To receive news and publication updates for Mobile Information Systems, enter your email address in the box below. This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. P2P networks are the mechanism used by cryptocurrencies to disseminate system information while keeping the whole system as much decentralized as possible.
Cryptocurrency P2P networks have new characteristics that propose new challenges and avoid some problems of existing P2P networks. By characterizing the most relevant cryptocurrency network, Bitcoin, we provide details on different properties of cryptocurrency networks and their similarities and differences with standard P2P network paradigms.
Our study allows us to conclude that cryptocurrency networks present a new paradigm of P2P networks due to the mechanisms they use to achieve high resilience and security. With this dogecoin wallet peers connected ed paradigm, interesting research lines can be further developed, both in the focused field of P2P cryptocurrency networks and also when such networks are combined with other distributed scenarios.
Sincewhen the Bitcoin cryptocurrency [ 1 ] was released, a plethora of more than different cryptocurrency proposals have appeared. The market capitalization of cryptocurrencies surpasses 51 billion US dollars data retrieved from http: Security and robustness are probably the most important properties for a currency, and cryptocurrencies achieve them by using cryptographic techniques and a decentralized approach.
Decentralization avoids both a single point of failure and a single trust anchor but potentially introduces discordances between parties. In order to reach consensus among nodes, cryptocurrencies take advantage of a distributed mechanism that dogecoin wallet peers connected ed the system to maintain a single unambiguous view of its state [ 2 ], the blockchain.
To support the communication between different entities of a cryptocurrency, a decentralized P2P approach is adopted to deploy dogecoin wallet peers connected ed so-called P2P cryptocurrency network, that is, the communication overlay that transports all data needed in the cryptocurrency system. The main goals of such a network are, firstly, to allow members of the network to synchronize their view of the system state and, secondly, to disseminate peer dogecoin wallet peers connected ed in order to allow peers to reenter the system after a disconnection.
Although the goals of P2P networks are shared among all blockchain-based cryptocurrencies, there is no standard for P2P cryptocurrency networks. In this paper, we analyze dogecoin wallet peers connected ed Bitcoin P2P network to characterize general P2P cryptocurrency networks.
Two main reasons made us choose Bitcoin as the subject of analysis. On one hand, far beyond the economic impact, being the largest cryptocurrency also conveys technical implications: On the other hand, being Bitcoin the first open-source cryptocurrency proposed, other new cryptocurrencies are developed as a software fork of the Bitcoin reference implementation. Although new cryptocurrencies have tweaked the Bitcoin source code in order to achieve different properties, an in-depth analysis shows that network mechanisms are usually unmodified and, in fact, even multiple cryptocurrencies share exactly the same network behavior as Bitcoin [ 3 ].
The first objective of this paper is twofold. On one hand, the paper fully describes the Bitcoin P2P network. On the other hand, it characterizes the network to show how the aforementioned network goals, together with the special format of the information being transmitted through the network, conform to a new paradigm for P2P networks. This characterization will dogecoin wallet peers connected ed out how, when considering cryptocurrency P2P networks, some of the well-known problems of P2P networks are not a concern, while other problems pose entirely new challenges.
The second objective of this paper is to dogecoin wallet peers connected ed to what extent the adoption of cryptocurrencies, and their underlying P2P networks, can be a powerful tool for the dogecoin wallet peers connected ed of distributed applications with mobile components. There are three relevant properties of cryptocurrencies that can be used as building blocks for such applications: The structure of this paper is the following.
First of all, in Section 3 and preceded by a basic description of the Bitcoin system, we provide a global description of all the elements in the Bitcoin P2P network, an overview that, to our best dogecoin wallet peers connected ed, lacked in the scientific literature the only reference we are aware of is [ 4 ], and it is mainly focused on the economic aspects of the Bitcoin network.
Second, in Sections 4 and 5we perform a deep analysis of the Bitcoin network, which is compared to other existing P2P paradigms through a well-known P2P taxonomy. This characterization allows us to provide enough evidence to show that P2P cryptocurrency networks represent a new paradigm for P2P networks.
