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Hex Stablecoin Design

HTMI issued USD backed ERC-20 token smart contract which is minted and burned by HTMI Limited and is backed by USD reserve managed by trusted custodian. UUPS proxies are implemented using an ERC-1967 for upgrade the contract for bug fixing or additional features.

Roles

Hashed string values for each roles are defined in RoleConstant.sol

  • MINTER_ROLE: issue / create / mint token. Increase total supply
  • BURNER_ROLE: destroy / burn token. Burning burner's address balance
  • PAUSER_ROLE: pause the contract for all transfers, minting, and burning
  • BLACKLISTER_ROLE: edit blacklisted user list which prevent all balance update. Including all transfers to or from / minting to / burning from blacklisted address
  • UPGRADE_ADMIN_ROLE: manage the proxy-level functionalities such as switching the implementation contract
  • DEFAULT_ADMIN_ROLE: manage admin role granting

ERC20WithRolesUpgradeable.sol

USDX implements the standard methods of the ERC-20 interface with admin role limitation. Define ERC-20 Functionalities along with supply control functions (minting and burning). We have also introduced a function to seize the Token of a blacklisted party when required.

  • transfer, transferFrom will fail if the contract has been paused.
  • burnBlackFunds(address blacklistedAccount) : BURNER_ROLE can burn blacklisted address balance

AccessControlDefaultAdminRulesUpgradeable.sol

Extension of {AccessControl} that allows specifying special rules to manage the DEFAULT_ADMIN_ROLE holder, which is a sensitive role with special permissions over other roles that may potentially have privileged rights in the system.

This is forked from Openzepplin's AccessControlDefaultAdminRulesUpgradeable.sol.

  • pendingDefaultAdmin()
  • beginDefaultAdminTransfer(address newAdmin)
  • cancelDefaultAdminTransfer()
  • acceptDefaultAdminTransfer()

BlacklistableWithRolesUpgradeable.sol

Functions to allow and remove blacklisted users in the contract. Only BLACKLISTER_ROLE can add or remove blacklisted users.

  • addBlacklist(address user)
  • removeBlacklist(address user)
  • isBlacklisted(address user)

PausableUpgradeable.sol

Functions to pause and unpause transfer in the event of emergency. Inherited from Openzepplin PausableUpgradeable.sol. Only PAUSER_ROLE can control the functions.

  • pause()
  • unpause()

Upgradability

Upgradable mechanism is based on UUPS proxies pattern. The _authorizeUpgrade function is overridden to include access restriction to the upgrade mechanism allowed only by UPGRADE_ADMIN_ROLE and defaultAdmin

LayerZero OFT Bridging Support

USDX support LayerZero OFT standard which allows user bridging USDX among Ethereum Mainnet & Flare Mainnet. Checkout via LayerZero OFT & Stargate Finance