The Truth Machine: The Blockchain and the Future of Everything. Paul Vigna

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СКАЧАТЬ hope that it will become an everyday medium of exchange, is its primary purpose. Without its existence as an incentive for computer owners to honestly validate exchanges of valuable information, Satoshi’s censorship-resistant distributed ledger simply wouldn’t work.

      Of course, for this all to tie together, the miners must regard bitcoin currency as having value—they must believe they’ll be able to exchange it for other things of established value, be they goods and services or fiat currencies such as dollars. Fully exploring how they, and millions of others, came to conclude that bitcoins did have value requires a deeper dive into how human communities reach agreements on what constitutes a common medium of exchange, store of value, and unit of account—the three qualities of money. (For that dive, we again will shamelessly recommend The Age of Cryptocurrency.) What we can say is that, contrary to popular opinion, a currency need not be backed by anything, be it the commitment of a government or a fixed amount of commodity such as gold, only that it be sufficiently recognized as a useful means of measuring and clearing exchanges of value. This might seem counterintuitive because we tend to think of money as a physical thing that somehow contains value within the particular item—the paper note, or the gold coin. But in reality currencies only convey a symbolic tokenized value, one that’s derived solely from the collective will of society to commonly accept the token as a marker of that value. This same malleability of thinking can be applied to any token, so long as enough people accept it. That’s what happened to bitcoin.

      The structure of the ledger is also important for keeping Bitcoin secure. Nakamoto conceived of his as an ever-growing, unbroken chain of blocks, each representing a batch of transactions strung together and validated within a ten-minute bitcoin reward period. Hence the word that’s now on every CIO’s lips: “blockchain.” (Notably, the term “blockchain” never appeared in the original Bitcoin white paper—a good argument for why Bitcoin should have no exclusive claim to the term.)

      Within each block period, every miner that’s engaged in the proof-of-work race for the next bitcoin reward is simultaneously gathering new incoming transactions and arranging them into their own new block. The details of each transaction—date, time, addresses of senders and recipients, the amounts sent, etc.—are captured and run through a special cryptographic algorithm to produce an alphanumeric string known as a hash. A hashing algorithm can convert any arbitrary amount of original source data into a single, fixed-length string of letters and numbers, providing a means of mathematically proving the existence of that underlying information. Anyone in possession of the transaction information can easily run it through the same hashing algorithm to confirm that whoever made the original hash must be in possession of the same data.

      A key feature of hashes is that they are hypersensitive to changes in the underlying data. Here’s one we generated from the previous paragraph’s raw text by running it through the highly secure SHA-256 algorithm that Bitcoin uses:

      63f48074e26b1dcd6ec26be74b35e49bd31a36f849033bdee4194b6be8505fd9

      Now, note that when we simply remove the last period from that paragraph of text, the algorithm came back with a completely different alphanumeric string:

      8f5967a42c6dc39757c2e6be4368c6c5f06647cc3c73d3aa2c0abdec3c6007a5

      If you think about this in terms of someone trying to secretly change transaction data, you can see how this hypersensitivity is vital to the blockchain’s integrity. If anyone tries to introduce changes to existing transactions, other miners will clearly recognize that the new hash output doesn’t match what they have in their versions of the blockchain. So they will reject it.

      Bitcoin also takes advantage of the fact that it’s possible to take two hashes, combine them, and produce a root hash that encapsulates the two separate data proofs. This process can be repeated ad infinitum, creating hashes of hashes of hashes in a hierarchical structure known as a Merkle Tree. This is how transactions within each block are bundled and cryptographically tied together.

      Bitcoin then takes this linking function one step further. Through another cryptographic hashing function, the winning miner ties their newly created block to the previous one. This turns the entire blockchain into a never-ending, mathematically linked chain of hashed transactions that goes all the way back to the “Genesis” block of January 3, 2009. Make a change to a transaction from January 15, 2011, and the blockchain’s interlinked hash-based record of all the data recorded in the subsequent seven years will be completely altered. It’s a bit like how banks use exploding dye to protect banknotes: any thief who tries to spend the stolen money is immediately exposed.

      This unbroken record of transactions provides the foundation that miners use to verify the legitimacy of the transactions contained in the winning miner’s new block. If a miner is satisfied with the contents of that block they will commit to connecting their next block to it if they are lucky enough to be the winner. If they’re unsatisfied, they would attach their new block to an earlier block whose contents they trust, leaving the suspicious one as an “orphan.” This decision-making forms the basis for Bitcoin’s consensus logic, which is based on a convention known as the “longest chain.” The idea is that if no miner has amassed more than 50 percent of total computing capacity, then mathematical probability will ensure that any attempt by a rogue minority to add a series of new ten-minute blocks to a previously rejected and orphaned one will soon fall behind the majority’s longer chain and will be abandoned. The caveat, of course, is that if bad actors do control more than 50 percent of the computing power they can produce the longest chain and so incorporate fraudulent transactions, which other miners will unwittingly treat as legitimate. Still, as we’ve explained, achieving that level of computing power is prohibitively expensive. It’s this combination of math and money that keeps Bitcoin secure.

      These cobbled-together concepts comprise Satoshi Nakamoto’s breakthrough: a decentralized, censorship-resistant record of the past. If we acknowledge that all accounting systems are merely estimates—that it’s impossible to arrive at a perfect representation of reality—then this one, a system that collectively captures the shared opinions of a community with no central authority, results in the most objective representation of the truth yet devised.

      In solving the double-spend problem, Bitcoin did something else important: it magically created the concept of a “digital asset.” Previously, anything digital was too easily replicated to be regarded as a distinct piece of property, which is why digital products such as music and movies are typically sold with licensing and access rights rather than ownership. By making it impossible to replicate something of value—in this case bitcoins—Bitcoin broke this conventional wisdom. It created digital scarcity

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