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In Detail, resilient side chain SKALE: Technical solutions, cross-chain Bridges, and token economies

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With the implementation of various capacity expansion schemes, SKALE has a relatively stable advantage in technology due to years of accumulation, but it still needs to catch up in ecological construction.

原文标题：《详解弹性侧链网络 SKALE：技术方案、跨链桥与代币经济》

原文来源： ZKSwap中文社区

What is the side chain? Barry Whitehat (author of the Rollup concept) is quoted here as defining a side chain.

Basically, a system in which a group of verifiers submits the latest state of a chain to a smart contract (on the main chain). These checkpoints can be used by a Bridge Contract to support the user's deposits and withdrawals. In general, there will also be a leadership election process among the group of verifiers to determine who will create the side chain block at a given moment, such as the PoA authority proof algorithm and PoS algorithm [1].

Barry also mentioned that as some Layer2 extension solutions mature, it is important to consider how side chains can be better integrated with other solutions. And in some specific situations, side chain features can shine.

At present, the mainstream side chain schemes mainly include: Polygon (original Matic Network), xDai Stable Chain and SKALE Network. This paper will review SKALE's technical solutions, expansion packages, IMA cross-chain Bridges, SKALE tokens and governance, SKALE's ecological development, investment and financing.

SKALE profile

The SKALE network is positioned as an "resilient side-chain network" for Ethereum, capable of supporting thousands of individual blockchains, side chains, storage chains, and other types of sub-chains. These blockchains are all connected to the Ethereum mainnet and are fully compatible with the Ethereum ecosystem.

The side chain of the SKALE network is run by an Virtualized Subnodes selected from the set of nodes on the network. Each side chain is highly configurable, and users can freely choose the side chain specifications, consensus protocols, VMS, female chains, and customized security measures.

The SKALE Network uses Solidity as the programming language for smart contracts, runs models that are fully EVM compliant, supports the mainstream Ethereum token standards, also has access to the web via Web3.js and Web3.py, and uses tools like Truffle and Remix. Developer friendly.

SKALE network composition

详解弹性侧链网络 SKALE：技术方案、跨链桥与代币经济

Credit: SKALE Network Whitepaper

The SKALE network consists of SKALE nodes and SKALE administrators, who are smart contracts deployed on the Main ethereum network. SKALE administrator contract plays the role of "entry", undertaking the creation and destruction of nodes, the creation and destruction of elastic side chain, the rotation of virtual child nodes and the issuance of SKALE rewards.

Credit: SKALE Network Whitepaper

The virtual child nodes are participants in the elastic side chain, responsible for implementing SKALE consensus, running SKALE EVM, and facilitating inter-chain communication.

Node creation and destruction

The following steps are required for potential nodes to be transformed into nodes of SKALE network :(1) first, run SKALE background program to evaluate whether potential nodes meet the hardware requirements of the network; (2) If the evaluation is successful, the potential node can submit an application to the SKALE administrator to join the network. To submit the application, you need to pledge network security and provide node metadata such as IP address, port and public key. (3) After submission, potential nodes join the system and are called "full node" or "light node" (the difference between the two types of nodes is that the full node provides all resources for a certain elastic side chain, while the light node participates in multiple elastic side chains).

When a node is created, the SKALE network assigns it a set of peers (currently 24). The peer periodically reviews the downtime and latency of the node to determine the rewards to be granted to the node per network cycle.

If a node wants to exit the network, it broadcasts an exit message to the network and waits for a period of termination. The node can then get back the network security it pledged.

Creation and destruction of elastic side chains

Customizable "resilient side chains" are one of SKALE's innovations. "Elastic" means that the blockchain is not fixed, and users can choose the configuration of the blockchain according to their needs, with 1/128 (small), 1/16 (medium) or 1/1 (large) node resources and 3, 6 and 12 month duration options, as well as the storage capacity of the network. And use the SKALE token to pay the corresponding rent. (The current cost of resource consumption in the SKALE network depends on the chain specification and lifecycle, and will be dynamically calculated in the future based on current network conditions and system load.)

After the user submits the application to the SKALE administrator, a new elastic side chain is created.

Credit: SKALE Network Whitepaper

If the rent paid by the user is exhausted or the user deletes its elastic side chain, the elastic side chain will be destroyed. In addition, users can rotate the virtual child nodes of the elastic side chain to avoid collusion and ensure the decentralization of the elastic side chain.

Overall, the creation and destruction of SKALE's elastic side chain is similar to the way we rent cloud servers, which is to select and pay for resources on demand. After the rent runs out, users can choose to renew or remove the server (i.e., elastic side chain). Just as Docker and Kubernetes allow easily customizable and scalable cloud services, SKALE's vision is to provide decentralized "chain services."

