Explained: blockchain technology

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Bitcoin was invented by an unknown person or group of people under the name Satoshi Nakamoto [11] and released as open-source software in Bitcoins are created as a reward for a process known as mining. They can be exchanged for other currencies, [13] products, and services. As of Februaryovermerchants and vendors accepted bitcoin as payment. The word bitcoin first occurred and was defined in the white paper [5] that was published on 31 October There is no uniform convention for bitcoin capitalization.

Some sources use Bitcoincapitalized, to refer to the technology and network and bitcoinlowercase, to refer to the unit of account. The unit of account of the bitcoin system is a bitcoin. Named in homage to bitcoin's creator, a satoshi is the smallest amount within bitcoin representing 0. As with most new symbols, font support is very limited. Typefaces supporting it include Horta. On 18 Augustthe domain name "bitcoin. In Januarythe bitcoin network came into existence after Satoshi Nakamoto mined the first ever block on the chain, known as the genesis block.

This note has been interpreted as both a timestamp of the genesis date and a derisive comment on the instability caused by fractional-reserve banking. The receiver of the first bitcoin transaction was cypherpunk Hal Finneywho created the first reusable proof-of-work system RPOW in In the early days, Nakamoto is estimated to have mined 1 million bitcoins.

So, if I get hit by a bus, it would be clear that the project would go on. Over the history of Bitcoin there have been several spins offs and deliberate hard forks that have lived on as separate blockchains. These have come to be known as "altcoins", short for alternative coins, since Bitcoin was the first blockchain and these are derivative of it.

These spin offs occur so that new ideas can be tested, when the scope of that idea is outside that of Bitcoin, or when the community is split about merging such changes.

Since then there have been numerous forks of Bitcoin. See list of bitcoin forks. The blockchain is a public ledger that records bitcoin transactions. A novel solution accomplishes this without any trusted central authority: The blockchain is a distributed database — to achieve independent verification of the chain of ownership of any and every bitcoin amount, each network node stores its own copy of the blockchain. This allows bitcoin software to determine when a particular bitcoin amount has been spent, which is necessary in order to prevent double-spending in an environment without central oversight.

Whereas a conventional ledger records the transfers of actual bills or promissory notes that exist apart from it, the blockchain is the only place that bitcoins can be said to exist in the form of unspent outputs of transactions. Transactions are defined using a Forth -like scripting language. When a user sends bitcoins, the user designates each address and the amount of bitcoin being sent to that address in an output.

To prevent double spending, each input must refer to a previous unspent output in the blockchain. Since transactions can have multiple outputs, users can send bitcoins to multiple recipients in one transaction. As in a cash transaction, the sum of inputs coins used to pay can exceed the intended sum of payments.

In such a case, an additional output is used, returning the change back to the payer. Paying a transaction fee is optional. Because the size of mined blocks is capped by the network, miners choose transactions based on the fee paid relative to their storage size, not the absolute amount of money paid as a fee.

The size of transactions is dependent on the number of inputs used to create the transaction, and the number of outputs. In the blockchain, bitcoins are registered to bitcoin addresses. Creating a bitcoin address is nothing more than picking a random valid private key and computing the corresponding bitcoin address. This computation can be done in a split second.

But the reverse computing the private key of a given bitcoin address is mathematically unfeasible and so users can tell others and make public a bitcoin address without compromising its corresponding private key.

Moreover, the number of valid private keys is so vast that it is extremely unlikely someone will compute a key-pair that is already in use and has funds. The vast number of valid private keys makes it unfeasible that brute force could be used for that. To be able to spend the bitcoins, the owner must know the corresponding private key and digitally sign the transaction. The network verifies the signature using the public key.

If the private key is lost, the bitcoin network will not recognize any other evidence of ownership; [9] the coins are then unusable, and effectively lost. Mining is a record-keeping service done through the use of computer processing power. To be accepted by the rest of the network, a new block must contain a so-called proof-of-work PoW.

