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Use Case

An oracle is a mechanism used to fetch data from an external source and use it to make decisions within a protocol. Make sure that an oracle is working as expected. Manipulation of oracles is a very common attack vector. An oracle can be manipulated to return a price that is not representative of the true price of an asset. Oracles are used in many DeFi protocols, including lending protocols, derivatives protocols, and more.

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Explanation

This assertion makes sure that the oracle has been updated within the last 10 minutes and that the price doesn’t deviate more than 10% from the pre-state price. There are two triggers, one for the liveness of the oracle and one for the price.

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Code Example

// SPDX-License-Identifier: MIT
pragma solidity 0.8.28;

import {Assertion} from "../../lib/credible-std/src/Assertion.sol";

interface IOracle {
    function lastUpdated() external view returns (uint256);
    function price() external view returns (uint256);
}

// Checks that the oracle is live
contract OracleLivenessAssertion is Assertion {
    IOracle public oracle = IOracle(address(0xbeef));

    function fnSelectors() external pure override returns (bytes4[] memory assertions) {
        assertions = new bytes4[](2);
        assertions[0] = this.assertionOracleLiveness.selector;
        assertions[1] = this.assertionOraclePrice.selector;
    }

    // Make sure that the oracle has been updated within the last 10 minutes
    function assertionOracleLiveness() external {
        ph.forkPostState();
        require(block.timestamp - oracle.lastUpdated() <= 10 minutes, "Oracle not updated within the last 10 minutes");
    }

    // Make sure that price doesn't deviate more than 10%
    function assertionOraclePrice() external {
        ph.forkPreState();
        uint256 prePrice = oracle.price();
        ph.forkPostState();
        uint256 postPrice = oracle.price();
        // Calculate the absolute price difference as a percentage
        // If post price is higher than pre price, subtract pre from post
        // Otherwise subtract post from pre to get positive difference
        // Multiply by 100 to convert to percentage points for 10% check
        uint256 priceDeviation =
            (((postPrice > prePrice) ? postPrice - prePrice : prePrice - postPrice) * 100) / prePrice;
        require(priceDeviation <= 10, "Price deviation is too large");
    }
}
Timelock VerificationTWAP Deviation