For example, let’s say we have side chain 1 (SC1) and side chain 2 (SC2). A transaction occurs on SC1. A node in SC1 broadcasts the transaction to nodes in the main chain to record this transaction. The same node of SC1 calls a function from SC2 with a proof. The function in the nodes of SC2 verifies the proof on the main chain. The function gets executed.

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.

Unfortunately our second option cannot be done yet, because to use these sidechains, main chain (here it is bitcoin) needs to do some upgrade (soft fork). By the way, upgrades in public blockchains are very painful yet. There will be a user activated soft fork (UASF) on August 1. All bitcoin forms’ trend topic is this soft fork which is about a code change for Segregated Witness Adoption.

3) the argument ‘let’s harden internal IT as if it worked outside the firewall’ makes a ton of sense to me. We need to construct a lot of hoops for hackers to jump through, as permitter defense is not holding up anymore. And we need to make our systems anti-fragile. The blockchain data structure is a good tool, other P2P tools can be used too. Also, the blockchain has initiated a renaissance of crypto tech, like multisig, payment channels., HD wallets, hot-cold storage, and other innovations in key management.

Pegged sidechains employ a two-way peg to transfer assets between chains, and they consist of providing proof of possession in the transferring transactions. The idea is to enable the capability of locking an asset on an original parent chain, which can then be transferred to a sidechain before eventually being redeemed on the original chain. Notably, the original asset on the parent chain is locked in a specific output address and is not destroyed like early implementations of sidechains.

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.
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.
2) Yes – I had to keep things short/simple in this intro article in order to get across the key ideas. But you’re right: the sidechains need to be secured. But how that happens is a matter for the sidechain. If somebody can produce a false “proof” that the locked Bitcoins should be released on the Bitcoin side then that’s a problem for the sidechain, of course (somebody presumably just had their coins stolen!) but it’s irrelevant (at a macro level) on the Bitcoin side.

If you want a deeper look at Proof of Stake check out our detailed POS post. In short, while Proof of Work is an effective mechanism to secure the blockchain and provides a trustless consensus paradigm, it’s extremely energy intensive because of all the computing power required to solve hash problems. Also, while it was meant to be decentralized, it’s actually becoming more centralized as miners consolidate and massive mining setups eat up larger shares of winning blocks.
“We believe that public blockchains with censorship resistance have the potential to disrupt society, when private blockchains are merely a cost-efficiency tool for banking back offices. One can measure its potential in trillions of dollars, the other in billions. But as they are totally orthogonal, both can coexist in the same time, and therefore there is no need to oppose them as we can often see it.” 
That is however not all. Sidechains also have some specific use cases, unique to a certain blockchain. One example is the usage of sidechains in EOS. EOS is currently facing a RAM problem. RAM is too expensive and developers are complaining. Sidechains could compete with the EOS mainchain by having lower RAM prices, this would lead to competition, incentivizing both the EOS mainchain block producers and sidechain block producers (mainchain and sidechains of EOS are maintained by the same group of block producers) to keep the RAM price as low as possible. This also means there is more RAM available, so the RAM price will go down as a result.
Since 2008 when Satoshi Nakamoto published a white paper considering Bitcoin and blockchain technology, the latter gained fame as a tool for combating trust issues and bringing transparency to transactions between independent participants. Even though a decade passed, for a lay public, blockchain is still not the easiest concept to deal with. As a rule, people generalize things they don’t understand deeply in detail. Thus, when they hear “blockchain,” they tend to think there’s just one transcendental blockchain that hosts thousands of projects. But it’s a wrong perception as there are numerous blockchains and they differ.
Blockchain was invented by Satoshi Nakamoto in 2008 to serve as the public transaction ledger of the cryptocurrency bitcoin.[1] The invention of the blockchain for bitcoin made it the first digital currency to solve the double-spending problem without the need of a trusted authority or central server. The bitcoin design has inspired other applications,[1][3] and blockchains which are readable by the public are widely used by cryptocurrencies. Private blockchains have been proposed for business use. Some marketing of blockchains has been called "snake oil".[9]
Sidechains interactuando con blockchain. Blockstream explica en su paper como, a las sidechains, se les añade una nueva pieza llamada two-way peg. Two-way peg es “el conector” entre ambas cadenas y se encarga de hacer la “magia” para que los bitcoins “salten” a la otra cadena. Juntando ambas cosas obtenemos las pegged sidechain: cadenas laterales conectadas en todo momento. En la imagen puedes observar como, incluso, las sidechain pueden interactuar entre ellas. ¿Llegaremos a un escenario de blockchains interactuando con aspecto fractal?

