Private and Public Blockchain occurs when the financial enterprises start to explore the various blocks of the Blockchain technology. These two Blockchains are coming up with business oriented models as to obtain the difference between the two. The private blockchain generates at a lower cost and faster speed than the public blockchain. In the previous years, the blockchain has grown to become an interesting subject globally. It is becoming an integrated part in the financial sectors all over the digital world.
However, the Lightning Network would, again, require a change to the existing Bitcoin protocol. (Though again it would be a “soft fork,” i.e. the existing blockchain would remain fully valid.) And/or — you guessed it — a Lightning sidechain. What’s more, one of the changes it requires, the elimination of transaction malleability, is handled by the Segregated Witness work in Sidechain Elements. (correction: all of of the changes required are incorporated into Elements Alpha — it’s Lightning-ready out of the box.)

We use node 2 to receive a payment of 200 via the smart contract function, receivePayment(). Note that the receivePayment() function can accept a second parameter for the account address that is used to create this transaction. (Note that you can also set web3.eth.defaultAccount = "<…account address…>", after which you can just call receivePayment(200) with one parameter.)
External Account, which stores ETH balance – This contains the address of the User that was created using the Web3.js API, e,g, personal.newAccount(…). These accounts are used for executing smart contract transactions. ETH is your incentive received for using your account to mine transactions. The address of the account is the public key, and the password of the account is the private key.

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You cannot be a crypto investor or entrepreneur without having a real understanding of the differences between these types of blockchains as well as their implications. Even if they are based on similar principles, their operation is, in fact, different to all levels. So the tokens issued by these blockchains will not be assessed in the same manner.
Private institutions like banks realized that they could use the core idea of blockchain as a distributed ledger technology (DLT), and create a permissioned blockchain (private or federated), where the validator is a member of a consortium or separate legal entities of the same organization. The term blockchain in the context of permissioned private ledger is highly controversial and disputed. This is why the term distributed ledger technologies emerged as a more general term.
What Bitcoin’s development team is essentially doing through feature-creep is forcing everyone in the non-tech world to use Bitcoin through commercial proxies to avoid all this complexity (crypto-what? security? sidechain?), which effectively results in the loss of security, relative anonymity and decentralized properties that helped to make it interesting in the first place.

