Transfer Compliance

TIP-20 tokens integrate with the TIP-403 transfer policy registry to enforce programmable compliance rules on all token transfers, mints, and burns.

Overview

Each TIP-20 token references a transfer policy by ID:

// Policy ID (stored in token contract)
uint64 public transferPolicyId;

// TIP-403 Registry (protocol precompile)
TIP403Registry constant TIP403_REGISTRY = 
    TIP403Registry(0x403c000000000000000000000000000000000000);

Before executing any transfer, the token checks authorization:

if (!TIP403_REGISTRY.isAuthorizedSender(transferPolicyId, from)
    || !TIP403_REGISTRY.isAuthorizedRecipient(transferPolicyId, to)) {
    revert PolicyForbids();
}

Policy Types

TIP-403 supports three policy types:

Whitelist Policies

Only addresses on the whitelist can participate:

// Policy: Only whitelisted addresses can send/receive
policyType = PolicyType.WHITELIST

// Check: Is address on whitelist?
if (policyType == WHITELIST) {
    return policySet[policyId][user];  // true if whitelisted
}

Use cases:

KYC-required tokens (only verified users)
Private securities (only accredited investors)
Internal company tokens (only employees)

Blacklist Policies

All addresses except those on the blacklist can participate:

// Policy: Blocked addresses cannot send/receive
policyType = PolicyType.BLACKLIST

// Check: Is address blocked?
if (policyType == BLACKLIST) {
    return !policySet[policyId][user];  // true if not blocked
}

Use cases:

Sanctions compliance (block OFAC addresses)
Fraud prevention (block compromised addresses)
Terms of service enforcement (block violators)

Compound Policies (TIP-1015)

Different rules for senders, recipients, and mint recipients:

struct CompoundPolicyData {
    uint64 senderPolicyId;        // Policy for senders
    uint64 recipientPolicyId;     // Policy for recipients  
    uint64 mintRecipientPolicyId; // Policy for mint recipients
}

Use cases:

Vendor credits (anyone can receive, only vendor can be paid)
Asymmetric compliance (different rules for in/out flows)
Restricted minting (tight control on issuance, loose on transfers)

See Compound Policies for details.

Transfer Authorization

Standard Transfers

All transfer methods check both sender and recipient authorization:

modifier transferAuthorized(address from, address to) {
    if (!TIP403_REGISTRY.isAuthorizedSender(transferPolicyId, from)
        || !TIP403_REGISTRY.isAuthorizedRecipient(transferPolicyId, to)) {
        revert PolicyForbids();
    }
    _;
}

function transfer(address to, uint256 amount)
    external
    notPaused
    validRecipient(to)
    transferAuthorized(msg.sender, to)  // Policy check
    returns (bool)
{
    _transfer(msg.sender, to, amount);
    return true;
}

Checked functions:

transfer(to, amount)
transferFrom(from, to, amount)
transferWithMemo(to, amount, memo)
transferFromWithMemo(from, to, amount, memo)
systemTransferFrom(from, to, amount) (FeeManager only)

Mint Operations

Mints check mint recipient authorization:

function _mint(address to, uint256 amount) internal {
    if (!TIP403_REGISTRY.isAuthorizedMintRecipient(transferPolicyId, to)) {
        revert PolicyForbids();
    }
    
    // ... perform mint
}

Why separate mint checks?

Stricter control over token issuance
Prevent minting to unauthorized addresses
Support vendor credit scenarios (loose minting, tight transfers)

Burn Operations

Standard Burn

Burning from caller’s own balance checks sender authorization:

function burn(uint256 amount) external onlyRole(ISSUER_ROLE) {
    // Checks sender authorization implicitly via _transfer
    _transfer(msg.sender, address(0), amount);
    _totalSupply -= uint128(amount);
    emit Burn(msg.sender, amount);
}

Burn Blocked (TIP-1015)

Burning from blocked addresses requires sender to be unauthorized:

function burnBlocked(address from, uint256 amount)
    external
    onlyRole(BURN_BLOCKED_ROLE)
{
    // Only allow burning from blocked addresses
    if (TIP403_REGISTRY.isAuthorizedSender(transferPolicyId, from)) {
        revert PolicyForbids();  // Sender can still send, cannot burn
    }
    
    // ... perform burn
}

Use case: Seize funds from sanctioned addresses without affecting legitimate holders.