SKALE awards

After the end of each SKALE network cycle, SKALE tokens released during that period are equally distributed to all nodes that participated in the network before the cycle began.

The number of tokens assigned to each node depends on the average metrics submitted by 16 of its 24 peers (excluding the four highest and lowest metrics). Tokens that are not distributed to a node due to lack of runtime/delay will flow to the N.O.D.E Foundation.

Elastic side chains and consensus processes

The elastic side chain consists of virtual children in the SKALE network that participate in the creation and validation of blocks through an asynchronous, leadless, and provably secure protocol. As long as more than two-thirds of the virtual child node validation set is online, they continue to create and validate new blocks on the chain. The consensus process of SKALE is shown in the figure below:

Credit: SKALE Network Whitepaper

Block the proposal

Virtual child nodes need to follow the following principles to create a block proposal :(1) check their backlog transaction queue; (2) If the transaction size in the queue is less than or equal to MAX_BLOCK_SIZE, then the virtual child node takes out all the transactions and adds them to the block proposal; (3) If the transaction size in the to-do queue is larger than MAX_BLOCK_SIZE, the virtual child node takes out the to-do transactions in the receiving order and adds them to the block proposal of MAX_BLOCK_SIZE; (4) After that, virtual child nodes collect block proposals for transactions sorted from minimum to maximum based on the SHA-256 root node. (5) If the queue is empty, the virtual child will wait for a BEACON_TIME. If the queue is still empty after that, a block proposal is created that does not contain any transactions.

After a virtual child creates a block proposal, it notifys the other virtual children according to the data availability protocol. The data availability protocol ensures that information can be delivered to the vast majority of virtual child nodes.

Consensus and rounds

The consensus on the block proposal uses the asynchronous binary Byzantine Protocol (ABBA). SKALE currently uses a variant of the ABBA protocol derived from Mostefaoui et al.

After the proposal phase, each virtual child node A that receives the majority of signatures S of proposal P will immediately vote on ABBA in A consensus round R. The protocol is as follows :(1) for each round of R, N ABBA instances will be executed by the virtual child node; (2) Each ABBA[I] is equivalent to one vote of virtual child node I in the block proposal; (3) Each ABBA[I] closes the consensus vote with a "yes" or "no"; (4) After ABBA[I] is complete, there will be a generated voting vector V [I], which includes the "yes" or "no" of each proposal; (5) If there is only one "yes" vote, the relevant block proposal P is submitted to the elastic side chain; (6) If there are more votes for "yes", a pseudo-random number R will be used to select P from the pseudo-random ballot proposal of "yes". The selected proposals are indexed by the remainder of R divided by N_WIN, where N_WIN is the total number of proposals that voted "yes"; (7) The random number R is the sum of all common_coins (a random number source) of ABBA. (8) If all votes are "no", an empty block is submitted to the blockchain. The probability that all votes will be "no" is very small and decreases as N increases.

Once consensus has successfully selected block P on any virtual child node A, the virtual child node will perform the following algorithm to determine the proposal and submit it to the blockchain. (1) A will check whether it has received the selected proposal P; (2) If A does not receive the proposal, it will apply to its equivalent virtual child node for download; (3) A will sign A signature fragment S to P and send it to all other virtual child nodes; (4) A waits to receive signature fragments from most of its virtual child nodes, including its own; (5) Once A receives most of the signature fragments, it combines them into A threshold signature; (6) Finally, A submits P to the blockchain together with the threshold signature S.

In addition, the container of SKALE structure also provides enterprise performance for dApp developers with the option to choose, to achieve the same level of flexibility, centralized system configurability and modularity, SKALE management service, node monitoring service, virtual child node deployment of services, and integrate a series of emergency strategy and disaster recovery plan, To respond to emergencies such as cyber attacks and glitches.

SKALE network extension

SKALE has developed two extension packs: file storage and interchain communication.

File storage

Photo credit: SKALE Network Blog

The SKALE network's file storage relies on its built-in data availability protocol, which ensures that data is stored on at least two-thirds of the virtualized child nodes of each elastic side chain. Filestorage.js is an NPM package that allows users to integrate SKALE fileStorage into their dApp with just a few lines of code. And by calling uplodaFile, downloadFileIntoBrowser/downloadFileIntoBuffer, deleteFile method to the file upload, download, and delete.

SKALE network users can divide files into 1MB "blocks" and submit them to fileStorage smart contracts for sequential storage on each node's file system.

