenario. Ideally,this should be reasonable, close to zero, for the success ofa M2M economy. The time required for the approval of atransaction (i.e., speed ,) is another desirable feature, whichshould be real-time for a frictionless implementation. Finally,the solutions should be lightweight in terms of computationand storage requirement to be able to run on an IoT device asthese devices are mostly resource-constrained.
CryptocurrencySolutions for M2MDirect Integration Payment ChannelNetworks NewCryptocurrencyDesign
Fig. 2: Solution Classifications.
Solution Classification:
We divide the efforts into three broadlasses to address the above issues: 1) Direct Integration; 2)PCNs and 3) IoT Cryptocurrencies (Fig. 2) as detailed next.III. D
IRECT I NTEGRATION TO E XISTING C OINS
Integration of IoT to existing major coins such as Bitcoinand Ethereum is achieved either using a gateway or light client:
A. Gateway-based Integration
In this integration scheme, the IoT device does not run ablockchain node, but relies on another node as shown in Fig. 3which should be operated by the same owner or a trusted thirdparty. IoT devices are registered to the gateway which issuestransactions on behalf of them. The communication betweenIoT and the gateway can be achieved via any protocol suchas Wi-Fi, Bluetooth, LoRa etc. For instance, Bitcoin clientAPI (BCCAPI) is designed for such a purpose. The serverholds only public key of the client and tracks the client’swallet balance. However, it requires client’s consent to make atransaction. Ozyilmaz et al. [4] exemplifies this concept withEthereum and LPWAN. Gateway based integration method isutilized by some popular ledgers such as Hyperledger to enableIoT devices to input their data into the system through a peer.The communication between the device and the gateway mustbe secured using cryptographic techniques. Any corruptionthat may happen during transmission or on the device willnot be detected by the blockchain.
Full Node
Ledger
Fig. 3: A trusted node is utilized to connect to blockchain.
B. Light Clients
Another method that has been proposed for IoT devicesto communicate with heavy weight blockchains is by usinga light client . While full nodes store the whole blockchainto verify the integrity of the blocks, these clients do notneed to so. For example in Bitcoin, they can still verify theaccuracy of a transaction using a method called
SimplifiedPayment Verification (SPV) by using only the headers of theblocks which are requested from an untrusted full node. Ablock header has the hash of all the transactions in that blockand very small in size compared to the real block. Using theMerkle tree structures, it is checked whether the transactionis included in the block header or not. Some of the popularlight clients are Electrum, BitPay and Geth.While light clients can help mainstream adoption, they stillrelies on the existence of other full nodes. They might alsosuffer from security and privacy issues. For instance, BIP37 protocol, being used to create lightclients, was exploited tomake DDoS attacks on full nodes. Even further, Electrum lightclient was hacked and resulted in financial loss of the users[5]. To fix these issues, a new light client protocol, namelyBIP157/158 was proposed. In this scheme, in addition the theblock headers, block filters are used which helps anonymizethe requesting client from the full node.IV. P
AYMENT C HANNEL N ETWORKS
PCN (also known as off-chain transaction network) conceptis a promising solution to solve scalability and latency prob-lems of major blockchains. Thus, it has received great attentionfrom the research community. Lightning Network (LN) [6] forBitcoin and Raiden for Ethereum are two prominent examplesto this concept. The idea is leveraging smart-contracts to avoidbroadcasting every transaction to the Blockchain. Instead, thetransactions are recorded off-chain (Fig. 4) until the accountsare reconciled. Off-chain mechanism brings a huge advantagesince the peers do not need to publish every transactionto the blockchain. That is, the payments are theoreticallyinstantaneous. Moreover, as there is no need for frequenton-chain transactions, the transaction fees are protected fromfluctuating compared to highly variant on-chain fees. In fact,a transaction fee can be 0 (zero) if the peers agree so. Inthis aspect, PCN is an attractive solution to use in M2Minteractions.When many nodes come together, the off-chain transactionchannels turn into a network of payment channels. Insteadof opening a direct channel, a peer makes use of an alreadyestablished channel to forward money over existing nodes bypaying a transaction fee as long as a path exists from the payerto the payee. Multi-hop payment scheme also helps users tosave on fees when they want to make a payment to someonerather than establishing direct new channel as opening andclosing channels incur on-chain Bitcoin transaction fees.
