EIP-3643: T-REX - Token for Regulated EXchanges

An institutional grade security token standard that provides interfaces for the management and compliant transfer of security tokens.

Simple Summary

The T-REX token is This standard

Abstract

Standards should be backwards compatible with ERC-20 and should be able to interact with ERC-735 to validate the claims linked to an ONCHAINID, based on ERC-734 and ERC-735. The standard defines several interfaces that are described hereunder:

• Token
• Identity Registry
• Identity Registry Storage
• Compliance
• Trusted Issuers Registry
• Claim Topics Registry

Motivation

Give standard interfaces for security tokens issued on Ethereum, through which any third party could interact with the security token. The functions described by these interfaces vary and allow the appropriate users to call a range of different actions, such as forced transfers, freeze tokens (partially or totally on a wallet or even freeze the entire token), minting, burning, recover lost tokens (if an investor loses access to his wallet), etc.

The following requirements have been compiled following discussions with parties across financial institutions that are looking to issue securities on a DLT infrastructure such as ethereum.

• MUST be ERC-20 compatible.
• MUST be used in combination with an Identification system onchain (ONCHAINID)
• MUST be able to apply any rule of compliance that is required by the regulator or by the token issuer (about the factors of eligibility of an identity or about the rules of the token itself)
• MUST have a standard interface to pre-check if a transfer is going to pass or fail before sending it to the blockchain
• MUST have a recovery system in case an investor loses access to his private key
• MUST be able to freeze tokens on the wallet of investors if needed, partially or totally
• MUST have the possibility to pause the token
• MUST be able to mint and burn tokens
• MUST define an Agent role and an Owner (token issuer) role
• MUST be able to force transfers from an Agent wallet
• MUST be able to issue transactions in batch (to save gas and to have all the transactions performed in the same block)
• MUST be upgradeable (code of the smart contract should be upgradeable without changing the token smart contract address)

Rationale

Transfer Restrictions

Transfers of securities can fail for a variety of reasons. This is in direct contrast to utility tokens, of which generally only require the sender to have a sufficient balance. These conditions can be related to the status of an investor’s wallet, the identity of the sender and receiver of the securities (i.e. whether they have been through a KYC process, whether they are accredited or an affiliate of the issuer) or for reasons unrelated to the specific transfer but instead set at the token level (i.e. the token contract enforces a maximum number of investors or a cap on the percentage held by any single investor). For ERC-20 tokens, the balanceOf and allowance functions provide a way to check that a transfer is likely to succeed before executing the transfer, which can be executed both on-chain and off-chain. For tokens representing securities, the T-REX standard introduces a function canTransfer which provides a more general purpose way to achieve this. I.e. when the reasons for failure are related to the compliance rules of the token and a function isVerified which allows to check the eligibility status of the identity of the investor.

Upgradeability

The token contract should be upgradeable without changing its address on the blockchain, therefore, we decided to make it proxiable through ERC-1822 (Universal Upgradeable Proxy Standard)

Identity Management

Security and compliance of transfers is issued through the management of onchain identities.

• ONCHAINID
• Claim
• Identity Storage/registry Transfers of securities can fail for a variety of reasons in contrast to utility tokens which generally only require the sender to have a sufficient balance.

Specification

This standard is backwards compatible with ERC-20, therefore, all ERC-20 functions can be called on an ERC-3643 token, the interfaces being compatible. But the functions are not implemented in the same way as a classic ERC-20 as ERC-3643 is a permissioned token, which implies a check to be performed on each single token transfer to validate the compliance of the transfer and the eligibility of the stakeholder’s identities.

