SAFE Protection

Building and integrating saviour contracts for SAFEs

1. Overview

The GEB LiquidationEngine allows governance to whitelist external insurance contracts for SAFEs. SAFE users can attach insurance contracts to their positions and this way have an extra layer of protection against liquidation.

Anyone can build and propose new insurance contracts, assuming that the contracts abide by the requirements and principles outlined below. A central repository with SAFE insurance contracts (also called saviors) and interfaces can be found here.

2. Contract Interface

Every insurance contract must implement one of the official interfaces (the oldest interface can be found here):

abstract contract SafeSaviourLike is ReentrancyGuard {
    // Checks whether a saviour contract has been approved by governance in the LiquidationEngine
    modifier liquidationEngineApproved(address saviour) {
        require(liquidationEngine.safeSaviours(saviour) == 1, "SafeSaviour/not-approved-in-liquidation-engine");
        _;
    }
    // Checks whether someone controls a safe handler inside the GebSafeManager
    modifier controlsSAFE(address owner, uint256 safeID) {
        require(owner != address(0), "SafeSaviour/null-owner");
        require(either(owner == safeManager.ownsSAFE(safeID), safeManager.safeCan(safeManager.ownsSAFE(safeID), safeID, owner) == 1), "SafeSaviour/not-owning-safe");

        _;
    }

    // --- Variables ---
    LiquidationEngineLike   public liquidationEngine;
    OracleRelayerLike       public oracleRelayer;
    GebSafeManagerLike      public safeManager;
    SAFEEngineLike          public safeEngine;
    SAFESaviourRegistryLike public saviourRegistry;

    // The amount of tokens the keeper gets in exchange for the gas spent to save a SAFE
    uint256 public keeperPayout;          // [wad]
    // The minimum fiat value that the keeper must get in exchange for saving a SAFE
    uint256 public minKeeperPayoutValue;  // [wad]
    /*
      The proportion between the keeperPayout (if it's in collateral) and the amount of collateral or debt that's in a SAFE to be saved.
      Alternatively, it can be the proportion between the fiat value of keeperPayout and the fiat value of the profit that a keeper
      could make if a SAFE is liquidated right now. It ensures there's no incentive to intentionally put a SAFE underwater and then
      save it just to make a profit that's greater than the one from participating in collateral auctions
    */
    uint256 public payoutToSAFESize;

    // --- Constants ---
    uint256 public constant ONE               = 1;
    uint256 public constant HUNDRED           = 100;
    uint256 public constant THOUSAND          = 1000;
    uint256 public constant WAD_COMPLEMENT    = 10**9;
    uint256 public constant WAD               = 10**18;
    uint256 public constant RAY               = 10**27;
    uint256 public constant MAX_UINT          = uint(-1);

    // --- Boolean Logic ---
    function both(bool x, bool y) internal pure returns (bool z) {
        assembly{ z := and(x, y) }
    }
    function either(bool x, bool y) internal pure returns (bool z) {
        assembly{ z := or(x, y)}
    }

    // --- Events ---
    event SaveSAFE(address indexed keeper, bytes32 indexed collateralType, address indexed safeHandler, uint256 collateralAddedOrDebtRepaid);

    // --- Functions to Implement ---
    function saveSAFE(address,bytes32,address) virtual external returns (bool,uint256,uint256);
    function getKeeperPayoutValue() virtual public returns (uint256);
    function keeperPayoutExceedsMinValue() virtual public returns (bool);
    function canSave(bytes32,address) virtual external returns (bool);
    function tokenAmountUsedToSave(bytes32,address) virtual public returns (uint256);
}

3. Implementation Guidelines

In order to get an idea of how a savior contract should be implemented and what checks must be in place, let's analyze the components of a demo contract that allows SAFE users to deposit & withdraw collateral used to save their positions.

