Introducing Synapse Chain
July 28th, 2022

Introducing Synapse Chain

Today, we’re excited to announce Synapse Chain, a novel smart contract execution layer built atop Synapse’s generic cross-chain messaging system and value bridge.

Synapse Chain is the first sovereign execution environment dedicated to the development of cross-chain applications and primitives. By leveraging Synapse’s generic cross-chain messaging system and token bridge, Synapse Chain serves as the organizational hub and execution layer for all cross-chain smart contract activity.


Synapse was first deployed with the vision of allowing users to seamlessly move assets across blockchains. As new blockchains were launched to help alleviate congested networks and expensive gas fees, millions of new users were finally able to onboard into crypto. With this sharp increase in usage across a suite of different blockchains came a growing need for secure and user-friendly interoperability.

Upon launch, Synapse offered some of the deepest and most affordable pools of cross-chain liquidity, making it extremely easy for users to move stablecoins and ETH across the most popular blockchains. Over the course of the last 9 months, Synapse has become the most widely used generalized cross-chain token bridge and messaging protocol, facilitating over $11 billion in total bridge volume, nearly 1 million in unique transactions, supporting over 150k unique users, and partnering with mass-market decentralized applications like DeFi Kingdoms.

Synapse now serves as critical cross-chain infrastructure for DeFi and the multi-chain ecosystem more broadly, empowering users to interact with any blockchain in a safe and secure manner.

Synapse Chain will further cement Synapse’s role in the multi-chain future, making it simple for developers of decentralized applications to host their state across any blockchain in a safe and secure manner.

Along with Synapse Chain, the protocol is moving to its next iteration, Synapse V2.

Synapse V2 introduces:

Generalized cross-chain messaging

Generalized cross-chain messaging enables any arbitrary data to be sent across blockchains, expanding mass-market use cases of cross-chain infrastructure to NFTs, smart-contract calls, governance, and much more. With generalized cross-chain messaging, any decentralized application can be natively multi-chain, connecting its business logic across every blockchain.

Optimistic verification

Optimistic verification is a security model for verifying cross-chain messages that is far more secure than traditional externally verified bridges. In optimistic verification, a network of off-chain actors coordinate to flag malicious transactions during a latency window. Synapse’s optimistic verification implementation will be the first model with in-production economic security.

Economic Security and Delegated Proof of Stake (PoS)

SYN will be used to provide economic security to Synapse’s optimistic verification system. Notaries and guards will be required to bond and stake SYN as a way to incentivize them to act honestly and to submit fraud proofs when faulty transactions are identified. In the event that either the notary or guard behave dishonestly, they will see their stake slashed. All holders of SYN can back guards through a delegated proof-of-stake (DPoS) mechanism.

These core upgrades of the Synapse Protocol not only make possible the launch of Synapse Chain, but also make Synapse the most robust cross-chain communications platform in production.

Along with these high-level features, V2 will include a wide variety of improvements to Synapse’s smart contract architecture as well as improvements to our core SDK and API tools.

What follows is an in-depth overview of Synapse Chain and the core upgrades to the Synapse Protocol.

Synapse Chain

Synapse Chain is an Ethereum-based optimistic rollup designed to serve as a sovereign execution environment for cross-chain use cases. Synapse Chain will offer developers a generalized smart contract interface for building natively cross-chain use cases by leveraging Synapse’s cross-chain messaging system. Applications built on Synapse Chain will be able to execute their business logic across any blockchain.

The impetus to build a sovereign chain to facilitate cross-chain messaging comes from the core contributing team’s learnings working with teams building cross-chain applications, namely that a programming environment specifically suited for use cases built atop the messaging system makes managing deployment and state across chains much simpler, and that cross-chain business logic is much more efficient when hosted on a single execution environment. This allows for users to interact with state in an atomic way, even if it’s deployed across various blockchains. As a principle, complex business logic shouldn’t be spread amongst 10 blockchains.

Similarly, developers can birth a whole suite of new primitives with multi-chain state that’s deployed on a single blockchain. These primitives can then be used as building blocks for completely new user experiences and applications that are better tailored to our multi-chain reality.

Another novel feature of Synapse Chain is that it will be used to store the attestations made by Synapse’s security system on the validity of cross-chain transactions. In most other messaging systems, as the number of connected chains goes up, so does the number of contracts that have to be updated to keep track of every message. With Synapse Chain, only one chain needs to be updated with each valid cross-chain transaction, decreasing smart contract complexity, and ultimately, the gas costs required to use the system. Since Synapse Chain is a rollup that settles back to Ethereum, all historical attestations of the system’s cross-chain transactions are made available via Ethereum.