Burn At (TIP-1006)

Burning from any address bypasses policy checks:

function burnAt(address from, uint256 amount)
    external
    onlyRole(BURN_AT_ROLE)
{
    // No policy check - privileged operation
    // Still protects FeeManager and DEX addresses
    
    // ... perform burn
}

Use case: Bridge contracts burning tokens without policy constraints.

Reward Operations

Reward distribution and claims check policies:

// Distributing rewards: sender to contract
function distributeReward(uint256 amount) external notPaused {
    if (!TIP403_REGISTRY.isAuthorizedSender(transferPolicyId, msg.sender)
        || !TIP403_REGISTRY.isAuthorizedRecipient(transferPolicyId, address(this))) {
        revert PolicyForbids();
    }
    // ... distribute rewards
}

// Claiming rewards: contract to recipient
function claimRewards() external notPaused returns (uint256) {
    if (!TIP403_REGISTRY.isAuthorizedSender(transferPolicyId, address(this))
        || !TIP403_REGISTRY.isAuthorizedRecipient(transferPolicyId, msg.sender)) {
        revert PolicyForbids();
    }
    // ... claim rewards
}

// Setting reward recipient
function setRewardRecipient(address newRecipient) external notPaused {
    if (newRecipient != address(0)) {
        if (!TIP403_REGISTRY.isAuthorizedSender(transferPolicyId, msg.sender)
            || !TIP403_REGISTRY.isAuthorizedRecipient(transferPolicyId, newRecipient)) {
            revert PolicyForbids();
        }
    }
    // ... set recipient
}

Built-In Policies

The TIP-403 registry includes two built-in policies:

// Policy 0: Always reject
policyId = 0
isAuthorized(0, anyAddress) == false

// Policy 1: Always allow (default)
policyId = 1  
isAuthorized(1, anyAddress) == true

All TIP-20 tokens default to policy 1 (always-allow) on creation:

uint64 public transferPolicyId = 1;

Changing Policies

Token administrators can change the active policy:

function changeTransferPolicyId(uint64 newPolicyId)
    external
    onlyRole(DEFAULT_ADMIN_ROLE)
{
    // Validate policy exists
    if (!TIP403_REGISTRY.policyExists(newPolicyId)) {
        revert InvalidTransferPolicyId();
    }
    
    emit TransferPolicyUpdate(msg.sender, transferPolicyId = newPolicyId);
}

Impact:

Takes effect immediately
All future transfers use new policy
Existing balances are not affected
Users may become unable to transfer if newly unauthorized

Example flow:

// 1. Create new policy
uint64 kycPolicyId = TIP403_REGISTRY.createWhitelistPolicy();

// 2. Add KYC-verified addresses
TIP403_REGISTRY.addToWhitelist(kycPolicyId, verifiedUser1);
TIP403_REGISTRY.addToWhitelist(kycPolicyId, verifiedUser2);

// 3. Switch token to new policy
token.changeTransferPolicyId(kycPolicyId);

// Now only verified users can transfer

Compound Policies (TIP-1015)

Overview

Compound policies enable different authorization rules for different transfer directions:

struct CompoundPolicyData {
    uint64 senderPolicyId;        // Who can send tokens
    uint64 recipientPolicyId;     // Who can receive tokens
    uint64 mintRecipientPolicyId; // Who can receive mints
}

Creating Compound Policies

// Create component policies
uint64 anyonePolicy = 1;  // Built-in always-allow
uint64 vendorPolicy = TIP403_REGISTRY.createWhitelistPolicy();
TIP403_REGISTRY.addToWhitelist(vendorPolicy, vendorAddress);

// Create compound policy
uint64 vendorCreditPolicy = TIP403_REGISTRY.createCompoundPolicy(
    anyonePolicy,  // Anyone can send (spend credits)
    vendorPolicy,  // Only vendor can receive
    anyonePolicy   // Anyone can receive mints (get credits)
);