Main functions

Transfer

To be able to perform a transfer on T-REX you need to fulfill several conditions :

• The sender needs to hold enough free balance (total balance - frozen tokens, if any)
• The receiver needs to be whitelisted on the Identity Registry and verified (hold the necessary claims on his ONCHAINID)
• The sender’s wallet cannot be frozen
• The receiver’s wallet cannot be frozen
• The transfer has to respect all the rules of compliance defined in the Compliance smart contract (canTransfer needs to return TRUE)

Here is an example of transfer function implementation :

function transfer(address _to, uint256 _amount) public override whenNotPaused returns (bool) {
        require(!frozen[_to] && !frozen[msg.sender], 'wallet is frozen');
        require(_amount <= balanceOf(msg.sender).sub(frozenTokens[msg.sender]), 'Insufficient Balance');
        if (tokenIdentityRegistry.isVerified(_to) && tokenCompliance.canTransfer(msg.sender, _to, _amount)) {
            tokenCompliance.transferred(msg.sender, _to, _amount);
            _transfer(msg.sender, _to, _amount);
            return true;
        }
        revert('Transfer not possible');
    }

The transferFrom function works the same way while the mint function and the forcedTransfer function only require the receiver to be whitelisted and verified on the Identity Registry (they bypass the compliance rules). The burn function bypasses all checks on eligibility.

isVerified

The isVerified function is called from within the transfer functions transfer, transferFrom, mint and forcedTransfer to instruct the Identity Registry to check if the receiver is a valid investor, i.e. if his wallet address is in the Identity Registry of the token, and if the ONCHAINIDcontract linked to his wallet contains the claims (see ERC-735) required in the Claim Topics Registry and if these claims are signed by an authorized Claim Issuer as required in the Trusted Issuers Registry. If all the requirements are fulfilled, the isVerified function returns TRUE, otherwise it returns FALSE. An implementation of this function can be found on the T-REX repository.

canTransfer

The canTransfer function is also called from within transfer functions. This function checks if the transfer is compliant with global compliance rules applied to the token, in opposition with isVerified that only checks the eligibility of an investor to hold and receive tokens, the canTransfer function is looking at global compliance rules, e.g. check if the transfer is compliant in the case there is a fixed maximum number of token holders to respect (can be a limited number of holders per country as well), check if the transfer respects rules setting a maximum amount of tokens per investor, … If all the requirements are fulfilled, the canTransfer function will return TRUE otherwise it will return FALSE and the transfer will not be allowed to happen. An implementation of this function can be found on the T-REX repository.

Other functions

Description of other functions of the ERC-3643 can be found in the interfaces folder. An implementation of the ERC-3643 suite of smart contracts can be found on the T-REX repository.

Token interface

ERC-3643 permissioned tokens are based on a standard ERC-20 structure but with some functions being added in order to ensure compliance in the transactions of the security tokens. The functions transfer and transferFrom are implemented in a conditional way, allowing them to proceed with a transfer only IF the transaction is valid. The permissioned tokens are allowed to be transferred only to validated counterparties, in order to avoid tokens being held in wallets/ONCHAINIDs of ineligible/unauthorized investors. The ERC-3643 standard also supports the recovery of security tokens in case an investor loses his/her wallet private key. A history of recovered tokens is maintained on the blockchain for transparency reasons. ERC-3643 tokens are implementing a lot of additional functions to give the owner or his agent the possibility to manage supply, transfer rules, lockups and everything that could be required in the management of a security. A detailed description of the functions can be found in the interfaces folder.

interface IERC3643 is IERC20 {

   // events
    event UpdatedTokenInformation(string _newName, string _newSymbol, uint8 _newDecimals, string _newVersion, address _newOnchainID);
    event IdentityRegistryAdded(address indexed _identityRegistry);
    event ComplianceAdded(address indexed _compliance);
    event RecoverySuccess(address _lostWallet, address _newWallet, address _investorOnchainID);
    event AddressFrozen(address indexed _userAddress, bool indexed _isFrozen, address indexed _owner);
    event TokensFrozen(address indexed _userAddress, uint256 _amount);
    event TokensUnfrozen(address indexed _userAddress, uint256 _amount);
    event Paused(address _userAddress);
    event Unpaused(address _userAddress);