Sidechains are responsible for their own security. If there isn’t enough mining power to secure a sidechain, it could be hacked. Since each sidechain is independent, if it is hacked or compromised, the damage will be contained within that chain and won’t affect the main chain. Conversely, should the main chain become compromised, the sidechain can still operate, but the peg will lose most of its value.
The idea emerged that the Bitcoin blockchain could be in fact used for any kind of value transaction or any kind of agreement such as P2P insurance, P2P energy trading, P2P ride sharing, etc. Colored Coins and Mastercoin tried to solve that problem based on the Bitcoin Blockchain Protocol. The Ethereum project decided to create their own blockchain, with very different properties than Bitcoin, decoupling the smart contract layer from the core blockchain protocol, offering a radical new way to create online markets and programmable transactions known as Smart Contracts.
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Implemented by The initial design was published by Blockstream in 2014, but the implementation is blocked by the lack of native support for SPV proofs in Bitcoin (which may not be added at all). Rootstock workaround this by sacrificing decentralization (still work in progress). The Ardor platform created by Jelurida is the first to propose and implement the concept of Child Chains. Already running on testnet, the production Ardor launch is scheduled for Q4 2017.
Public chains to the rescue! Public chains offer public transaction data that can be verified in real-time by anybody that cares to run a node. The more independent users or institutions that take part in verification, the more secure and decentralised the chain becomes! At Iryo, we strive to have every clinic doing full validation of the global state for the relevant smart contracts (EOS based). Public blockchains are mainly useful for two things; value routing (including initial creation and distribution) and trustless timestamping of messages.
Third option is to write your own blockchain protocol according to your needs. You will be able to answer all your what if questions if you design it by yourself. Ripple, Hyperledger projects (Fabric, Burrow, Indy), Corda, Multichain and most flexible and popular one Ethereum can be examples of that option. That option is the most costly and risky one. You have to invest a lot, and after you create your blockchain, you have to find people & companies to use it. Also you need to attract community of developers to upgrade, enhance your blockchain for coming requirements in the future. Above blockchains are the ones I remember immediately, also there are others.
Walmart recently filed patents that could allow the retailer to store vendor and consumer e-commerce payment data using blockchain technology to improve security. This application would encrypt payment information in digital shopping systems and create a network able to automatically conduct transactions on behalf of a customer. The payments would be received by one vendor or more, depending on the services and who provided them.
Blockstream believes that to be secure, blockchain systems must be built with open source technology. Towards that goal, we've created the Elements Project, a community of people extending and improving the Bitcoin codebase. As open source, protocol-level technology, developers can use Elements to extend the functionality of Bitcoin and explore new applications of the blockchain. Join the expanding group of individual and corporate developers using Elements to build robust, advanced, and innovative blockchains.
Sidechain is a chain of blocks based on the main parental blockchain. Sidechains realize the new financial ecosystems via integration into Bitcoin. Relatively new to Bitcoin, the sidechain is an extension that enables the ability both to build a link between BTC and an altcoin and to create new independent services that work via the main Bitcoin blockchain. Using sidechains allows for the creation of various types of smart contracts, stocks, derivatives, etc. It is possible to develop a limitless number of Bitcoin or Ethereum-based sidechains with different tasks and features, assets of which will depend on the main blockchain’s volatility. It allows traditional blockchains to support several kinds of assets, payments, smart contracts and also to increase the level of security and anonymity of transactions.
To scale Blockchain, sidechain or childchain solutions cannot be undermined. Sidechains are separate Blockchains that are linked to the main Blockchain using a two-way peg. They are an auxiliary network that executes the complementary function of: faster transactions, lower transaction costs and greater scalability in terms of the number of transactions that can be supported in a network at a given time.
The words block and chain were used separately in Satoshi Nakamoto's original paper, but were eventually popularized as a single word, blockchain, by 2016. The term blockchain 2.0 refers to new applications of the distributed blockchain database, first emerging in 2014.[13] The Economist described one implementation of this second-generation programmable blockchain as coming with "a programming language that allows users to write more sophisticated smart contracts, thus creating invoices that pay themselves when a shipment arrives or share certificates which automatically send their owners dividends if profits reach a certain level."[1]
The block time is the average time it takes for the network to generate one extra block in the blockchain.[27] Some blockchains create a new block as frequently as every five seconds.[28] By the time of block completion, the included data becomes verifiable. In cryptocurrency, this is practically when the transaction takes place, so a shorter block time means faster transactions. The block time for Ethereum is set to between 14 and 15 seconds, while for bitcoin it is 10 minutes.[29]
The public blockchain is open to anyone who wants to deploy smart contracts and have their executions performed by public mining nodes. Bitcoin is one of the largest public blockchain networks today. As such, there is limited privacy in the public blockchain. Mining nodes in the public blockchain requires a substantial amount of computational power to maintain the distributed ledger at a large scale. In the Ethereum public blockchain, smart contract codes can be viewed openly.
Smart contracts are immutable pieces of code and their outcomes are irreversible. Hence, formal verification of their code is very important before deploying them. It’s very hard to verify smart contracts in the Ethereum Virtual Machine (EVM). A business can’t afford to deploy faulty but immutable smart contracts and suffer the consequences of their irreversible outcome. This article details the challanges: “Fundamental challenges with public blockchains”.
Sidechains as an idea have existed and had been floating around for quite some time now, the bases is to extend the decentralization of trust into other sectors and to other digital assets. However, while this all sounds great it's a perfect example of good in theory but not so much in practice. Nevertheless, this hasn't stopped people from trying with groups such as Blockstream exploring the idea and our friends over at Rootstock co-creating a Sidechain which is allowing Litecoin and Bitcoin to execute smart contracts and all without changing the core software of the original currency.

