Используйте «blockchain» в предложении

1. Online personal wallets, like the My Wallet service provided by Blockchain

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2. For small transactions, you can now consider the exchange complete! However, for larger transactions, ask the seller to wait for additional confirmations in the blockchain

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3. One of the benefits of Bitcoin is that the Bitcoin blockchain has a builtin scripting language that allows you to use some convenient and secure techniques that are impossible with other types of money

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4. The first block in the blockchain, often referred to as the genesis block, was added by Satoshi on January 3, 2009

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5. When he added the block to the blockchain, he inserted a short message, which all miners can do

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6. By including this message in the genesis block, Satoshi proved that he couldn’t have added it to the blockchain before that date

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7. Similarly, bitcoins are traceable by following coins through the public blockchain

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8. If the signature is missing or doesn’t match the public key, nodes on the Bitcoin network will consider the transaction invalid and will not add it to the blockchain

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9. Bitcoin depends on the blockchain being widely distributed among the nodes in the network

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10. But how can you be sure that any individual node in the network with a copy of the blockchain has not been surreptitiously altered? A malicious attacker could try to distribute a fraudulent blockchain where just a single transaction has been modified in the attacker’s favor

11. Each block in the blockchain contains a list of transactions and a hash of the transactions in the previous block in the chain

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12. This verification provides an efficient way for a single node to check whether transactions in its copy of the blockchain have been tampered with

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13. Let’s assume that our message is this: Please update the blockchain so that 5 bitcoins from Crowley are given to Satoshi

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14. By adding a new block of transactions to the blockchain, the miner who added the block is rewarded with newly minted bitcoins (as well as old bitcoins in the form of transaction fees)

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15. ” By continuing this process indefinitely, these blocks will form a blockchain, adding weight to the time suggested in the initial block (a genesis block)

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16. This exact blockchain strategy was described by Satoshi soon after he created Bitcoin

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17. However, this approach of using proof-of-work and a blockchain to coordinate the attacks of the generals still has a subtle flaw: A general who is lazy could cheat the network by never using her computer to mine blocks

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18. An abusive peer could first add a transaction to the blockchain to send bitcoins to you, and then after you gave her something of value (e

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19. , has the longest blockchain)

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20. A blockchain with 12 blocks has existed for longer than one with 7 blocks

21. Therefore, all the relay nodes check that the transaction is correctly formatted, make sure it has valid signatures, and look through the most current version of the blockchain to ensure the money being spent is verifiably present in the source account of the transaction

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22. Ultimately, every transaction must be recorded on the blockchain

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23. However, just because some nodes ignore a transaction doesn’t mean others will: As long as the transaction finds a mining node that accepts it, the transaction will eventually be added to the blockchain

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24. , a block that will be accepted by others as part of the blockchain and the one the miner is paid for) occurs when the double SHA256 hash of the block header results in a number that is less than some predetermined threshold, known as the difficulty target

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25. It exists to facilitate the ability to distinguish blocks in the old and new format if ever a major change in the blockchain structure occurs in the future, as Bitcoin is refined

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26. The difficulty stored in the blockchain header is expressed as a ratio between the initial target used by Bitcoin (when it started) and the current target

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27. Instead, the difficulty is adjusted every time the blockchain grows by 2,016 blocks, which happens approximately every two weeks (2,016 × 10 minutes = 14 days)

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28. The original purpose of this self-imposed limit14 was to prevent the blockchain from becoming bloated with pointless transactions (i

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29. In addition to having a computing device that can perform SHA256 hashes very quickly, mining nodes and relay nodes must have sufficient storage space to store a full copy of the blockchain

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30. In this context, it is important to distinguish between the blockchain (the immutable public document that correctly lists every valid Bitcoin transaction) and someone’s copy of the blockchain, which is what you have access to

31. Bitcoin wallet programs can verify transactions either by keeping their own complete copy of the blockchain, which is referred to as full payment verification, or by using an abridged version, which is called simplified payment verification (SPV)

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32. The blockchain, in its 5th year, was greater than 15GB in size and comprised 35 million transactions (by its 10th birthday, it may likely be 100 times larger)

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33. A fresh installation of a full payment verification Bitcoin wallet program can take several days (depending on bandwidth) to download the entire blockchain

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34. Obtaining the blockchain requires connecting to other full nodes and checking to determine whose blockchain has the greatest proof-of-work total (by definition, this is assumed to be the consensus blockchain)

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35. The goal of a thin wallet is to check that a transaction has been verified by miners and included in some block in the blockchain

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36. This method works reliably as long as miners, who are adding blocks to the blockchain, act honestly and allow only valid transactions to be included (which is a safe assumption as long as no individual miner is in control of more than 51 percent of the hashing power of the network)