    // functions
    // getters
    function decimals() external view returns (uint8);
    function name() external view returns (string memory);
    function onchainID() external view returns (address);
    function symbol() external view returns (string memory);
    function version() external view returns (string memory);
    function identityRegistry() external view returns (IIdentityRegistry);
    function compliance() external view returns (ICompliance);
    function paused() external view returns (bool);
    function isFrozen(address _userAddress) external view returns (bool);
    function getFrozenTokens(address _userAddress) external view returns (uint256);

    // setters
    function setName(string calldata _name) external;
    function setSymbol(string calldata _symbol) external;
    function setOnchainID(address _onchainID) external;
    function pause() external;
    function unpause() external;
    function setAddressFrozen(address _userAddress, bool _freeze) external;
    function freezePartialTokens(address _userAddress, uint256 _amount) external;
    function unfreezePartialTokens(address _userAddress, uint256 _amount) external;
    function setIdentityRegistry(address _identityRegistry) external;
    function setCompliance(address _compliance) external;

    // transfer actions
    function forcedTransfer(address _from, address _to, uint256 _amount) external returns (bool);
    function mint(address _to, uint256 _amount) external;
    function burn(address _userAddress, uint256 _amount) external;
    function recoveryAddress(address _lostWallet, address _newWallet, address _investorOnchainID) external returns (bool);

    // batch functions
    function batchTransfer(address[] calldata _toList, uint256[] calldata _amounts) external;
    function batchForcedTransfer(address[] calldata _fromList, address[] calldata _toList, uint256[] calldata _amounts) external;
    function batchMint(address[] calldata _toList, uint256[] calldata _amounts) external;
    function batchBurn(address[] calldata _userAddresses, uint256[] calldata _amounts) external;
    function batchSetAddressFrozen(address[] calldata _userAddresses, bool[] calldata _freeze) external;
    function batchFreezePartialTokens(address[] calldata _userAddresses, uint256[] calldata _amounts) external;
    function batchUnfreezePartialTokens(address[] calldata _userAddresses, uint256[] calldata _amounts) external;

    // roles setting
    function transferOwnershipOnTokenContract(address _newOwner) external;
    function addAgentOnTokenContract(address _agent) external;
    function removeAgentOnTokenContract(address _agent) external;
}

Identity Registry Interface

This Identity Registry is linked to storage that contains a dynamic whitelist of identities. The Identity Registry makes the link between a wallet address, an ONCHAINID and a country code corresponding to the country of residence of the investor, this country code is set in accordance with the ISO-3166 standard. It also contains a function called isVerified(), which returns a status based on the validity of claims (as per the security token requirements) in the user’s ONCHAINID. The Identity Registry is managed by the agent wallet(s) i.e. only the agent(s) can add or remove identities in the registry (note: the agent role on the Identity Registry is set by the owner, therefore the owner could set himself as the agent if he wants to keep everything under his own control). There is a specific identity registry for each security token. A detailed description of the functions can be found in the interfaces folder.

Note that IClaimIssuer and IIdentity are needed in this interface and are coming from ONCHAINID

interface IIdentityRegistry {


    // events
    event ClaimTopicsRegistrySet(address indexed claimTopicsRegistry);
    event IdentityStorageSet(address indexed identityStorage);
    event TrustedIssuersRegistrySet(address indexed trustedIssuersRegistry);
    event IdentityRegistered(address indexed investorAddress, IIdentity indexed identity);
    event IdentityRemoved(address indexed investorAddress, IIdentity indexed identity);
    event IdentityUpdated(IIdentity indexed oldIdentity, IIdentity indexed newIdentity);
    event CountryUpdated(address indexed investorAddress, uint16 indexed country);


    // functions
    // identity registry getters
    function identityStorage() external view returns (IIdentityRegistryStorage);
    function issuersRegistry() external view returns (ITrustedIssuersRegistry);
    function topicsRegistry() external view returns (IClaimTopicsRegistry);

