bytes32 fingerprint = keccak256(channelId, nonce, balanceA, balanceB);
bytes32 signTypedDataFingerprint = keccak256(
    keccak256("bytes32 hash"),
    keccak256(fingerprint)
);
require(ECTools.isSignedBy(signTypedDataFingerprint, sigA, channel.agentA) == true);

async signTx ({ channelId, nonce, balanceA, balanceB }) {
  // fingerprint = keccak256(channelId, nonce, balanceA, balanceB)
  let hash = abi
    .soliditySHA3(
      ['bytes32', 'uint256', 'uint256', 'uint256'],
      [channelId, nonce, balanceA, balanceB]
    )
    .toString('hex')
  hash = `0x${hash}`
  console.log('hash: ', hash)

  const sig = await new Promise((resolve, reject) => {
    this.web3.currentProvider.sendAsync(
      {
        method: 'eth_signTypedData',
        params: [
          [
            {
              type: 'bytes32',
              name: 'hash',
              value: hash
            }
          ],
          this.web3.eth.accounts[0]
        ],
        from: this.web3.eth.accounts[0]
      },
      function (err, result) {
        if (err) reject(err)
        if (result.error) {
          reject(result.error.message)
        }
        resolve(result)
      }
    )
  })
  console.log('sig: ', sig)
  return sig
}