Constructor Requirements:

• Sanitize every parameter (addresses must be non-null, uint values are non-null and within expected bounds etc)

• In case of a saviour that adds more collateral in Safes, you must set the CollateralJoin contract of the specific collateral type you're targeting

• In case of a savior that repays debt instead of adding collateral, you must set the CoinJoin contract

• Every savior type should also have the LiquidationEngine, OracleRelayer, SAFEEngine, GebSafeManager, SAFESaviourRegistry and SaviourCRatioSetter set

• You must set:

  • keeperPayout - amount of collateral awarded to the address that was initially called LiquidationEngine.liquidateSAFE

  • minKeeperPayoutValue - the minimum fiat value of the keeperPayout which makes it compelling for keepers to save the SAFE instead of waiting even more to liquidate it

  • defaultDesiredCollateralizationRatio - the default CRatio that a SAFE will have after it's saved; this CRatio must be greater than the liquidation ratio stored in the OracleRelayer and that is associated with collateralToken

• Optionally, you can set:

  • payoutToSAFESize - how many times more collateral there must be in a SAFE compared to keeperPayout; this prevents keepers from purposefully liquidating SAFEs so they get a reward that is bigger than the one offered in a collateral auction

• When comparing a liquidationCRatio from the OracleRelayer with a desired collateralization ratio, you must first divide liquidationCRatio by CRATIO_SCALE_DOWN so you have the same scale for both numbers

• You must integrate your savior with GebSafeManager in order to take advantage of its modularity and friendlier interface compared to core contracts (such as SAFEEngine)

Covering & Uncovering SAFEs:

There is no specific way in which users should cover a SAFE. They can store collateral in the savior, they can also store aTokens or cTokens that are then used to redeem the underlying assets and add them in the SAFE or they can use a protocol similar to Nexus Mutual which automatically fulfills claims and saves positions. There are, though, certain things that a savior developer must take into account:

• The function used to add more cover for a SAFE (like deposit) must revert if the savior contract is not whitelisted inside the LiquidationEngine

• Users can only add cover if their SAFEs have generated debt

• Users can withdraw cover (with something like withdraw) even if the savior contract is not whitelisted inside the LiquidationEngine

• Only the SAFE's owner or an authorized address inside the GebSafeManager can withdraw cover

Reentrancy

Make sure to protect your cover/uncover functions against re-entrancy.

View Function Requirements:

keeperPayoutExceedsMinValue:

• It must verify if the fiat value of keeperPayout exceeds or is equal to minKeeperPayoutValue

• It must read the collateral's price from the same oracle used inside OracleRelayer in order to maintain consistency between the core system and the savior

• It must return false if the oracle price is invalid

getKeeperPayoutValue:

• It must read the collateral's price from the same oracle used inside OracleRelayer in order to maintain consistency between the core system and the savior

• It must return 0 if the oracle price is invalid

• It must return the fiat value of keeperPayout collateral tokens used to pay keepers for saving SAFEs

tokenAmountUsedToSave:

• It must return the amount of collateral tokens that will be used to save a SAFE and bring its CRatio to the desired ratio

• It must read the collateral's price from the same oracle used inside OracleRelayer in order to maintain consistency between the core system and the savior

• It must return early if the targeted SAFE has no debt or if the oracle feed is invalid

canSave:

• It must return true if a SAFE can currently be saved, false if not

• It must check that, when the SAFE is saved, the contract has enough tokens to both reward the keeper that called LiquidationEngine.liquidateSAFE and also bring the SAFE's CRatio to the desired level

Saving a SAFE:

The process of saving a SAFE has its own requirements:

• You must implement and use saveSAFE(address keeper, bytes32 collateralType, address safeHandler) external returns (bool, uint256, uint256) in order to save SAFEs

• saveSAFE must check that msg.sender is the LiquidationEngine

• The keeper parameter must not be null

• There is a special condition you must add where, if the collateralType is null, the keeper is the LiquidationEngine itself and the safeHandler is null, you return a tuple like (true, uint(-1), uint(-1)). This condition will help the LiquidationEngine to check that you implemented saveSAFE. You can see an example of this condition here

• You must check that keeperPayoutExceedsMinValue returns true. If it returns false, you must return early

• You must check that the SAFE has debt in it

• You must check that the saviour can both reward the keeper for saving the SAFE and also add enough collateral in the SAFE so its CRatio goes to the desired level