    //identity registry setters
    function setIdentityRegistryStorage(address _identityRegistryStorage) external;
    function setClaimTopicsRegistry(address _claimTopicsRegistry) external;
    function setTrustedIssuersRegistry(address _trustedIssuersRegistry) external;

    // registry actions
    function registerIdentity(address _userAddress, IIdentity _identity, uint16 _country) external;
    function deleteIdentity(address _userAddress) external;
    function updateCountry(address _userAddress, uint16 _country) external;
    function updateIdentity(address _userAddress, IIdentity _identity) external;
    function batchRegisterIdentity(address[] calldata _userAddresses, IIdentity[] calldata _identities, uint16[] calldata _countries) external;

    // registry consultation
    function contains(address _userAddress) external view returns (bool);
    function isVerified(address _userAddress) external view returns (bool);
    function identity(address _userAddress) external view returns (IIdentity);
    function investorCountry(address _userAddress) external view returns (uint16);

    // roles setters
    function transferOwnershipOnIdentityRegistryContract(address _newOwner) external;
    function addAgentOnIdentityRegistryContract(address _agent) external;
    function removeAgentOnIdentityRegistryContract(address _agent) external;
}

Identity Registry Storage Interface

The Identity Registry Storage stores the identity addresses of all the authorized investors in the security token(s) linked to the storage contract i.e. all identities of investors who have been authorized to hold the token(s) after having gone through the appropriate KYC and eligibility checks. The Identity Registry Storage can be bound to one or several Identity Registry contract(s). The goal of the Identity Registry storage is to separate the Identity Registry functions and specifications from its storage, this way it is possible to keep one single Identity Registry contract per token, with its own Trusted Issuers Registry and Claim Topics Registry but with a shared whitelist of investors used by the isVerifed() function implemented in the Identity Registries to check the eligibility of the receiver in a transfer transaction. A detailed description of the functions can be found in the interfaces folder.

interface IIdentityRegistryStorage {

    //events
    event IdentityStored(address indexed investorAddress, IIdentity indexed identity);
    event IdentityUnstored(address indexed investorAddress, IIdentity indexed identity);
    event IdentityModified(IIdentity indexed oldIdentity, IIdentity indexed newIdentity);
    event CountryModified(address indexed investorAddress, uint16 indexed country);
    event IdentityRegistryBound(address indexed identityRegistry);
    event IdentityRegistryUnbound(address indexed identityRegistry);

    //functions
    // storage related functions
    function storedIdentity(address _userAddress) external view returns (IIdentity);
    function storedInvestorCountry(address _userAddress) external view returns (uint16);
    function addIdentityToStorage(address _userAddress, IIdentity _identity, uint16 _country) external;
    function removeIdentityFromStorage(address _userAddress) external;
    function modifyStoredInvestorCountry(address _userAddress, uint16 _country) external;
    function modifyStoredIdentity(address _userAddress, IIdentity _identity) external;

    // role setter
    function transferOwnershipOnIdentityRegistryStorage(address _newOwner) external;
    function bindIdentityRegistry(address _identityRegistry) external;
    function unbindIdentityRegistry(address _identityRegistry) external;

    // getter for bound IdentityRegistry role
    function linkedIdentityRegistries() external view returns (address[] memory);
}

Compliance Interface

The Compliance is used to set the rules of the offering itself and ensures these rules are respected during the whole lifecycle of the token, e.g. the compliance contract will define the maximum amount of investors per country, the maximum amount of tokens per investor, the accepted countries for the circulation of the token (using the country code corresponding to each investor in the Identity Registry). The compliance smart contract is a “tailor-made” contract that is implemented in accordance with the legal requirements and following the desires of the token issuer. This contract is triggered at every transaction by the Token and returns TRUE if the transaction is compliant with the rules of the offering and FALSE otherwise. A detailed description of the functions can be found in the interfaces folder.