Finally, in Section 6we identify different applications in the field of mobile computation where cryptocurrencies may be applied, and we point out some of the opportunities and challenges that such an interaction may entail. In this section, we point out the main ideas to understand the basic functionality dogecoin wallet peers connected ed the Bitcoin cryptocurrency.
Such a background is needed to understand the underlying P2P network that supports the communication between Bitcoin entities. However, the complexity of Bitcoin makes it impossible to provide a full description of the system in this review, so interested readers can refer to Dogecoin wallet peers connected ed et al.
Bitcoin is a cryptocurrency based on accounting entries [ 5 ]. Therefore, bitcoins should not be seen as digital tokens but as the balance of a Bitcoin account.
A Bitcoin account is defined by an elliptic curve cryptography key pair. The Bitcoin account is publicly identified by its Bitcoin addressobtained from its public key. Then, the corresponding private key is needed dogecoin wallet peers connected ed spend the bitcoins of the account.
Special purpose software, commonly referred as walletshas been developed to create and manage those private keys and addresses. Payments in the Bitcoin system are performed through transactions between Bitcoin accounts. A Bitcoin transaction indicates a Bitcoin movement from source addresses to destination addresses. Source addresses are known as input addresses in a transaction, and destination addresses are named output addresses.
As it can be seen in Figure 1a single transaction can have one or multiple input addresses and one or multiple output addresses.
A transaction implicitly details the exact amount of bitcoins to be transferred from each input address. The same applies to the output addresses, indicating the total amount of bitcoins that would be transferred to each account although in this case, the specification is explicitly made.
The Bitcoin protocol forces input addresses to spend the exact amount of a previously received transaction notice that, in Figure 1there are two input addresses that are exactly the same, which indicates that bitcoins have arrived to this Bitcoin account in two separate transactions.
Therefore, each input must unambiguously indicate the previous transaction identifier a transaction is identified in the Bitcoin system by its hash value and the index of the output where the bitcoins were received. As a consequence, at any given moment, an output may be in two states: An output that has not been spent is known as unspent transaction output, or UTXO. Finally, the owner of the input addresses should perform a digital signature using dogecoin wallet peers connected ed private keys to authorize a Bitcoin transfer, proving that he is the real owner of such accounts although dogecoin wallet peers connected ed is the standard form of Bitcoin verification for regular Bitcoin transfer transactions, the verification of a transaction can be much more complex and is based on the execution of a stack-based scripting language more details can be found in Chapter 3 of [ 2 ].
Before accepting a payment from a standard transaction, the receiver should i validate that the digital signatures are correct; ii validate that the bitcoins of the input addresses are not previously spent. The first validation can be performed with the information included in the transaction itself field ScriptSig together with the information of the transaction identified in the Previous output Index field scriptPubKey. The second validation prevents double-spending in the Bitcoin system, and it is performed through a ledger, the blockchain, where all previous transactions are annotated.
The blockchain is a general append-only ledger containing all Bitcoin transactions performed since the system started to operate back inand it is freely replicated and stored in different nodes of the Bitcoin network, making the Bitcoin a completely distributed system. Transactions are included in the blockchain at time intervals, rather than in a flow fashion, and such an addition is performed by collecting all new transactions of the system, compiling them together dogecoin wallet peers connected ed a data structure called block, and including the block at the top of the blockchain.
Every time that a block containing a specific transaction is included dogecoin wallet peers connected ed the blockchain such a transaction is said to be a confirmed transaction since it has already been included in the blockchain and can be checked for double-spending prevention.
Blocks are data structures that mainly contain a set of transactions that have been performed in the system Figure 2. To achieve the append-only property, the inclusion of a block in the blockchain is a hard problem, so adding blocks to the blockchain is time- and work-consuming.
Furthermore, every block is indexed using its hash value, and every new block contains the hash value of the previous one see the field Previous block in Figure 2. Such a mechanism ensures that the modification of a block from the middle of the chain would imply to modify all remaining blocks of the chain from that point to the top in order to match all hash values.