Communication between the chain

Credit: SKALE Network Whitepaper

SKALE network adopts BLS (Boneh-Lynn -- Shacham) threshold signature. BLS signature algorithm is an algorithm that can achieve signature aggregation and key aggregation (that is, multiple keys can be aggregated into a key and multiple signatures can be aggregated into a signature), which can avoid redundant communication between signers [2].

Each elastic side chain in the SKALE network supports this signature, enabling fast and secure inter-chain communication. That is, an independent elastic side chain in SKALE network can verify the block signed and submitted by another elastic side chain, so that SKALE network can implement smart contract execution and crypto asset conversion between elastic side chains.

IMA bridge across the chain

Photo credit: SKALE Network Blog

In July, SKALE launched the IMA (Interchain Messaging Agent) cross-chain bridge, which allows users to transfer mainstream ERC-enabled digital assets and generic Messaging data between Ethereum and any SKALE chain.

If a user needs to move an asset from Ethereum to the SKALE network, the IMA cross-chain bridge deposits the asset on Ethereum into a Deposit Box contract, waits for confirmation from 10 Ethereum blocks, and then sends a transmission request to a SKALE IMA Agent. The agent will in turn call the SKALE TokenManager running in the SKALE network to handle the transport in their respective SKALE chains.

If an asset needs to be transferred from the SKALE chain to Ethereum, the token is burned on the SKALE chain and unlocked on the Ethereum mainnet. If the token to be transferred is minted on the SKALE chain, it will be minted on Ethereum as part of the transfer to retain ownership of the token.

SKALE tokens and governance

The SKALE Token represents the right to participate in the network as a verification node, or as part of the resources that the developer obtains by deploying and renting the elastic side chain for a certain period of time.

(1) In the form of elastic side chain, users rent (computing, storage, bandwidth) resources through subscription mode within a predetermined period of time. (2) Verify that the node pledges the SKALE token to the network and then gains the right to run the node and earn transaction fees and inflation tokens.

Generally speaking, SKALE governance adopts the entrusted pledge model, that is, stakeholders can either directly participate in governance through the pledged vote, or entrust their voting power to other stakeholders. The default voting model adopted by SKALE is a simple majority voting. Proposals usually involve a 14-day voting period. SKALE tokens that have been "loyal and formally pledged" for more than 90 days are eligible to vote on key issues raised by the SKALE Board.

Ecological development and investment and financing

SKALE launched the first phase of its main network in June last year. In May, after completing the Denali upgrade, the SKALE chain announced the launch of its upgraded main network. The network upgrade brings multi-chains to Ethereum and introduces a modular architecture to the SKALE network, allowing it to include local and third-party chain services, including file storage, inter-chain messaging, Oracles, Rollups, and more. And the introduction of high-performance app-specific means that each dApp and protocol can run on its own EVM compatible chain, which is isolated from other network traffic but inherits the security of the Ethereum mainnet.

Photo credit: SKALE Network Blog

At the end of July, SKALE announced the first dApps to run on SKALE's main network, including: Boot.finance (decentralized liquidity Protocol), Covey (portfolio sharing application), CurioDAO (real estate asset towing platform), Human Protocol (decentralized Labor market framework), Ivy (NFT) And token trading protocols) and Minds (decentralized social networking platforms). In addition to the dapps that have joined the SKALE Innovator program and are being built on the platform, SKALE has more than 40 partnerships with partners and validators, according to SKALE officials.

The SKALE network is supported by the world's leading Validators platform, Including 01NODE, Ankr, Anonstake, Audit One, Blockdaemon, Blockware, Chainflow, Chainode, Chorus One, Cypher Core, Dokia Capital, and Figment Networks, FreshSkale, Hashed X DELIGHT, Hashquark, Staked, Stakin, StakedWithUs, WolfEdge Capital, and Staking Facilities. The SKALE network currently has 48 veriers running 160 nodes.

In terms of funding, SKALE Labs announced back in October 2019 that it was raising a total of $17.1 million, More than 40 acquisitions include Arrington XRP Capital, Blockchange, ConsenSys Labs, Hashed, HashKey, Multicoin Capital, Recruit Holdings, and others Angel investors and venture capital institutions.

summary

Compared to Rollup's hot expansion plans and side chain projects like Polygon and xDai, SKALE seems like a bit of a no-go. As an established project that started operations in 2017, SKALE has made a series of ecological advances since the launch of Denalis' upgraded main network, such as launching the first dapps and establishing partnerships with other projects and verifier platforms. With the implementation of various capacity expansion schemes, SKALE has a relatively stable advantage in technology due to years of accumulation, but it still needs to catch up in ecological construction.