Utilize signature module from ethereumjs-util

This replaces the use of the `sign` function in `ethereumjs-tx` with the
`ecsign` function from the `ethereumjs-util` package as requested in

We currently chose not to use EIP155 when generating the signatures. To
add this, we would need to know the chain ID for the Ethereum chain we are
signing the transaction. Activating EIP155 would make the generated
signatures replay-resistant on other Ethereum blockchains.

Author: Sword-Smith

app/sign.js

@@ -225,6 +225,7 @@ const handleSignEthereum = function(recoveryRequest, key, skipConfirm) {
  */
 const signEthTx = function(recoveryRequest, key, skipConfirm, isToken) {
   const EthTx = require('ethereumjs-tx');
+  const EthUtil = require('ethereumjs-util');
 
   const txHex = getTransactionHexFromRequest(recoveryRequest);
   const transaction = new EthTx(txHex);
@@ -242,10 +243,20 @@ const signEthTx = function(recoveryRequest, key, skipConfirm, isToken) {
     outputs[0].amount = outputs[0].amount.div(TEN.pow(decimals));
   }
 
-  key = promptForConfirmationAndKey(recoveryRequest, outputs, skipConfirm, key);
-  const signingKey = getBackupSigningKey(key, recoveryRequest.backupKey);
+  // When generating signatures, we don't currently use EIP155 but this could
+  // be activated if we wanted to. This would protect against replay attacks on other
+  // blockchains, such as Ethereum Classic. To activate the EIP155, we would have to
+  // know the chain ID of the Ethereum blockchains we are using as this value goes
+  // into the V field when using EIP155.
+  // cf. https://github.com/ethereum/EIPs/blob/master/EIPS/eip-155.md
+  const useEip155 = false;
 
-  transaction.sign(signingKey);
+  key = promptForConfirmationAndKey(recoveryRequest, outputs, skipConfirm, key);
+  const signingKey = Buffer.from(getBackupSigningKey(key, recoveryRequest.backupKey), "hex");
+  const signature = EthUtil.ecsign(transaction.hash(useEip155), signingKey, transaction.chainId);
+  transaction.v = signature.v; // Change this if activating EIP155
+  transaction.r = signature.r;
+  transaction.s = signature.s;
 
   return transaction.serialize().toString('hex');
 };