Crosschain Treasury Introduction

The Crosschain Treasury enables secure asset transfers between EVVM and external blockchains. This multi-chain solution uses interoperability protocols to coordinate asset management across different blockchain networks.

Architecture

The system uses two coordinated stations:

Host Chain Station

• Operates on the same blockchain as EVVM
• Handles withdrawals from EVVM to external chains
• Receives deposits from external chains
• Manages EVVM balance updates

External Chain Station

• Deployed on external blockchains where user assets exist
• Handles deposits from users to EVVM
• Receives withdrawals from EVVM
• Manages real assets (tokens and native coins)

Supported Protocols

Protocol	ID	Description
Hyperlane	0x01	Modular interoperability framework
LayerZero	0x02	Omnichain protocol
Axelar	0x03	Decentralized cross-chain network

Fisher Bridge System

Advanced feature enabling gasless transactions:

• Gasless Operations: Users don't need native tokens for gas
• Signature Authorization: Users sign messages to authorize transfers (see Fisher Bridge Signature Structure)
• Priority Fees: Incentives for fisher executors
• Authorized Executors: Permissioned addresses that facilitate transfers

When to Use Crosschain Treasury

Ideal for:

• EVVM on different blockchain than user assets
• Multi-chain support requirements
• Advanced features like gasless transactions
• Interoperability protocol integration

Available Functions

Host Chain Station

• withdraw: Withdraw assets to external chains
• Fisher Bridge Functions: Gasless transaction support
• Admin Functions: System management

External Chain Station

• depositERC20: Deposit tokens to EVVM
• depositCoin: Deposit native coins to EVVM
• Fisher Bridge Functions: Gasless transaction support
• Admin Functions: System management

Cross-Chain Flow

External Chain          Host Chain
     │                      │
User Assets  ──────→  EVVM Balances
     │                      │ 
External Station ←──→ Host Station

The stations coordinate through cross-chain messaging to maintain synchronized asset management.

Available Functions

Host Chain Station Functions

• withdraw: Withdraw assets from EVVM to external chains
• fisherBridgeReceive: Receive fisher-mediated deposits
• fisherBridgeSend: Send fisher-mediated withdrawals
• setExternalChainAddress: Configure external station addresses
• Admin Functions: Management and governance functions

External Chain Station Functions

• depositERC20: Deposit ERC20 tokens to EVVM
• depositCoin: Deposit native coins to EVVM
• fisherBridgeReceive: Receive fisher-mediated transactions
• fisherBridgeSendERC20: Send ERC20 via fisher bridge
• fisherBridgeSendCoin: Send native coins via fisher bridge
• Admin Functions: Management and governance functions

Supporting Libraries

For Fisher Bridge signature requirements and verification, see the Fisher Bridge Signature Structure documentation.

The Treasury Crosschain system implements standardized error handling and data structures for cross-chain operations.

Security Features

Security Considerations

• Principal token withdrawals are blocked to protect ecosystem integrity
• All cross-chain messages require proper authorization verification
• Fisher bridge operations use cryptographic signatures for user consent (see Fisher Bridge Signature Structure)
• Time-delayed governance for administrative changes (1-day delay)
• Protocol-specific validation for each supported interoperability solution

Gas Management

Each protocol requires different gas payment mechanisms:

• Hyperlane: Native tokens paid to mailbox contract
• LayerZero: Estimated fees through LayerZero endpoint
• Axelar: Gas service payments for cross-chain execution

Users must provide sufficient native tokens to cover cross-chain transaction costs when initiating transfers.