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.

@mowliv I think a good way to think about it is by looking at our economy. The Federal Reserve prints US dollars for the US Government (the main blockchain) to boost the US economy. However, US dollars can be exported to other countries (a side chain) that could have a completely independent economy but still use a currency backed by the US government. – Olshansk May 30 '17 at 0:56
Open blockchains are more user-friendly than some traditional ownership records, which, while open to the public, still require physical access to view. Because all early blockchains were permissionless, controversy has arisen over the blockchain definition. An issue in this ongoing debate is whether a private system with verifiers tasked and authorized (permissioned) by a central authority should be considered a blockchain.[36][37][38][39][40] Proponents of permissioned or private chains argue that the term "blockchain" may be applied to any data structure that batches data into time-stamped blocks. These blockchains serve as a distributed version of multiversion concurrency control (MVCC) in databases.[41] Just as MVCC prevents two transactions from concurrently modifying a single object in a database, blockchains prevent two transactions from spending the same single output in a blockchain.[42]:30–31 Opponents say that permissioned systems resemble traditional corporate databases, not supporting decentralized data verification, and that such systems are not hardened against operator tampering and revision.[36][38] Nikolai Hampton of Computerworld said that "many in-house blockchain solutions will be nothing more than cumbersome databases," and "without a clear security model, proprietary blockchains should be eyed with suspicion."[9][43]
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.
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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".
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.

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.
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There are many critics of payment channels. Finding the quickest path between unconnected nodes is no trivial exercise. This is a classic “traveling salesman” problem that has been worked on by top computer scientists for decades. Critics argue that it is highly unlikely payment channels like Bitcoin’s Lightning and Ethereum’s Raiden will work as expected in practice due to complexities like the traveling salesman problem. The key for you is just to know that these projects and potential solutions to blockchain scalability issues exist. Many of the smartest minds in the industry are working actively to bring them to life.
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.” 
The great thing about Bitcoin, for a tech columnist like me, is that it’s simultaneously over-the-top cinematic and technically dense. Richard Branson recently hosted a “Blockchain Summit” at his private Caribbean island. There’s a Bitcoin Jet. At the same time, 2015 has seen the release of a whole slew of technically gnarly–and technically fascinating–proposals built atop the Bitcoin blockchain.

“Amit Goel is the Founder & Chief Strategy & Innovation Officer for MEDICI. Amit’s vision is to build a strong FinTech market network that involves financial institutions, banks, startups, investors, analysts & other key stakeholders across the ecosystem – helping each one of them in a meaningful way by removing the asymmetry of information and providing a platform to engage & transact.\ \ Amit is passionate about bringing actionable FinTech-focused insights, innovative products & services for the FinTech ecosystem. Some of his work involves startup scores, bank scores/assessments, predictive viewpoints & other innovations that have helped MEDICI’s customers and the ecosystem. He has been named amongst the Top 100 FinTech thought leaders/influencers in the world & Top 10 in Asia multiple times by reputed agencies, consulting firms as well as financial institutions. Amit has built MEDICI (formerly LTP) as a new-age, tech-enabled advisory/research firm, which is now considered the #1 global research & innovation platform for FinTech in the world.\ \ Amit has been writing pioneering viewpoints on financial technology space that have been ahead of the curve since 2010. His data-driven predictions have helped the customers as well as the ecosystem. His past work experience includes a strong background in strategy & market analysis and advisory to clients (from big business houses to Fortune 500 firms) in payments, commerce, financial services & IT/technology. In the past, Amit had also founded a successful consulting & research practice called GrowthPraxis and has worked at Boston Analytics, Frost & Sullivan, and Daimler Chrysler in strategy & research.”
The ShipChain platform unifies shipment tracking on the Ethereum blockchain, using a sidechain to track individual encrypted geographic waypoints across each smart contract. With this system, the meaning of each cryptographic waypoint is only accessible for interpretation by the parties involved in the shipment itself. This gives shippers more visibility across their supply chain, and allows carriers to communicate with ease.
Jump up ^ Iansiti, Marco; Lakhani, Karim R. (January 2017). "The Truth About Blockchain". Harvard Business Review. Harvard University. Archived from the original on 18 January 2017. Retrieved 17 January 2017. The technology at the heart of bitcoin and other virtual currencies, blockchain is an open, distributed ledger that can record transactions between two parties efficiently and in a verifiable and permanent way.
A blockchain is a continuously growing list of records called blocks, these blocks are linked and secured using cryptographic algorithms. Each block typically contains a hash (a link to a previous block), a timestamp as well as transaction data. Full nodes validate all the transactions, but are unable to settle the disagreements in regards to the order in which they were received. To prevent double-spending, the entire network needs to reach global consensus on the transaction order. It achieves this by using centralised parties or a decentralised proof of work or proof of stake algorithm (and its derivatives).
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.
Plasma, a project by Ethereum, uses this side chain concept. It encourages transactions to happen on side chains (or child chains). An authority governs each of the child chains. If the authority starts acting maliciously, anyone on the child chain can quit the child chain and take back their pegged assets on the main chain. It’s in its early stages of development but shows a lot of promise in handling some of Ethereum’s scalability issues.