Adding a block to the blockchain is known as the mining processa process that is also distributed and that can be performed by any user of the Bitcoin network using specific-purpose software and hardware. The mining process uses a hashcash proof-of-work system, first proposed by Back as an antispam mechanism [ 6 ]. The proof of work consists of finding a hash of the new block with a value lower than a predefined target notice that the value of the target determines the difficulty of the mining process.
Bitcoin adjusts the target value depending on the hash power of the miners dogecoin wallet peers connected ed order to set the throughput of new blocks to 1 every 10 minutes in mean. This process is performed by brute force varying dogecoin wallet peers connected ed nonce value of the block. Once the value has been found, the new block becomes the top block of the blockchain, and all miners discard their work on that dogecoin wallet peers connected ed and move to the next one.
Mining new blocks is a structural task in the Bitcoin system since it helps to confirm the transactions of the system. For that reason and also assuming that mining implies a hard work, miners have to be properly rewarded. In the Bitcoin system, miners are rewarded with two mechanisms.
The first one provides them with newly created bitcoins. Every new block includes a special transaction, called generation transaction or coinbase transaction see the first transaction in Figure 2in which it does not appear to have any input address and the output address is determined by the miner who creates the block, who obviously indicates one of its own addresses the amount of a generation transaction is not constant, and it is determined by the Bitcoin system.
Such a value, started in 50 bitcoins, is halved every four years, fixing asymptotically to 21 million the total number of bitcoins that will ever be created. The Bitcoin system needs to disseminate different kinds of information, essentially, transactions and blocks. Since both are generated in a distributed way, dogecoin wallet peers connected ed system transmits such information over the Internet through a P2P network, that we describe in detail in the next section.
Bitcoin was first presented to the public in a white paper [ 1 ] describing its main concepts. Some months later, an open-source implementation of the Bitcoin client was released, giving birth to the cryptocurrency we now know and the P2P network that supports it. Such P2P network definition and implementation have been cloned in multiple new cryptocurrencies that derive from the Bitcoin implementation.
In such new cryptocurrencies, the dogecoin wallet peers connected ed configuration has been implemented almost identically. For instance, as described in [ 3 ], Litecoin, Dogecoin, Dash, and Peercoin have exactly the same network message types of Bitcoin, being the resulting networks for those cryptocurrencies very similar and in some cases identical to the Bitcoin dogecoin wallet peers connected ed.
Since its deployment inwhere the only Bitcoin client available was the reference client, the Bitcoin network is now made up of very heterogeneous peers, whose hardware capabilities and software implementations differ largely from each other. Moreover, even new protocols have been created with the goal of optimizing certain tasks the Bitcoin ecosystem needs.
In order to describe the existing Bitcoin network, we first identify some of the properties that characterize Bitcoin peers. After that, we review the most common peer configurations, using the properties described before.
Finally, dogecoin wallet peers connected ed describe the composition of the current Bitcoin network. As we have already mentioned, Bitcoin peers are heterogeneous, dogecoin wallet peers connected ed notable differences in both their hardware and software. In this section, we focus on describing the main properties that define a Bitcoin node: Figure 3 summarizes such a classification.
Peers participating in the network store some data about the blockchain. However, the exact data they store differ largely, from a few megabytes to dozens of gigabytes. Pruned blockchain peers store an up-to-date version of the blockchain with complete dogecoin wallet peers connected ed data for at least the last 2 days the number of days for which to store complete blockchain data can be tuned by users.
Although only storing complete blockchain data for a few days, pruned nodes are able to securely validate transactions dogecoin wallet peers connected ed they indeed store the required information from their previous history of the blockchain, that is, metadata about all known blocks and the UTXO set. Simplified payment verification SPV clients have an up-to-date version of the blockchain headers a block header is an byte structure.
Additionally, SPV clients may store transaction data from some transactions of interest. SPV clients are usually deployed in mobile devices such as smartphones, where having dogecoin wallet peers connected ed full blockchain is generally unaffordable. Peers can also be classified on the basis of their functionality. There are three functionalities needed for the Bitcoin system to work.
Mining is the computationally expensive task of trying to create blocks. New blocks are appended to the end of the blockchain, thus making the public dogecoin wallet peers connected ed grow.
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