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Trusted: Participants do not need to mortgage assets, and users cannot rbitcoin bank wienetrieve assets when the system fails or commits malicious behavior. Therefore, security mainly depends on the reputation of the bridge operator.

XCM aims to be a language for the exchange of ideas between consensus systems. It should be generic enough to remain correct and useful throughout the evolving ecosystem. It is extensible, and extensibility means changeable, and it also means forward compatibility. It can run efficiently on the chain and can run in a metering environment.bittorrent classic for windows 10XCM can be used in a variety of systems, including gas metering smart contract platforms and community parachains, and trusted interactions between system parachains and their relay chains.

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Although the goal of XCM is universal, flexible and future-oriented, it must of course meet actual needs, especially the transfer of tokens between chains. Throughout the DeFi world, optional fee payment is very common. You can use the XCM language to perform some specific operations.Importantly, there are many token transfer models that we hope to support: it may only be necessary to simply control the account on the remote chain, allowing the local chain to have an address on the remote chain to receive funds and ultimately transfer the funds under its control to that remote In other accounts on the chain.But there may be two consensus systems in this process, both of which are specific token systems. For example, tokens such as USDT or USDC have instances on several different chains and are completely interchangeable. It should be possible to destroy such tokens on one chain and mint corresponding tokens on another supported chain. In XCM, it can be called teleport, because the transfer of assets is actually achieved by destroying it on one side and creating a clone on the other side.The core of the XCM format is XCVM. This stands for cross-consensus virtual machine. This is an ultra-high-level non-Turing complete computer whose instructions are designed to be roughly at the same level as transactions.The "message" in XCM is actually just a program running on XCVM. It is one or more XCM commands. The program will continue to execute, and will not end and stop until it runs to the end or encounters an error.

The position in XCM is hierarchical, and some parts of the consensus are completely encapsulated into separate parts. For example, the Parachain of Polkadot completely exists in the internal position of the entire Polkadot consensus. As long as there is any change in one consensus system, it means a change in another consensus system, and the former system is the internal system of the latter.When working in XCM, it is usually necessary to quote some kind of asset. This is because almost all existing public blockchains rely on some native digital assets to provide the backbone for their internal economic and security mechanisms. For proof-of-work blockchains such as Bitcoin, native assets (BTC) are used to reward miners who develop the blockchain and prevent double spending. For proof-of-stake blockchains such as Polkadot, native assets (DOT) are used as a form of collateral, and network administrators (called equity holders) must take risks to generate valid blocks and obtain physical rewards.From an abstract perspective, a bridge can be defined as follows: a system that transmits information between two or more blockchains. And "information" can refer to assets, contract calls, proofs, or status. Most bridge designs consist of the following parts:

Monitoring: There is usually a participant (or a "oracle", "verifier", "relayer") monitoring the status of the source chain.Message delivery/relay: After the participants receive the event, they need to transfer information from the source chain to the target chain.Consensus: In some models, in order to forward information to the target chain, a consensus must be reached between participants monitoring the source chain.Signature: Participants need to encrypt and sign the information sent to the target chain, which can be single-signatured or as part of a threshold signature scheme.

There are roughly four types of bridging schemes, each of which has its advantages and disadvantages:Asset-specific: The sole purpose of this bridge type is to provide access to specific assets on external chains. These assets are usually "wrapped" assets (assets that are fully mortgaged by the underlying assets in custody or non-custody). Bitcoin is the most common asset bridged to other chains, and there are seven different bridges on Ethereum alone. This kind of bridging is the easiest to achieve, and obtain huge liquidity from it. But its functions are limited and need to be re-implemented on each target chain. Examples are wBTC and wrapped Arweave.

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Chain-specific: A bridge between two chains, which usually supports the locking and unlocking of tokens on the source chain and the casting of arbitrary encapsulated assets on the target chain. Due to the limited complexity of these bridges, they can usually be marketed faster, but they are not easy to expand into the broader ecosystem. The use case is Polygon’s PoS bridge, which allows users to transfer assets from Ethereum to Polygon and vice versa, but only on these two chains.Application-specific: An application that provides access to two or more blockchains, but only for use in that application. The advantage of this kind of application itself is that the code base is small; instead of having a separate instance of the entire application on each blockchain, there are usually more lightweight and modular on each blockchain "Adapter". A blockchain that implements an "adapter" can access all other blockchains it is connected to, so there is a network effect. Their disadvantage is that it is difficult to extend this function to other applications (for example, from lending applications to transaction applications). Specific use cases are Compound Chain and Thorchain, which respectively build independent blockchains dedicated to cross-chain lending and transactions.Generalized: A protocol designed to transmit information across multiple blockchains. Due to its low complexity, this design enjoys a strong network effect-a single integration of the project allows it to access the entire ecosystem within the bridge. The disadvantage is that some designs usually trade-off between security and decentralization to achieve this scalability effect. This may have complex and unexpected consequences for the ecosystem. One of the use cases is IBC, which is used to send information in two heterogeneous chains (with a guarantee of finality).In addition, according to the mechanism used to verify cross-chain transactions, there are roughly three types of bridge designs:

Type 1: External validators & Federations (External validators & Federations)This type of bridging scheme usually has a group of verifiers that monitor the "mailbox" addresses on the source chain and perform operations on the target chain based on consensus. Asset transfer usually works like this: lock assets on the "mailbox", and then mint the same amount of assets on the target chain. These validators usually deposit separate tokens as collateral to ensure the security of the network.Type 2: Light clients & RelaysParticipants monitor events on the source chain and generate encrypted packaging proofs about past events recorded on the chain. These proofs will be forwarded to the contract on the target chain (such as "light client") along with the block header, and then verify whether an event is recorded, and perform operations after verification. This design mechanism requires some participants to "relay" the block headers and proofs. Although users can "self-relay" transactions, there is indeed an active assumption that the relay will continue to forward data. This is a relatively secure bridging design because it guarantees the effective delivery of trustlessness without trusting intermediate entities. But it is also resource-intensive, because developers must build a new smart contract on each new target chain to parse the source chain's state proof; the verification process itself requires a large amount of gas.

Type 3: Liquidity networksThis is similar to a peer-to-peer network, where each node acts as a "router", holding a "library" of source and target chain assets. These networks usually take advantage of the security of the underlying blockchain; through the use of locking and dispute mechanisms, it can be ensured that routers will not steal users' funds. Because of this, a liquid network like Connext may be a safer choice for users who transfer large amounts of value. In addition, this type of bridge may be most suitable for cross-chain asset transfer, because the assets provided by the router are the original assets of the target chain, rather than derivative assets that cannot be completely replaced by each other.

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It should be noted that any given bridge above is a two-way communication channel. There may be independent models in each channel, so this classification cannot accurately represent mixed models such as Gravity, Interlay, and tBTC. Because they all have light clients in one direction and validator nodes in the other direction.In addition, the design of a bridge can be roughly evaluated based on the following factors:

Security: Trust and liveness assumptions, tolerance for malicious behavior, security and reflexivity of user funds.Speed: The delay time of transaction completion, and the guarantee of final certainty. There is usually a trade-off between speed and safety.Connectivity: The choice of target chains for users and developers, and the different difficulty levels of integrating additional target chains.Capital efficiency: economic mechanism, which sets the transaction cost of capital and asset transfer required to ensure the security of the system.Statefulness: The ability to transfer specific assets, more complex states, and/or perform cross-chain contract calls.In summary, the trade-offs of these three design mechanisms can be evaluated from the perspective of the following figure:

In addition, security is a scope, we can roughly divide it into the following categories:Trust-less: The security of the bridge is bound to the underlying blockchain it bridges. Unless the underlying blockchain is attacked by consensus-level attacks, users' funds will not be lost or stolen. In other words, this is not complete trustlessness, because all the economic, engineering, and cryptographic components of these systems contain trust assumptions (for example, there are no loopholes in the code).

Insured (Insured): Attackers can steal user funds, but they may be unprofitable in doing so. Because they need to provide collateral to participate in the network, and they will be punished for wrongdoing and malicious behavior. If the user's funds are lost, the agreement will compensate the user by confiscation of the attacker's collateral.Bonded (Bonded): Similar to the insurance model (for example, the economic benefits of participants are closely related to their behavior), except that the user's collateral is forfeited due to his mistakes and malicious behavior. The type of collateral is important for both the insurance and the mortgage model; endogenous collateral (protocol tokens as collateral) is more risky, because if the bridge fails, the value of the token is also likely to collapse, which further reduces Security guarantee for bridging.

Trusted: Participants do not need to mortgage assets, and users cannot retrieve assets when the system fails or commits malicious behavior. Therefore, security mainly depends on the reputation of the bridge operator."External validators and federalism" are generally better in terms of state and connectivity because they can trigger transactions, store data, and allow data to interact with any number of target chains. However, this comes at the cost of security, because by definition, users rely on the security of the bridge rather than the source or target chain. Although most of the current external validator mechanisms are based on trust models, some require collateralized assets, and a subset of assets is used to insure end users. Unfortunately, their insurance mechanisms are usually reflexive. If the agreement token is used as collateral, it is assumed that the value of the token is sufficient to compensate the user's loss. In addition, if the mortgage asset is different from the insurance asset, it will also depend on the price flow of the oracle, so the security of the bridge will be downgraded to that of the oracle. If a trust model is not required, these bridges are also the least capital efficient, because they promote economic throughput and also need to scale up the scale of collateral.