ABA B Create multi-sig wallet onchain
Initial state offchain
A sends 50 to B. offchain
A sends 50 to B.A is out of fund. offchain
B sends 70 to A. offchain
Final amounts are distributed. onchain
Fig. 4: Off-chain transactions are fast.Currently the LN is the most widely used off-chain cryp-ocurrency payment network which was deployed in 2017 ontoBitcoin mainnet. It has 13,504 nodes and 37,093 channelsat the time of writing of this paper. In its current form, LNachieves almost real-time Bitcoin transactions with negligiblefees. However, running LN software requires running a Bitcoinclient since LN acts as an overlay network on top of Bitcoin.Current Bitcoin blockchain is not suitable for an IoT device tostore. Additionally, each newly added block has to be verifiedby the CPU which will be computationally very expensive foran IoT device. Thus new techniques are required to enable IoTdevice & payment channel integration. We investigate some ofworks on this topic below:
Ptarmigan [7] is an implementation of the LN protocolspecific to the IoT devices. It is designed and developed withthis purpose in mind; to enable light hardware to run thefull LN protocol natively as well as still complying withthe Basis of Lightning Technology (BOLT) specifications.All LN implementations follow the BOLT specifications toenable compatibility between different LN implementations.The mainnet version of Ptarmigan went live in 2019, however,it is still at experimental stage.
Neutrino [8] is another Bitcoin light client implementationspecifically designed for LN. It works based on synchroniz-ing only the block headers and filters instead of the wholeblockchain. These filters use Golomb-Rice coding which rep-resent the addresses inside a block and they are much moresmaller in size compared to the block headers. Even thoughsome IoT devices might have enough resources to run suchlight clients, they still have to remain online to synchronizethe block headers and filters.A different approach was proposed in [9] through a proto-col that enables IoT devices to open and maintain paymentchannels with traditional Bitcoin nodes without a view ofthe blockchain. In this scheme, there are two untrusted thirdparties which are called
IoT payment gateway and watchdog respectively. IoT payment gateway posts the transactions tothe blockchain by creating an additional output. Since there isa chance that IoT payment gateway can post a revoked state tothe blockchain, a watchdog is used to inform the IoT devicewhen such thing happens. Both the IoT payment gateway andthe watchdog is economically incentivized for their services.Another proposed protocol is ticket-based verification proto-col (TBVP) [10]. In their protocol, the authors introduce twoentities which are called contract manager (CM) and trans-action verifier (TV) . Their motivation for introducing thesetwo entities is to separate the blockchain-related operationsfrom blockchain-agnostic operations which are handled by CMand TV respectively. Blockchain-related operations includesetting up a smart contract, moving money into the contract,sending commit messages (verified promises) to the contract,closing the contract and claiming the funds. Blockchain-agnostic operations include receiving a commit message froma partner and validating that message. Each IoT device has aCM and TV. The authors assume every IoT device will workwith a separate trusted gateway and these gateways will talkto each other for transactions. Different than light clients and protocols, the authors of[11] proposes a module to integrate LN into an existing IoTecosystem. In their design, each entity has their own LN noderunning as part of the system. Once the payment is performed,data provider release the data to the consumer. The proposedsystem does the integration by decoupling the IoT and LNnode and defining the communication API between them.Authors integrated LN into their IoT ecosystem through apayment module that they called
LN module which consistsof a Bitcoin node, an LN node, web-service and web UI.The role of LN module is to create channels between dataconsumers and owners as well as routing of payments anddata. This approach assumes that Bitcoin wallets are hold bythe third parties in the IoT marketplace which raises privacyand reliability concerns.V. I O T C
RYPTOCURRENCY P ROPOSALS
In this section, we explore various DLT-based coins, asshown in Table I, traded in the cryptocurrency market andpresent themselves as IoT compatible solutions.TABLE I: IoT Coin Proposals.
Network Type Structure Consensus Additional InfoIOTA
Semi-centralized DAG PoW MCMC
Nano
Semi-centralized DAG ORV Nlock-lattice
IoTeX
Semi-centralized blockchain Roll-DPOS hierarchical
ITC
Decentralized blockchain PBFT Hardware-based
Walton
Semi-centralized blockchain PoC Hardware-based
IOTA : IOTA [12] is one of the first coins adopted DAG asan alternative to single blockchain structure. It is consideredhighly scalable, near-instant and low-fee cryptocurrency witha focus on micro-payments in IoT universe. The idea,
Tangle ,aims to improve the scalability by enabling parallel transactionapproval. Block concept which contains multiple transactionsas in blockchains does not exist, but each transaction is con-nected to two previous transaction by the confirmation whichcreates a web of connections. Each vertex in Fig. 5 representsa transaction which should validate two previous transactions.Whenever someone wants to add a transaction, s/he shouldvalidate two others by selecting according to Markov ChainMonte Carlo (MCMC) algorithm. Thus, transactions issuer areat the same time approvers. Once a transaction is referred byenough number of transactions, it is considered that the systemhas reached agreement on this record. That is, consensus isbased on cumulative PoW of stacked transactions. The systemdoes not have specific miners because users confirms eachother, thus the transactions are feeless. The IOTA node stillneeds to find a nonce for PoW which is much lighter thanBitcoin and thus this makes it scalable and cost efficient. Itmay take several minutes for a transaction to get approved.The ledger is completely transparent, thus transactions arenot private. The current definition of IOTA requires that atransaction must be directly or indirectly signed by the coordi-nator node, then it is assumed 100% confirmed. The existenceof coordinator ensures the security of the transactions while onfirmed Unconfirmed Tip
Fig. 5: Directed Acyclic Graph for IOTA.the system converges to centralized approach and might bevulnerable to failures [13].IOTA is not the only coin that utilizes DAG, it has beenadopted in various forms. The approach is criticized in generalby blockchain supporters as it does not rely on heavy hash-based PoW. However, proponents view this feature as asolution to post-quantum threats [13].