The main point of a side-chain is to allow cryptocurrency networks to scale and interact with one-another. For example alt-coins and Bitcoin run on separate chains, however side chains allow for these separate currencies to be transferred through these two-way 'portal's or interfaces via a fixed conversion amount. Added benefits of side-chains are different asset classes like,stocks, bonds etc being integrated through a converted price onto the main chain, along with additional functionality like smart contracts,unique D-Apps, micro-payments and security updates that can be later incorporated into the primary network from these side-chains.
Fully private blockchains: a fully private blockchain is a blockchain where write permissions are kept centralized to one organization. Read permissions may be public or restricted to an arbitrary extent. Likely applications include database management, auditing, etc internal to a single company, and so public readability may not be necessary in many cases at all, though in other cases public auditability is desired.
The top 10 Ethereum decentralized apps (DApps) have daily active user counts in the thousands. Compare this with a centralized platform like Facebook, which has over a billion daily users, and you can see just how small scale blockchain use still remains. For a detailed comparison, read “State of the DApps: 5 Observations From Usage Data (April 2018)”.
Blockchain, trust, decentralization, Bitcoin, transparency, anonymity, blockchain, blockchain, blockchain. These words seem to appear randomly on the Web regardless the theme of an article you read. Don’t you know how to implement blockchain in art? There’s definitely someone who can tell you. Do you wonder how banking can benefit from blockchain? No worries, some projects already do it – just search for the use cases.
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.
2) Yes – I had to keep things short/simple in this intro article in order to get across the key ideas. But you’re right: the sidechains need to be secured. But how that happens is a matter for the sidechain. If somebody can produce a false “proof” that the locked Bitcoins should be released on the Bitcoin side then that’s a problem for the sidechain, of course (somebody presumably just had their coins stolen!) but it’s irrelevant (at a macro level) on the Bitcoin side.
A partir de este momento, se podrán intercambiar y mover estas monedas para hacer uso del potencial de esa sidechain siguiendo las directrices y protocolo que ésta tenga estipulado. Por ejemplo, quizá la velocidad de creación de los bloques es más rápida en esta o quizá los scripts de transacción en esa cadena son turing completos (disponen de un poder de cómputo equivalente a la máquina universal de Turing).
Using Rootstock as an example, in order to transfer assets from one chain to the other a user on the parent first has to send their coins to a special output address where they will consequently become locked and un-spendable. Once the transaction is completed, SPV then confirms it across the chains and after waiting out a contest period, which is just a secondary method to help prevent double spending, the equivalent amount will be credited and spendable on the Sidechain and vice versa.
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.
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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]
Note: Some would argue that such a system cannot be defined as a blockchain. Also, Blockchain is still in it’s early stages. It is unclear how the technology will pan out and will be adopted. Many argue that private or federated Blockchains might suffer the fate of Intranets in the 1990’s, when private companies built their own private LANs or WANs instead of using the public Internet and all the services, but has more or less become obsolete especially with the advent of SAAS in the Web2.
Private blockchains, or as I like to call them, shared databases, have a place in improving efficiency for financial institution for back-office settlement processes. They should not be seen as controversial, or part of some dialectic struggle between punks and police. To the extent that the identifying shroud of AML/KYC can be placed into public blockchain metadata (possible in Omni Layer transactions over the Bitcoin blockchain) there may even be interoperability between these two sides of the train tracks. Right now, due to state-granted monopolies to issue credit, most of the world's liquidity is still in banks. However, we believe that in the long-term, public blockchains, especially those based on work, will come to take a more significant part in the ‘System D’ informal economy, which is where most of the global economic growth will originate.”