oracles.cash

oracles.cash is a platform for creating Oracles on Bitcoin Cash.

Oracles allow outside information to be provided which can trigger execution in smart-contracts. Oracles.cash is a template for easily spinning up a backend to publish oracle data as well as an example of a Bitcoin Cash smart-contract which consumes data from the oracle service.

Oracles can be used for:

• Prediction markets
• trustless gambling
• Covenants

Oracles.cash was created by @cgcardona for the 2019 WyoHackathon

More info at https://oracle.bitcoin.com/

Price Data

/v1/price/details returns a data object with 4 properties.

• price: USD price in cents
• height: block height
• message is a byte sequence of 8 bytes encoded as a hex string. The first 4 bytes are the blockheight and the 2nd 4 bytes are USD price in cents. The price is fetched from Bitcoin.com's price index
• signature is the message signed by an ECPair.

curl -X GET "http://localhost:3000/v1/price/details" -H "accept: application/json"

{
  "price": 30350,
  "height": 601406,
  "message": "3e2d09008e760000",
  "signature": "304502210082180bc9cc4a4e41a5fe8b6c04d5c0d47d6a3174b3c0f3b7694550ad2bc72bbb02202250e01c018a760b30593ad9b71f1b6e0b0192c44183c4d38b0bdbc9f9edd3fd"
}

Smart contract

This contract forces HODLing until a certain price target has been reached A minimum block is provided to ensure that oracle price entries from before this block are disregarded i.e. when the BCH price was $1000 in the past, an oracle entry with the old block number and price can not be used. Instead, a message with a block number and price from after the minBlock needs to be passed. This contract serves as a simple example for checkDataSig-based contracts.

Credit to Rosco Khalis, creator of CashScript, for creating the HodlVault Cash Contract.

./src/routes/v1/contracts/hodl_vault.cash ./hodl_vault.ts

Fund the contract

First, take note of the following line in hold_vault.ts

const instance: Instance = HodlVault.new(
  bitbox.ECPair.toPublicKey(owner),
  bitbox.ECPair.toPublicKey(oracle.keypair),
  597000,
  30000
)

That is the line where you instantiate the contract. the 3rd arg is the blockheight and the 4th arg is the USD price in cents.

Those values will matter later when you want to spend the funds which are locked in this contract. You'll need to pass in a blockheight and price which are greater than what you pass in when you instantiate the contract.

Comment out the following lines in hold_vault.ts

// Produce new oracle message and signature
const oracleMessage: Buffer = oracle.createMessage(597000, 30000)
const oracleSignature: Buffer = oracle.signMessage(oracleMessage)

// Spend from the vault
const tx: TxnDetailsResult = await instance.functions
  .spend(new Sig(owner, 0x01), oracleSignature, oracleMessage)
  .send(instance.address, 1000)

Then run the script using ts-node

./node_modules/.bin/ts-node ./hodl_vault.ts
contract address: bchtest:pr6a369a5s3k5fqfnkhnnjw2a0rq6rkrkgvaqy7g7l
contract balance: 0

Notice it displays the contracts P2SH (pay-to-script-hash) address. Send some funds to that address where they will be locked.

Spend the contract

Now you're ready to spend the funds which are locked in the contract. To do that first uncomment out the lines which we commented out in the previous step:

// Produce new oracle message and signature
const oracleMessage: Buffer = oracle.createMessage(597000, 30000)
const oracleSignature: Buffer = oracle.signMessage(oracleMessage)

// Spend from the vault
const tx: TxnDetailsResult = await instance.functions
  .spend(new Sig(owner, 0x01), oracleSignature, oracleMessage)
  .send(instance.address, 1000)

Next update the following line to have a valid block height and BCH price

const oracleMessage: Buffer = oracle.createMessage(597000, 30000)

Keep in mind that the blockheight and price must be greater than what you passed in when you instantiated the contract.