Sidechains are an essential innovation in the blockchain field with some interesting long-term implications and effects on the broader interoperability and scalability of blockchain networks. They are effectively extensions of existing blockchains that increase their functionality and allow for validation of data from other blockchains and for assets to be seamlessly transferred between them.
Things get a bit more interesting when you replace the single custodian with a federation of notaries by way of a multisignature address. In this model, a federation of entities must sign-off on movements to and from the sidechain, so more parties must be compromised for a failure situation to unfold where the bitcoins frozen on the main chain are stolen.
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New distribution methods are available for the insurance industry such as peer-to-peer insurance, parametric insurance and microinsurance following the adoption of blockchain.[71][72] The sharing economy and IoT are also set to benefit from blockchains because they involve many collaborating peers.[73] Online voting is another application of the blockchain.[74][75]
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Cohen recently noted that before blockchain is practical in retail, brands have to understand its relevance. NPD said it’s not just about payment methods or sourcing transparency. It also has the potential to touch all areas of a company. Cohen highlights a few areas where blockchain has the ability to impact retail including revolutionizing supply chain management, preventing against counterfeiting, simplifying payments and creating safer data security.

Consortium blockchains: a consortium blockchain is a blockchain where the consensus process is controlled by a pre-selected set of nodes; for example, one might imagine a consortium of 15 financial institutions, each of which operates a node and of which 10 must sign every block in order for the block to be valid. The right to read the blockchain may be public, or restricted to the participants, and there are also hybrid routes such as the root hashes of the blocks being public together with an API that allows members of the public to make a limited number of queries and get back cryptographic proofs of some parts of the blockchain state. These blockchains may be considered "partially decentralized".


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.
The second option will be to use sidechains. Blockstream first announced side chain in 2014 and published its whitepaper (https://blockstream.com/sidechai...). 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.
These kinds of blockchains are forks of the original implementations but deployed in a permissioned manner. Mainly hyped because the companies behind these chains want to onboard corporations in order to generate buzz around their their chain. It’s tolerable for proof of concepts or if they plan to move to public as soon as possible; otherwise they are just using the wrong set of tools for the job.

Over the last year the concept of “private blockchains” has become very popular in the broader blockchain technology discussion. Essentially, instead of having a fully public and uncontrolled network and state machine secured by cryptoeconomics (eg. proof of work, proof of stake), it is also possible to create a system where access permissions are more tightly controlled, with rights to modify or even read the blockchain state restricted to a few users, while still maintaining many kinds of partial guarantees of authenticity and decentralization that blockchains provide. Such systems have been a primary focus of interest from financial institutions, and have in part led to a backlash from those who see such developments as either compromising the whole point of decentralization or being a desperate act of dinosaurish middlemen trying to stay relevant (or simply committing the crime of using a blockchain other than Bitcoin). However, for those who are in this fight simply because they want to figure out how to best serve humanity, or even pursue the more modest goal of serving their customers, what are the practical differences between the two styles?
A sidechain is a separate blockchain that is attached to its parent blockchain using a two-way peg. The two-way peg enables interchangeability of assets at a predetermined rate between the parent blockchain and the sidechain. The original blockchain is usually referred to as the ‘main chain’ and all additional blockchains are referred to as ‘sidechains’. The blockchain platform Ardor refers to its sidechains as ‘childchains’.
@tetsu – not sure what you mean. My reading of the sidechains paper is that the worst case scenario is that an attacker manages to “reanimate” Bitcoins on the main blockchain that had been sent to the sidechain… but that would be the attacker stealing the coins from the rightful owner on the sidechain. From Bitcoin’s perspective, the coins were always going to be reanimated…. so the risk is entirely borne by the holder(s) on the sidechain. Am I missing something?
Liquid is the world's first federated sidechain that enables rapid, confidential, and secure bitcoin transfers. Participating exchanges and Bitcoin businesses deploy the software and hardware that make up the Liquid network, so that they can peg in and out of the Bitcoin blockchain and offer Liquid’s features to their traders. Liquid provides a more secure and efficient system for exchange-side bitcoin to move across the network.
Another technology that could see more widespread use in the coming years is side chains. A side chain is defined for one specific use case. There can be multiple side chains where different tasks are distributed accordingly for improving the efficiency of processing. Maybe one application needs to optimize for high speeds and another needs to optimize for large computations. In any case, side chains can be used to handle commercial blockchain usage. CryptoKitties would have greatly benefitted from an optimized high-speed side chain. At one point, they jammed up the Ethereum blockchain with 25% of all transactions coming from their application.
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.