– The transactions added to the blockchain are public: the whole world (Member of the network as non-members) can access transactions that are added to the blockchain. The information of the transactions is made public for the miners who do not know the other members, to check the conformity (for example that the person who has created a transaction holds enough bitcoins). These transactions are obviously not nominative, only your public key appears, but if someone knows your public key, he will be able to find all the transactions that you have created.
The Blockstream Satellite network broadcasts the Bitcoin blockchain to the entire planet. The satellite network provides an opportunity for nearly 4 billion people without Internet access to utilize bitcoin while simultaneously ensuring bitcoin use is not interrupted due to network interruption. Utilizing the latest open source Software Defined Radio (SDR) technologies, the Blockstream Satellite network offers a breakthrough in the cost effectiveness of satellite communications.
– The transactions added to the blockchain are public: the whole world (Member of the network as non-members) can access transactions that are added to the blockchain. The information of the transactions is made public for the miners who do not know the other members, to check the conformity (for example that the person who has created a transaction holds enough bitcoins). These transactions are obviously not nominative, only your public key appears, but if someone knows your public key, he will be able to find all the transactions that you have created.
Tú, o el usuario en cuestión de las sidechains, envía los bitcoins a una dirección Bitcoin específica, sabiendo que, una vez mandados, estarán fuera de tu control y fuera del control de cualquier otra persona. Estarán completamente inmovilizados y sólo se podrán desbloquear si alguien puede demostrar que no se están utilizando en ningún otro lugar.

A side-chain is a secondary blockchain layer designed to facilitate lower-cost and/or higher-speed transactions between two or more parties. One case in which they're often deployed is between parties who make many transactions amongst each other. Committing all of those transactions to the public blockchain would may undesirable for cost or other reasons, so the side-chain's job in this example would be to aggregate the activity into the least transactional activity necessary to reflect the final state of the side-chain's ledger.
Let's explore if there is a hybrid blockchain concept (third type). A consortium blockchain would be a mix of both the public and private. Wherein the ability to read & write could be extended to a certain number of people/nodes. This could be used by groups of organization/firms, who get together, work on developing different models by collaborating with each other. Hence, they could gain a blockchain with restricted access, work on their solutions and maintain the intellectual property rights within the consortium.
Las sidechains son otro de los conceptos más famosos entorno a Bitcoin, no los pierdas de vista. La teoría indica que permitirían añadir funcionalidades nuevas a Bitcoin, pero sin necesidad de modificar constantemente el código de éste, ya que la funcionalidad es desarrollada utilizando otra cadena de bloque para finalmente ser conectada a la de Bitcoin. Al mismo tiempo esto evitaría la saturación de una sola cadena de bloques, como actualmente ocurre, al utilizar cadenas diferentes para cada caso de uso.

