Permissioned MTS Tokens

Leverage Injective’s permissions module in MultiVM Token Standard (MTS) tokens

Injective’s Permissions Module

The permissions module is native to Injective, and allows custom management (e.g. roles) for Denoms. This capability is extended to MultiVM Token Standard (MTS) tokens, where you can implement those custom management rules within your EVM smart contract code.

Why Use Permissions on MTS Tokens?

If you are tokenizing real-world assets (RWAs) using MTS on Injective, and that underlying asset inherently requires permissions, that is a great use case for tapping into Injective’s permissions module.

The EVM smart contract of your MTS token simply needs to implement an additional Solidity interface to leverage the power of the permissions module.

Smart Contract Implementation

In your smart contract, import IPermissionsHook from PermissionsHook.sol and extend it.

interface IPermissionsHook

This will involve implementing the isTransferRestricted function, with the following signature:

function isTransferRestricted(
  address from,
  address to,
  Cosmos.Coin calldata amount
)

You may find the full file on Github: PermissionsHook.sol

Smart Contract Example

Create a smart contract that extends PermissionsHook:

import { Cosmos } from "../src/CosmosTypes.sol";
import { PermissionsHook } from "../src/PermissionsHook.sol";
contract RestrictedAddressTransferHook is PermissionsHook {
  /*
  ...
  */
}

Add a custom implementation of the isTransferRestricted function. For example, this function will allow all transfers, except for ones involving a specific address:

  function isTransferRestricted(
    address from,
    address to,
    Cosmos.Coin calldata amount
  ) external pure override returns (bool) {
    address restrictedAddress = "0x...";
    if (from == restrictedAddress || to == restrictedAddress) {
      // this particular address is not allowed to transfer
      return true;
    }

    // All other transfers are allowed
    return false;
  }

You may find a more detailed example of this on Github: PermissionsHookExamples.sol

Registering Hook

To register the hook for the permissions, you will need the following:

• Control of the same account that deployed the MTS token.
• The deployed address of the MTS token
• The deployed address of the Permissions Hook

With the above, you can create a JSON file similar to this one.

Then run injectived for the registration, using the same account that deployed the MTS token.

injectived tx permissions create-namespace ...

Note that the MTS token and the Permissions Hook can have the same address. That is an architectural decision that is up to you.

Registering Hook Example

Create a file named register-hooks.json, with the following content:

{
  "denom": "erc20:0x...", // <-- EVM address of the MTS token
  "evm_hook": "0x...", // <-- EVM address of the permissions hook
  "role_permissions": [
    {
      "name": "EVERYONE",
      "role_id": 0,
      "permissions": 10
    }
  ],
  "actor_roles": [
  ]
}

Be sure to replace the value of the denom and evm_hook fields with the appropriate values.

Delete all comments as well, so that the file is valid JSON.

Then run the following command:

injectived tx permissions create-namespace register-hooks.json [flags]

Note that this is merely one specific way to define permissions hooks on an MTS token. There are multiple variations. For additional details on this step, including other variations, refer to How to Launch Permissioned Assets.

Reference Implementation

A more complete example that demonstrates the use of permissioned MTS tokens for a stable coin is also available.

This example involves a permissions hook which prevents transfers when the token is paused, and also maintains a blacklist of addresses.

function isTransferRestricted(
  address _from,
  address _to,
  Cosmos.Coin calldata /* _amount */
) external view returns (bool) {
  if (fiatToken.paused()) {
    return true;
  } else if (fiatToken.isBlacklisted(_from) || fiatToken.isBlacklisted(_to)) {
    return true;
  }

  return false;
}

See PermissionsHook_Inj.sol.