Styks

The very first onchain price oracle for Casper.

Styks is deployed on the Casper Testnet.

Recent changes:

Below you can find detailed description of the Styks project.

Why does Casper need a price oracle?

The price oracle is a piece of public infrastructure, that ports a price data from the outside world to the blockchain in safe manner. Lack of it, prevented Casper community from developing complex DeFi protocols, such as lending, borrowing, derivatives, complex liquidity pools, leverage trading, prediction markets and more.

Styks brings a reliable and secure price feeds to the Casper ecosystem for others to build on top of it.

It is free to use!

Onchain integration

Before diving into details of how Styks works, if you just want to use the price feed in your smart contract, just call get_twap_price entry point of the StyksPriceFeed smart contract. It returns the latest price for the requested price_feed_id, or None if the price feed is not available.

Example using Odra:

let styks = StyksPriceFeedContractRef::new(env, styks_price_feed_address);
let price: Option<u64> = styks.get_twap_price(String::from("CSPRUSD"));

Example using casper-contract:

let price: Option<u64> = runtime::call_versioned_contract(
    styks_price_feed_address,
    None,
    "get_twap_price",
    runtime_args! {
        "id" => String::from("CSPRUSD")
    }
);

System High Level Architecture

Styks architecture consists of four main components:

flowchart TB subgraph Blocky Server BlockyAPI CoinGecko end subgraph Offchain Actors PriceProducer StyksAdmin end subgraph Casper Blockchain OnchainConsumer StyksBlockySupplier StyksPriceFeed end %% Retrieve the latest price. OnchainConsumer -->|"get_twap_price(symbol)"| StyksPriceFeed StyksPriceFeed -->|price| OnchainConsumer %% Bringing the price onchain using blocky. PriceProducer -->|"call guest program"| BlockyAPI BlockyAPI -->|"get_prices(symbols)"| CoinGecko CoinGecko -->|"prices"| BlockyAPI BlockyAPI -->|"prices"| PriceProducer PriceProducer -->|"post_prices(signed_prices)"| StyksBlockySupplier StyksBlockySupplier -->|"post_prices(prices)"| StyksPriceFeed %% Define price feeds. StyksAdmin -->|"configure"| StyksPriceFeed StyksAdmin -->|"configure"| StyksBlockySupplier

Blocky

Styks leverages Blocky, a trusted execution service that solves a key challenge in oracle design: how to verify that external data hasn't been tampered with.

Traditional oracles face a trust issue - how can smart contracts verify that price data actually came from the claimed source (like CoinGecko) and wasn't modified by the oracle operator?

The Solution Blocky provides verifiable computation through these steps:

  1. Guest Program: A small WebAssembly (WASM) program that contains the exact logic for fetching data.
  2. Secure Execution: Blocky runs this program in a secure environment.
  3. Cryptographic Proof: Blocky signs the results, proving the data came from running the specific program.

How Styks Uses Blocky

PriceProducer uploads a simple guest program to Blocky that:

This signature proves that:

The PriceProducer simply executes this verified program and submits the signed results to the blockchain.

Heartbeat

Styks uses the heartbeat mechanism to control the price feed updates. It is a simple, but effective way of scheduling tasks. It requires PriceProducer to update the price feed once per given time interval, labelled as heartbeat_interval. For example if the interval is 5 minutes, then heartbeats are at 00:00, 00:05, 00:10, etc. If the PriceProducer misses the heartbeat, then it should try to catch the next one.

It is not possible to send the updates exactly at the heartbeat time, so PriceProducer is allowed to send it within some time around the heartbeat time, defined as heartbeat_tolerance. For example if the tolerance is 2 minutes, and the next heartbeat is at 11:05, then the PriceProducer can send the update between 11:03 and 11:07 (inclusive).

Actions taken within the tolerance window are treated as they would happen exactly at the heartbeat time. This decision was made to simplify the system's design and allow for multiple PriceProducers to work in parallel in future.

Data can be sent only once per heartbeat, so if the PriceProducer sends multiple updates within the tolerance window, only the first one is accepted and the rest are rejected.

