Get smart. In this article, we continue our series about Smart Contracts that build on Ethereum’s blockchain backbone, with a focus on deploying and verifying the Smart Contract we wrote previously.

Smart Contracts are the new way to verify anything before you (or your customers or even other smart contracts) make a transaction. It’s just one way that businesses have been using Ethereum in commercial projects - and one of the most useful.

The Ethereum Smart Contracts that we talk about today live on the Ethereum blockchain in an Ethereum-specific binary format (Ethereum Virtual Machine or EVM bytecode), although there are other options in the blockchain cosmos as it starts to bubble over. In order to build trust between your Ethereum-based Smart Contract and its users it’s good idea to verify it (meaning all source code will be available to read). This can be done on the Etherscan or EthTools websites that display transactions, token transfers, and source code for each Smart Contract. You can also search contract, transaction, etc. by its hash.

However before the contract can be verified in needs to be placed on the EVM first. Following on from our second article, developing a sound Smart Contract, let’s deploy it to the EVM and then verify it. Sound good? Let’s go!

Deploying a Smart Contract

Before deploying to the Ethereum network you need to have an Ethereum client installed and configured. The client needs to sync the Ethereum blockchain, which can be both time and storage consuming - how much have you got? To deploy a Smart Contract as soon as possible we will use Infura - a 3rd party service that us allows to run applications on an EVM without setting up the client locally.

Let’s start by visiting the Infura website to create a new account. Since Infura does not manage your private keys for security reasons, we will need the truffle-hdwallet-provider library, to sign transactions.

Before adding the provider, let’s clean up our smart contract code [Link] a little:

  1. First, remove all contracts from our contracts/ directory except CustomerSupport.sol and Migrations.sol.
  2. Remove tests for previously removed contracts from the test/ directory
  3. Update migrations/2_deploy_contracts.js to exclude previously removed contracts - it should look like the example below:
var CustomerSupport = artifacts.require("./CustomerSupport.sol");

module.exports = function(deployer) {

Now let’s install truffle-hdwallet-provider:

npm install -D truffle-hdwallet-provider

We will use the Ropsten test network. The same steps apply for the main network, but with Ropsten you can test the whole process without spending any ETH (yet!).

We will use dotenv for storing mnemonics and credentials to Infura in our application. Let’s install the library first:

npm install -D dotenv

and then modify truffle.js file to include truffle-hdwallet-provider:

// trufle.js

var HDWalletProvider = require("truffle-hdwallet-provider");
var mnemonic = process.env.ETH_MNEMONIC;
var accessToken = process.env.INFURA_ACCESS_TOKEN;

module.exports = {
  networks: {
    development: {
      host: "localhost",
      port: 8545,
      network_id: "*" // Match any network id
    ropsten: {
      provider: HDWalletProvider(mnemonic, '' + accessToken, 0),
      network_id: 3,
      gas: 4712388

The last argument given to the HDWalletProvider function (0 in out example here) is the account number that should be used - in this case it’s the first account (here where accounts are indexed starting from 0).

We also provide a Gas limit for deploying the contract so we don’t accidentally blow out our budget with a bug - 4712388 is the default value for truffle.

Now let’s go to and create a new wallet on the Ropsten network. Then, sign in (this is important, as requesting Ether does not work for anonymous users) and visit to request some ETH so you can perform deployment. Remember, of course, that on the main network you would need to transfer real ETH though!

Now you can create a .env file in the root of the project with your mnemonic and Infura access token:


Now we are ready to compile the project and deploy to the Ropsten network:

truffle compile
truffle migrate --reset --network ropsten

You should see an output similar to the one below:

$ truffle migrate --reset --network ropsten
Using network 'ropsten'.

Running migration: 1_initial_migration.js
  Deploying Migrations...
  ... 0x4f41e26b2356e7eb2e68349017c69749af65b143d6cf65163e17fc30cae168ef
  Migrations: 0xc76f9c3231fa43dbc5601cf1d3fb9d457b05e3e2
Saving successful migration to network...
  ... 0xe17dbe7a52e869545386435d347cca776a9fadf013d0e15636594a3684695351
Saving artifacts...
Running migration: 2_deploy_contracts.js
  Deploying CustomerSupport...
  ... 0xe7930c1d96e05d40b9758aa5560f798861fa62c9a23a4f52f8edcc445fa1978e
  CustomerSupport: 0x67aedb5967b4446f708d72316d51724ab88d463e
Saving successful migration to network...
  ... 0x35fa15d0414f57e6feb0f56b0b412dc2ac0e46430e22f626e2fa867bf43575ed
Saving artifacts...

Now if you go to the ETH Tools website and paste the CustomerSupport address (0xe7930c1d96e05d40b9758aa5560f798861fa62c9a23a4f52f8edcc445fa1978e in our case) into the search input you will see your newly deployed contract:

If you switch to the Source code tab you will see:

We do not have the source code for this contract. If you are the contract author, consider verifying your contract such that other users can verify that your contract does what they expect it to.

Let’s change that and get verified!

Verifying a Smart Contract

We will use the Etherscan page for verifying our smart contract - since we came across a problem when attempting to verify with the ETH tools page on the Ropsten test network. For the main network, the ETH tools page works perfectly for verification.

Let’s go to the Etherscan website and search our contract by its address and then click on the Contract code tab:

Now click Verify and publish link and fill all fields:

To get our Solidity compiler version:

  1. Check where truffle is installed (which truffle)
  2. In the same directory, there should be the solcjs binary
  3. Run solcjs --version

Once you are done, click on the Verify and Publish button.

Now your contract should be correctly verified:

If you go to the contract page again, you should be able to read the source code:

You will also see a new tab for reading the current state of the contract:

Unfortunately, any contract verified on Etherscan is not automatically verified on EthTools, but for the purposes of this tutorial Etherscan is enough.

Interacting with your Smart Contract

Since our contract is deployed and verified, let’s try to interact with it. Let’s add some people so we can rotate them.

Let’s launch the truffle console on the ropsten network:

truffle console --network ropsten

Then add some people to the pool:

truffle(ropsten)> var contract;
truffle(ropsten)> CustomerSupport.deployed().then(function(instance) { contract = instance; });
truffle(ropsten)> var people = ['Alice', 'Bob'].map(function(p) { return web3.toHex(p); });
truffle(ropsten)> contract.addPeople(people);

and check the current person:

truffle(ropsten)> var person;
truffle(ropsten)> contract.getPerson().then(function(result) { person = result; });
truffle(ropsten)> person
truffle(ropsten)> web3.toUtf8(person);

If you refresh the Read Smart Contract tab on the Etherscan you will see the same result:

Let’s try to switch the person a couple of times to see if our contract is working correctly:

truffle(ropsten)> contract.switchPerson();
truffle(ropsten)> contract.getPerson().then(function(result) { person = result; });
truffle(ropsten)> person
truffle(ropsten)> web3.toUtf8(person);
truffle(ropsten)> contract.switchPerson();
truffle(ropsten)> contract.switchPerson();
truffle(ropsten)> contract.getPerson().then(function(result) { person = result; });
truffle(ropsten)> web3.toUtf8(person);

As you can see, it correctly rotates people through the customer support role. Those changes are reflected on Etherscan, as well as the EthTools pages:

Ethereum is a powerful technology for running Smart Contracts - which may be arbitrary programs and not involving cryptocurrency at all, save for the fees required to run them over the Ethereum network.

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