signing-methods.md

Signing a transaction

The OMG Network childchain uses eth_signTypedData as described in EIP-712

This means that a web3 provider (e.g. Metamask) can do the signing.

Creating and signing with eth_signTypedData

The steps involved in creating and signing a transaction are as follows:

1. Create the transaction body by specifying inputs, outputs and optional metadata.
2. Convert the transaction body into typedDataformat.
3. Call eth_signTypedData to sign it. Note that you must JSON.stringify() the typed data.
4. Assemble the signatures and the transaction body into an RLP encoded format.
5. Submit the transaction to the child chain.

    // create the transaction body
    const txBody = transaction.createTransactionBody(fromAddress, fromUtxos, toAddress, toAmount, currency)

    // Get the transaction typed data
    const typedData = transaction.getTypedData(txBody, verificationContract)

    // Sign the typed data
    const signatures = await new Promise((resolve, reject) => {
      web3.currentProvider.sendAsync(
        {
          method: 'eth_signTypedData_v3',
          params: [signer, JSON.stringify(typedData)],
          from: signer
        },
        (err, result) => {
          if (err) {
            reject(err)
          } else if (result.error) {
            reject(result.error.message)
          } else {
            resolve(result.result)
          }
        }
      )
    })

    // Build the signed transaction
    const signedTx = childchain.buildSignedTransaction(typedData, signatures)

    // Submit transaction
    const tx = await childchain.submitTransaction(signedTx)

Creating and signing without eth_signTypedData

If you want to manage your private keys yourself, you don't have to use eth_signTypedData. You must create a hash of the typed data and sign that using ecsign. There is a convience function provided to do this: childchain.signTransaction(typedData, privateKeys) . Or you can do it manually, similar to the above:

1. Create the transaction body by specifying inputs, outputs and optional metadata.
2. Convert the transaction body into typedDataformat.
3. Call transaction.getToSignHash(typedData) to get the hash to sign
4. Sign it using elliptic curve signing (e.g. ecsign)
5. Assemble the signatures and the transaction body into an RLP encoded format.
6. Submit the transaction to the child chain.

    // create the transaction body
    const txBody = transaction.createTransactionBody(fromAddress, fromUtxos, toAddress, toAmount, currency)

    // Get the transaction typed data
    const typedData = transaction.getTypedData(txBody, verificationContract)

    // Get the hash to sign
    const toSign = transaction.getToSignHash(typedData)

    // Sign the hashed data (once for each input spent)
    const privateKeys = [...the private keys of the spent inputs...]
    const signatures = privateKeys.map(key => ecsign(toSign, key))

    // Build the signed transaction
    const signedTx = childchain.buildSignedTransaction(typedData, signatures)

    // Submit transaction
    const tx = await childchain.submitTransaction(signedTx)