So, there is a kind of centralized authority that decides who has a right to contribute to and to audit the network. What is more – it’s possible to restrict viewing information stored on private blockchains. It might seem that in such conditions, a blockchain is no longer the blockchain as it lacks transparency and decentralization. Well, these remarks are fair, but only when the network is estimated from the outside. Within it, the rules remain the same as for public networks: it is still transparent for all the members.
The distributed Bitcoin mining network performs quadrillions of calculations every second that maintain the integrity of its blockchain. Other blockchains aren’t remotely as secure, but they innovate much faster. Sidechains, an innovation proposed and developed by the startup Blockstream, allow for the best of both worlds; the creation of new blockchains “pegged” to Bitcoin, so that value can be transferred between them, which can conceivably be automatically secured by Bitcoin miners via “merged mining.”
– A consensus much faster: the fact that the consensus mechanism is centralized makes it much quicker. In fact, the term “consensus” is no longer adapted since it is rather a recording of transactions on the blockchain. Note that the entity responsible for managing the blockchain can decide to change the parameters of the blockchain and in particular to increase the size of the blocks to be able to add more transactions.

In some cases, these advantages are unneeded, but in others they are quite powerful - powerful enough to be worth 3x longer confirmation times and paying $0.03 for a transaction (or, once scalability technology comes into play, $0.0003 for a transaction). Note that by creating privately administered smart contracts on public blockchains, or cross-chain exchange layers between public and private blockchains, one can achieve many kinds of hybrid combinations of these properties. The solution that is optimal for a particular industry depends very heavily on what your exact industry is. In some cases, public is clearly better; in others, some degree of private control is simply necessary. As is often the case in the real world, it depends.

Lisk es una plataforma open source en la que se pueden desarrollar y ejecutar smart contracts en forma de aplicaciones descentralizadas o DAPPS multiplataforma. Éstas, y como uno de los puntos fuertes de Lisk, son desarrolladas con, posiblemente, el lenguaje de programación más famoso y usado, Javascript. Aunque con un enfoque genérico, ya han empezado a aparecer algunas soluciones e interés en sectores concretos, como es el caso del Internet de las cosas que, junto a Chain of Things, están empezando a explotar.

Security: RSK´s blockchain is secured by merge-mining, which means that they can achieve the same security as Bitcoin in terms of double-spend prevention and settlement finality. The 2way peg security will first rely in a federation holding custody of bitcoins, and later switch to an automatic peg, when the community accepts the security trade-offs of the automatic peg.
Jump up ^ Redrup, Yolanda (29 June 2016). "ANZ backs private blockchain, but won't go public". Australia Financial Review. Archived from the original on 3 July 2016. Retrieved 7 July 2016. Blockchain networks can be either public or private. Public blockchains have many users and there are no controls over who can read, upload or delete the data and there are an unknown number of pseudonymous participants. In comparison, private blockchains also have multiple data sets, but there are controls in place over who can edit data and there are a known number of participants.
Contrary to popular belief, aided by deceptive blockchain marketing, blockchains are not a good solution for storing data. Each piece of information that you store in the blockchain sits in hundreds or more nodes (more than 100,000 in the case of Bitcoin) making it an extremely costly solution. This is why the Iryo Network doesn’t store data on blockchain but instead, uses blockchain to ensure the transparency of transactions. As a disclaimer, competitors also don’t save medical data on the chain itself (even those who use private chains). Instead, only the fingerprint aspect of a medical record file or a hash is stored on the blockchain.
Function	Transactions executed between the locks and unlocks of the main chain tokens don't bloat the main chain. As the technology of a side chain is connected to its main chain, it can be used to build on the developments of the main chain and introduce new features to the market.	Child chains serve as the transactional chains of the parent-child architecture, as the parent chain retains minimal features.

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.

Sidechains are blockchains that allow for digital assets from one blockchain to be used securely in a separate blockchain and subsequently returned to the original chain. The term “sidechain” in this case is used for context, in that the paper initially refers to Bitcoin as the “parent chain” and connected blockchains (altcoins) as “sidechains,” but the term is interchangeable so that altcoins interacting with each other can each be a parent chain interacting with sidechains. You may have also heard of “childchains,” which are also sidechains.

The second option will be to use sidechains. Blockstream first announced side chain in 2014 and published its whitepaper ( I believe in the future, bitcoin will have its desired flexibility with its sidechains. The idea of the sidechain is you can innovate and design your solution freely in the sidechains. These sidechains are independent, if they are failed or hacked, they won't damage other chains. So damage will be limited within that chain, for that reason you can be less conservative. Otherwise you would be more risk averse, if you had 42.5 billion dollar market cap like Bitcoin.

It is different with a private blockchain (or closed) since the members of the network are selected before being able to download the protocol and therefore use the proposed service by the network. The mining capabilities and the system of consensus as a whole are centralized within the hands of the same entity. A network based on a private blockchain is therefore not decentralized in itself.
They rely on a technology called SPV (simplified payment verification) proofs, which work like this: in order to send money to a sidechain and back to the main bitcoin network again, users need to attach a proof that they really have the funds. Without these proofs, when users or miners move their money back to the main chain, under certain conditions, they could take more money than they really have.
That might sound like a problem, but it isn’t because the box can only be opened infrequently (two or three times a year), and a super-majority of miners must leave a note on the box in advance. This note states exactly where the miners intend to transfer the money. The “correct” note is automatically generated by sidechain software, and is easy to check.

@tradles – thanks for taking the time to explain this. OK – so I get the debate around blockchain bloat and the (grudging) inclusion of OP_RETURN, etc., but what I’m missing is that I can only really see one scenario where embedding any identity data into the blockchain makes sense…. and that’s when I want to *associate* an identity with a transaction I’m performing.
"Proof of Work" used by Bitcoin is a competitive consensus algorithm. Each node races to solve a difficult puzzle first. Doing so earns the right to produce a block and you are rewarded in Bitcoin. The block is where the transaction (value of data) is written and confirmed. However, this race is a waste of time and money for those that don’t win. You get nothing unless you are the first to solve the puzzle. Since no one wants to lose, nodes started working together to solve the puzzle and share the reward based on your computational power (the hash rate).
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.
A blockchain is so-called “public” (or open) when anyone can become a member of the network without conditions of admission. In other words, anyone wishing to use the service proposed by the network can download the protocol locally without having to reveal his or her identity or meet predetermined criteria. A protocol is a computer program that could be compared to a Charter in that it defines the rules of operation of a network based on a blockchain. For example, the members of the bitcoin network download the Bitcoin protocol (through the intermediary of their “wallet”) to be able to join the network and exchange bitcoins, but the only condition is to have an Internet connection.
This approach isn’t fool-proof, but it’s not by mistake that the system looks the way it does today (that’s my history degree talking). Despite best technical efforts, human problems remain within the realm of probability. From “…blame cannot be easily assigned: not even the most sophisticated economists of the era could accurately predict disaster, let alone guard against it. The effects of a public herd mentality at the time of the [insert catastrophe here] are depicted, all too recognizably, as unstoppable.”
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