Explore

Blockchain fundamentals

Blockchain functions

Consensus Protocol

Bitcoin

Bitcoin Mechanism

Bitcoin transaction Inputs and Outputs

Blockchain philosophy

Blockchain in practice

Bitcoin transaction

Stories of Web3 - by the people who build it

Blockchain governance

Blockchain transactions

Crypto regulation

Bitcoin keys and addresses

Bitcoin wallets

Bitcoin consensus and mining

Bitcoin network

Bitcoin blockchain

Bitcoin private keys

Bitcoin public key

Bitcoin address

On the importance of decentralization

Blockchain ideological basis

Blockhain ecosystem

Mining

Mining and ecology

What is money

History of the Gold Standard

Wallets

Exchanges

Oracles

Smart contract platforms

Ethereum

Cryptocurrencies

Stablecoins

Ethereum design

Blockchain use cases

Tokenization: easy creation and transfer of values

Blockchain in finance

How Bitcoin works

Austrian economic school

Bitcoin governance

Proof of Work

Proof of Stake

Bitcoin security and double spending

Bitcoin block structure

Bitcoin forks

Merkle Tree

Smart contracts

Tokens

DeFi

Bitcoin mining and ecology

Blockchain underlying technologies

Bitcoin Whitepaper by Satoshi Nakamoto

BUILD/ blockchain infrastructure

CREATE / NFTs, metaverse and gaming

INSTRUCT/ crypto knowledge

ADVOCATE / crypto regulation

Web3

Web3 Music

Web3 Fashion

Top 5 DeFi protocols to illustrate the space

Dynamic information source on all things blockchain: Bitcoin and other cryptocurrencies, Dapps, real life use cases, crypto ecosystem, technical details, crypto regulation and more.

D.Center – All things Blockchain

Start your crypto journey by hitting the Explore button!

<figure class="wp-block-image"><img src="https://web.d.center/wp-content/uploads/2021/08/bitcoin-security-double-spending-2-1024x424.png" alt="" class="wp-image-2718"/></figure>



Can you cheat in Bitcoin? How do you hack an impartial system run on a worldwide network of independent peers?&nbsp;



Bitcoin is a digital money, and executing a Bitcoin transaction means transferring a digital item, i.e. something easily duplicated. However, because it is money we’re speaking about, such duplication must be avoided at all costs: while it is not at all problematic to send a photo by email and still have a copy of it on our computer, it would not make any sense for money transfer. This problem is known as double spending.



In the case of [tooltip content="fiduciary money with no intrinsic value, dependent on the government and the central bank (like dollars or euros) "] fiat money [/tooltip], the banks make sure that the amount of money sent is deduced from the account of the sender. Bitcoin protocol allows to do this without any trusted third party: the network is keeping a real-time ledger with all previous transactions and checks all incoming transactions against this ledger, thus preventing any attempt to spend the same bitcoin more than once.&nbsp;



<h2>Double spending mechanism</h2>



In theory, there is a way to double spend bitcoins, even if it is extremely difficult to execute.



Such possibility is in the hands of the miners and unfolds as follows:



<div class="wp-block-image"><figure class="aligncenter"><img src="https://web.d.center/wp-content/uploads/2021/08/Bitcoin-double-spending.svg" alt="" class="wp-image-2717"/></figure></div>



<ul><li>A miner spends bitcoins and gets something in return ( a merchandise, another cryptocurrency etc). This transaction indicates which bitcoins are being sent, or more precisely their UTXO (unspent transaction output) referenced in transaction’s input</li><li>This transaction will be confirmed as a part of the block added to the blockchain. The receiver of bitcoins sees its confirmation in their <a href="https://d.center/explore/bitcoin-wallets">wallet</a></li><li>An ill-intentioned miner starts to secretly mine another block at the same height as the one with the first transaction. This secret block contains a transaction sending the same bitcoins (referencing the same UTXO) to the miner himself</li><li>Still secretly, a miner continues to mine this new blockchain branch, adding new blocks to the one with the second transaction. As soon as the new branch, until now unknown by the network, becomes longer than the old one (more precisely it has a bigger sum of <a href="https://d.center/explore/proof-of-work" class="ek-link">PoW</a>), a miner will propagate it to the network</li><li>Upon receiving a new branch with valid blocks and a bigger sum of PoW than the actual blockchain, the network will switch to the new branch, which will effectively become the new blockchain. At this moment the bitcoins will disappear from the first transaction receiver’s wallet, despite all previous confirmations</li><li>The new blockchain does not contain the block with the first transaction, so it will appear as non-confirmed. It could be integrated into the mempool, where the miners pick new transactions to confirm, but, since the new blockchain already contains a transaction using the same bitcoins, it will be definitely rejected by the network</li><li>At the end, the receiver of the first transaction will see it disappear from the blockchain and thus will lose their bitcoins, whereas the fraudulent miner will still have their bitcoins and the goods they received in return from the first transaction.</li></ul>







Taking into consideration the methodology of the attack, a miner can execute double spending only with their own transactions.



