There is a whole other issue of identity theft that needs to be addressed. Just a short note here as this is a big subject: If the private key to identity object is stolen, the true owner of the identity needs to have a way to change the key. One approach to that would be to use the private key of the bitcoin transaction that created the first version of the identity object. Another way could be to prove the ownership of other public keys on the identity object, like the one used for encryption (PGP key management suggests a separate key for each purpose, signing, encryption, etc.). Other non-automatic ways could include a trusted third-party, social proof, etc.

Frankly, secure implementation of Bitcoin is already a pain in the ass .. adding more complexity just seems like the wrong move at this point. It’s already trying to be a currency, a networking protocol and a client in the same codebase. Adding turing complete (or not) scripts with arbitrary outcomes, multiple versions of the official client cooperating, multiple clients, and now multiple blockchains is basically the nail in the coffin in terms of widespread implementation.
“The only reason the banks have gotten to the point of thinking about permissioned ledger is because they finally reached the stage of bargaining, third stage in five stages of grief, for industry they’re about to lose. They start with denial, and the basis of denial is, well, this thing isn’t gonna work, it’s gonna die any day soon, and it doesn’t. And then they say, it’s just silly money and it doesn’t have any value, until it does; and no one else is gonna play with it, except they are; serious investors won’t put money into this, except they did; and it still refuses to die. We go from denial to bargaining. Somewhere in between might be anger, some depression, and eventually they’re going to reach acceptance, but it’s gonna take a long time. 

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 typical use case for a private blockchain is intra-business: when a company decides to implement blockchain as a business solution, they may opt for a chain to which only company members have access. This is useful if there’s no need for anybody outside of the company to become part of the chain, because private blockchains are more efficient than public and consortium chains. Also, because they are smaller and contained, it is easier for a consensus process or other technical stipulation to be altered on a blockchain. So, for example, if the developers or proprietors want to change the cryptographic method which runs its consensus process, it is much easier to do this on a private blockchain than a public or consortium chain.

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In general, so far there has been little emphasis on the distinction between consortium blockchains and fully private blockchains, although it is important: the former provides a hybrid between the “low-trust” provided by public blockchains and the “single highly-trusted entity” model of private blockchains, whereas the latter can be more accurately described as a traditional centralized system with a degree of cryptographic auditability attached. However, to some degree there is good reason for the focus on consortium over private: the fundamental value of blockchains in a fully private context, aside from the replicated state machine functionality, is cryptographic authentication, and there is no reason to believe that the optimal format of such authentication provision should consist of a series of hash-linked data packets containing Merkle tree roots; generalized zero knowledge proof technology provides a much broader array of exciting possibilities about the kinds of cryptographic assurances that applications can provide their users. In general, I would even argue that generalized zero-knowledge-proofs are, in the corporate financial world, greatly underhyped compared to private 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.

Peer-to-peer blockchain networks lack centralized points of vulnerability that computer crackers can exploit; likewise, it has no central point of failure. Blockchain security methods include the use of public-key cryptography.[4]:5 A public key (a long, random-looking string of numbers) is an address on the blockchain. Value tokens sent across the network are recorded as belonging to that address. A private key is like a password that gives its owner access to their digital assets or the means to otherwise interact with the various capabilities that blockchains now support. Data stored on the blockchain is generally considered incorruptible.[1]
There are promising works in sidechains like there can be transactions at higher speed and volume. For example micropayments can be done directly with minimal fee by using Lightning Network side chain. You won't have to wait for 10 minutes for miners to create a block. Or we can have privacy in our transactions by Zerocash side chain. If you want privacy, you send your bitcoin to sidechain and use Zerocash protocol for sending bitcoin to your recipient. This protocol makes your transaction not to be seen in the transaction history, at the same time it won't damage the integrity and security of the Bitcoin. If you use Zerocash protocol in your sidechain, you cannot be tracked anymore. By the way, test results say that its performance is very poor now, but I believe it will be better in the near future.
But, rather than go back to the drawing board, many people are figuring out alternative way to eke better performance outbid the system, and one approach is to use a sidechain.. sonrsther than process many transactions on the bitcoin network, two parties that transact a lot together might deposit down bitcoin into a side chain and conduct a bunch of transactions there (avoiding the absurd cost and delay of bitcoin) and then when they want to “settle up” they then invoke a balancing transaction on the bitcoin network.

"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).
Given all of this, it may seem like private blockchains are unquestionably a better choice for institutions. However, even in an institutional context, public blockchains still have a lot of value, and in fact this value lies to a substantial degree in the philosophical virtues that advocates of public blockchains have been promoting all along, among the chief of which are freedom, neutrality and openness. The advantages of public blockchains generally fall into two major categories:

Blockchain-based smart contracts are proposed contracts that could be partially or fully executed or enforced without human interaction.[55] One of the main objectives of a smart contract is automated escrow. An IMF staff discussion reported that smart contracts based on blockchain technology might reduce moral hazards and optimize the use of contracts in general. But "no viable smart contract systems have yet emerged." Due to the lack of widespread use their legal status is unclear.[56]