interface ICompliance {

    // events
    event TokenAgentAdded(address _agentAddress);
    event TokenAgentRemoved(address _agentAddress);
    event TokenBound(address _token);
    event TokenUnbound(address _token);

    // functions
    // initialization of the compliance contract
    function addTokenAgent(address _agentAddress) external;
    function removeTokenAgent(address _agentAddress) external;
    function bindToken(address _token) external;
    function unbindToken(address _token) external;

    // check the parameters of the compliance contract
    function isTokenAgent(address _agentAddress) external view returns (bool);
    function isTokenBound(address _token) external view returns (bool);

    // compliance check and state update
    function canTransfer(address _from, address _to, uint256 _amount) external view returns (bool);
    function transferred(address _from, address _to, uint256 _amount) external;
    function created(address _to, uint256 _amount) external;
    function destroyed(address _from, uint256 _amount) external;

    // setting owner role
    function transferOwnershipOnComplianceContract(address newOwner) external;
}

Trusted Issuer’s Registry Interface

The Trusted Issuer’s Registry stores the contract addresses (ONCHAINID) of all the trusted claim issuers for a specific security token. The ONCHAINID of token owners (the investors) must have claims signed by the claim issuers stored in this smart contract in order to be able to hold the token. The ownership of this contract is given to the token issuer allowing them to manage this registry as per their requirements. A detailed description of the functions can be found in the interfaces folder

interface ITrustedIssuersRegistry {

    // events
    event TrustedIssuerAdded(IClaimIssuer indexed trustedIssuer, uint[] claimTopics);
    event TrustedIssuerRemoved(IClaimIssuer indexed trustedIssuer);
    event ClaimTopicsUpdated(IClaimIssuer indexed trustedIssuer, uint[] claimTopics);

    // functions
    // setters
    function addTrustedIssuer(IClaimIssuer _trustedIssuer, uint[] calldata _claimTopics) external;
    function removeTrustedIssuer(IClaimIssuer _trustedIssuer) external;
    function updateIssuerClaimTopics(IClaimIssuer _trustedIssuer, uint[] calldata _claimTopics) external;

    // getters
    function getTrustedIssuers() external view returns (IClaimIssuer[] memory);
    function isTrustedIssuer(address _issuer) external view returns(bool);
    function getTrustedIssuerClaimTopics(IClaimIssuer _trustedIssuer) external view returns(uint[] memory);
    function hasClaimTopic(address _issuer, uint _claimTopic) external view returns(bool);

    // role setter
    function transferOwnershipOnIssuersRegistryContract(address _newOwner) external;
}

Claim Topics Registry Interface

The Claim Topics Registry stores all the trusted claim topics for the security token. The ONCHAINID of token owners must contain claims of the claim topics stored in this smart contract. The ownership of this contract is given to the token issuer allowing them to manage this registry as per their requirements. A detailed description of the functions can be found in the interfaces folder

interface IClaimTopicsRegistry {

    // events
    event ClaimTopicAdded(uint256 indexed claimTopic);
    event ClaimTopicRemoved(uint256 indexed claimTopic);

    // functions
    // setters
    function addClaimTopic(uint256 _claimTopic) external;
    function removeClaimTopic(uint256 _claimTopic) external;

    // getter
    function getClaimTopics() external view returns (uint256[] memory);

    // role setter
    function transferOwnershipOnClaimTopicsRegistryContract(address _newOwner) external;
}

Test Cases

The standard is implemented and tested with full coverage on Tokeny’s T-REX repository

Security Considerations

The suite of Smart Contracts has been audited by an external and independent company. The results can be found in this document.

Copyright

Copyright and related rights waived via CC0.

Citation

Please cite this document as:

Joachim Lebrun, Tony Malghem, Kevin Thizy, Luc Falempin, Adam Boudjemaa, "EIP-3643: T-REX - Token for Regulated EXchanges [DRAFT]," Ethereum Improvement Proposals, no. 3643, July 2021. [Online serial]. Available: https://eips.ethereum.org/EIPS/eip-3643.