Debt Auction House

Debt auctioneer that covers deficit by minting protocol tokens in exchange for system coins

1. Summary

Debt auctions are used to recapitalize the system by auctioning off protocol tokens for a fixed amount of system coins. In this process, bidders compete by offering to accept decreasing amounts of protocol tokens for the coins they will end up paying.

2. Contract Variables & Functions

Variables

• contractEnabled - settlement flag (1 or 0).

• AUCTION_HOUSE_TYPE - flag set to bytes32("DEBT")

• authorizedAccounts[usr: address] - addresses allowed to call modifyParameters() and disableContract().

• safeEngine - storage of the SAFEEngine's address.

• protocolToken - token minted in exchange for system coins.

• accountingEngine - address of the AccountingEngine (receiver of system coins).

• bids[id: uint] - storage of all bids.

• bidDuration - bid lifetime.

• bidDecrease - minimum bid decrease.

• amountSoldIncrease - increase for size of amountToSell during restartAuction (default to 50%).

• totalAuctionLength - maximum auction duration.

• auctionsStarted - number of auctions that have started up until now.

Data Structures

• Bid - state of a specific auction. Contains:

  • bidAmount - paid system coins

  • amountToSell - quantity of protocol tokens up for auction

  • highBidder

  • bidExpiry - when a bid expires (and the auction ends)

  • auctionDeadline - max auction duration

Modifiers

• isAuthorized **** - checks whether an address is part of authorizedAddresses (and thus can call authed functions).

Functions

• modifyParameters(bytes32 parameter, uint256 data) - update a uint256 parameter.

• modifyParameters(bytes32 parameter, address data) - update an address parameter.

• startAuction(incomeReceiver: address, amountToSell: uint256, initialBid: uint256) - start a new debt auction.

• restartAuction(id: uint256) - restart an auction if there have been 0 bids and the auctionDeadline has passed.

• decreaseSoldAmount(id: uint256, amountToBuy: uint256, bid: uint256) - submit a fixed system coin bid with an increasingly lower amount of protocol tokens you are willing to accept in exchange.

• disableContract() - disable the contract.

• settleAuction(id: uint256) - claim a winning bid / settles a completed auction

• terminateAuctionPrematurely(id: uint256) - used during GlobalSettlement to terminate

  decreaseSoldAmountphase auctions and repay system coins (using safeEngine.createUnbackedDebt with the accountingEngine as the debtDestination) to the highest bidder.

Events

• AddAuthorization - emitted when a new address becomes authorized. Contains:

  • account - the new authorized account

• RemoveAuthorization - emitted when an address is de-authorized. Contains:

  • account - the address that was de-authorized

• StartAuction- emitted when startAuction(address, uint256, uint256) is successfully executed. Contains:

  • id - auction id

  • auctionsStarted - total amount of auctions that have started up until now

  • amountToSell - amount of protocol tokens sold in (to be minted after) the auction.

  • initialBid - starting bid for the auction.

  • incomeReceiver **** - address that receives the system coins from an auction (usually the AccountingEngine)

  • auctionDeadline - deadline for the auction with ID id

  • activeDebtAuctions - the current number of active debt auctions

• ModifyParameters - emitted after a parameter is modified

• RestartAuction - emitted after an auction is restarted. Contains:

  • id - the ID of the auction being restarted

  • auctionDeadline - the new auction deadline

• DecreaseSoldAmount - emitted when someone bids a smaller amount of protocol tokens for the same amount of system coins given in return. Contains:

  • id - the ID of the auction that's being bid on

  • highBidder - the new high bidder

  • amountToBuy - the protocol token bid

  • bid - the amount of system coins offered

  • bidExpiry - the timestamp when the auction will end even if it's earlier than the auctionDeadline

• SettleAuction - emitted after an auction is settled. Contains:

  • id - the ID of the settled auction

  • activeDebtAuctions - the new number of active debt auctions

• TerminateAuctionPrematurely - emitted after an auction is settled before its official deadline. Contains:

  • id - the ID of the auction that was terminated

  • sender - the address that terminated the auction

  • highBidder - the auction's high bidder

  • bidAmount - the auction's bid amount

  • activeDebtAuctions - the new number of active debt auctions

• DisableContract - emitted after the contract is disabled. Contains:

  • sender - the address that disabled the contract

3. Walkthrough

The DebtAuctionHouse is a reverse auction, meaning that participants bid with increasingly lower amounts of protocol tokens they are willing to accept for a fixed amount of system coins. The auction will end when the latest bid duration (bidDuration) has passed since the last submitted bid or when the general auction deadline (auctionStartTime + totalAuctionLength) has been reached.

The first bidder will pay back the system debt (that the auction tries to cover) and submit their preference for the amount of protocol tokens they would like to receive. Each subsequent bid will pay back the previous (no longer winning) bidder. When the auction is over, the process ends by cleaning up the bid and minting protocol tokens for the winning bidder.

If the auction expires without receiving any bids, anyone can restart the auction by calling restartAuction(uint auction_id). This will do two things:

1. It resets bids[id].auctionDeadline to now + totalAuctionLength

2. It resets bids[id].amountToSell to bids[id].amountToSell * amountSoldIncrease / ONE

4. Gotchas (Potential Source of User Error)

Keepers

In the context of running a keeper (more info here) to perform bids within an auction, a primary failure mode would occur when a keeper specifies an unprofitable price for RATE.

• This failure mode is due to the fact that there is nothing the system can do stop a user from paying significantly more than the fair market value for the token in an auction (this goes for all auction types, collateral, debt, and surplus).

• This means, in the case of Flop, that since the Coin amount is fixed for the entire auction, the risk to the keeper is that they would make a "winning" bid that pays the bid amount in Coin but does not receive any RATE (amountToSell == 0). Subsequent executions of this bad strategy would be limited by the amount of Coin (not RATE) in their vat balance.

5. Failure Modes (Bounds on Operating Conditions & External Risk Factors)

DebtAuctionHouse has the potential to issue an excessively huge amount of RATE and despite the mitigation efforts (the addition of the initialDebtAuctionMintedTokens and amountSoldIncrease parameters), if initialDebtAuctionMintedTokens is not set correctly by governance, the huge issuance of RATE could still occur.