<h2>Obstacles to a double spending</h2>



Among the main obstacles to a double spending we can name the blockchain structure itself, the number of confirmations and the absence of an economic interest.



<h3>Blockchain structure</h3>



Since every block contains a unique hash of the previous block’s header, a fraudulent miner must mine not a single block, but a whole new branch - a series of blocks linked together. In order to do so, they will not only have to find all the PoW of this branch, but to do it faster than the rest of the network - a highly ambitious task, which gets more difficult as the computational power of the network grows.&nbsp;



Theoretically, if a miner achieves more than 50% of the network’s [tooltip content="number of hash operations done per second, reflecting a miner's computational power"] hashrate [/tooltip] and is capable of maintaining it indefinitely, at one moment they will get a chain containing more work (as in PoW) than the actual chain - a situation called 51% attack. It is possible to try double spending with less than 50% of the network’s power, but the attack is much less likely to succeed.



<h3>Number of confirmations</h3>



A successful attack is useful only if an attacker receives the goods they spent their bitcoins on in the first transaction. That is why for important deals it is recommended to wait for a certain number of confirmations (blocks mined after the block containing the transaction in question) before sending the goods: if an attacker can’t gather more than 50% of the network’s power, they will not be able to mine several blocks in a row faster than the network. Indeed, the probability of a successful attack is an increasing function of an attacker’s hashrate percentage and a decreasing function of the number of confirmations needed before delivering the goods in return. In case of Bitcoin the standard number of confirmations required for serious transfers is 6.



<h3>Economic interest</h3>



Even if this kind of double spending is theoretically possible, its execution appears unlikely: from the economic standpoint the gain must be higher than the expenses. Taking into account the actual Bitcoin hashrate and thus the huge quantity of energy needed to get the half of it, this sounds quite unrealistic. An attacker would also need to buy or rent the specialist hardware to gather this computational power, which itself presents a serious logistic and financial challenge. Theoretically a collision of miners could gather the power needed for an attack, but mining being their primary occupation and means of subsistence, it is hard to imagine they would cut off the branch they're sitting on.



One can imagine a not-for-profit attack aiming at damaging the network, but once again its cost would be exorbitant, not to mention that the Bitcoin community would react and counter-attack in one way or another.

<figure class="wp-block-image aligncenter size-full"><img src="https://web.d.center/wp-content/uploads/2023/08/bitcoin-block-structure-l.jpg" alt="" class="wp-image-6474"/></figure>



A block is the basic element of the blockchain. A Bitcoin block is made up of 4 parts: 



<ul>
<li>the block size, </li>



<li>the header (which itself has a specific structure), </li>



<li>the number of transactions, and </li>



<li>the list of transactions.</li>
</ul>



<figure class="wp-block-image aligncenter size-full"><img src="https://web.d.center/wp-content/uploads/2023/08/Bitcoin-block-structure@3x.png" alt="" class="wp-image-6476"/></figure>



The block header contains particularly important information:



➡️ the version number of the protocol used to create the block



➡️ the ID (unique identifier) of the previous block (n-1), which is the hash of its header. The ID of block n will be found in the header of block n+1. The block ID is calculated by applying the SHA256 hash function twice to the header data. The only block that has no reference to the previous block is the first block created - the Genesis block. It is statically present in all Bitcoin clients from the outset, preventing its alteration and thus providing a secure basis for loading the blockchain.



➡️ the <a href="https://d.center/explore/merkle-tree" class="ek-link">Merkle root</a> is the cryptographic fingerprint of all transactions confirmed in this block (read more here).



➡️ the Timestamp is the approximate time at which the block was created.



➡️ difficulty target and Nonce are characteristics relating to mining operations, indicating the quantity of '0s' required to obtain a PoW of the block and the number used to achieve it.



