Doubt blockchain chain 23 | 9012 years, the side chain is still a dead and alive Schrödinger cat?

Written in front of the text: the video version and the text version are slightly different, want to see my affectionate interpretation, please see the video version, thinking logic blame please see the long extension of the copy. I am, not relying on the value of talented fat little 喵~

But as a concept, federation surely represents the future of networks, so that they become not as islands of digital power, but overlapping 'networks of networks'. It is happening already. ——John Dunn

In the past series of "Uncle Blockchain" series, we have introduced the problems currently faced by many blockchains. Speaking of the problem, one of the more dams is the “cross-chain & sidechain” problem, which is the core of the blockchain that wants to disintegrate data and realize the “value Internet”. Therefore, this article will first take you to understand the side chain — Sidechain.

The concept of sidechains is native to the Bitcoin community. We know that if you want to add new features to the Bitcoin network, you need a high level of consensus in the community, so the progress has been slow. In order to quickly iterate the function of cryptocurrency, people's first instinct is to create a new cryptocurrency. The result is that everyone repeatedly copies the bitcoin code and then superimposes a new function, and the new project is hot. This will not only lead to the proliferation of cryptocurrencies, but also the disintegration of community power.

So at that time, the community's small partners were wondering if there was any way to converge all the power on Bitcoin, and the other functions that could not be realized by Bitcoin were attached to the Bitcoin network through the form of sidechains. Around 2012, there was a “one-way peg one-way anchoring technology” in the Bitcoin community that enabled the destruction of bitcoin and the 1:1 release of sidechain tokens.

With One-Way Peg, there will naturally be a two-way peg, which means that the token is transferred from the main chain to the side chain, and then back to the main chain from the side chain.

On October 22, 2014, Adam Back [ Adam Back, the founder of Hash Cash, can be seen in the slogan blockchain seventh? Before the birth of Bitcoin, how many times did the cryptocurrency "dead"? "] and his friends Matt Corallo, Luke Dashjr, Mark Friedenbach, Gregory Maxwell [Matt Corallo, Luke Dashjr, Mark Friedenbach, Gregory Maxwell are both bitcoin core developers. ], etc., released the side chain technical white paper "Enabling Blockchain Innovations with Pegged Sidechains", advocated the creation of sidechains to create innovation, and initially explored the two-Way Peg two-way anchoring form.

So what is the side chain?

First of all, the side chain does not refer to which chain, but a protocol that allows the token to be "transferred" from the main chain to other blockchains, and the protocol that can safely return from other chains to the main chain is called Side chain protocol. Secondly, what we call “token transfer” is not to actually circulate coins from one chain to another, but to lock the main chain on one chain and the side chain on the other. There are many ways to implement this two-way Peg. Common ones include Single Custodian (single hosting mode), Federated peg (multi-signal mode), SPV Proof (SPV proof mode), Drivechain (drive chain). Mode), Hybrid Models, this article mainly analyzes the first three types.

1.Single Custodian (single hosting mode)

The easiest way to achieve bidirectional transfer between the main chain and the side chain is to send the digital assets on the main chain to a host, similar to the form of the exchange. When the custodian receives the relevant information, it transfers the value to the side chain. Side chain coins and vice versa. This form is quite simple and rude, and the shortcomings are quite obvious – the centralization problem is serious.


2.Federated peg (multi-signal alliance mode)

The difference between the multi-signal alliance mode and the single hosting mode is that the middle escrow party is not one, but multiple, each transaction requires M-of-N multi-signature confirmation (M-of-N explanation: for example, this alliance is 30 For a member, a successful cross-chain implementation requires more than 25 confirmations, which is 25-of-30, which varies according to the scenario and rules. This prevents a single notary from having a veto, weakening the centralization of power (as opposed to the first option) and vice versa.


3.SPV Proof (SPV proof mode)

This model is the focus of the Adam Back sidechain white paper (and what everyone wants), let's talk about it~

For example, Xiao A wants to exchange 1 bitcoin and B for 1 side chain token, because he wants to cross another chain in the far distance, so his trading output must be different from normal trading. We call it " SPV Lock Output, etc. The transaction passed the Confirmation Period. After confirmation, the miner will detect that the transaction is different and put the SPV Proof (SPV certificate) for the transaction. ) [SPV Proof, Simple Payment Verification, referred to as SPV. The goal of the SPV is to verify the existence of a transaction payment and how many acknowledgments (how many blocks) the Bitcoin network has. Broadcast to the side chain, SPV Proof means: "hey, we have completed the deduction operation on the main chain, you grab the corresponding token on the side chain to release it"

After receiving the information, the side chain miner releases the corresponding token on the side chain and writes the transaction into the block. After the reorganization period, the transaction from the main chain to the side chain is officially completed. finished.

Regarding the Confirmation Period and the Reorganization Period, we can also expand and explain here: Bitcoin can not guarantee the ultimate security of the transaction after the transaction has been confirmed once, that is, when some nodes receive the block that has packaged the transaction. After that, other branches may become the longest chain, thus causing the reorganization of the blockchain, causing the block that packaged the previous transaction to become a lone block, and the previously confirmed transaction may be invalid. In order to prevent the above possibilities, we must pass the Confirmation Period and the Reorganization Period to ensure the security of the transaction.

In turn, the process from the side chain to the main chain is the same.


Although the third option seems to be the most perfect trustless solution, Adam Back also mentioned in the sidechain white paper: "One of the challenges in deploying pegged sidechains is that Bitcoin script is currently not

Expressive enough to encode the verification rules for an SPV proof.” In short, deploying the rules for verifying SPV proofs is a huge challenge. This requires bitcoin to implement soft forks. Codes that need to change bitcoin (such as adding an OP_SPVProofverify operation) Code, but the deployment related operations are not yet available in the Bitcoin code, here is a sentence The "special SPV output" we mentioned earlier is special here, because there is no specific case yet, so we can't directly point out the specific situation, and change the bitcoin code instead of casually. There is a high level of consensus across the community, so although we have had a lot of attempts on the sidechain, such as Bitcoin's smart contract sidechain RSK, Blockstream's Bitcoin commercial sidechain Liquid, etc., still use Federated peg ( Multi-signal alliance mode).

Example details:

1. The updated version of the RootStock RSK white paper also shows that the RSK is currently using the form of joint wedge .


2.Liquid is also in the form of Ferredpeg, which consists of 23 well-known companies in the digital currency industry including Bitbank, Bitfinex, BitMEX and OKCoin.

The above is some basic concepts and status descriptions about the side chain. If you have any questions, please leave a message to discuss with us~

Remarks: This issue of science content is supported by the ignorant think tank & Babbitt columnist – Peter Wang Guangzhong

Bobby Sea of hacking: Peter Wang Guangzhong Github @ happypeter








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