Price Oracles
OUSD uses Chainlink to secure the protocol from pricing attacks

Stablecoin Pricing

OUSD is designed to stay pegged at 1 USD and be 1:1 backed with its underlying stablecoins. This is trickier than it sounds because these underlying stablecoins are constantly deviating from their own desired 1 USD pegs. While the majority of daily fluctuations are minor, there have been major swings in price that have occurred in the past and are likely to occur again in the future.
Coin
Low
High
Delta
Source
USDC
$0.929222
Mar 13, 2020
$1.11
Oct 15, 2018
$0.180778
USDC
$0.924188
Aug 02, 2020
$1.17
May 08, 2019
$0.245812
CoinGecko
DAI
$0.945505
May 10, 2020
$1.11
Mar 13, 2020
$0.164495
DAI
$0.903243
Nov 25, 2019
$1.22
Mar 13, 2020
$0.316757
CoinGecko
USDT
$0.849809
Feb 02, 2017
$1.21
May 27, 2017
$0.360191
CoinGecko
USDT
$0.572521
Mar 02, 2015
$1.32
Jul 24, 2018
$0.747479
The rebasing function treats 1 stablecoin as 1 OUSD for simplicity and to protect OUSD balances from being affected by the daily fluctuations in the price of the underlying stablecoins. Since the rebase function only counts coins, OUSD balances should only increase.
In order to mint and redeem the appropriate number of OUSD on entry and exit, the smart contracts need to accurately price the USDT, USDC, and DAI that is entering and exiting the system.
As an added precaution, OUSD never pays more than a dollar for a stablecoin, nor sells a stablecoin for less than a dollar. Oracles giving wrong prices will not result in a reduction of the number of stablecoins held. Gains that are collected as a result of stablecoins slipping from their peg are redistributed to the remaining holders of OUSD in the form of additional yield.
As a decentralized protocol, OUSD must rely on non-centralized sources for these prices. OUSD uses Chainlink oracles for pricing data for DAI, USDC and USDT. You can read more about our decision to work with Chainlink on our blog. Here are the Chainlink oracles we are currently using for stablecoin pricing:
USDT / USD price today | Chainlink
chainlink
USDC / USD price today | Chainlink
chainlink
DAI / USD price today | Chainlink
chainlink

Reward Token Oracles & Front Running Protection

When reward tokens from OUSD strategies are sold for additional yield, Chainlink oracles are checked to ensure that the sale price slippage has not exceeded normal bounds. These oracles are listed on our registry page under the "Oracles" tab.
The same is also true for OGN buybacks from OUSD yield. When minting and redeeming OUSD, a miniumun required amount can be passed into the contract call to ensure that the entire transaction fails if not enough OUSD or stablecoins would be returned to the user due to changing prices.