Every 2, blocks approximately 14 days at roughly 10 min per blockthe difficulty target is adjusted based on the network's recent performance, with the aim of keeping the average time between new blocks at ten minutes. In this way the system automatically adapts to the total amount of mining power on the network. The proof-of-work system, alongside the chaining of blocks, makes modifications of the blockchain extremely hard, as an attacker must modify all subsequent blocks in order for the modifications of one block to be accepted.

Computing power is often bundled together or "pooled" to reduce variance in miner income. Individual mining rigs often have to wait for long periods to confirm a block of transactions and receive payment.

In a pool, all participating miners get paid every time a participating server solves a block. This payment depends on the amount of work an individual miner contributed to help find that block.

The successful miner finding the new block is rewarded with newly created bitcoins and transaction fees. To claim the reward, a special transaction called a coinbase is included with the processed payments. The bitcoin protocol specifies that the reward for adding a block will be halved everyblocks approximately every four years.

Eventually, the reward will decrease to zero, and the limit of 21 million bitcoins [f] will be reached c. Their numbers are being released roughly every ten minutes and the rate at which they are generated would drop by half every four years until all were in circulation. A wallet stores the information necessary to transact bitcoins. While wallets are often described as a place to hold [60] or store bitcoins, [61] due to the nature of the system, bitcoins are inseparable from the blockchain transaction ledger.

A better way to describe a wallet is something that "stores the digital credentials for your bitcoin holdings" [61] and allows one to access and spend them. Bitcoin uses public-key cryptographyin which two cryptographic keys, one public and one private, are generated. There are three modes which wallets can operate in. They have an inverse relationship with regards to trustlessness and computational requirements.

Third-party internet services called online wallets offer similar functionality but may be easier to use. In this case, credentials to access funds are stored with the online wallet provider rather than on the user's hardware. A malicious provider or a breach in server security may cause entrusted bitcoins to be stolen. An example of such a security breach occurred with Mt.

Physical wallets store offline the credentials necessary to spend bitcoins. Another type of wallet called a hardware wallet keeps credentials offline while facilitating transactions. The first wallet program — simply named "Bitcoin" — was released in by Satoshi Nakamoto as open-source code. While a decentralized system cannot have an "official" implementation, Bitcoin Core is considered by some to be bitcoin's preferred implementation.

Bitcoin was designed not to need a central authority [5] and the bitcoin network is considered to be decentralized. In mining pool Ghash. The pool has voluntarily capped their hashing power at Bitcoin is pseudonymousmeaning that funds are not tied to real-world entities but rather bitcoin addresses. Owners of bitcoin addresses are not explicitly identified, but all transactions on the blockchain are public. In addition, transactions can be linked to individuals and companies through "idioms of use" e.

To heighten financial privacy, a new bitcoin address can be generated for each transaction. Wallets and similar software technically handle all bitcoins as equivalent, establishing the basic level of fungibility. Researchers have pointed out that the history of each bitcoin is registered and publicly available in the blockchain ledger, and that some users may refuse to accept bitcoins coming from controversial transactions, which would harm bitcoin's fungibility. The blocks in the blockchain were originally limited to 32 megabyte in size.

The block size limit of one megabyte was introduced by Satoshi Nakamoto inas an anti-spam measure. On 24 August at block, Segregated Witness SegWit went live, introducing a new transaction format where signature data is separated and known as the witness. The upgrade replaced the block size limit with a limit on a new measure called block weightwhich counts non-witness data four times as much as witness data, and allows a maximum weight of 4 megabytes.

Bitcoin is a digital asset designed by its inventor, Satoshi Nakamoto, to work as a currency. The question whether bitcoin is a currency or not is still disputed. According to research produced by Cambridge Universitythere were between 2. The number of users has grown significantly sincewhen there wereto 1. Inthe number of merchants accepting bitcoin exceededReasons for this fall include high transaction fees due to bitcoin's scalability issues, long transaction times and a rise in value making consumers unwilling to spend it.