Recordemos, como hemos mencionado anteriormente, que actualmente son cientos los proyectos y monedas alternativas que trabajan con su propia cadena de bloques, totalmente desconectadas de la de Bitcoin. Todas con su cotización volatil. El problema de estas monedas es que ninguna de ellas dispone del efecto red ni de la seguridad que sí tiene Bitcoin. De hecho muchas, pese a haber implementado propuestas interesantes, se quedan en nada, con miles de horas y esfuerzo “tirado a la basura”. Incluso algunas de ellas han replicado el codigo de Bitcoin, pero también los fallos que en ese momento pudiera tener y mientras que en Bitcoin si se han solucionado, en esa Altcoin no.
¡Por supuesto! para todo ello existen muchas propuestas con soluciones muy interesantes, pero hacer cambios experimentales sobre el código de Bitcoin es arriesgado y, que la mayoría de nodos se adapten, lleva tiempo. Bitcoin es grande y esto hace que la toma de decisiones sea lenta al reflexionarse los cambios de manera muy profunda. Esta toma de decisiones lenta e incapacidad del protocolo de ampliar con modulos las capacidades de Bitcoin es el principal motivo por el que empezaron a salir otras criptomendas centradas en nichos y casos de usos concretos. Era más sencillo clonarse el código abierto de Bitcoin y adaptartlo que esperar a que en Bitcoin se decidiese aceptar su funcionalidad. Este es, principalmente, el motivo por el cual hay cientos de criptomonedas y se necesita un wallet por cada una de ellas, siendo un absoluto caos a veces, ya que todas están desconectadas entre ellas.

What if we could run heavy computations in a more centralized fashion, say on a single server, and then periodically integrate the results onto the main blockchain for posterity. We temporarily expose some vulnerability while the parallel server runs the heavy computation, but we get a massive benefit in that we don’t have to run the computation on chain, and simply need to store the results for future verification. This is the general premise behind Truebit. We won’t get into all the details of Truebit but there is a concept of challengers, who check to see the computations that were made have high fidelity.
Because decentralization has been viewed by many as intrinsic to the revolutionary potential of blockchain, the point of private blockchains might be called into question. However, blockchains offer much more than a structure that accommodates decentralization. Among other features, their strong cryptography and auditability offers them more security than traditional protocols (although not bulletproof, as noted), and they allow for the development of new cryptocurrencies. Furthermore, voting platforms, accounting systems, and any type of data archive can arguably be optimized with blockchain technology. We are still in the early days of blockchain technology, and the power it has to reshape older systems has yet to be seen.

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.)
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.
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 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.”
Miners are needed to ensure the safety of the sidechains. This makes the formation of new sidechains a costly venture. Hefty amounts of investments have to be made before any new sidechain can be created. Another downside to sidechains is the requirement of a federation. The extra layer formed by the federation could prove to be a weak point for attackers.
"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).
2. I have not had a chance to read the original article on side chains, but I am sure they deal with my next problem quite adequately. However it is not addressed in the above article. The primary problem that must be addressed with the notion of side chains, as I see it, would be the issue of the mining required to authenticate transactions and enter them into the block chain. The article mentions that side chain system more or less leaves the issue of verification within the side chain transactions as something of a black box, somewhat implying that they don’t have to be considered. But for any user, they would need to be both considered and understood. Such a process would presumably require mining verification of some kind, (our mental model must include consideration of the somewhat unusual verification method for bitcoin transactions themselves, – as everyone would agree, the verification process is not just a “checklist” of valid transaction strings. The validation process requires mining in much the same sense as mining new coin. None of this is mentioned or discussed in the article. ) As a result, the verification of side chain transactions outside the block chain introduces whole new layers of risk into the Bitcoin model, and new layers of unknowns.
A private blockchain network requires an invitation and must be validated by either the network starter or by a set of rules put in place by the network starter. Businesses who set up a private blockchain, will generally set up a permissioned network. This places restrictions on who is allowed to participate in the network, and only in certain transactions. Participants need to obtain an invitation or permission to join. The access control mechanism could vary: existing participants could decide future entrants; a regulatory authority could issue licenses for participation; or a consortium could make the decisions instead. Once an entity has joined the network, it will play a role in maintaining the blockchain in a decentralized manner.
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