A company called Blockstream has been focusing on these developments and has announced the release of Sidechain Elements, which is an open-sourced framework for sidechain development. It includes a functioning code and a testing environment for working with sidechains with several components: the core network software to build an initial testing sidechain, eight new features not currently supported by bitcoin, a basic wallet and the code for moving coins between blockchains.
Developers and Cryptocurrency enthusiasts have been looking at expanding Bitcoins functionality as mainstream adoption increases. Side chains would increase the resilience of Bitcoin: If one of the sidechains was to be compromised, only the Bitcoins on that chain would be lost, while other sidechains and the Blockchain would continue like normal. This would further stabilize the Bitcoin network and increase security.
What is the difference between a public blockchain and a private blockchain? Does it matter? Which is better? Gallactic believes that currently there are pros and cons between both Private and Public Blockchains, but time and “convergence”, a term that is gaining prominence in the Blockchain Industry, is clearly showing that the lines between these categories, once clear, are starting to fade.

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.
Sidechain is a blockchain that runs parallel to the main blockchain. It extends the functionality of interplorable blockchain networks. Interpolable blockchain networks signifies the ability to share data between different computer systems on different machines. It means that data can be sent and received between interconnected networks eliminating the possibility of negative impact to the networks. Sidechain enables this to be done in a decentralised manner to transfer and synchronise tokens between two chains.
– we provide no uniqueness of names, unlike the domain registrars, social networks, namecoin, onename.io, etc. There is no uniqueness of names in real life either. Instead the identity is just a hash of a [json] object that contains a public key. Identity object can not be modified directly, but a new version of it can be created, pointing to a previous version. The owner of the identity object can optionally connect it with the real life credentials, e.g. the social account, internet domain, email, etc. by proving the proof of ownership of that account the way onetime.io does it, the way Google Analytics does it, etc. This allows a spectrum of identities from fully anonymous to fully disclosed and verified. This also allows a person to have multiple identities, for work, for social, for gaming, for interest-specific forums. To simulate OAUTH2, a new site-specific identity can be created and signed with person’s other identity.
Thus Tradle set out to build a meta-protocol that saves the data in the overlay network, and only puts minimal referencing data on the blockchain. There is a general grumpy consensus among bitcoin core devs and mining pool operators on allowing one small data chunk, a hash, per transaction. Many devs say it is not possible to secure this second overlay network. I agree, unless we use the blockchain to help with the task. We have a partial solution working, and are preparing a new design to improve it (partial, as it can not yet handle all known attacks). We are actively sharing the designs at various meetups (and on the github) and are inviting devs to find attack vectors and propose solutions. Tradle’s protocol not only relieves the pressure on bitcoin’s blockchain but is also able to handle larger transaction sizes than Counterparty and Mastercoin, so it can be used for complex identity, supply chain management and many other applications. It is also capable of handling attachment files, needed in the healthcare and financial industries.

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.
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.

The “three-part” transaction structure is very general but it only allows you to transfer ownership of Bitcoins. Some people would like to transmit richer forms of information across these sorts of systems. For example, a decentralized exchange needs a way for participants to place orders. Projects such as Mastercoin, Counterparty, NXT and others either build layers on top of Bitcoin or use entirely different codebases to achieve their goals.

Aelf uses a consensus algorithm called DPoS (Delegated Proof of Stake) that takes the best of both cooperative and competitive consensus algorithms. DPoS uses votes from stakeholders to achieve consensus. The competitive part is larger stakeholders having an influence on their delegate of choice. The delegates that have the most votes will take their turn to produce a block cooperatively in a sequence. DPoS makes transactions permanent. A rollback isn’t possible so a confirmation can be fast. DPoS is also scalable because anyone can participate in the consensus. Additionally, DPoS is environmentally friendly because electricity isn’t wasted like in Proof of Work.
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.
Write permissions are kept centralized to one organization. Read permissions may be public or restricted to an arbitrary extent. Example applications include database management, auditing, etc. which are internal to a single company, and so public readability may in many cases not be necessary at all. In other cases public audit ability is desired. Private blockchains are a way of taking advantage of blockchain technology by setting up groups and participants who can verify transactions internally. This puts you at the risk of security breaches just like in a centralized system, as opposed to public blockchain secured by game theoretic incentive mechanisms. However, private blockchains have their use case, especially when it comes to scalability and state compliance of data privacy rules and other regulatory issues. They have certain security advantages, and other security disadvantages (as stated before).
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Sometimes separate blocks can be produced concurrently, creating a temporary fork. In addition to a secure hash-based history, any blockchain has a specified algorithm for scoring different versions of the history so that one with a higher value can be selected over others. Blocks not selected for inclusion in the chain are called orphan blocks.[22] Peers supporting the database have different versions of the history from time to time. They keep only the highest-scoring version of the database known to them. Whenever a peer receives a higher-scoring version (usually the old version with a single new block added) they extend or overwrite their own database and retransmit the improvement to their peers. There is never an absolute guarantee that any particular entry will remain in the best version of the history forever. Because blockchains are typically built to add the score of new blocks onto old blocks and because there are incentives to work only on extending with new blocks rather than overwriting old blocks, the probability of an entry becoming superseded goes down exponentially[23] as more blocks are built on top of it, eventually becoming very low.[1][24]:ch. 08[25] For example, in a blockchain using the proof-of-work system, the chain with the most cumulative proof-of-work is always considered the valid one by the network. There are a number of methods that can be used to demonstrate a sufficient level of computation. Within a blockchain the computation is carried out redundantly rather than in the traditional segregated and parallel manner.[26]
Structure Side chains are independent blockchains that have a kind of "pegging mechanism", where at least one of the chains (main chain and side chain) is "aware" of the other chain and both tokens are pegged at a set ratio. Side chains need their own network security and block processing. "Child Chains" of the Ardor platform are tightly integrated into the main Ardor parent chain. All transactions are processed and secured by the parent chain forgers. This makes cross-chain transactions possible. Pruning will be enabled on child chain transactions in order to significantly reduce blockchain bloat by pruning the transactions on regular basis from the blockchain.
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.
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.
In private blockchains, only specific, pre-chosen entities have the ability to create new transactions on the chain (this is known as “write permissions”). Thus, a private blockchain is a closed network that offers constituents the benefits of the technology, but is not necessarily decentralized or distributed, even among its members. The extent to which each constituent can view (“read”) and create and validate transactions (“write”) is up to the developers of the chain.

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.