Time Weighted Average Price (TWAP)

Styks uses the Time Weighted Average Price (TWAP) algorithm to calculate the price. Due to the interval nature of the heartbeat mechanism, which ensures prices are updated in the constant intervals, the TWAP is calculated as a simple average of the price records over the last few heartbeats, defined as twap_window. It can be 1 (to use the latest price) or more.

Algorithm should also handle missed heartbeats and allow some amounts of hertbeats to be missed before the price feed is considered invalid. It is defined as twap_tolerance. If it is set to 0, then no missed heartbeats are allowed. If 1 or more, then the price feed is still valid if the PriceProducer missed 1 heartbeat. For example if twap_window is 3 and twap_tolerance is 2, then the price feed is still valid if the PriceProducer missed 2 heartbeats, within the last 3 heartbeats. Final price is calculated as a simple average of all available prices in the last twap_window heartbeats and in this example it is based on a single valid price, because 2 heartbeats were missed.

It still has the TW in its name, even that it is a simple average, but the algorithm might be extended in the future to use more complex TWAP version if heartbeat mechanism is changed.

Price Feed Id

Each price feed is identified by a unique identifier, called PriceFeedId. The convention in Styks is to use the format <base_currency><quote_currency>, for example CSPRUSD for Casper to USD price feed. Each PriceFeedId have associated information about the name of the CoinGecko symbol.

StyksPriceFeed Smart Contract

The StyksPriceFeed smart contract is the main smart contract of the system. It has multiple security roles. Each role is responsible for different aspects of the system.

The roles are defined as follows:

Anyone can read the twap price using the get_twap_price(price_feed_id) entry point. It returns the value or None if the price feed is not available, because of the missed heartbeats or not being configured.

Configuration of the contract:

StyksBlockySupplier Smart Contract

The StyksBlockySupplier smart contract is a bridge between the Blocky server and the StyksPriceFeed smart contract. It is responsible for receiving the signed prices from the PriceProducer and posting them to the StyksPriceFeed after verifying authenticity and freshness.

It is configured as follows:

Security roles:

Note: - Anyone can submit signed data via report_signed_prices, but only data that is correctly signed with public_key, produced by the expected wasm_hash, and whose timestamp is within timestamp_tolerance will be forwarded to the feed. - The StyksBlockySupplier contract must have the PriceSupplierRole assigned in the StyksPriceFeed contract in order to be able to post the prices there.

Price Update Procedure

Below is the exact sequence of actions that are taken to update the price feed with the latest prices.

sequenceDiagram participant PriceProducer participant BlockyAPI participant StyksBlockySupplier participant StyksPriceFeed PriceProducer->>BlockyAPI: get_prices(symbols) BlockyAPI-->>PriceProducer: signed_prices PriceProducer->>StyksBlockySupplier: post_prices(signed_prices) StyksBlockySupplier->>StyksBlockySupplier: validate signature, wasm hash, timestamp, mapping StyksBlockySupplier->>StyksPriceFeed: post_prices(prices) StyksPriceFeed->>StyksPriceFeed: validate input StyksPriceFeed-->>StyksBlockySupplier: prices_validated StyksBlockySupplier-->>PriceProducer: prices_posted

Step 1: PriceProducer offchain sequence

Step 2: StyksBlockySupplier onchain sequence

Step 3: StyksPriceFeed onchain sequence

Further Work

Above version of the Styks is the first one, that meets the basic requirements of the price oracle. It is simple, secure and efficient. However, there are some features that we are considering to implement.

Multiple Price Producers

In the above model, there is only one PriceProducer that is responsible for fetching the prices from the BlockyAPI and posting them to the StyksBlockySupplier contract. To make system more resilient, we must allow multiple PriceProducers to work in parallel.

We would like to introduce a token-based staking mechanism, that would allow anyone to become a PriceProducer.

Governance

Initially, Odra.dev team will act as the StyksAdmin. We will monitor and maintain the system, but it is natural to us to transfer the ownership to the community. We think of a token-based voting DAO that would allow the community to vote on the changes to the system, such as adding new price feeds, changing the configuration and manage roles.

Beyond Price Feeds

Styks is a price oracle, but it can be used for porting any data from the outside world to the blockchain. There are two main use cases we are internally exploring:

Join the Community

Join our Telegram to leave your feedback and follow the project. This is a community-driven project, so we are looking for contributors to help us with the development, testing, documentation and marketing.