IBC

Inter-Blockchain Communication protocol implementation with EVM callbacks

The x/ibc module from Ontomir evm implements Inter-Blockchain Communication (IBC) protocol support with specialized EVM callback functionality for cross-chain smart contract interactions.

Overview

The IBC module extends the standard IBC protocol with EVM-specific features:

• IBC Callbacks: Execute EVM contracts automatically during IBC packet lifecycle

• Cross-chain Contract Calls: Enable smart contracts to interact across chains

• Packet Lifecycle Management: Handle acknowledgments and timeouts through EVM contracts

Components

IBC Callbacks

The EVM Callbacks module implements the EVM contractKeeper interface that interacts with ibc-go's callbacks middleware, specifically for ICS-20 transfer applications.

Key Features:

• Destination Callbacks: Execute contracts on packet receipt (onRecvPacket)

• Source Callbacks: Handle acknowledgments (onAcknowledgePacket) and timeouts (onTimeoutPacket)

• Atomic Execution: Contract calls happen atomically with token transfers

IBC Transfer Integration

The module works closely with the ICS20 transfer application to enable:

• Cross-chain token transfers to EVM contracts

• Automatic contract execution with received funds

• Custom calldata propagation across chains

Smart contracts can initiate IBC transfers using the [ICS20 Precompile](/docs/evm/next/documentation/smart-contracts/precompiles/ics20), which provides the `transfer` function with memo field support for callbacks. **Address Format Limitation**: Currently, IBC transfer receiver addresses must be in bech32 format (e.g., `Ontomir1...`). While sender addresses are automatically converted from hex to bech32, receiver addresses must be provided in bech32 format. Full hex address support for receivers is planned for a future release.

Callback Types

Destination Callbacks (onRecvPacket)

Executed on the destination chain when a packet is received, allowing contracts to:

• Receive cross-chain tokens

• Execute custom logic with the received funds

• Perform operations like DEX swaps or liquidity provision

Source Callbacks (onAcknowledgePacket & onTimeoutPacket)

Executed on the source chain when packet lifecycle completes, enabling contracts to:

• Handle successful transfer acknowledgments

• Recover funds from failed/timed out transfers

• Implement retry logic for failed transfers

Implementation Details

Memo Format

EVM callbacks use the memo field in ICS-20 transfers with specific JSON structure:

Destination Callback:

{
  "dest_callback": {
    "address": "0x...",
    "gas_limit": "1000000", 
    "calldata": "0x..."
  }
}

Source Callback:

{
  "src_callback": {
    "address": "0x...",
    "gas_limit": "1000000"
  }
}

Security Considerations

• Isolated Addresses: Destination callbacks use ephemeral addresses to prevent confusion with local accounts

• Sender Validation: Source callbacks validate that only the packet sender can set callbacks

• Gas Limits: Callback execution is bounded by specified gas limits

• IBC Overview - IBC concepts and fundamentals

• ICS20 Precompile - Cross-chain token transfers

• Callbacks Interface - Smart contract callback interface