In the part of the block that assembles the transactions, the first transaction is always special - it's the coinbase, the transaction by which the miner is remunerated.

A blockchain fork is often cited as a means of creating a new blockchain, or attempting a fraudulent action. In most cases, however, it's a completely trivial and unintentional event. Let's take a look at what happens on Bitcoin when the two valid blocks are released simultaneously.



<figure class="wp-block-image aligncenter size-full"><img src="https://web.d.center/wp-content/uploads/2023/08/bitcoin-forks-1.jpg" alt="" class="wp-image-6482"/></figure>



When the two valid candidate blocks that can be attached to the blockchain are propagated on the network at roughly the same time, its nodes will find themselves with two possible branches. In this case, the nodes will keep a copy of both branches and wait for the next blocks to be broadcasted before deciding which will be the valid branch.



Receiving the new blocks, the nodes reproduce the same process, searching for the parent block to the blocks proposed to them. A branch is then built that is longer than the other - the branch that will be considered the main one. More precisely, it's not the longest blockchain, but the blockchain containing the greatest amount of work (the most <a href="https://d.center/explore/bitcoin-consensus-and-mining" class="ek-link">Proof-of-Work</a>) that will be chosen, although in most cases this will correspond to the longest blockchain.



<figure class="wp-block-image size-full"><img src="https://web.d.center/wp-content/uploads/2023/08/Bitcoin-forks@3x.png" alt="" class="wp-image-6484"/></figure>



There may also be so-called "orphan" blocks, i.e. blocks for which the node has not been able to find a parent. This usually happens when two successive blocks are created in a very short space of time, and the child bloc arrives before the parent. When the node receives the parent, things will return to normal.



<h2 class="wp-block-heading">Choosing the right chain</h2>



The amount of work in a branch is the sum of the difficulties of each block in the branch. The difficulty of a given block A is calculated by the following formula:



Difficulty of A = (target of genesis block / target of A) = ((216 - 1) * 25626)) / (target of A)



As it is the branch with the greatest amount of work that is retained, should another branch subsequently have more work than the main chain, the node will reposition itself on the new one as the main branch.



If we look at the difficulty calculation, we see that the longest chain is generally the chain with the greatest difficulty (and two chains of the same length have the same amount of work). One case where this will be different is when adjusting the difficulty with blocks produced at roughly the same time, but with different targets.



The existence of forks explains why it is prudent for the recipient of a transaction to wait for several confirmations to be certain of its validity (i.e. several blocks added after the one containing the transaction). If the branch with the block containing the transaction is not the selected branch, the transaction will disappear.



That being said, if it's a valid transaction, it will undoubtedly be found in both branches at the same block height, or in a subsequent block. The danger is greater in the case of a deliberate fraudulent fork aimed at double spending.

A Merkle root is a cryptographic method of taking a digital fingerprint of a set of data, making it possible to quickly and easily verify whether a particular piece of data is present in the set, or whether a piece of data in the set has been altered.



This technique was unveiled in 1979 by Ralph Merkle at Stanford University in a publication entitled "Certified Digital Signature", in which he described a new method of proof based on a binary hash tree, since known as the Merkle Tree. This technique has been widely used, particularly in distributed computing systems where the same set of data must be present in multiple locations. 



The technology is mentioned several times in Satoshi Nakamoto's white paper describing Bitcoin for the first time.



<h2 class="wp-block-heading">Merkle Tree structure</h2>



The Merkle Tree applies to a set of data - in the case of Bitcoin, to all the transactions in a block. The Merkle Tree is a binary tree with a piece of data at the top called the Merkle root, from which the tree divides into two, then each piece divides into two, and so on. At the base are the leaves, which are the hashes of the transactions confirmed in the block in the order corresponding to the order in which these transactions were recorded. The tree is built from the base of the leaves, which must be an even number. If this is not the case, the last transaction is copied and hashed, providing the missing data.



To build the tree, the leaves are concatenated two by two, this concatenation is hashed, and the operation is repeated until the last hash is obtained. That will be the Merkle root. Hashing is performed by using the SHA256 function two consecutive times.



Therefore, the calculation of the Merkle root depends on all the transactions confirmed in the block. Any change in these transactions, or even just in their order, will result in a change in the Merkle root.