As mentioned above, Synapse Chain is built as an Optimistic Rollup. Why this route, as opposed to constructing a new monolithic chain? There are four primary reasons for this design choice:

  • EVM Compatibility
  • Security
  • User Experience
  • Simplicity

EVM Compatibility

Synapse Chain will leverage the EVM to ensure composability with the rich developer and application ecosystem built around it. Not only will building applications on Synapse Chain match the developer experience of existing EVM blockchains, but existing decentralized applications can easily be deployed to Synapse Chain with little to no architectural changes. This ensures that Synapse Chain can bootstrap a vibrant ecosystem of cross-chain applications from its earliest days.


While blockspace designed for more granular use cases can dramatically increase throughput, fees, and overall user experience, it often does so at the expense of security. Instead of needing to bootstrap independent security systems, optimistic rollups enable dapps to leverage the security and decentralization of Ethereum’s base layer, which has the highest security spend out of any generalized smart contract blockchain.

User Experience

Rollups offer throughput and scalability that is orders of magnitude higher than that of Ethereum. Transactions on Synapse Chain will be near instant and will cost a fraction of what they would on competing base layers, ensuring applications built on Synapse Chain can foster a user experience akin to that of centralized competitors.


Optimistic rollups provide a construction for an execution environment that is both simple and secure. By borrowing from Ethereum’s battle-tested infrastructure, Synapse Chain does not have to re-engineer new features from scratch. To that end, Geth will be Synapse Chain’s client software, meaning Synapse Chain is as close to Ethereum under the hood as possible. Adhering to Ethereum’s core design principles helps minimize new attack vectors that come with creating a new execution environment from scratch.

Synapse Chain Construction

Consistent with most rollup constructions, all Synapse Chain blocks will be stored within a smart contract on the Ethereum blockchain. Similarly, block production on Synapse Chain will be initially managed by a sequencer, which is also responsible for state updates and submitting transactions back to Ethereum. Decentralization of Synapse Chain’s sequencer will follow the roadmap of prominent rollup protocols.

Upon launch of Synapse Chain, gas will be paid to the sequencer in ETH in order to foster the best user experience possible. Shortly after launch, the Synapse DAO could explore a number of mechanisms to tie use of Synapse Chain to SYN in order to fortify the symbiotic relationship between Synapse Chain and the messaging system. While they are unique components, Synapse Chain can only succeed if the messaging system can provide trustless security, which SYN strives to incentivize.


Over the coming months, more detailed information will be shared about how to deploy decentralized applications on Synapse Chain, along with more robust developer documentation. Expect to see a public testnet in a few weeks where developers can deploy contracts and dapps, with a mainnet release following shortly after.

Synapse V2

Generalized Cross-Chain Messaging

Synapse’s original deployment included logic specifically designed to move assets across any blockchain. With this narrow focus, the Synapse Bridge was able to focus on the most prominent and in-demand cross-chain use case: bridging.

Synapse V2 extends messaging logic to include any generalized data, providing a structured communications format that specifies how that data is sent and received on any chain. By doing so, the design space for the types of decentralized applications that can be built on increases by an order of magnitude.

With Synapse’s generalized messaging system, any arbitrary data can be sent across chains in a secure and seamless way. Applications no longer have to be separately deployed across multiple blockchains; they can be deployed on a single chain and communicate with other chains to create the exact same user experience from one central application layer. Generic message passing also includes smart contract calls, enabling smart contracts on different chains to easily interoperate with one another. Stated simply, Synapse’s generic messaging acts as a framework for universal blockchain composability.

Optimistic Verification

Synapse V2 also introduces a new security model for the cross-chain messaging system: optimistic verification.

Synapse’s optimistic verification is inspired by Celo’s Optics protocol, which is live in production on Nomad today.

A multi-chain future is an inevitability. In such a future, generalized messaging and bridge protocols become integral pieces of infrastructure; unfortunately, the security models underlying many of today’s interoperability platforms leave much to be desired.

The security models of most bridges today can be characterized in three ways:

  • Locally verified — only parties involved in a given cross-chain interaction verify transactions
  • Natively verified — all validators of the two blockchains involved in a transaction verify the message
  • Externally verified — an external validator set is used to verify transactions between chains

Even with these three main archetypes for cross-chain verification, most bridges today still effectively operate as basic multi-sig consensus schemes in order to create a faster user experience. While these systems are useful for fast finality, that speed comes at a cost, exposing users to security threats. As espoused in the Interoperability Trilemma, certain tradeoffs are inherent in cross-chain communication. Trading security for speed has resulted in a multitude of bridge hacks totaling well over $500 million USD in cumulative funds lost.

Synapse V2 includes a move away from the protocol’s existing M of N Proof of Stake consensus to a new optimistically verified security model.