Merchants accepting bitcoin ordinarily use the services of bitcoin payment service providers such as BitPay or Coinbase. When a customer pays in bitcoin, the payment service provider accepts the bitcoin on behalf of the merchant, converts it to the local currency, and sends the obtained amount to merchant's bank account, charging a fee for the service.

Bitcoins can be bought on digital currency exchanges. According to Tony Gallippia co-founder of BitPay"banks are scared to deal with bitcoin companies, even if they really want to". In a report, Bank of America Merrill Lynch stated that "we believe bitcoin can become a major means of payment for e-commerce and may emerge as a serious competitor to traditional money-transfer providers.

Plans were announced to include a bitcoin futures option on the Chicago Mercantile Exchange in Some Argentinians have bought bitcoins to protect their savings against high inflation or the possibility that governments could confiscate savings accounts.

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In Part 1 we took a look at the incentives involved in Bitcoin mining and how they are used guarantee a single transaction history needed to prevent bitcoins from being double spent.

In this post we will take more a technical look at the cryptography involved and how it is used to secure the network. As I said previously, Bitcoin is very accessible. Before moving forward we should take a moment to learn about hash functions since they are used all throughout the Bitcoin protocol. To put it simply, a hash function is just a mathematical algorithm that takes an input and turns it into an output.

For example, suppose we have an algorithm which just adds all the digits in the input string together. If our input is we would get an output of However, there are certain properties of really good hash functions that make them suitable to use in cryptography. Keep these properties in mind as they are vital to the operation of the Bitcoin protocol. The output should be the same length regardless of whether the input has 10 characters or 10 thousand characters.

A tiny change in the input should produce an entirely different output that in no way relates to the original input. You might wonder how we can trust something that came from the NSA.

The consensus is that they are secure. Now that we have the preliminaries out of the way we can start focusing in on the protocol. If you read Part 1 you will recall that all Bitcoin transactions are relayed to each of the peers in the network. The first step in the process is to hash each transaction in the memory pool using SHA The raw transaction data may look something like this:.

These hashes are then organized into something called a Merkle Tree or hash tree. The hashes of the transactions are organized into pairs of twos, concatenated together, then hashed again. The same is done to each set of outputs until something like a tree is formed or an NCAA bracket.

In the above example there are only four transactions tx stands for transaction. A real block will contain hundreds of transactions so the bracket tree will be much larger. The hash at the very top of the tree is called the Merkle Root. The block header will look something like this:.

Now having done all this can we go ahead and relay the block to the rest of the network? If you recall the last post, the answer is no. We still need to produce a valid proof of work. The output must be less than the specified number.

Another way of saying this is that the hash of the block header must start with a certain number of zeros. For example a valid hash may look like this: Any block whose header does not produce a hash that is less than the target value will be rejected by the network.

The target value is adjusted by the protocol every two weeks to try to maintain an average block time of 10 minutes.

This is where the nonce comes in. The nonce is simply a random number that is added to the block header for no other reason than to give us something to increment in an attempt to produce a valid hash. If your first attempt at hashing the header produces an invalid hash, you just add one to the nonce and rehash the header then check to see if that hash is valid.

This is Bitcoin mining in a nutshell. This is essentially what Bitcoin mining is, just rehashing the block header, over, and over, and over, and over, until one miner in the network eventually produces a valid hash. When he does, he relays the block to the rest of the network. If so, they add the block to their local copy of the block chain and move on to finding the next block. However, the more hashes that you can perform per second, the greater the probability that you will mine a block and earn the block reward.

CPU mining quickly gave way to GPU mining graphics processing units which proved much more efficient at calculating hash functions. Basically, these are purpose built computer chips that are designed to perform SHA calculations and do nothing else. At present, the total hashing power in the network is about terrahashs per second and closing in on one petahash per second. Because each miner is sending these 25 bitcoins to his own address, the first transaction in each block will differ from miner to miner.

Now remember the properties of a cryptographic hash function? If an input changes even in the slightest, the entire output changes. Since the hash of the coinbase transaction at the base of the hash tree is different for each miner, the entire hash tree including the Merkle root will be different for each miner. That means the nonce that is needed to produce a valid block will also be different for each miner.