Here's a simplifying diagram based on 16 transactions A,B,…,P. The 16 leaves forming the base of the tree are the hashes (double SHA256) ordered by the 16 transactions in the block:



<figure class="wp-block-image size-full"><img src="https://web.d.center/wp-content/uploads/2023/08/Merkle-root@3x.png" alt="" class="wp-image-6457"/></figure>



<h2 class="wp-block-heading">Advantages of the Merkle Tree</h2>



The fundamental property of the Merkle Tree is that it enables efficient verification of the integrity of block data, or of the presence of a specific transaction in that block, with a much smaller amount of data transferred than would otherwise be necessary. Many Bitcoin wallets are SPVs, or Simplified Payment Verification wallets, which rely on this property of the Merkle tree to function. They can verify whether a particular transaction is part of a given block by receiving targeted information from full-nodes, without having to load the entire blockchain and simply possessing the block headers.



<h2 class="wp-block-heading">How the Merkle Tree works</h2>



When an SPV wallet wants to verify that a transaction is part of the block for which it knows the Merkle root, it queries a full node, which will send it a Merkle path - the specific data set that will enable the SPV wallet to create a "verification path" from the transaction to the Merkle root.



In the scheme above, the SPV wallet will only need to receive 4 out of 16 data items (marked in white) to reconstruct this path. Knowing the transaction K, the wallet can calculate the hash of K, then concatenate it with the hash of L sent to it. It then hashes this concatenation, which provides it with the data it needs to continue the process with another hash sent to it. It continues this way until it reconstitutes the Merkle root, which it then compares with the one it has in memory. If the recalculated Merkle root is equal to the Merkle root it has in memory, then transaction K is indeed part of this block. By reconstructing a Merkle path, checking the presence of a transaction in a block containing N transactions simply requires access to log base 2(N) hashes of 32 bytes each, 32 bytes being the size of the hash by SHA256. Since blocks contain thousands of transactions, the use of Merkle trees drastically reduces the size of the data to be exchanged and stored for an SPV wallet.

Bitcoinnn

Blockchain in use

Philosophy behind blockchain

Underlying technologies

Blockchain trilemma

Blockchain and DLT types

Bitcoin mechanism

Bitcoin Transaction

Bitcoin transaction inputs and outputs

Bitcoin implementations

Script

UTXO

Mainchain functions

Transaction inputs

Sidechain solutions

Cryptography

Transaction Fees

Keys and addresses

Private key

Public key

Adress

What is Bitcoin and why it could be a valuable alternative to our usual currencies such as dollars and euros?



<figure class="wp-block-image aligncenter"><img src="https://web.d.center/wp-content/uploads/2020/10/bitcoin-l-2-1024x413.jpg" alt="" class="wp-image-1290"/></figure>



<h2 class="wp-block-heading">Bitcoin and bitcoin</h2>



Bitcoin is both the blockchain and the cryptocurrency that exists on it. To distinguish the two, Bitcoin as the blockchain is usually written with a capital B. 



The basis of the technology were first outlined in Satoshi Nakamoto's (pseudonyme) <a href="https://d.center/en/explore/bitcoin-a-peer-to-peer-electronic-cash-system" class="ek-link">White Paper</a> published in 2008 and titled "A Peer-to-Peer Electronic Cash System". 



It was not the first try to create a digital currency, but it was the first to succeed in solving all the intricate problems that led to previous attempts’ failures. Satoshi Nakamoto exploited decades of research, in particular in the fields of cryptography and distributed systems, and brilliantly brought them together to create a fast, secure, independent, and borderless digital money.



<h3 class="wp-block-heading">Bitcoin consists of:</h3>



<ul>
<li>Bitcoin protocol - a set of rules and algorithms that enable bitcoin issuance and transactions validation via&nbsp;network consensus (a way to ensure that network participants are well-intentioned and will update transactions ledger fairly; Bitcoin consensus is called a <a href="https://d.center/explore/proof-of-work" class="ek-link">Proof-of-Work</a>)</li>



<li>decentralized <a href="https://d.center/explore/p2p-network" class="ek-link">peer-to-peer network</a><a href="https://d.center/explore/p2p-network" class="ek-link"> </a>to run the Bitcoin protocol. Without any central server, a P2P network is composed of computers with equal rights that verify transactions and, if they wish, participate in bitcoin issuance and transactions’ recording.</li>
</ul>



Running the Bitcoin protocol results in a public distributed ledger called the blockchain, where all the transactions are stored. Everyone can consult the blockchain and its transactions from the Genesis block up to now.