Nano:
This is also known as
RaiBlocks [14] adopting DAGapproach. It aims to be a high-performance cryptocurrency thatcan run on low-power hardware. The ledger design is based onindividual accounts each of which has their own blockchain.The global ledger consists of these individual chains called block lattice in the form of DAG. An account is representedby public portion of a public/private key pair. Transactions aresigned by private key of the account holder to confirm that thecontent is generated by the user. A transfer from one accountto another requires creating two blocks; send and receive . Theformer one debits the sender’s account as the latter credits thereceiver account. Once a sending transactions is confirmed,it can not be reversed. Nano adopts a consensus mechanism,
Open Representative Voting , which is delegation based andbalance-weighted vote mechanism, a variant of DelegatedProof-of-Stake. Account owners select a delegate to vote onbehalf of him and can change it any time. The weight of thevoter is proportional to the sum of investment of the users whodelegated to him. As the votes of principal representatives arebroadcast and counted, a transaction which has enough votewill be counted as confirmed. Hardware requirements of sucha node is 4GB RAM, 200 Mbps bandwidth with 80GB+ offree space. So, IoT devices rely on principal nodes in termsof system consistency whose success depends on the existenceof enough number of nodes.
IoTeX:
This approach positions itself as IoT-oriented,privacy-centric and scalability maximizing [15]. It proposesa model called ”seperation of duties” by creating sub-blockchains in order to make it manageable in size. Eachnode interacts only with a specific group and each groupmay have its own features which optimizes different prioritiesas IoT devices also differ in capacity. Each blockchain maycontact another one through root blockchain as shown in Fig.6. Rootchain is public while sub-chains may be public orprivate. The insight behind the idea of allowing heterogeneous sub-blockchains is the fact that the requirements of variousapplication domains is different as there is no solution thatsatisfies all. Thus, they may be optimized towards differentdirections. Moreover, hosting all IoT devices in one blockchainwill make it grow fast which might impact the performance.The rootchain has three main functionalities, relay of valueand data accross subchains, supervision of subchains and settlement of payments. The rootchain proposes RandomizedDelegated Proof-of-Stake (Roll-DPoS), which is the combina-tion of Verifiable Random Function (VRF), DPoS and PracticalByzantine Fault Tolerance (PBFT). Participants of the networkvote to elect candidates which will be in the committee for aperiod of time. VRF is fed with the hash of previous blockand node’s private key, then others can verify the committeemembers using their public keys. In each round, committeemembers propose blocks which are voted based on PBFT andadded to the chain if approved.
Rootchainsubchain subchainsubchain c r o s s c h a i n VRF + PBFTsubchain subchain
Fig. 6: Rootchain and subchains.
ITC : IoT Chain (ITC) [16] is another DAG-based currencydesigned as a lite operating system. It aims at creating asecure communication environment as well as asset transfer.All nodes are considered equal, so decentralized approach istargeted which protects privacy. It adopts PBFT and SimplifiedVerification Protocol (SPV), which allows to verify transac-tions by using headers only, to address the size expansionproblem. The developers aims designing specific chips em-bedded with security credentials which means devices joiningthe system mush have a built-in ITC.
Walton Chain:
This approach [17] focuses on data re-liability with tamper-proof devices. It proposes a hardware-based and hierarchical blockchain. The intuition behind usinghardware-based solution is that software solutions are vulner-able to compromises. It aims to ensure data authenticity asBlockchain can guarantee the data integrity after it has beenrecorded. They have a chip design embedded with securitycredentials and compatible with various communication proto-cols. It uses Waltonchain Proof-of-Contribution (WPoC) whichis defined as the combination of PoW, PoS and Proof-of-Labor(PoL). First two is used on the parent chain as the PoL isdefined to perform coin exchange between child chains.VI. Q
UALITATIVE E VALUATION
In this section, we evaluate and compare the three categoriesof solutions by using some qualitative metrics as shownn Table II. We picked the following metrics:
Transactionper second (TPS) is the total number of transactions thatthe system can confirm which is the major issue that earlydesigns suffer because of PoW and limited blocksize. PCNhas substantially solved this problem as new designs mostlyfocus on this and made some improvements.