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37. But without a copy of the blockchain, how does a thin wallet know whether or not a received transaction was included in a block? The transaction can claim it was included in block #24371 on the blockchain, for example, but how would you know whether the claim was true or false? One strategy would be for your wallet program to connect to several full nodes and ask to download block #24371 along with all of its other transactions

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38. However, if your SPV wallet program has to check several hundred transactions a day and each time you need to download an entire block (with all of its transactions), from an efficiency standpoint, this strategy is hardly better than just downloading the entire blockchain

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39. To do so, SPV wallets need to download the headers of every block in the blockchain

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40. Recall from Chapter 8 that each block in the blockchain contains two parts, a long list of transactions and a short summary of the block’s contents (the header)

41. 3 Using this Merkle tree design, thin wallets can safely confirm that transactions they receive have been included in the blockchain without downloading the full blockchain

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42. Downloading just the block headers requires only a fraction of the memory that’s needed for the entire blockchain; therefore, SPV wallets can easily run on your smartphone and other inexpensive mobile devices

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43. A full wallet that can access a complete blockchain can quickly validate new transactions, ensuring that it is sending money from a valid and adequately funded source address

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44. Even if a transaction is 100 percent valid, just because a transaction is broadcast doesn’t mean it will make it into the blockchain, especially if the spender creates an additional transaction that attempts to doublespend the money to another address

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45. But as the blockchain grows year after year, the percentage of nodes that can’t perform full validation may increase, and problems may arise

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46. Nonetheless, improving storage capacity and faster network speeds will likely continue to allow people to cope with the growing blockchain, and definite benefits will be gained by running a full node

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47. (Off-chain transactions are Bitcoin transactions that are not handled by the blockchain but are instead handled by the ledgers managed by Bitcoin wallet vendors, in order to save on transaction fees for smaller payments

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48. ) Consequently, those 10 billion transactions per day may be only 1 million transactions per day as recorded on the blockchain

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49. By analyzing the blockchain, you could theoretically follow each milibit through the past and verify each was among the 400 you initially sent out

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50. Of course, in practice it would be painful to track each of these coins in the blockchain yourself

51. In the middle of his favorite movie (Harry Potter and the Forked Blockchain), a pizza commercial appears

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52. But one fact is clear: In the same way that Newton had to first discover calculus to explain the motions of the stars, so Satoshi had to first discover the idea of a distributed anonymous ledger, the blockchain, to invent the idealistic notion of a fully distributed cryptocurrency

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53. However, unlike calculus and the laws of gravitation, the concepts of a blockchain and cryptocurrency are inextricably linked; they are yin and yang

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54. A distributed form of money simply cannot exist without the security provided to it by the blockchain

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55. Similarly, a blockchain cannot be created without giving people incentives to create it, and the only possible incentive that could work is a distributed form of money!

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56. However, the Bitcoin blockchain can sometimes trigger situations that cause the balance of a wallet to jump in ways that are unexpected and could make our app produce incorrect results

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57. For instance, suppose our wallet receives some money with one confirmation, but the blockchain suddenly forks, unconfirming the transaction that was tied to that money and causing the wallet to suddenly lose much of the confirmed money

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58. For the first task, the blockchain allows us to examine all the historical blocks in the blockchain and compile comprehensive data about every Bitcoin address ever used and how much money each contains

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59. Here’s a quick refresher of how SPV works: If you know you’re interested in a single wallet ahead of time, you can just tally up how much money is in that one wallet as you pull the entire historical blockchain off the Bitcoin network

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60. In doing so, the SPVBlockStore (as of 2014) is less than 1GB in size, less than a one-tenth the size of the official blockchain, and this is why we use SPVBlockChain to store our data

61. With a wallet and a place to store the blockchain data, we can now connect to the actual Bitcoin network

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62. Because we added the event listener after we downloaded the initial blockchain, the onCoinsReceived function will be called only when new transactions appear as the program is running

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63. If we had declared it before downloading the initial blockchain, the design of bitcoinJ is such that onCoinsReceived would also have been called on relevant historical transactions

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64. This block store won’t create a file, but by using it, our program will need to redownload the blockchain every time the program runs

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65. Because this program churns through the blockchain in memory, you’ll need to wait a few minutes or more for it to complete (even when you rerun it)

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66. You can also access a blockchain information site (such as http://blockchain

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67. As you saw when we constructed a BlockChain object, bitcoinJ expects the app to pass in a wallet object

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68. This allows the wallet to be updated when relevant historical transactions are found in downloaded blocks and allows rule #1 to be enforced: Be sure not to add additional keys to your wallet after the fact and expect your wallet to work without redownloading the blockchain

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69. This causes a split in the blockchain but is resolved by waiting to see which branch grows by yet another block first

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70. The protocols encoded in this core software are typically supported by a majority of miners and therefore usually determine the properties of the longest blockchain on the network

71. ” It is possible that the blockchain technology could be adopted by other cryptocurrencies in the future, and those currencies could overtake Bitcoin in popularity

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