Routing Mechanics

ITS Hub modifies the existing token transfer mechanism by introducing a centralized routing point. Instead of ITS Edge Contracts communicating directly, all ITS calls are routed through the ITS Hub. This approach allows for enhanced security measures, balance tracking, and prepares the system for future features.

ITS Hub routing works in the following way:

  • Dual GMP calls
  • Payload wrapping

Each token transfer or deployment involves two General Message Passing (GMP) calls:

  1. From Source Chain to ITS Hub: The ITS Edge Contract on the source chain sends a GMP call to the ITS Hub, wrapping the original payload.
  2. From ITS Hub to Destination Chain: The ITS Hub processes the payload, applies security measures, and forwards it to the ITS Edge Contract on the destination chain.

To facilitate routing through the ITS Hub, new message types are introduced:

uint256 private constant MESSAGE_TYPE_SEND_TO_HUB = 3;
uint256 private constant MESSAGE_TYPE_RECEIVE_FROM_HUB = 4;
  • MESSAGE_TYPE_SEND_TO_HUB (3): Indicates the message is intended for the ITS Hub.
  • MESSAGE_TYPE_RECEIVE_FROM_HUB (4): Indicates the message is coming from the ITS Hub.

Example Payload Wrapping:

On the source chain:

string destinationAddress = trustedAddresses[destinationChain];


if (destinationAddress == itsHubAddress) {
    payload = abi.encode(
        MESSAGE_TYPE_SEND_TO_HUB,
        destinationChain,  // True destination chain
        originalPayload    // Original ITS payload
    );
    destinationChain = axelarChainName; // Route to ITS Hub
}


gateway.callContract(destinationChain, destinationAddress, payload);

On the ITS Hub:

// Unwrap the payload
(destinationChain, originalPayload) = abi.decode(payload, (string, bytes));


// Process the payload (apply security checks, balance tracking, etc.)


// Wrap the payload to send to the destination chain
payload = abi.encode(
    MESSAGE_TYPE_RECEIVE_FROM_HUB,
    sourceChain,       // True source chain
    originalPayload    // Original ITS payload
);


gateway.callContract(destinationChain, destinationAddress, payload);
graph LR
    ITSA[ITS Chain A]
    ITSB[ITS Chain B]
    ITSHub[ITS Hub]


    ITSA -->|Wrapped Payload GMP| ITSHub
    ITSHub -->|Wrapped Payload GMP| ITSB


    subgraph Axelar Network
        ITSHub
    end
  • ITS Tokens: Managed entirely by the ITS protocol. The ITS Hub handles their deployment and transfer without special considerations.
  • Gateway Tokens: Minted and burned via the Axelar protocol. The ITS Hub interacts with the Axelar Gateway to handle these tokens, ensuring proper minting and burning.
  • Smart Contract Chains: Have ITS Edge Contracts similar to EVM chains. The routing mechanics are consistent with the dual GMP call approach.
  • Non-Smart Contract Chains: The Axelar Gateway on these chains acts as an ITS Edge Contract, translating ITS commands into custom token transfer or deployment transactions.

Amplifier Chain to ITS Hub

sequenceDiagram
    participant User
    participant ITS as ITS Edge Contract
    participant EG as External AxelarGateway
    participant G as Internal Gateway
    participant R as Amplifier Router
    participant A as Axelarnet Gateway
    participant ITSHub


    User->>ITS: interchainTransfer
    ITS->>EG: CallContract
    EG->>G: VerifyMessage
    G->>R: RouteMessage
    R->>A: RouteMessage
    A->>ITSHub: Execute

ITS Hub to Amplifier Chain

sequenceDiagram
    participant ITSHub
    participant A as Axelarnet Gateway
    participant R as Amplifier Router
    participant AG as Internal Gateway
    participant E as External Gateway
    participant ITS as ITS Edge Contract


    ITSHub->>A: CallContract
    A->>R: RouteMessage
    R->>AG: RouteMessage
    AG->>E: ConstructProof
    E->>ITS: Execute
  • Use the existing Axelar protocol for GMP calls.
  • The ITS Hub interacts with consensus modules to handle GMP calls with tokens (Gateway tokens).

Consensus Chain to ITS Hub with Gateway Token

sequenceDiagram
    participant User
    participant ITS as ITS Edge Contract
    participant E as EVM Gateway (Legacy)
    participant EM as EVM Module
    participant NR as Nexus Module
    participant AM as Nexus Gateway
    participant ITSHub


    User->>ITS: interchainTransfer
    ITS->>E: CallContractWithToken
    E->>EM: ConfirmGatewayTx
    EM->>NR: RouteMessage with payload
    NR->>AM: routeMsg
    AM->>ITSHub: wasm Execute

The ITS Hub enhances security through:

  • Balance Tracking: Keeps track of the total bridged balance per token per chain to prevent over-escrow or unauthorized minting.
  • Rate Limits: Applies per-token rate limits to mitigate risks from compromised chains or contracts.
  • Centralized Control: Allows pausing or disconnecting specific chain connections in case of security threats.

The ITS Hub is designed to accommodate future features:

  • GMP Express: Support for faster message passing without compromising security.
  • Integration with Axelar and Cosmos Chains: Enabling ITS functionalities on these chains through the ITS Hub.
  • Migration Support: Existing P2P ITS connections can be migrated to route through the ITS Hub.

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