Transaction fee metric indicates the amount charged to the sender for thetransaction. Direct integration based approach does not impactthe original fee (charged by Bitcoin), thus it is high, whilePCN enables very low fee. New coins are designed mostlyto provide feeless transactions by using alternative PoW andeliminating mining.
Confirmation time refers to the total timeto get transaction validated. As seen, PCNs and new coins offerfaster speed as they address the slower transaction times ofexisting coins.
Security is related to the prevention of double-spending and robustness of chain to various attacks. As Bitcoinand Ethereum are highly secure, implementation of integrationprotocol will determine the security level. PCN (i.e., LN) hasbeen investigated deeply in last years, and it is perceived asecure design based on HTLC. Newly designed coins havenot been able to establish trust yet. As the general approachis converging to semi-centralized structure, they are criticizedfor being less secure.
Privacy is defined as the anonymityof sender and receiver information. Bitcoin and Ethereumare not privacy preserving as the transactions are transparent.Moreover the approaches that apply gateway integration mayalso let the gateway to observe the transactions. PCN providesprivacy by using onion type routing.TABLE II: Comparison of Approaches.
Direct PCN NewIntegration Based CoinsTPS ∞ > Transaction ≈ $10 < $0.01 $0 FeeConfirmation
10 min 1-5 sec 1 min
Time for Bitcoin
Security
High High Vary
Privacy
Low High Vary
When all the solution types are considered, direct inte-gration allows to use major cryptocurrencies by inheritingthe features of used coins, which means that it will notchange their negative sides. Thus, it will not help to createa transaction-intensive M2M economy, but it may still beuseful for some scenarios. Although new cryptocurrenciesbring promising designs, they have not been tested enough,thus there is no consensus on adopting any of them yet.Among them, IOTA prevails over others as it improves thecrucial metrics with its alternative design. However, it stillneeds to be improved to lower confirmation times. At thisstage, PCNs with light client and other integration methodsmight be the best solution as they offer all the features of newcoins in addition to being secure and operable with Bitcoinetc. Although they have not been perfected yet, they promisegreat potential with their second layer architecture. VII. C
ONCLUSION
In this paper, we aimed to shed light on IoT and cryptocur-rency integration that can foster M2M economy. We reviewedand discussed existing solutions under three broad categories; direct integration is utilizing a gateway to communicate withblockchain, payment channel networks is an effective methodto increase number of transactions and lower the fee and
IoT cyrptocurrency designs are mainly focusing on novelPoW algorithms that requires less computation resources. Wethen evaluated these approaches by comparing using variousmetrics.The interest in cryptocurrency from formal institutions andgovernments and wide adoption of IoT towards smartizationwill accelerate the efforts for IoT and cryptocurrency amalga-mation. In this sense, since the altcoins have not establishedenough trust, the efforts to integrate Bitcoin and Ethereum toIoT will continue. While the direct integration does not solvethe fundamental scalability issue, it can still be feasible forsome scenarios. However, novel approaches such as delagatedand randomized confirmation models, secure and lightweightconsensus algorithms will be investigated in more detail bythe community until there is a convergence. The authorsof this article considers PCN as a promising solution toparticular problem of IoT and cryptocurrency integration asit allows instant and limitless transaction. However, it is notIoT compatible in terms of resource requirement. Thus, webelieve that some cryptographic methods such as thresholdsignature, proxy-encryption should be investigated to achievea secure integration to Lightning Network.Rare mainly focusing on novelPoW algorithms that requires less computation resources. Wethen evaluated these approaches by comparing using variousmetrics.The interest in cryptocurrency from formal institutions andgovernments and wide adoption of IoT towards smartizationwill accelerate the efforts for IoT and cryptocurrency amalga-mation. In this sense, since the altcoins have not establishedenough trust, the efforts to integrate Bitcoin and Ethereum toIoT will continue. While the direct integration does not solvethe fundamental scalability issue, it can still be feasible forsome scenarios. However, novel approaches such as delagatedand randomized confirmation models, secure and lightweightconsensus algorithms will be investigated in more detail bythe community until there is a convergence. The authorsof this article considers PCN as a promising solution toparticular problem of IoT and cryptocurrency integration asit allows instant and limitless transaction. However, it is notIoT compatible in terms of resource requirement. Thus, webelieve that some cryptographic methods such as thresholdsignature, proxy-encryption should be investigated to achievea secure integration to Lightning Network.R