EVM Support
The following section details Sygma's compatibility with EVM chains via its ecosystem of smart contracts.
Sygma uses Solidity smart contracts to enable transfers to and from Ethereum Virtual machine (EVM) compatible chains. These contracts consist of a core bridge contract (Bridge.sol), and a set of handler contracts (e.g. ERC20Handler.sol, ERC721Handler.sol, PermissionlessGenericHandler.sol, FeeHandlerRouter.sol, BasicFeeHandler.sol). Different verification systems also require separate sets of smart contracts. These onchain components establish a relationship with the offchain actors via generation and detection of onchain contract events.
Sygma's Smart Contracts
Bridge
The bridge contract is responsible for initiating and executing proposed transfers. It facilitates and manages cross-chain transfer of assets and messages by recording and verifying deposit, executeProposals, and other cross-chain events. The actual handling of the deposits/withdrawals is handled by the appropriate handler contracts. The Bridge.sol contract serves as the primary gateway for a cross-chain interaction.
Handlers
The handlers are used by the bridge contract to interact with other existing contracts. For example, the ERC20Handler contract handles fungible ERC-20 tokens, enabling their deposit, withdrawal, and management within the protocol. On the other hand, the PermissionlessGenericHandler contract processes generic message deposits and their execution. It is designed to handle complex data encoding for executing transactions across chains.
Beyond contracts handling asset/message types, there are handler contracts that route fees (FeeHandlerRouter) and collect/manage fees (BasicFeeHandler, PercentageFeeHandler) based on the destination domain sygmaID and sygmaResourceID (see Configuring Sygma).
For more information on both the Bridge and Handler contracts, please visit the sygma-solidity repo.
Spectre
Sygma's zk verification system, Spectre, implements a separate set of smart contracts, including the Bridge and Handler contracts discussed previously. Additionally, Spectre implements Spectre-specific smart contracts such as Spectre, the SpectreProxy, AccessControlSegregator, Router, and Executor. Crucially, the Spectre and SpectreProxy contracts follow Ethereum's sync committee rotations, allowing lightweight verification of source computation. On the other hand, the Executorcontract is responsible for receiving 1) block header zk-SNARK proofs from the offchain Spectre relayer node and 2) execution submissions and inclusion proofs from the offchain inclusion prover, and then finally 3) "executing" on a cross-chain interaction.
For more information on these contracts, please visit the sygma-x-solidity repo.