Bitcoins are issued according to the protocol as a reward for maintaining the network, and their transfer is carried out&nbsp; without intermediaries and centralized authorities. This means that, unlike [tooltip content=" fiduciary money with no intrinsic value backed by and dependent on the government (e.g. dollars or euros) "] fiat [/tooltip] currencies, Bitcoin does not depend on the government or banks to issue money or to settle and validate transactions. 



The only thing that gives control over bitcoins is the private key associated with every Bitcoin address and available exlusively to its owner.



<h2 class="wp-block-heading">Bitcoin alternative to fiat money</h2>



Store of value. No single entity could ever change Bitcoin code: it is stored and run on the network nodes - literally thousands of independent computers all over the world. This ensures that the code is law, and the rules embedded into code won’t change unless the majority of the network decides so. 



This stability is particularly important when it comes to the emission rules: bitcoin emission rate is predefined, with the supply divided by two every 4 years, meaning that there won’t ever be more than 21 million bitcoins. In the world where Central Banks can print as much fiat money as they wish, Bitcoin represents a remarkable store of value.



Free use. Bitcoin is also public and open source, allowing anyone to join, participate or use it. Anyone can open a Bitcoin wallet and send/receive bitcoins, without any approval from whatever organization. 



This is a significant improvement compared to the red tape of the banking system, not to mention a precious access to the world's finance for the unbanked. Furthermore, in the authoritarian countries where access to money is often used as a tool of repression, Bitcoin’s accessibility is vital. 



<h2 class="wp-block-heading">Bitcoin updates and developments</h2>



The rules that define Bitcoin protocol were first introduced by Satoshi Nakamoto, but as every computer program, they have to be regularly revised and updated, in order to reinforce the protocol security and introduce new functionalities. The way such updates are agreed upon is usually referred to as the <a href="https://d.center/explore/bitcoin-governance" class="ek-link">governance</a>, and in Bitcoin case its community plays a critical role.&nbsp;



Beyond the Bitcoin protocol itself, there have been numerous developments of the so-called layer 2, allowing&nbsp; to execute transactions off the mainchain. Such solutions usually aim to improve Bitcoin’s performance or introduce new functionalities.



Bitcoin's most popular layer-2 solution is Lightning Network, which increases dramatically its transaciton throughput and decreases network fees.

<figure class="wp-block-image"><img src="https://web.d.center/wp-content/uploads/2020/10/bitcoin-mechanism-l-1024x414.jpg" alt="" class="wp-image-1267"/></figure>



Bitcoin is an assembly of&nbsp; technologies and principles that interact in a predefined manner, securing the whole system performance.&nbsp;So how does it work? 



<div class="wp-block-image"><figure class="aligncenter"><img src="https://web.d.center/wp-content/uploads/2020/10/Bitcoin-mechanism-1.svg" alt="" class="wp-image-1316"/></figure></div>



<a href="https://d.center/explore/keys-and-addresses" class="ek-link">Keys and addresses</a>. Bitcoin is a decentralized system without any trusted third party, which means that no one can dispose of coins except for their rightful owner. Such feature necessitates extensive security measures, and Bitcoin ensures them using a system of cryptographic keys and addresses. 



<a href="https://d.center/explore/bitcoin-wallets" class="ek-link">Wallets</a><a href="https://d.center/explore/bitcoin-wallets" class="ek-link"> </a>are programs capable of communicating with the Bitcoin network. They generate keys and addresses that allow sending and receiving bitcoins, and can reconstitute the bitcoin balance of a particular account by researching the blockchain. 



<a href="https://d.center/explore/bitcoin-transaction" class="ek-link">Transactions </a>are generated and sent by wallets. Bitcoin transactions have a simple structure called UTXO, and a limited coding language script, which ensure the system’s robustness. 



<a href="https://d.center/explore/bitcoin-network" class="ek-link">Bitcoin network</a> enjoys a Peer-to-Peer, or <a href="https://d.center/explore/p2p-network" class="ek-link">P2P</a>, architecture - its nodes communicate with each other without any central server. Network nodes run Bitcoin protocol to verify if a transaction is valid (the sender has enough coins on their account and their signatures are correct) and if a candidate block (set of confirmed transactions) sent by a miner is OK, then propagate them to the network. 



