Dampened Security Module

An OSM-like contract that bounds price feed changes between consecutive updates

1. Summary

The DSM (Dampened Security Module) is an OSM-like contract that, apart from emposing a delay between prices coming from a medianizer and them being added into the system, it bounds the maximum price change between the currentFeed and the nextFeed. This ensures that in case of an oracle attack or extreme market volatility, governance has more time to react and defend the system.

2. Contract Variables & Functions

Variables

• authorizedAccounts[usr: address] - addresses allowed to call authed functions.

• stopped - flag that disables price feed updates if non-zero

• priceSource - address of the medianizer that the OSM will read from

• ONE_HOUR - 3600 seconds

• updateDelay - time delay between updateResult calls; defaults to ONE_HOUR

• lastUpdateTime - time of last update (rounded down to nearest multiple of updateDelay)

• newPriceDeviation - max deviation accepted between the current and the next feed

• currentFeed - Feed struct that holds the current price value

• nextFeed - Feed struct that holds the next price value

Modifiers

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

Functions

• addAuthorization/removeAuthorization - add or remove authorized users (via modifications to the authorizedAccounts mapping)

• stop/start - toggle whether the OSM price feed can be updated (by changing the value of stopped)

• changePriceSource(source: address) - change data source for prices (by setting priceSource)

• changeDelay(delay: uint16) - change interval between price updates (by setting updateDelay)

• changeNextPriceDeviation(deviation: uint256) - change the newPriceDeviation

• restartValue - similar to stop, except it also sets currentFeedand nextFeed to a Feed struct with zero values

• getResultWithValidity - returns the current feed value and a boolean indicating whether it is valid

• getNextResultWithValidity - returns the next feed value (i.e. the one that will become the current value upon the next updateResult call), and a boolean indicating whether it is valid

• getNextBoundedPrice - get the next currentFeed price according to the current newPriceDeviation

• getNextPriceLowerBound - get the lower bound of the next currentFeed update

• getNextPriceUpperBound - get the upper bound of the next currentFeed update

• read - returns the current feed value; reverts if it was not set by some valid mechanism

• updateResult - updates the current feed value and reads the next one

Data Structures

• Feed - struct used to store price feed data. Contains:

  • value - the feed value

  • isValid - whether the price feed value is valid

3. Walkthrough

In order for the DSM to work properly, an external actor must regularly call updateResult() to update the current price and read the next one. The contract stores the timestamp of the last updateResult() and will not allow another update until block.timestamp is at least lastUpdateTime + updateDelay. Values are read from the priceSource. The next price accepted in the DSM can be at max newPriceDeviation deviated from the current price stored in the contract. In case of an oracle attack, governance can call stop() orrestartValue()

4. DSM Variations

SelfFundedDSM

This contract pulls funds from the StabilityFeeTreasury so it can reward addresses for callingupdateResult.

ExternallyFundedDSM

This contract calls an FSMWrapper in order to reward addresses that call updateResult.