A private blockchain on the other hand provides only the owner to have the rights on any changes that have to be done. This could be seen as a similar version to the existing infrastructure wherein the owner (a centralized authority) would have the power to change the rules, revert transactions, etc. based on the need. This could be a concept with huge interest from FI’s and large companies. It could find use cases to build proprietary systems and reduce the costs, while at the same time increase their efficiency. Some of the examples could be:


Bitcoin está demostrando un potencial enorme, y desarrolladores de todo el mundo quieren llevar esta tecnología aún más lejos, por ejemplo con los smart contracts turing completo o las llamadas smart property. El problema es que Bitcoin tiene un lenguaje de programación deliberadamente limitado. Además sus transacciones se confirman relativamente despacio, cada 10 minutos. Y ya por último y muy importante, su cadena de bloques está saturándose de transacciones debido a la creciente fama de Bitcoin.


The first question to answer is “What is public blockchain?” The very name of this type of networks implies that they are open and permissionless. It means that anyone in the world can join the network, add blocks and view the information stored there. Indeed, public blockchains are totally transparent as any of their members can audit them. For this reason, independent participants can easily agree on transactions without middlemen and the fear of deception.
Congratulations! You’ve just educated yourself on the most common advanced topics in blockchain that you’ll hear about. By understanding these concepts, you have a firmer grasp on the fundamental tradeoffs and latest research on the blockchain than most industry “experts”! Better yet, next time you hear your colleagues around the water cooler talking about state channels, the Lightning Network and Byzantine fault tolerance, not only will you know what they’re talking about but you might be able to teach them a thing or two!
At Iryo, we consider databases and blockchains that are not opened to the public to be insecure they, can easily be altered by the business running it, at their discretion and it goes against the ethos of the open and transparent cryptocurrency space. Designed to keep public out and introducing “trusted” middlemen, private chains forget that trusted third parties are security holes.
RSK is the first open-source smart contract platform with a 2-way peg to Bitcoin that also rewards the Bitcoin miners via merge-mining, allowing them to actively participate in the Smart Contract revolution. RSK goal is to add value and functionality to the Bitcoin ecosystem by enabling smart-contracts, near instant payments and higher-scalability.
Jump up ^ Kopfstein, Janus (12 December 2013). "The Mission to Decentralize the Internet". The New Yorker. Archived from the original on 31 December 2014. Retrieved 30 December 2014. The network's 'nodes'—users running the bitcoin software on their computers—collectively check the integrity of other nodes to ensure that no one spends the same coins twice. All transactions are published on a shared public ledger, called the 'block chain.'
Elements Alpha functions as a sidechain to Bitcoin’s testnet, though the peg mechanism currently works through a centralized protocol adapter, as described in the Sidechains whitepaper. It relies on an auditable federation of signers to manage the testnet coins transferred into the sidechain via the “Deterministic Pegs” Element, and to produce blocks via the “Signed Blocks” Element. This makes it possible to immediately explore the new chain’s possibilities, using different security trade-offs. They plan to, in a later release, upgrade the protocol adapter to support fully decentralized merge-mining of the sidechain, and ultimately to phase in the full 2-way peg mechanism.
By design, a blockchain is resistant to modification of the data. It is "an open, distributed ledger that can record transactions between two parties efficiently and in a verifiable and permanent way".[7] For use as a distributed ledger, a blockchain is typically managed by a peer-to-peer network collectively adhering to a protocol for inter-node communication and validating new blocks. Once recorded, the data in any given block cannot be altered retroactively without alteration of all subsequent blocks, which requires consensus of the network majority. Although blockchain records are not unalterable, blockchains may be considered secure by design and exemplify a distributed computing system with high Byzantine fault tolerance. Decentralized consensus has therefore been claimed with a blockchain.[8]
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@gendal, good question. Think of the identity hash as a bitcoin address, it is indeed public. So to assert anything with this identity you need to sign the object you are creating or changing with the identity’s private key. Specifically it is a private key that corresponds to a public key that you published in your identity’s object (json). The signature is not placed on the bitcoin transaction, as OP_RETURN has only 40 bytes. The signature is added to a [json] object that is modified with this identity. If you see any fault with this, please let me know.