This is the reason why the Merkle tree is employed after all. Any change to a single transaction will cause an avalanche up the hash tree that will ultimately cause the hash of the block to change. If an attacker wants to alter or remove a transaction that is already in the block chain, the alteration will cause the hash of the transaction to change and spark off changes all the way up the hash tree to the Merkle Root. Given the probabilities, it is unlikely a header with the new Merkle Root will produce a valid hash the proof of work.

Hence, the attacker will need to rehash the entire block header and spend a ton of time finding the correct nonce. But suppose he does this, can he just relay his fraudulent block to the network and hope that miners will replace the old block with his new one or, more realistically, that new users will download his fraudulent block? The reason is because the hash of each block is included in the header of the next block.

If the attacker rehashes block number , this will cause the header of block to change, requiring that block to be rehashed as well. A change to the hash of block will cause the header of block to change and so on all the way through the block chain. Any attempt to alter a transaction already in the block chain requires not only the rehashing of the block containing the transaction, but all other subsequent blocks as well.

Depending on how deep in the chain the transaction is, it could take a single attacker weeks, months, or years, to rehash the rest of the block chain. The only exception to the above rule is if the attacker simply gets lucky. As we noted, it takes the entire network an average of 10 minutes to find a valid block. The deeper a transaction is in the block chain, however, the more times in row the attacker would need to get lucky and mine a block before the rest of the network to extend his chain longer than the main chain.

From a probability standpoint, the chances of such an attack succeeding decrease exponentially with each subsequent block. In the original white paper Satoshi Nakamoto calculated the probabilities that an attacker could get lucky and pull off a double spend. In the following table q is the percentage of the network controlled by the attacker, P is the probability an attacker could get lucky and override z number of blocks.

Which is usually why it is recommended that if you are selling something expensive, you should wait until your transaction is six blocks deep six confirmations in Bitcoin lingo before actually handing over the merchandise.

This post got long in a hurry. Hope you enjoyed these posts and I hope you learned something. I found your post comments while searching Google. It is very relevant information.

Regularly I do not make posts on blogs, but I have to say that this posting really forced me to do so. Really fantastic and I will be coming back for more information at your site and revisit it! I still have one question though: Smart Contracts Great Wall of Numbers.

Part 2 — Mechanics … Bitcoin. For the hash chaining, does it mean if somebody get one valid hash, I need to update and download it and re-calculate based on his block?

Or can I make a new branch based on previous block? Bitcoin Online resources collected The Bitcoin Journey How Cryptocurrencies Work Bitcoin Getter. Bitcoin has seen rapid increases during the last year and there are now those who are claiming that the bubble is soon to burst and Bitcoin crumble.

Those of us continue believe in the idea of a user owned system away from the reach of the banks. We do not believe that the currency is finished. We shall be staying with Bitcoin and I am quite confident that it will continue to rise more rapidly than before. Bitcoin Frenzy — Is it the next gold or just a bubble?

How Cryptocurrencies Work - Cryptocurrency How Cryptocurrencies Work — Bitcoin Support. Thanks for a great article. How then does the miner broadcast that to the rest of the network to get consensus on the work if his nonce is unique from what another miner would have theoretically found?

Cryptocurrency trading is becoming a profession — The Glimpse. How Cryptocurrencies Work — Bitcoin Supports. You are commenting using your WordPress. You are commenting using your Twitter account. You are commenting using your Facebook account. Notify me of new comments via email. Notify me of new posts via email. Cryptographic Hash Functions Before moving forward we should take a moment to learn about hash functions since they are used all throughout the Bitcoin protocol.

It should be very easy to compute an output for any given input, however it should be impossible given current knowledge of mathematics and the state of computers to compute the input for a given output even while knowing the mathematical algorithm.

In this case there are many possible inputs that could add up to 10 55, , , etc. However, given the simplicity of our function one could still figure out the input relatively easily.