// Apply to token
token.changeTransferPolicyId(vendorCreditPolicy);

Result:

Users can receive minted credits (mint recipient = anyone)
Users can spend credits only to vendor (recipient = vendor only)
Peer-to-peer transfers are blocked (recipient must be vendor)

Use Case: Vendor Credits

contract VendorCredits {
    ITIP20 public immutable creditToken;
    address public immutable vendor;
    
    constructor(ITIP20 _token, address _vendor) {
        creditToken = _token;
        vendor = _vendor;
        
        // Set up compound policy
        uint64 anyonePolicy = 1;
        uint64 vendorOnlyPolicy = createVendorOnlyPolicy(_vendor);
        
        uint64 compoundPolicy = TIP403_REGISTRY.createCompoundPolicy(
            anyonePolicy,      // Senders: anyone
            vendorOnlyPolicy,  // Recipients: vendor only
            anyonePolicy       // Mint recipients: anyone
        );
        
        _token.changeTransferPolicyId(compoundPolicy);
    }
    
    // Issue credits to users (anyone can receive)
    function issueCredits(address user, uint256 amount) external {
        creditToken.mint(user, amount);
    }
    
    // User spends credits (only vendor can receive)
    function redeemCredits(uint256 amount) external {
        creditToken.transferFrom(msg.sender, vendor, amount);
        // Vendor fulfills service
    }
}

Use Case: Asymmetric Compliance

Different rules for sending vs. receiving:

// Senders must be KYC verified
uint64 kycSenders = TIP403_REGISTRY.createWhitelistPolicy();

// Recipients can be anyone (for refunds, seizures)
uint64 anyRecipients = 1;

// Mints require full compliance
uint64 kycMintRecipients = kycSenders;  // Same as sender policy

// Create asymmetric policy
uint64 asymmetricPolicy = TIP403_REGISTRY.createCompoundPolicy(
    kycSenders,          // Only KYC users can send
    anyRecipients,       // Anyone can receive
    kycMintRecipients    // Only KYC users can receive mints
);

Result:

KYC users can send to anyone (including blocked addresses for seizures)
Non-KYC users cannot send
Non-KYC users can receive (e.g., refunds)
Only KYC users can receive new token issuance

Authorization Logic

For compound policies, authorization delegates to component policies:

function isAuthorizedSender(uint64 policyId, address user)
    external view returns (bool)
{
    PolicyRecord storage record = policyRecords[policyId];
    
    if (record.base.policyType == PolicyType.COMPOUND) {
        // Delegate to sender policy
        return isAuthorized(record.compound.senderPolicyId, user);
    }
    
    // For simple policies, sender auth = general auth
    return isAuthorized(policyId, user);
}

Gas cost: 1 keccak + 2 SLOADs for compound policies.

Immutability

Compound policies are immutable once created:

Cannot change component policy IDs
No admin (admin = address(0))
Cannot add/remove addresses from compound policy itself

To change behavior:

Modify component policies (if they have admins)
Or create new compound policy and switch token to it

Policy Administration

Creating Policies

interface ITIP403Registry {
    // Create whitelist policy
    function createWhitelistPolicy() external returns (uint64 policyId);
    
    // Create blacklist policy
    function createBlacklistPolicy() external returns (uint64 policyId);
    
    // Create compound policy (TIP-1015)
    function createCompoundPolicy(
        uint64 senderPolicyId,
        uint64 recipientPolicyId,
        uint64 mintRecipientPolicyId
    ) external returns (uint64 policyId);
}

Policy IDs:

Start at 2 (0 and 1 are built-in)
Increment sequentially
Unique across all policy types
Permanent (cannot be deleted)

Modifying Policies

Simple policies (whitelist/blacklist) can be modified by their admin:

// Add to whitelist/blacklist
function addToSet(uint64 policyId, address user) external {
    require(msg.sender == policyData[policyId].admin);
    policySet[policyId][user] = true;
    emit SetMembershipUpdated(policyId, user, true);
}

// Remove from whitelist/blacklist  
function removeFromSet(uint64 policyId, address user) external {
    require(msg.sender == policyData[policyId].admin);
    policySet[policyId][user] = false;
    emit SetMembershipUpdated(policyId, user, false);
}

// Batch operations
function batchUpdateSet(
    uint64 policyId,
    address[] calldata users,
    bool[] calldata statuses
) external;

Transferring Policy Admin

function setPolicyAdmin(uint64 policyId, address newAdmin) external {
    require(msg.sender == policyData[policyId].admin);
    policyData[policyId].admin = newAdmin;
    emit PolicyAdminUpdated(policyId, newAdmin);
}

Note: Compound policies have no admin and cannot be modified.

