After years of research and development , We finally entered a Multi Chain Market Structure . Yes 100 Multiple active public blockchains , Many of them have their own unique applications 、 user 、 Geography 、 Security models and design tradeoffs . Although individual communities believe , But the reality is that the universe tends to increase entropy , And the number of these networks may continue to increase in the future .
This type of market structure requires interoperability between these different networks . Many developers have realized this , Last year we witnessed the explosive growth of blockchain bridges , These chain bridges attempt to unify the increasingly dispersed blockchain . At the time of writing , Yes 40 Several different chain bridge projects .
By 2021 year 9 month 8 Japan ; Illustrative / Not comprehensive
In this article , I will ：
Explain why chain bridges are important
Various chain bridge designs and their advantages and disadvantages are summarized
Provide an overview of the current chain bridge Ecology
Describe what the future of chain bridge may look like
Interoperability opens innovation
With the development of various ecosystems , They will develop their own unique advantages , For example, higher security 、 Faster throughput 、 A cheaper deal 、 Better privacy 、 Specific resource supply （ Such as storage 、 Calculation 、 bandwidth ） And regional developer and user communities . The chain bridge is very important , Because they enable users to access the new platform 、 Protocols interoperate , And developers working together to build new products . More specifically , They can ：
Improve the productivity and usability of existing encrypted assets
Chain bridges enable existing encrypted assets to go to new places and do new things . for example ：
take DAI Send to Terra In the Mirror Buy Synthetic assets on or at Anchor Make a profit on
from Flow towards The etheric fang send out TopShot To be used as NFTfi Security for
Use DOT and ATOM As collateral in Maker Get on DAI The loan
More powerful product features for existing agreements
Bridging extends the design space that the protocol can implement . for example ：
Longing for Solana (Solana) And avalanches (Avalanche) Carry out high-yield agriculture on the
On Ethereum NFT Cross chain shared order book and Rarible Agreed Flow
Index Coop Proof of interest index
Unlock new functions and use cases for users and developers
Chain bridge provides users and developers with more choices . for example ：
Optimism、Arbitrum and Polygon Step up DEX Arbitrage in China SUSHI Price
Pay with bitcoin Arweave Storage costs on
stay Tezos Up for NFT Join in PartyBid
Chain bridge 101
On an abstract level , One can define a bridge as a system that transmits information between two or more blockchains . under these circumstances ,“ Information ” Can refer to assets 、 Contract call 、 Proof or condition . Most chain bridge designs have several components ：
monitor ： There is usually one participant ,“oracle”、“validator” or “relayer”, Responsible for monitoring the status of the source chain .
The messaging / relay ：Actor After receiving the event , Information needs to be transferred from the source chain to the target chain .
Consensus ： In some models , Consensus needs to be reached among the participants in the monitoring source chain , To relay this information to the target chain .
Signature ： Participants need to encrypt and sign the information sent to the target chain individually or as part of the threshold signature scheme .
There are about four types of chain bridges , Each has its own advantages and disadvantages ：
Specific assets ： A chain bridge , Its sole purpose is to provide access to specific assets from the external chain . These assets are usually “ packing ” assets , It is fully mortgaged by the underlying assets in the form of custody or unmanaged . Bitcoin is the most common asset bridging to other chains , There are seven different bridges on Ethereum alone . These chain bridges are the easiest to implement and enjoy mobility , But the function is limited , It needs to be re implemented on each destination chain . Examples include wBTC And packaging Arweave.
Specific chains ： A chain bridge between two blockchains , Simple operations around locking and unlocking tokens on the source chain and casting any wrapped assets on the target chain are usually supported . Due to the limited complexity of these chain bridges , They can usually go public faster , But it's not easy to expand to a wider ecosystem . One example is Polygon Of PoS Bridge , It allows users to transfer assets from Ethereum to Polygon, vice versa , But only these two chains .
Specific applications ： An application that provides access to two or more blockchains , But only for use in this application . The application itself benefits from a smaller code base ; Not every blockchain has a separate instance of the entire application , It usually has lighter... On each blockchain 、 Modular “ Adapter ”. The blockchain implementing the adapter can access all other blockchains to which it is connected , Therefore, there is a network effect . The disadvantage is that it is difficult to extend this functionality to other applications （ For example, from borrowing to exchange ）. Examples include Compound Chain and Thorchain, They have built independent blockchains dedicated to cross chain lending and trading .
