Xmr cryptocurrency calculator Архив
Bitcoin blockchain readerАвтор: Zolosho | Category: Xmr cryptocurrency calculator | Октябрь 2, 2012
Bitcoin and blockchain enable the ownership of virtual property without the need for a central authority. Additionally, Bitcoin and other cryptocurrencies make. Block explorer and the most powerful API for the most popular blockchains that allows you to find, sort, and filter blockchain blocks, transactions. Answers to the 40+ most popular questions about blockchain, including definitions of Bitcoin, Ethereum, smart contracts, gas, DeFi, and more. FOUR ETHERS CHORDS
Merkle trees are binary trees containing cryptographic hashes. Figure Blocks linked in a chain, by reference to the previous block header hash Merkle trees are used in bitcoin to summarize all the transactions in a block, producing an overall digital fingerprint of the entire set of transactions, providing a very efficient process to verify whether a transaction is included in a block.
A Merkle tree is constructed by recursively hashing pairs of nodes until there is only one hash, called the root, or merkle root. The merkle tree is constructed bottom-up. In the following example, we start with four transactions, A, B, C and D, which form the leaves of the Merkle tree, as shown in Figure For example, to construct the parent node HAB, the two byte hashes of the children are concatenated to create a byte string.
That byte hash is stored in the block header and summarizes all the data in all four transactions. Calculating the nodes in a merkle tree Because the merkle tree is a binary tree, it needs an even number of leaf nodes. If there is an odd number of transactions to summarize, the last transaction hash will be duplicated to create an even number of leaf nodes, also known as a balanced tree. This is shown in Figure , where transaction C is duplicated. Duplicating one data element achieves an even number of data elements The same method for constructing a tree from four transactions can be generalized to construct trees of any size.
In bitcoin it is common to have several hundred to more than a thousand transactions in a single block, which are summarized in exactly the same way, producing just 32 bytes of data as the single merkle root. In Figure , you will see a tree built from 16 transactions. Note that although the root looks bigger than the leaf nodes in the diagram, it is the exact same size, just 32 bytes. Whether there is one transaction or a hundred thousand transactions in the block, the merkle root always summarizes them into 32 bytes.
To prove that a specific transaction is included in a block, a node only needs to produce log2 N byte hashes, constituting an authentication path or merkle path connecting the specific transaction to the root of the tree. If instead of taking 0. The resulting difference is the transaction fee that is collected by the miner as a fee for including the transaction in a block and putting it on the blockchain ledger. The resulting transaction can be seen using a blockchain explorer web application, as shown in Figure Now, the transaction must be transmitted to the bitcoin network where it will become part of the distributed ledger the blockchain.
Transmitting the transaction Because the transaction contains all the information necessary to process, it does not matter how or where it is transmitted to the bitcoin network. The bitcoin network is a peer-to-peer network, with each bitcoin client participating by connecting to several other bitcoin clients.
The purpose of the bitcoin network is to propagate transactions and blocks to all participants. Any bitcoin network node other client that receives a valid transaction it has not seen before will immediately forward it to other nodes to which it is connected. Thus, the transaction rapidly propagates out across the peer-to-peer network, reaching a large percentage of the nodes within a few seconds.
At this point Bob can assume, with little risk, that the transaction will shortly be included in a block and confirmed. Although confirmations ensure the transaction has been accepted by the whole network, such a delay is unnecessary for small-value items such as a cup of coffee. A merchant may accept a valid small-value transaction with no confirmations, with no more risk than a credit card payment made without an ID or a signature, as merchants routinely accept today.
Bitcoin Mining The transaction is now propagated on the bitcoin network. It does not become part of the shared ledger the blockchain until it is verified and included in a block by a process called mining. See Chapter 8 for a detailed explanation.
The bitcoin system of trust is based on computation. Transactions are bundled into blocks, which require an enormous amount of computation to prove, but only a small amount of computation to verify as proven. The mining process serves two purposes in bitcoin: Mining creates new bitcoins in each block, almost like a central bank printing new money.
The amount of bitcoin created per block is fixed and diminishes with time. Mining creates trust by ensuring that transactions are only confirmed if enough computational power was devoted to the block that contains them. More blocks mean more computation, which means more trust. A good way to describe mining is like a giant competitive game of sudoku that resets every time someone finds a solution and whose difficulty automatically adjusts so that it takes approximately 10 minutes to find a solution.
Imagine a giant sudoku puzzle, several thousand rows and columns in size. If I show you a completed puzzle you can verify it quite quickly. However, if the puzzle has a few squares filled and the rest are empty, it takes a lot of work to solve! The difficulty of the sudoku can be adjusted by changing its size more or fewer rows and columns , but it can still be verified quite easily even if it is very large.
Jing is participating in the bitcoin network as a miner. Every 10 minutes or so, Jing joins thousands of other miners in a global race to find a solution to a block of transactions. Finding such a solution, the so-called proof of work, requires quadrillions of hashing operations per second across the entire bitcoin network.
The algorithm for proof of work involves repeatedly hashing the header of the block and a random number with the SHA cryptographic algorithm until a solution matching a predetermined pattern emerges. The first miner to find such a solution wins the round of competition and publishes that block into the blockchain.
Jing started mining in using a very fast desktop computer to find a suitable proof of work for new blocks. As more miners started joining the bitcoin network, the difficulty of the problem increased rapidly. Soon, Jing and other miners upgraded to more specialized hardware, such as high-end dedicated graphical processing units GPUs cards such as those used in gaming desktops or consoles.
At the time of this writing, the difficulty is so high that it is profitable only to mine with application-specific integrated circuits ASIC , essentially hundreds of mining algorithms printed in hardware, running in parallel on a single silicon chip. He pays his electricity costs by selling the bitcoin he is able to generate from mining, creating some income from the profits. His computer runs a copy of bitcoind, the reference bitcoin client, as a backend to his specialized mining software.
Mining Transactions in Blocks A transaction transmitted across the network is not verified until it becomes part of the global distributed ledger, the blockchain. Every 10 minutes on average, miners generate a new block that contains all the transactions since the last block. New transactions are constantly flowing into the network from user wallets and other applications. As these are seen by the bitcoin network nodes, they get added to a temporary pool of unverified transactions maintained by each node.
As miners build a new block, they add unverified transactions from this pool to a new block and then attempt to solve a very hard problem a. The process of mining is explained in detail in Introduction. Transactions are added to the new block, prioritized by the highest-fee transactions first and a few other criteria.
Each miner starts the process of mining a new block of transactions as soon as he receives the previous block from the network, knowing he has lost that previous round of competition. He immediately creates a new block, fills it with transactions and the fingerprint of the previous block, and starts calculating the proof of work for the new block.
Each miner includes a special transaction in his block, one that pays his own bitcoin address a reward of newly created bitcoins currently 25 BTC per block. Jing, who participates in a mining pool, has set up his software to create new blocks that assign the reward to a pool address. From there, a share of the reward is distributed to Jing and other miners in proportion to the amount of work they contributed in the last round.
A few minutes later, a new block, , is mined by another miner. Each block mined on top of the one containing the transaction is an additional confirmation. As the blocks pile on top of each other, it becomes exponentially harder to reverse the transaction, thereby making it more and more trusted by the network. Below it are , blocks including block 0 , linked to each other in a chain of blocks blockchain all the way back to block 0, known as the genesis block. By convention, any block with more than six confirmations is considered irrevocable, because it would require an immense amount of computation to invalidate and recalculate six blocks.
We will examine the process of mining and the way it builds trust in more detail in Chapter 8.
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