USDX Payments Processing Microservices Architecture

Features

• Access Control
• Rebasing token mechanism
• Minting and burning functionality
• Block/Unblock accounts
• Pausing emergency stop mechanism
• Reward multiplier system
• EIP-2612 permit support
• OpenZeppelin UUPS upgrade pattern

Use Cases

• Cash management
• Yield-bearing collateral
• Cross-border payments

Token Types

• USDX: ERC-20, rebasing, yield-bearing collateral
• wUSDX: ERC-4626, accumulating, DeFi

USDX

Public and External Functions

• initialize(string memory name_, string memory symbol_, address owner)
• name()
• symbol()
• decimals()
• convertToShares(uint256 amount)
• convertToTokens(uint256 shares)
• totalShares()
• totalSupply()
• balanceOf(address account)
• sharesOf(address account)
• mint(address to, uint256 amount)
• burn(address from, uint256 amount)
• transfer(address to, uint256 amount)
• blockAccounts(address[] addresses)
• unblockAccounts(address[] addresses)
• isBlocked(address account)
• pause()
• unpause()
• setRewardMultiplier(uint256 _rewardMultiplier)
• addRewardMultiplier(uint256 _rewardMultiplierIncrement)
• approve(address spender, uint256 amount)
• allowance(address owner, address spender)
• transferFrom(address from, address to, uint256 amount)
• increaseAllowance(address spender, uint256 addedValue)
• decreaseAllowance(address spender, uint256 subtractedValue)
• DOMAIN_SEPARATOR()
• nonces(address owner)
• permit(address owner, address spender, uint256 value, uint256 deadline, uint8 v, bytes32 r, bytes32 s)

Private and Internal Functions

• _authorizeUpgrade(address newImplementation)
• _mint(address to, uint256 amount)
• _burn(address account, uint256 amount)
• _beforeTokenTransfer(address from, address to, uint256 amount)
• _afterTokenTransfer(address from, address to, uint256 amount)
• _transfer(address from, address to, uint256 amount)
• _blockAccount(address account)
• _unblockAccount(address account)
• _setRewardMultiplier(uint256 _rewardMultiplier)
• _spendAllowance(address owner, address spender, uint256 amount)
• _useNonce(address owner)
• _approve(address owner, address spender, uint256 amount)

Events

• Transfer(from indexed addr, to uint256, amount uint256)
• RewardMultiplier(uint256 indexed value)
• Approval(address indexed owner, address indexed spender, uint256 value)
• AccountBlocked(address indexed addr)
• AccountUnblocked(address indexed addr)
• Paused(address account)
• Unpaused(address account)
• Upgraded(address indexed implementation)

Roles

• DEFAULT_ADMIN_ROLE
• MINTER_ROLE
• BURNER_ROLE
• BLOCKLIST_ROLE
• ORACLE_ROLE
• UPGRADE_ROLE
• PAUSE_ROLE

wUSDX

Public and External Functions

• initialize(IUSDX _USDX, address owner)
• pause()
• unpause()
• paused()
• DOMAIN_SEPARATOR()
• nonces(address owner)
• permit(address owner, address spender, uint256 value, uint256 deadline, uint8 v, bytes32 r, bytes32 s)

Private and Internal Functions

• _beforeTokenTransfer(address from, address to, uint256 amount)
• _authorizeUpgrade(address newImplementation)
• _useNonce(address owner)

Events

• Transfer(from indexed addr, to uint256, amount uint256)
• Approval(address indexed owner, address indexed spender, uint256 value)
• Paused(address account)
• Unpaused(address account)
• Upgraded(address indexed implementation)

Roles

• DEFAULT_ADMIN_ROLE
• UPGRADE_ROLE
• PAUSE_ROLE

Description

USDX is a stablecoin designed to maintain a 1 USD valuation backed by short-term US Treasury bills. The yield generated by these T-bills is automatically distributed to USDX token holders through rebasing. This feature keeps the price of USDX stable while steadily increasing the balance of USDX for token holders.

X Protocol hosts the primary market that establishes the price peg. KYC-verified users can deposit collateral, either USDC or fiat currency, on our platform. In exchange, they receive USDX and can choose to redeem USDX for collateral or withdraw USDX to any Ethereum address. Since X Protocol offers an exchange rate of one dollar per USDX in both directions, any price movement in the external (secondary) market can be traded in the primary market to re-establish the peg.

USDX is a rebasing ERC-20 token with a set of additional features, including pausing, blocking/unblocking accounts, role-based access control, and upgradability. The contract’s primary objective is to reflect the T-bills’ annual percentage yield (APY) within the token’s value. It achieves this through a reward multiplier rebasing mechanism, where the addRewardMultiplier function is called daily to adjust the reward multiplier, guaranteeing an accurate representation of yield from the underlying assets.

Acknowledging the complexities of handling rebasing tokens in the DeFi ecosystem, the wUSDX contract serves as a wrapped token, simplifying integration while preserving stability. The wUSDX contract is an ERC-4626 token vault, enabling users to deposit USDX in exchange for wUSDX tokens. The USDX tokens are rebasing, whereas the wUSDX tokens are non-rebasing, making wUSDX ideal for seamless integration with protocols in the DeFi ecosystem.

The wUSDX contract incorporates the ERC-2612 permit functionality, allowing the use of signatures to grant token allowances. Additionally, the close relationship between the wUSDX and USDX contracts is also worth noting; the wUSDX contract leverages the account block list from the USDX contract to govern transfers and, specifically, prevent transfers from accounts included in the block list.

Finally, the wUSDX token transfers can be paused in two ways: either by being paused directly from within the wUSDX contract or in the event the USDX contract is paused.