<a href="https://d.center/explore/bitcoin-consensus-and-mining" class="ek-link">Consensus </a>is needed in order to determine which node will add the next block to the blockchain and to guarantee that this block is not fraudulent. Bitcoin utilizes <a href="https://d.center/explore/proof-of-work" class="ek-link">Proof-of-Work</a> consensus, where nodes need to find a solution to a cryptographic problem, which necessitates a big amount of electricity and specific equipment. As a reward for such work a node gets to add a block and receives newly created bitcoins. Such “bitcoin extraction” activity is called mining and the nodes engaging in it - miners. Mining is the only way to create new bitcoins.



 The node who finds a PoW solution first broadcasts a new block to the network, where, if the block is validated by the network, other nodes start working on the following blocks. Each block having a cryptographic reference to the previous one, a <a href="https://d.center/explore/bitcoin-blockchain" class="ek-link">blockchain </a>is being formed.

<div class="wp-block-image"><figure class="aligncenter"><img src="https://web.d.center/wp-content/uploads/2020/11/Bitcoin-blockchain.png" alt="" class="wp-image-1470"/></figure></div>



Bitcoin transactions are securely stored by the network, organized within a particular architecture called blockchain. 



<h2>Block structure </h2>



Transactions are gathered into blocks created by a miner approximately every 10 minutes. A block is made of a header, which contains specific data (notably the reference to the block’s content) and the <a href="https://d.center/explore/bitcoin-transaction" class="ek-link">transactions</a><a href="https://d.center/explore/bitcoin-transaction" class="ek-link"> </a>confirmed within the block. Every block contains a reference to the previous block in the form of its header’s 
 hash 
 fixed-length result of applying mathematical hash function to any volume of data. Hash is a one-way function: it is easy to get the result (also called hash) from the data, but impossible to get the data from the hash
 - its unique identifier. The blocks always carrying a reference to the previous ones, a chain of blocks is formed. 



The first block ever created is called the Genesis block, i.e. block 0. The block 1 was created with the reference to the block 0, and so on. Block number is also called the block height (as if the blocks were built one above the other) and measures the distance to the Genesis block. The block n, whose header hash is mentioned in the header of the block n+1, is called the parent block, whereas the block n+1 is called the child block. 



<div class="wp-block-image"><figure class="aligncenter"><img src="https://web.d.center/wp-content/uploads/2020/12/Bitcoin-blockchain.svg" alt="" class="wp-image-1546"/></figure></div>



<h2>Forks </h2>



While a block can have only one parent, it could have several children - a temporary situation that appears when several miners simultaneously propose a new block to the network. This situation is called a fork, because the blockchain splits into several valid branches. 



In the majority of cases the forks are not intentional, but rather due to the nature of the consensus. It is theoretically possible though to create them intentionally in order to try and fraud the system and execute a double spending (even if such endeavour would require more than 51% of the network computational power). 



Some estimate that a 10 minutes interval between blocks is a compromise between the scalability (theoretical number of possible transactions per second) and the probability to have a fork. The shorter the block creation time, the more nodes have a chance to find themselves with candidate blocks at the same time. In the case of Bitcoin it is quite rare that a fork holds for more than two blocks. 



In order to secure the blockchain the miners have to find a <a href="https://d.center/explore/proof-of-work" class="ek-link">Proof of Work</a> before submitting a block to the network. The PoW process is such that anyone willing to rewrite the history and modify the data within the block n must redo the PoW of this block and of all others that follow, since they will contain references to the previous blocks. Such electricity spending cannot possibly be cost-effective. It is thus considered that beyond n+5 (the 5th confirmed block after n), the n  becomes near definitive. 



<h2>Merkle root</h2>



 The <a href="https://d.center/explore/bitcoin-wallets" class="ek-link">wallets </a>refer to the data within the blockchain in order to keep their balances and to initialize transactions. Therefore they have to maintain a copy of the whole blockchain at any moment. Full node wallets keep the entire blockchain, which makes them reliable, but also quite heavy and cumbersome. There is also another way of accessing the blockchain without downloading all of it - by using a piece of data called the Merkle root. This data sits within the header of every block and enables the usage of the so-called SVP wallets (SPV for Simplified Payment Verification). These wallets only download block headers, which makes them lighter and more user-friendly, however they have to connect to a full node wallet in order to function properly (see <a href="https://d.center/explore/bitcoin-network" class="ek-link">Bitcoin network</a>).