Universal ： A protocol designed to transmit information across multiple blockchains . because O(1) complexity , This design enjoys a strong network effect —— The single integration of the project enables it to access the entire ecosystem within the bridge . The disadvantage is that some designs often trade off security and decentralization to achieve this scaling effect , This can have complex unintended consequences for ecosystems . One example is IBC, It is used in two heterogeneous chains （ With a final guarantee ） Sending messages between .
Besides , Bridge design can be roughly divided into three types , It can be classified according to the mechanism used to verify cross chain transactions ：
External validators and alliances
There is usually a set of validators that monitor data on the source chain “ mailbox ” Address , And operate the target chain according to the consensus . Asset transfer is usually accomplished by locking assets in the mailbox and casting the same amount of assets on the target chain . These are usually binding validators , Use a separate token as the security model .
High level description of external validators or federated systems
Light client and relay
Participants monitor events on the source chain , And generate an encrypted proof of past events recorded on the chain . Then forward these proofs together with the block header to the contract on the target chain （ namely “ Light client ”）, Then verify that an event is logged and perform the action after that verification . Some participants need “ relay ” Block head and proof . Although users can “ Self relay ” transaction , However, there is an active assumption that the repeater will continue to forward data . This is a relatively safe bridging design , Because it ensures effective delivery without trust , Without trusting the intermediary entity ,
Light client and / Advanced illustration of or relay system
This is similar to point-to-point networks , Each of these nodes acts as “ Router ”, Holding assets of source chain and target chain “ detailed list ”. These networks usually take advantage of the security of the underlying blockchain ; By using locking and dispute mechanisms , Ensure that users will not be taken away by the router . therefore , For users who transfer a lot of value , image Connext Such a mobile network may be a safer option . Besides , This type of bridge may be most suitable for cross chain asset transfer , Because the assets provided by the router are the native assets of the target chain , Not derivative assets , They are not completely interchangeable .
High level description of the mobility network
We can also look at the current chain bridge ecology from this perspective ：
By 2021 year 9 month 8 Japan
The important thing is to pay attention , Any given bridge is a two-way communication channel , There may be separate models in each channel , And this classification can not accurately represent the mixed model , Such as Gravity、Interlay and tBTC, Because they all have light client direction and verifier in another .
Besides , The chain bridge design can be roughly evaluated according to the following factors ：
Security ： Trust and activity assumptions 、 Tolerance for malicious actors 、 Security and reflexivity of user funds .
Speed ： Delay in completing the transaction , And the final guarantee . There is usually a trade-off between speed and safety .
connectivity ： Select the target chain for users and developers , And different difficulty levels of integrating additional target chains .
Capital efficiency ： Economics around the capital required to ensure system security and the transaction costs of transferred assets .
Statefulness ： Ability to transfer specific assets 、 More complex states and / Or execute cross chain contract call .
combined , The trade-offs of these three designs can be seen from the following perspectives ：
Besides , Security is within a range , It can be roughly classified as ：
No trust ： The security of the bridge is equal to the security of the underlying blockchain it bridges . In addition to the consensus level attack on the underlying blockchain , User funds will not be lost or stolen . in other words , In fact, there is nothing to distrust , Because all these systems in their economy 、 There are security and activity assumptions in both engineering and encryption components .
insure ： Malicious actors can steal user funds , But they may not be profitable , Because they need to provide collateral , And be reduced in case of error or misconduct . If the user's funds are lost , They will compensate by cutting collateral .
Bonded ： Similar to the insurance model （ That is, actors have financial interests in the game ）, Except that the user cannot recover the funds in case of error or misconduct , Because the reduced collateral may be burned . The type of collateral is important for both bonded and insured vehicles ; Endogenous collateral （ That is, the collateral is the agreement token itself ） The risk is greater , Because if the bridge fails , The value of tokens may collapse , This further reduces the safety guarantee of the bridge .
can Letter ： Participants do not issue collateral , Users will not recover funds in case of system failure or malicious activities , Therefore, users mainly rely on the reputation of chain bridge operators .
By 2021 year 9 month 8 Japan . In future upgrades , Several items will be removed “ Be trusted ” Category .
Summary of design tradeoffs
External validators and alliances usually do well in terms of statefulness and connectivity , Because they can trigger transactions 、 Store data and allow interaction with it on any number of target chains . However , This is at the expense of safety , Because by definition , Users depend on the security of the bridge , Not the source or target chain . Although most external validators today are trusted models , But some are mortgaged , One subset is used to provide insurance for end users . Unfortunately , Their insurance mechanism is usually reflective . If the agreement token is used as collateral , It is assumed that the dollar value of the token is sufficient to enable the user to complete . Besides , If the mortgaged asset is different from the insured asset , It also depends on the Oracle price feed , Therefore, the security of the bridge may be degraded to the security of the Oracle . If not trusted , The capital efficiency of these chain bridges is also the lowest , Because they need to expand collateral in proportion to the economic throughput they promote .
