Skip to main content

KUSD Module

  • Module Name: KUSD Module
  • Type/Category: Token → KUSD.sol and KUSDJoin.sol
  • Contract Sources:

1. Introduction​

The KUSD Module contains the KUSD token contract and the KUSDJoin adapter. KUSD is designed to represent a token that the core system considers equal in value to its internal debt unit (1 USD).

2. Module Details​

KUSD Token Functions​

FunctionDescription
mint(usr, wad)Mint KUSD to an address
burn(usr, wad)Burn KUSD from an address
transfer(dst, wad)Transfer KUSD
transferFrom(src, dst, wad)Transfer From
approve(usr, wad)Approve transfers
permit(...)Approve by signature (EIP-2612)

KUSD Token Properties​

PropertyValue
nameKUSD Stablecoin
symbolKUSD
version1
decimals18

KUSDJoin Adapter​

The KUSDJoin contract allows users to withdraw KUSD from the system into the standard ERC-20 token:

// Exit internal KUSD to ERC-20
function exit(address usr, uint256 wad) external {
    vat.move(msg.sender, address(this), rad);
    kusd.mint(usr, wad);
}

// Join ERC-20 KUSD to internal system
function join(address usr, uint256 wad) external {
    kusd.burn(msg.sender, wad);
    vat.move(address(this), usr, rad);
}

3. Key Mechanisms​

Why is the KUSD Module Important?​

The KUSD contract is the user-facing ERC-20 contract maintaining the accounting for external KUSD balances. Key features:

  • Standard ERC-20 with changing supply
  • EIP-2612 Permit — Approvals via signed messages (gasless approvals)
  • Mint/Burn — Only authorized contracts can mint/burn

KUSDJoin Flow​

┌──────────────┐     join()     ┌──────────────┐
│   ERC-20     │ ───────────────▶│   Internal   │
│    KUSD      │                 │     KUSD     │
│  (External)  │ ◀───────────────│    (Vat)     │
└──────────────┘     exit()      └──────────────┘

4. Gotchas (Potential User Errors)​

ERC-20 Race Condition

KUSD is susceptible to the known ERC20 race condition. This is mitigated with unlimited approvals. Users approving specific amounts should be aware of this issue.

Join Contract Risks​

  • Phishing Attacks: Malicious join contracts could steal funds instead of sending tokens to the Vat
  • Reversibility: Users who accidentally call join can always recover tokens via exit

5. Failure Modes​

Vat Upgrade​

A Vat upgrade may require new Join contracts to be deployed and authorized.

Collateral Token Issues​

If a collateral token undergoes:

  • Token upgrade
  • Token freeze

Users may temporarily be unable to redeem collateral. Token issuers typically coordinate with the KUSD community for such changes.

Contract Addresses​

NetworkKUSDKUSDJoin
TestnetTBDTBD
MainnetTBDTBD