"Light client and relay" is also better in terms of state, because the block header relay system can transmit any type of data. Although there are liveness assumptions due to the need for repeaters to transmit information, they are also very safe because they do not require additional trust assumptions. At the same time, they are the most capital efficient bridges because there is no need to lock any assets. However, these advantages come at the expense of connectivity. Every time a pair of chains is connected, the developer must deploy a new light client smart contract on the source chain and the target chain. The complexity of the contract is between O(LogN) and O(N) (the reason is between this The scope is because it is relatively easy to add chain support using the same consensus algorithm). There is also a significant speed flaw in the optimistic model that relies on fraud proofs, which may increase the delay to 4 hours."Liquidity networks" are strong in terms of security and speed because they are locally verified systems (that is, global consensus is not required). They are also more capital efficient than the external validator mechanism of the mortgage/insurance mechanism, because capital efficiency is related to transaction flow/volume, rather than security. For example, assuming that the transaction flows of the two chains are equal, and given a built-in rebalancing mechanism, the liquidity network can contribute to an arbitrarily large economic throughput.The trade-off lies in the state, because although the call data can be transmitted, its function is limited. For example, they can interact with data across chains, where the receiver has the right to interact based on the provided data (for example, using the signature information from the sender to call a smart contract), but there is no "owner" of the data for the transmission or the transmission belongs to Generalized state data (such as minting representative tokens) is not helpful.Building a strong cross-chain bridge is a difficult problem in distributed systems. Although there have been many attempts in this field, there are still some problems to be solved:

Finality & rollbacks: In a chain with probabilistic finality, how does bridging deal with block reorganization and time thief attacks? For example, if any chain has experienced a state rollback, what will happen to users who send themselves from Polkadot to Ethereum?NFT transfers & provenance: How can bridges trace the provenance of NFT across multiple chains? For example, if there is an NFT that has transacted in multiple markets of Ethereum, Flow, and Solana, how are all these transactions and owners recorded?

Stress testing: In the case of chain congestion or protocol and network level attacks, how will various bridge designs respond?Although bridging unlocks more innovation possibilities for the blockchain ecosystem, if the team takes shortcuts in R&D, it may also bring great risks. The Poly Network cross-chain attack event has shown us the potential economic loss scale of vulnerabilities and attacks, and I estimate that there will be more large-scale attacks in the future. Although for bridge builders, the current network is highly fragmented and competition is fierce. But each team should be highly self-disciplined and prioritize security rather than release speed.

Although the ultimate ideal state is to build a "isomorphic bridge" shared by all things, the reality is that there is probably no single "best" bridge design. Different types of bridges will be suitable for different specific applications (such as asset transfer, contract invocation, token minting, etc.).In addition, the best bridge should be the most secure, connectable, fast, capital efficient, cost-effective, and censorship-resistant. If we want to realize the vision of the "blockchain internet", these attributes need to be maximized by us.

So far, we have not constructed the optimal bridge. There are several interesting research directions for all bridging types:Reducing the cost of block header verification: The cost of block header verification for light clients is very high. If this problem can be solved, it will bring us closer to achieving fully universal and trustless interoperability. An interesting design is to bridge to L2 to reduce these costs. For example, implement the Tendermint light client on zkSync.Shift from a trust-based model to a mortgage model: Although the capital efficiency of mortgage verifiers is much lower, the security of "social contracts" is not enough to protect billions of dollars in user funds. In addition, the fancy threshold signature mechanism does not reduce trust; this group of signers still belongs to a trusted third party. Without collateral, users actually hand over their assets to an external custodian.Change from a mortgage model to an insurance model: Loss of assets is the last thing users want to encounter. Although verifiers and repeaters of mortgage assets can prevent malicious behavior to a certain extent, the agreement should go further and directly use the confiscated funds to compensate users.

Expanding the liquidity of the liquidity network: The "liquidity network" can be said to be the fastest bridge for asset transfer, and there are some interesting design trade-offs between trust and liquidity. For example, the liquidity network may be able to use the mortgage verifier model to outsource capital supply, where routing may also be a threshold multi-signature with mortgage liquidity.Bridge aggregation: Although the use of bridges may follow the law of exponential for a specific asset, an aggregator like Li Finance can improve the experience of developers and end users.

Nowadays, many GameFi projects continue to emerge, and provide a variety of participation methods and play-to-earn and pledge functions. So, how to judge which projects can be held for a long time and can add value? How to find potential NFT agreements?The calculation of agreement income is the focus of value investment.

First of all, let's take a look at what is the agreement income? What is the difference with income?Let me talk about the definition of revenue. Revenue measures the return of all participants, that is, the total cost paid to the contract supplier. For example, the fees paid to liquidity providers in AMM, the transaction fees of decentralized exchanges, and the amount of interest on the lending platform in DeFi. Revenue is obtained by charging a rate to the total flow of the agreement. Simply put, revenue refers to the total fees paid by end users of blockchain or decentralized applications. These revenues will eventually be distributed to token holders, liquidity holders and protocol libraries.

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Perspectives of a 2x entrepreneur turned VC at @UpfrontVC#

Mark Suster

Written by

2x entrepreneur. Sold both companies (last to salesforce.com). Turned VC looking to invest in passionate entrepreneurs 〞 I*m on Twitter at @msuster

Both Sides of the Table

Perspectives of a 2x entrepreneur turned VC at @UpfrontVC, the largest and most active early-stage fund in Southern California. Snapchat: msuster

Mark Suster

Written by

2x entrepreneur. Sold both companies (last to salesforce.com). Turned VC looking to invest in passionate entrepreneurs 〞 I*m on Twitter at @msuster

Both Sides of the Table

Perspectives of a 2x entrepreneur turned VC at @UpfrontVC, the largest and most active early-stage fund in Southern California. Snapchat: msuster