Smart Contracts

Overview & Contract Addresses

Code Repository

https://github.com/superstateinc/ustb/tree/main

Audits

Contract Addresses

Our smart contracts are upgradable and various functions are gated behind the Superstate Admin Address calling them. This includes all minting, adding or removing users from the allowlist, and forcibly burning an investor’s tokens (if required by exogenous legal circumstances, for example).

USTB and USCC

A standard Upgradable OpenZeppelin ERC-20 implementation with a few changes:

  1. USTB/USCC check that all holders are on the Superstate controlled Allowlist contract and are authorized for that token.

  2. Encumber functionality (see below)

  3. Burn - Investors can call the burn function or transfer their USTB/USCC to the contract address to kick off a redemption

  4. Mint - Superstate can call the mint function to mint new shares of USTB/USCC when investors subscribe to the fund

Transfers

USTB/USCC is freely transferrable between Ethereum addresses that are on the Allowlist via transfer or transferFrom. Each function checks that the sender and receiver are both on the Allowlist and authorized for that specific token.

Encumber

What is encumber?

A new EIP from Compound and Superstate. Encumber enables permissioned ERC-20s, like USTB, to be used in decentralized finance protocols.

Why is encumber needed?

Permissioned ERC-20s have allowlists, so not everyone can hold them. Given the structure of our Funds, Superstate must limit who may purchase/sell/hold its security tokens. Additionally, providing custody other than self custody may have additional requirements.

How does it work?

encumber is like a stronger version of ERC-20 approve. When you encumber an amount of your ERC-20 to an EOA or smart contract, they stay in your wallet. However, you cannot revoke an encumbrance. Whomever you encumbered to must call the release function to remove the encumbrance. You cannot transfer or approve encumbered tokens. If someone encumbered to you, you can call transferFrom at any time from the encumbered to anyone on the token allowlist. This spends the encumbrance. This functionality enables tokens like USTB and USCC to be used in DeFi. For example, User A encumbers 10 USTB to Compound, and borrows against it. The position becomes unhealthy and Compound must liquidate User A’s 10 USTB. User B wants to pay the loan to buy the collateral. Compound calls transferFrom on the USTB contract to transfer 10 USTB from User A to User B. Compound never has “custody” of USTB, but facilitates a transfer from one allowlist user to another.

How do I integrate? Here's some samples from Compound: https://github.com/compound-finance/encumber_samples

Allowlist

Adds/Removes Ethereum addresses to/from the allowlist with certain permissions. Right now, only the first two booleans in the Permission struct are used. Permission.isAllowed means the entity is onboarded to USTB. Permission.state1 means the entity is onboarded to USCC. Ethereum addresses are also grouped by their Entity Id. Entity Ids are how Superstate identifies investors. The USTB/USCC token contract calls getPermission on the Allowlist contract to see if the sender and receiver of USTB are allowed to hold it. Only the Superstate Admin Address can make any changes to the allowlist, using the following functions setEntityIdForAddress, setEntityIdForMultipleAddresses, setPermission, setEntityPermissionAndAddresses, and setNthPermission. We call these functions when onboarding or offboarding an investor. We only add Ethereum addresses for investors that have made it through our KYC / Investment Agreement processes.

USTB Oracle

Chainlink handles putting the USTB Net Asset Value per Share price onchain. The Oracle contract uses the AggregatorV3Interface.https://docs.chain.link/data-feeds/api-reference#functions-in-aggregatorv3interface

This oracle has the most up to date USTB NAV/S price and can be used like any other Chainlink oracle.

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