Lightweight clients and relays are also powerful in terms of statefulness , Because the head relay system can transmit any type of data . They are also powerful in terms of security , Because they don't require additional trust assumptions , Despite the activity Hypothesis , Because repeaters are still needed to transmit information . These are also the chain bridges with the highest capital efficiency , Because they don't need any capital lock-in . These advantages come at the expense of connectivity . For each chain pair , Developers must deploy a new light client smart contract on the source chain and target chain , Its complexity is between O(LogN) and O(N) Between （ Between this range , Because add support for having the same chain ） Consensus algorithms are relatively easy ）. This will delay the confirmation of the transaction by up to 4 Hours .
Mobile networks are good at speed and security , Because they are locally authenticated systems （ That is, there is no need for global consensus ）. They are also better than bonded / The external verifier of insurance is more capital efficient , Because capital efficiency and transaction flow / Volume, not security related . for example , Suppose the flow between the two chains is somewhat equal , And there is a built-in rebalancing mechanism , Mobility networks can promote any large amount of economic throughput . Trade offs are stateful , Because although they can pass calldata, But their functions are limited . for example , They can interact with data across chains , The receiver has the right to interact according to the data provided （ for example
Open ended questions
In distributed systems , Build robustIt's a very difficult problem . Although there are many activities in this field , But there are still several outstanding issues ：
Finality and rollback ： How does the bridge explain the block reorganization and time bandit attack in a chain with probabilistic termination ？ for example , If any chain encounters a state rollback , So from Polkadot What happens to users who send funds to Ethereum ？
NFT Transmission and provenance ： How bridges bridge across multiple chains NFT Keep the source ？ for example , If there is a NFT stay Ethereum、Flow and Solana Buy and sell in the market , How ownership records describe all these transactions and owners ？
Pressure test ： In the case of chain congestion or protocol and network level attacks , How the various bridging designs will be implemented ？
The future of blockchain bridges
Although the chain bridge has opened up innovation for the blockchain ecosystem , But if the team takes a shortcut in R & D , They also pose serious risks . The poly network hacker attack has proved the potential economic scale of vulnerabilities and attacks , I expect it will get worse before it gets better . Although for chain bridge builders , This is a highly decentralized and highly competitive pattern , But the team should maintain discipline , Give priority to time to market security .
Although the ideal state should be the isomorphic chain bridge of all things , But there is probably no single “ The best ” Chain bridge design , Different types of chain bridges are best suited for specific applications （ For example, asset transfer 、 Contract call 、 Making tokens ） .
Besides , The best chain bridge will be the safest 、 interconnection 、 Fast 、 High capital efficiency 、 Cost effective and anti censorship chain bridge . If we want to achieve “ Blockchain Internet ” Vision , These are the attributes that need to be maximized .
It's too early , The best design may not yet be found . All chain bridge types have several interesting research and development directions ：
Reduce the cost of header validation ： The block header verification cost of light client is very high , Finding ways to reduce these costs can bring us closer to fully universal interoperability without trust . An interesting design might be bridging to L2 To reduce these costs . for example , stay zkSync Implemented on Tendermint Light client .
Change from trusted model to binding model ： Although the capital efficiency of binding validators is much lower , but “ social contract ” It's a dangerous mechanism , It can ensure the safety of billions of dollars of user funds . Besides , Fancy threshold signature schemes do not significantly reduce trust in these systems ; Just because it is a group of singers does not eliminate the fact that it is still a trusted third party . Without collateral , Users are actually handing over their assets to an external custodian .
From bonded mode to insurance mode ： Losing money is a bad user experience . Although bound verifiers and repeaters can suppress malicious behavior , But the agreement should go further , Directly use the reduced funds to compensate users .
Expand the liquidity of the liquidity network ： These can be said to be the fastest chain bridge for asset transfer , And there are interesting design tradeoffs between trust and mobility . for example , It is possible to enable the liquidity network to outsource capital supply using the binding verifier style model , The router can also be a threshold multi signature with binding mobility .
To view more
This article is issued by qucoin.com , Opinions only represent the author , In no way does qucoin agree with its views or confirm its description . Part of the text / picture / video / Audio comes from the network , If it infringes upon the rights of the copyright owner , Please contact us （ WeChat /QQ:1074760229）. This article is not used as investment and financial advice . Reprint please indicate the source ： Qu coin network