First of all, one should not confuse private and public blockchains. They have one obvious similarity – they are blockchains, decentralized networks. Every participant of the network keeps a copy of this shared ledger, and all these copies are kept sync with the help of a certain consensus protocol. It means that all the participants of the network have access to identical information. Also, all the networks are immutable, and the information they contain can’t be altered.
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A federation is a group that serves as an intermediate point between a main chain and one of its sidechains. This group determines when the coins a user has used are locked up and released. The creators of the sidechain can choose the members of the federation. A problem with the federation structure is that it adds another layer between the main chain and the sidechain.
In the context of the two-way peg, the DMMS is represented by the Simplified Payment Verification Proof (SPV Proof), which is a DMMS confirming that a specific action on a PoW blockchain occurred. The SPV Proof functions as the proof of possession in the initial parent chain for its secure transfer to a sidechain. Symmetric two-way pegs are the primary type of two-way peg so we will only be referring specifically to the symmetric (compared to asymmetric) peg in this piece.
Nodes can be trusted to be very well-connected, and faults can quickly be fixed by manual intervention, allowing the use of consensus algorithms which offer finality after much shorter block times. Improvements in public blockchain technology, such as Ethereum 1.0's uncle concept and later proof of stake, can bring public blockchains much closer to the "instant confirmation" ideal (eg. offering total finality after 15 seconds, rather than 99.9999% finality after two hours as does Bitcoin), but even still private blockchains will always be faster and the latency difference will never disappear as unfortunately the speed of light does not increase by 2x every two years by Moore's law.
A public blockchain is a platform where anyone on the platform would be able to read or write to the platform, provided they are able to show the proof of work for the same. There has been a lot of activity in this space as the number of potential users that any technology in this space could generate is high.  Also, a public blockchain is considered to be a fully decentralized blockchain. Some of the examples are:
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.
Sidechains, just like any other Blockchain, need their own miners to help protect them from nefarious actors and attacks which people would like to leverage against the network. However, since wealth isn't actually created on the Sidechain there is far less incentive for miners to actually work on it and help protect it. Because of this, transaction fees are the basic reward that is offered to miners. However, these often equate to mere pennies.
Cohen said Walmart also has a patent on drone delivery systems that facilitate orders in a cleaner way, track package contents, environmental conditions and location. Walmart supplier Coca-Cola is starting a pilot to use blockchain to identify inhumane labor conditions in its sugar supply chains. Coca-Cola plans to create a secure decentralized registry for workers and their contracts to help securely record their workers’ identities while providing a trail in case employers abuse their power.
Further, despite sidechains being independent of each other, they are responsible for their individual security and need the requisite mining power to remain secure. Bitcoin’s blockchain has sufficient PoW mining power to remain secure even from the most coordinated of attacks, but many more nascent sidechains lack the necessary network effects and mining power to guarantee security to users.
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.
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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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.
A public blockchain is ideal when the network must be truly decentralized, which means that no central entity controls the entry of the members on the network and the consensus mechanism is democratic. A democratic mechanism of consensus means that all members can become a minor and that these miners are in competition to add the blocks to the blockchain (at least when the mechanism of the evidence of the work is used).
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.
Public blockchains are just that, public. Anyone that wants to read, write, or join a public blockchain can do so. Public chains are decentralized meaning no one body has control over the network, ensuring the data can’t be changed once validated on the blockchain. Simply meaning, anyone, anywhere, can use a public blockchain to input transactions and data as long as they are connected to the network.