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This shows that the threat response time makes a huge difference in the amount of funds recovered. The message passing between the source chain and the destination chain of a bridge happens off-chain. Consider the recent Wormhole bridge bug, where if a hacker was going to be malicious, they could have forged messaging for everything built on top of Wormhole that was secured before the upgrade, making it no longer secure. So basically the chains are forked, invariants are run and the message is not delivered if those invariants don’t hold true.

Bridging the Multichain Universe with Zero Knowledge Proofs

The deVirgo generalization essentially runs a Virgo prover on a set of relay nodes, and avoids the linear growth of the proof size by aggregating the proofs and polynomial commitments into a master node. The core component of a Virgo prover is based on a zero knowledge extension of the GKR protocol which runs sum check arguments for each sub-circuit in the layered circuit and a polynomial commitment scheme. This is the case, for instance, in the ed25519 signature verification discussed in an earlier section. The motivation is that a circuit for verifying N signatures essentially consists of N copies of identical sub-circuits, known as a data-parallel circuit, with each sub-circuit mutually exclusive from the rest. Thus if one wants to decrease the number of signatures in a batch, it will lower the proof time (decrease latency) , but increase the cost (gas fees), due to the increased number of proofs generated per batch. The circuit for the signature verification is constructed using the circom library and leads to about ~ 2M constraints per signature verification.

3 Analysis of the top 5 most expensive bridge exploits

So in the case where the message relayer isn’t running their own nodes but rather using the RPC provider, if the RPC provider gets hacked, they can launch false events and cause your bridge to get drained. Another way to compromise Implementation Security is to compromise the RPC endpoints that the bridge uses. You could also sensor the home chain, where disputes are initiated and fraud is proven. The question here is ‘How much would it cost to corrupt your system i.e. to corrupt the validators? However as time goes on, we will figure out which design patterns are more secure, technology will get more proven and this problem will be solved to a large extent. Decentralized validation can be natively verified or optimistically verified.

2 Decentralized Validation

The main functionality of a relay node on the bridge is to generate a ZKP that attests to the correctness of the block headers from one chain and relays it to the updater contract on the other chain. The solution is to construct a zkSNARK that produces a proof of signature validity off-chain and only verifies the proof itself on the Ethereum chain. Verification of the above requires the storage of 512 BLS public keys on-chain every 27 hours, and for each header verification the signatures are verified, which leads to 512 Elliptic curve additions (in the curve BLS12–381) and a pairing check on-chain, which is cost prohibitive. The two main challenges in applying the ideas behind ZKP rollups to bridges is that first, the circuit sizes involved in bridges are orders of magnitude larger compared to rollups, and secondly, how to reduce storage and computational overhead onchain. All of the above assume that there exists a light client protocol that ensures nodes can synchronize block headers of a finalized blockchain state.
It is important to note that the most common bridges are not able to physically move tokens between blockchains. Developers must implement effective threat mitigation measures to ensure the security and reliability of their blockchain bridges. There are different types of bridges that facilitate interoperability between different blockchains.

• As we saw, different bridges use different mechanisms to ensure that the message being relayed is valid, which then allows users to receive their tokens.
• In the natively verified bridges, the trust was on the two blockchains.
• In order to facilitate the exchange of value between different blockchains, interoperability is essential.
• For instance, if a user wants to exchange USDC on Arbitrum for ETH on Ethereum, they would require a bridge aggregator that integrates DEXs.
• Although the sequencers a.k.a the nodes that collect the transactions, are in some cases centralized, their aim is to be truly decentralized bridges in the future.
• Thus bridging assets from Ethereum to Polygon, for example, is dependent upon the security of the Ethereum chain and not on that of Polygon.
• The core idea here is to use a zk-SNARK (Groth16) to produce a validity proof (which is constant size) and can be efficiently verified on-chain on Gnosis.

The quickest way to compromise economic security is by stealing the private keys of the validators (i.e. the signer keys). ’ The higher the cost to gain control over the majority validators, the better is the economic security. In this section, we will dive into the three main pillars, how they can be compromised and compare three bridge models (Natively verified, Externally verified and Optimistically verified) against each other in these three pillars.
If qualified talent can be found from reputable organizations such as banks or tech companies that prioritize security, the centralized bridge can be as secure as possible. Securing centralized bridges can be relatively straightforward if best practices from traditional cybersecurity are followed. Suppose the validators of a source chain in IBC collude to submit a fraudulent transaction then the destination chain on IBC will still accept the transaction as the bridge only verifies that the source chain consensus was achieved. These include bridges that validate the consensus of a source chain on a destination chain. Polygon's existing non-ZK bridges are already in active use by many users, making it potentially simpler for them to transition their assets to the ZK bridge than to a newly developed bridge from another community.
For example, a token bridge is an application on top of this messaging protocol that allows you to send tokens across chains, an NFT bridge is an application on top of this messaging protocol that allows you to send NFTs across chains. Before we define a bridge, we need to introduce another term called ‘Messaging Protocol’ which is the interoperability layer and we can say that two chains are always connected by a messaging protocol. Lack of interoperability makes it difficult to use the different blockchains and to realize the full potential of the technology. In a world where blockchains are becoming increasingly popular and widespread, the need for interoperability is greater than ever. Additionally alternative Layer-1 blockchains were built with different consensus mechanisms, to tackle scalability and faster transaction throughput.