Optimistic verification borrows from optimistic rollups in that transactions are assumed to be honest by default with a network of off-chain actors responsible for submitting fraud proofs during the course of an optimistic window to disallow any fraudulent transactions. This mechanism adds a significant layer of security to the network, making it far more costly for a bad actor to conduct an attack versus the existing M of N mechanism. Externally verified networks rely on an honest majority assumption whereas optimistic verification relies on a single honest verifier assumption. Optimistic verification just needs one honest guard to behave honestly for the system to remain secure. Rather than a bad actor needing to co-opt M number of validators, that actor would need to co-opt all N actors, and the cost to attack the network becomes unbounded as the number of N fraud watchers increases. Naturally, the added security requires a trade-off - here, latency.

There are four off-chain actors responsible for security of Synapse’s optimistic verification mechanism:

  • Notary — responsible for signing merkle root on each supported chain and bonding SYN behind attestations
  • Broadcaster — responsible for forwarding updates from home contracts to replica contracts
  • Guard — responsible for observing cross-chain messages and submitting fraud proofs when detecting malicious state updates
  • Executor — responsible for posting the final transaction once the latency window is completed

Lifecycle of a Synapse Cross-Chain Message

  1. User or application initiates a message on the source chain and routes it to Synapse’s messaging contracts
  2. Synapse’s messaging contracts hashes the message and inserts it into its own merkle tree
  3. Notary signs the attestation with the new merkle root
  4. Broadcasters forward the signed attestation to the destination chain
  5. Guards observe the attestation to ensure it isn’t fraudulent
  6. Upon the optimistic window elapsing, the transaction is considered valid
  7. The transaction is executed on the destination chain by the Executor

Synapse’s optimistic verification model’s unique consensus system is detailed in the sections below.

SYN Staking

SYN will provide economic security to the new optimistic verification model, becoming an incentive mechanism for the off-chain actors to reach consensus on the validity of transactions, ultimately allowing the messaging system to operate in a trustless and decentralized manner.

Notaries in Synapse’s security model will be required to bond SYN in order to attest to outgoing transactions, thereby creating an economic cost to malicious behavior as a notary’s SYN will be slashed in the event that they attest to a faulty transaction. Similarly, guards will be required to stake SYN in order to prevent griefing attacks. Holders will be able to delegate their SYN to guards in order to participate in securing the network.

All entities participating in the off-chain actors will be eligible to receive transaction fees generated from the demand to use the cross-chain messaging system.

A New Synapse

Synapse V1 changed the way users interacted with blockchains. Through the world-class bridging experience provided by Synapse, users could seamlessly move their assets between blockchains and access a whole new suite of applications.

The introduction of Synapse Chain and the Synapse V2 upgrade bring secure interoperability to a whole new level:

  • Native cross-chain rollup: Synapse Chain offers developers an easy-to-use substrate to quickly build cross-chain dapps without compromising on security, usability, and composability.
  • More cross-chain use cases: Generalized cross-chain messaging allows developers to expand cross-chain utility past traditional asset swapping. Games, NFT platforms, and DAO governance can now leverage Synapse to deploy across any blockchain.
  • Secure consensus: Optimistic verification is a step-function improvement in the security of Synapse’s consensus. Additionally, our optimistic bridging implementation will feature in-production economic security.
  • SYN Staking: With economic security live, SYN holders will have the ability to delegate their stake to guards participating in optimistic verification.

Next Steps

Over the coming weeks, contributors to the Synapse DAO plan to:

  • Release a fully functional testnet for Synapse Chain accompanied by robust developer documentation.
  • Open source Synapse generalized cross-chain messaging contracts.
  • Open source optimistic verification contracts along with a fully detailed spec for economic security.
  • Release an interface for staking SYN in the optimistic security model.
  • Showcase some prototypes of dapps that can be built on Synapse Chain in coordination with other projects.

All Synapse smart contracts will undergo security audits before deployment to mainnet.

If you have an interesting cross-chain dapp idea that you want to build on Synapse Chain or using Synapse’s generalized cross-chain messaging, come chat on Discord!

About Synapse

Synapse is a universal cross-chain liquidity network. Synapse connects blockchains by offering an extensible cross-chain communication protocol that supports assets, smart contract calls, and more. By leveraging Synapse, blockchains can easily and securely interoperate with each other and developers can build truly cross-chain applications including cross-chain DEX, lending platforms, margining systems, derivatives markets, yield aggregators, and much more. The first application built using this cross-chain protocol is the Synapse Bridge, which uses AMMs deployed across 16+ EVM and non-EVM blockchains to help users seamlessly transfer assets between all chains.

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