Gas Costs

Policy Checks

Policy Type	Operation	Gas Cost
Always-allow (policy 1)	Any transfer	~0 (short-circuit)
Whitelist	Check membership	~2,100 (1 SLOAD)
Blacklist	Check membership	~2,100 (1 SLOAD)
Compound	Check both sender/recipient	~4,200 (2 SLOADs)

Policy Creation

Operation	Gas Cost
Create whitelist/blacklist	~50,000
Create compound policy	~100,000
Add to whitelist/blacklist (new)	~250,000 (TIP-1000 state creation)
Add to whitelist/blacklist (update)	~5,000
Remove from whitelist/blacklist	~5,000

Transfer Impact

Policy checks add to total transfer cost:

Scenario	Base Cost	Policy Cost	Total
Transfer with always-allow	50,000	~0	~50,000
Transfer with whitelist	50,000	~4,200	~54,200
Transfer with compound	50,000	~8,400	~58,400

Integration Patterns

KYC Token

contract KYCToken {
    ITIP20 public immutable token;
    uint64 public immutable kycPolicyId;
    
    mapping(address => bool) public kycVerified;
    
    constructor(ITIP20 _token) {
        token = _token;
        
        // Create KYC whitelist policy
        kycPolicyId = TIP403_REGISTRY.createWhitelistPolicy();
        
        // Apply to token
        _token.changeTransferPolicyId(kycPolicyId);
    }
    
    function verifyUser(address user) external onlyAdmin {
        kycVerified[user] = true;
        TIP403_REGISTRY.addToWhitelist(kycPolicyId, user);
    }
    
    function revokeUser(address user) external onlyAdmin {
        kycVerified[user] = false;
        TIP403_REGISTRY.removeFromWhitelist(kycPolicyId, user);
    }
}

Sanctions Compliance

contract SanctionsToken {
    ITIP20 public immutable token;
    uint64 public immutable sanctionsPolicyId;
    
    constructor(ITIP20 _token) {
        token = _token;
        
        // Create sanctions blacklist
        sanctionsPolicyId = TIP403_REGISTRY.createBlacklistPolicy();
        
        // Apply to token
        _token.changeTransferPolicyId(sanctionsPolicyId);
    }
    
    function blockAddress(address target) external onlyCompliance {
        TIP403_REGISTRY.addToBlacklist(sanctionsPolicyId, target);
    }
    
    function seizeFromBlocked(address blocked, uint256 amount) 
        external 
        onlyCompliance 
    {
        // Use burnBlocked to seize from blocked address
        token.burnBlocked(blocked, amount);
    }
}

Tiered Access

contract TieredToken {
    ITIP20 public immutable token;
    
    uint64 public tier1Policy;  // Basic access
    uint64 public tier2Policy;  // Enhanced access
    uint64 public tier3Policy;  // Full access
    
    function upgradeTier(address user, uint8 newTier) external onlyAdmin {
        // Remove from old tier
        if (tier1Policy != 0) TIP403_REGISTRY.removeFromWhitelist(tier1Policy, user);
        if (tier2Policy != 0) TIP403_REGISTRY.removeFromWhitelist(tier2Policy, user);
        if (tier3Policy != 0) TIP403_REGISTRY.removeFromWhitelist(tier3Policy, user);
        