Instead of adding new features directly to the bitcoin blockchain, sidechains allow developers to attach new features to a separate chain. Since the chains are still attached to the bitcoin blockchain, the features can take advantage of the cryptocurrency's network effects and test those applications, without harming the main network should vulnerabilities arise.
If you’ve been keeping track of developments in the bitcoin industry, you’d know that the blockchain refers to the public ledger of transactions associated with the cryptocurrency. As the bitcoin ecosystem has grown in size and scale throughout the years, the blockchain has also increased considerably in length and storage size, prompting debates on whether or not to increase its block size limit.
The differences between these types of blockchains are based on the levels of trust existing among the members of the network and the resulting level of security. Indeed, the higher the level of trust between the members of the network, the lighter the consensus mechanism (which aims to add the blocks to the blockchain securely). As we will see, there is no trust between the members of a public blockchain since it is open to everyone and inversely the confidence is much stronger on the private blockchain since members are pre-selected. In networks based on a blockchain, the level of trust among the members therefore directly impacts the structure and mechanisms of the network.
Many blockchain enthusiasts believe in the value of networks that are not only decentralized — which most closely resembles the current model of the Internet — but distributed. This includes Tim Berners-Lee, who founded the World Wide Web in 1989. Berners-Lee has proposed that blockchains can be used to reinvent the web in a more distributed and peer-to-peer fashion.
And now for the second clever part. The logic above is symmetric. So, at any point, whoever is holding these coins on the sidechain can send them back to the Bitcoin network by creating a special transaction on the sidechain that immobilises the bitcoins on the sidechain. They’ll disappear from the sidechain and become available again on the Bitcoin network, under the control of whoever last owned them on the sidechain.
Governance: Every enterprise needs to design standards, processes, methods, and tools to develop and operate a private blockchain. To achieve this they will need tools and frameworks such as IDE, testing framework, security auditing tool etc. For long-term successful operation, they also need to develop high-quality documentation. This requires proactive governance. Read more about the importance of the “Fundamental challenges with public blockchains” here.

Por lo tanto, y gracias a estas sidechains, se podrían conectar a Bitcoin soluciones con objetivos concretos, complementándole y aprovechando sus ventajas pero con la suficiente independencia. Para ello se usan unas piezas llamadas ‘two-way peg’, que son las encargadas de sincronizar las transferncias (validan y inmovilizan las monedas) entre ambas cadenas: la sidechain cuenta con unas monedas ya minadas pero sin dueño a la espera que, tras el intercambio, queden bajo el control del usuario que llega a esta cadena.

The creation of sidechains have been a direct result of scalability issues associated with the main blockchain for projects such as Ethereum. Making sidechains increasingly popular way to speed up transactions. Lisk was the first decentralized application (dapp) to implement sidechains. With Lisk, each dapp created exists on its own sidechain without interfering with the mainchain.
The public blockchain is open to anyone who wants to deploy smart contracts and have their executions performed by public mining nodes. Bitcoin is one of the largest public blockchain networks today. As such, there is limited privacy in the public blockchain. Mining nodes in the public blockchain requires a substantial amount of computational power to maintain the distributed ledger at a large scale. In the Ethereum public blockchain, smart contract codes can be viewed openly.
Many people believe this is the future of the blockchain. It maintains network security and allows for scalability. The biggest criticism is that it heavily favors those with more funds as smaller holders have no chance of becoming witnesses. But the reality is, smaller players have no hope of participating in Proof of Work either, as mining from your own laptop at home is no longer a reality. Smaller players get outcompeted by bigger players who have massive mining rigs. STEEM and EOS are examples of DPOS blockchains. Even Ethereum is moving to POS with its Casper project.
"I see quite a few use cases for private blockchains, and they definitely have their place. Traditional institutions won't switch to a completely public blockchain from one day to the other. A private blockchain is a great first step towards a more cryptographic future. The biggest advantages of private blockchains in comparison to centralized databases are the cryptographic auditing and known identities. Nobody can tamper with the data, and mistakes can be traced back. In comparison to a public blockchain it is much faster, cheaper and respects the company's privacy. As a conclusion, it's better to rely on a private blockchain than no cryptographic system at all. It has merits and pushes the blockchain terminology into the corporate world, making truly public blockchains a bit more likely for the future." 
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