• You must not add any collateral in the SAFE or repay the SAFE's debt in case it cannot be saved (its CRatio cannot be increased to the desired level). You must revert in case the SAFE cannot be saved

• You must call saviourRegistry.markSave(collateralType, safeHandler) so that the SAFESaviourRegistry knows a specific SAFE has just been saved. The registry enforces a delay between two consecutive save actions for a specific SAFE. The delay is there to make sure that SAFE users don't solely rely on saviors to protect their positions. This way we avoid a scenario where one or a couple of popular saviors fail (e.g bugs, lack of sufficient cover) and most positions in the system are liquidated at once

• You must emit a SaveSAFE event before you return

• The last thing you have to do is to return a tuple in the form of (true, tokenAmountUsed, keeperPayout) where:

  • tokenAmountUsed is the amount of collateral that was used to save the SAFE

  • keeperPayout is a non-null amount of collateral that was used to reward the keeper

You can check an example implementation for saveSAFE here.

4. Monetizing a Saviour

In some cases, savior builders may want to monetize the service they provide and charge some sort of fee for protecting SAFEs.

If you would like to submit a proposal for implementing a monetized savior, you must keep in mind several things:

• Monetization should happen outside of the savior contract. This keeps concerns separated, simplifies the savior implementation and gives you more flexibility when it comes to updating your business model

• You must mention that your savior will be monetized and you should give a detailed description of how you plan to charge SAFE users. You must include the description in your GIP as outlined in the section below

• Assuming you plan to use a smart contract to charge users, you should attach a detailed overview or implementation of your model inside your GIP

5. Launching on Mainnet

In order to launch and integrate a saviour with a mainnet deployed GEB, the saviour must first pass several checks:

1. You must first create a new GEB Improvement Proposal. Once you create the GIP you must ask for feedback on Reflexer's Discord server (in the development channel). To maximize your chances of having your idea accepted:

   • Your saviour must only do one thing. For example, you should only handle aTokens or cTokens, not both

   • Your saviour should only take into account a single collateral type (e.g ETH-A or ETH-B, not ETH-A and ETH-B) in case it's meant to add collateral. If the saviour repays debt, it can be generalized to handle any Safe with any collateral type

   • You should have a draft implementation of your saviour with estimated gas amounts for calling each function

   • You should give an initial estimate of the keeperPayout, minKeeperPayoutValue and payoutToSAFESize values you plan to set

   • You must specify if you plan to monetize the saviour service you're building and how you plan to do it

2. Once you receive feedback (and assuming it's positive), you can start to fully implement the saviour. Keep in mind that, aside from the saviour, you will need to create a proxy actions contract (like this one) that will be used by others to connect your saviour to Safes and also add cover.

3. Before you submit your full implementation and update the GIP, you must make sure that you have 100% test coverage for your code and also do several integration tests between the LiquidationEngine, SAFESaviourRegistry and the saviour code. In order to submit your implementation, update your GIP with a link to your code and a new summary of the gas amounts required to call each function, as well as updated values for keeperPayout, minKeeperPayoutValue, payoutToSAFESize and defaultDesiredCollateralizationRatio

   . After you update the GIP, ping the community on Discord.

4. Once your implementation is accepted and reviewed by the community, your code must also be audited twice. Each audit must be done by an independent party.

5. After your code gets audited, you should send a new message on Discord and let the community know that it's ready to be integrated in production. You must link to the audit reports.

6. Governance may decide to first try out your saviour on a testnet. In this case, you must deploy an instance of your saviour on a testnet GEB and liquidate a SAFE which can then be saved

7. Assuming that you pass all previous steps, you can deploy your saviour on mainnet so that governance can whitelist it in LiquidationEngine and in SAFESaviourRegistry

6. Integration Ideas

To help you get started, here are a couple of ideas for building RAI saviours:

• Allow users to deposit Aave aETH in a saviour which can then be used to redeem ETH that is then added in a SAFE

• Allow users to deposit Compound cETH in a saviour which can then be used to redeem ETH

  that is then added in a SAFE

• Opyn or Hegic options which can be exercised when saveSAFE is called