        // Add to new tier
        if (newTier == 1) TIP403_REGISTRY.addToWhitelist(tier1Policy, user);
        else if (newTier == 2) TIP403_REGISTRY.addToWhitelist(tier2Policy, user);
        else if (newTier == 3) TIP403_REGISTRY.addToWhitelist(tier3Policy, user);
    }
    
    function setTokenTier(uint8 tier) external onlyAdmin {
        if (tier == 1) token.changeTransferPolicyId(tier1Policy);
        else if (tier == 2) token.changeTransferPolicyId(tier2Policy);
        else if (tier == 3) token.changeTransferPolicyId(tier3Policy);
    }
}

Error Handling

error PolicyForbids();              // Transfer blocked by policy
error InvalidTransferPolicyId();    // Policy does not exist

Testing policy authorization:

// Check before attempting transfer
if (!TIP403_REGISTRY.isAuthorizedSender(policyId, from)
    || !TIP403_REGISTRY.isAuthorizedRecipient(policyId, to)) {
    revert PolicyForbids();
}

// Or use try/catch
try token.transfer(to, amount) returns (bool success) {
    // Transfer succeeded
} catch Error(string memory reason) {
    if (keccak256(bytes(reason)) == keccak256("PolicyForbids()")) {
        // Handle policy rejection
    }
}

Best Practices

Policy Design

Start permissive, tighten later
- Launch with policy 1 (always-allow)
- Collect KYC data off-chain
- Switch to whitelist when ready
Use compound policies for flexibility
- Separate sender and recipient rules
- Enable one-way flows (e.g., refunds to blocked users)
- Support vendor credit models
Test policy changes
- Verify policy exists before switching
- Check impact on existing holders
- Announce changes in advance

Security

Protect policy admin keys
- Policy admin can authorize/block any address
- Consider multisig for policy administration
- Monitor policy modification events
Monitor for abuse
- Track SetMembershipUpdated events
- Alert on unexpected policy changes
- Log policy switches for audit trail
Handle blocked users gracefully
- Provide off-chain notification before blocking
- Support appeals process
- Document policy enforcement criteria

Gas Optimization

Batch policy updates
- Use batchUpdateSet for multiple addresses
- Reduces transaction overhead
- Cheaper than individual calls
Reuse policies
- Share policies across multiple tokens
- Reduces deployment costs
- Simplifies administration
Consider policy complexity
- Simple policies are cheaper to check
- Compound policies add ~4,000 gas per transfer
- Balance compliance needs vs. gas costs

Transaction Types

TIP-20 Token Standard

Fee System

Precompiles

TIPs (Tempo Improvement Proposals)

​Overview

​Policy Types

​Whitelist Policies

​Blacklist Policies

​Compound Policies (TIP-1015)

​Transfer Authorization

​Standard Transfers

​Mint Operations

​Burn Operations

​Standard Burn

​Burn Blocked (TIP-1015)

​Burn At (TIP-1006)

​Reward Operations

​Built-In Policies

​Changing Policies

​Compound Policies (TIP-1015)

​Overview

​Creating Compound Policies

​Use Case: Vendor Credits

​Use Case: Asymmetric Compliance

​Authorization Logic

​Immutability

​Policy Administration

​Creating Policies

​Modifying Policies

​Transferring Policy Admin

​Gas Costs

​Policy Checks

​Policy Creation

​Transfer Impact

​Integration Patterns

​KYC Token

​Sanctions Compliance

​Tiered Access

​Error Handling

​Best Practices

​Policy Design

​Security

​Gas Optimization

​See Also

Overview

Policy Types

Whitelist Policies

Blacklist Policies

Compound Policies (TIP-1015)

Transfer Authorization

Standard Transfers

Mint Operations

Burn Operations

Standard Burn

Burn Blocked (TIP-1015)

Burn At (TIP-1006)

Reward Operations

Built-In Policies

Changing Policies

Compound Policies (TIP-1015)

Overview

Creating Compound Policies

Use Case: Vendor Credits

Use Case: Asymmetric Compliance

Authorization Logic

Immutability

Policy Administration

Creating Policies

Modifying Policies

Transferring Policy Admin

Gas Costs

Policy Checks

Policy Creation

Transfer Impact

Integration Patterns

KYC Token

Sanctions Compliance

Tiered Access

Error Handling

Best Practices

Policy Design

Security

Gas Optimization

See Also