• Centralized validation is less complex to build but comes with less security.
• Even if they outsource their RPC to a 3rd party, they are only risking their own funds.
• What was notable was that the community members openly discussed the ‘Cross-Chain Bridge Assessment Process’ and allowed the various bridge teams to present their architecture and security assumptions in the Uniswap governance forum.
• This method allows for the efficient and cheap verification of Ed25519 signatures from the Cosmos SDK on the Ethereum blockchain without introducing any new trust assumptions.
• The main functionality of a relay node on the bridge is to generate a ZKP that attests to the correctness of the block headers from one chain and relays it to the updater contract on the other chain.
• Once the user spends some funds and wishes to return the remaining funds to C1, he “burns” the funds in C2, which the bridging entity verifies, and “releases” the remaining funds in C1.
• Optimizations include usage of the 512 Public key (PK) inputs of the validators as a commitment using a ZK friendly Poseidon hash.

Finally, a standardized risk assessment framework should be used to guide users and applications to the right bridge for their transaction requirements and desired level of security. Additionally, it’s worth exploring other frameworks like the one developed by Hacken that can be used for reviewing off-chain components of externally verified bridges. Meaning, the smart contracts for the liquidity providers are separate for each bridge pair and hence hacking one contract doesn’t affect the others.

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The tricky thing about bridges is that we can formally verify the source side and the destination side of it, but we can't formally verify the working between those two because that happens off-chain. Open sourcing code and offering bug bounties can be a great way to help keep bridges secure. Currently in smart contracts, when there is an actual exploit, because everything is atomic, attackers are able to steal funds in one single transaction.

This eliminates the need for the Web 3.0 component and focuses solely on traditional cyber security. It’s important to note that each Bridge Node communicates directly with the secure SGX enclave for submitting eligible transactions and are being operated by four wardens Ava Labs, HALBORN, BWARELABS and AVASCAN. The SGX application requires 6 of 8 Bridge Nodes to submit the same transaction before generating the signed transaction to process the Bridge transfer on the other network. It is essential that, while new technology is being implemented in the Web 3.0 world, the underlying tech stack remains secure. Most established best practices for traditional cybersecurity are already in place. Private keys, which are more prevalent in DeFi, must be properly secured through access management, logging, auditing, and other measures.
Light clients validating consensus is another way that is less secure than the previous one. Nevertheless, competition is essential to ensure both teams strive to create better, more secure, and faster solutions, ultimately benefiting the sector as a whole. This serves to illustrate the level of development that has been achieved by Polygon and the network effects that will benefit them as first movers.
The invariants could be for example the total supply of a token has to be a billion and it can check that all the chains the token exists on, have the total supply to 1 billion before and after the delivery of the message. Pre-Crime takes all the chains involved in the messaging, forks them, delivers the message, and then checks them against a set of invariants. As a bridge supports more and more networks, it increases the probability of being exploited.
A bridge is a two way communication protocol that proves the occurrence of events in one chain C1 to applications in another chain C2 and vice-versa. In summary, using ZKP for designing bridges solves the problems of decentralization and security, but creates a computational bottleneck due to large circuit sizes. As of the time of writing, there are several active cross-chain bridge projects.‍A bridge is a two way communication protocol that proves the occurrence of events in one chain C1 to applications in another chain C2 and vice-versa.

Below we provide a quick comparison of the various features of the three bridge constructions discussed in this article. More specifically, leaving aside the MPC complexity of the deVirgo relay network, the NTT’s are the bottleneck in the individual Virgo prover component of the relay nodes. Once the user spends some funds and wishes to return the remaining funds to C1, he “burns” the funds in C2, which the bridging entity verifies, and “releases” the remaining funds in C1. Besides the list of headers continuing to increase, the client would require the storage and verification of new headers as they come along. In general, C1 and C2 could operate in different domains, and verification operations require out of field arithmetic. For simplicity we use the terminology, origin chain (C1) and target chain (C2), though it is interchangeable.
As we saw, different spinmaya casino bonus bridges use different mechanisms to ensure that the message being relayed is valid, which then allows users to receive their tokens. Any external information is hard to validate since the blockchain has no way of knowing what is happening in the outside world or on other chains. In the next section we explore the reason why bridges break and aim to highlight the different security aspects of importance in bridges. Finally we discussed the role of bridge aggregators in making crosschain transactions more efficient, secure and user friendly.
This includes following smart contract best practices, testing, audits, security updates, monitoring, and using the Forta tool or others for real-time detection. At Coinchange we have built DeFi Risk Assessment Frameworks for DEXes, Money Market protocols and Blockchains. Standardized Risk frameworks are necessary in choosing the right bridge because they provide a systematic approach to analyzing and evaluating potential security and risks involved in using it. The faster your response, the safer the bridge in terms of recovering users’ funds.