Eth

A simple library to build and sign Ethereum transactions. Allows separation of key and node management. Sign transactions and handle keys anywhere you can run ruby, broadcast transactions through any node.

Installation

Add this line to your application's Gemfile:

gem 'eth'

And then execute:

$ bundle

Or install it yourself as:

$ gem install eth

Usage

First of all, require this gem:

require 'eth'

Keys

Create a new public/private key and get its address:

key = Eth::Key.new
key.private_hex
key.public_hex
key.address # EIP55 checksummed address

Import an existing key:

old_key = Eth::Key.new priv: private_key

Or decrypt an encrypted key:

decrypted_key = Eth::Key.decrypt File.read('./some/path.json'), 'p455w0rD'

You can also encrypt your keys for use with other ethereum libraries:

encrypted_key_info = Eth::Key.encrypt key, 'p455w0rD'

How to make a trasaction?

Let's take an example of sending ETH to another address:

Step1. Build a transaction from scratch:

tx = Eth::Tx.new({

  # 0x00 or something else
  data: "0x00",

  # 21000 for sending eth, and 50_000 or more for sending erc-20 tokens.
  gas_limit: 21_000,

  # assume current fast price is 50 gwei
  gas_price: (50 * 1e9).to_i,

  # you must get the correct nonce for the "from address", otherwise
  # the signed-tx will NOT be broadcasted
  # you can query the nonce from interface such as infura's `eth_getTransactionCount`
  nonce: 0,

  # this is where the crypto will be sent to
  to: "0x3Ae7a18407B17037B2ECC4901c1b77Db9836888",

  # let us send 0.12 ETH
  value: (BigDecimal("0.12") * 1e18).to_i
})

Or decode an encoded raw transaction:

tx = Eth::Tx.decode hex

Step2. Then sign the transaction with your private key:

# step 2.1 get the private key of the "from address"
from_address_json_file = './from_address_json'
from_address_password = 'p455w0rD'
the_private_key = Eth::Key.decrypt File.read(from_address_json_file), from_address_password

# step 2.2 sign the tx with private key

tx.sign the_private_key

Step3. Get the raw transaction( signed transaction) with:

# will return a hex value with length 200+, depends on `data` parameter
tx.hex

# e.g.  =>  0xf86c82039585174876e800825208943ae7a18407b17037b2ecc4901c1b77db98367cda866d23ad5f80008026a085b81f23b7e80c65f6e8d97f2c6482c0cc7d660fc538f566c47c22e57c841726a07351fe455188b160c726d3032d03ddcdf1929716bb1c5aa06274fdf2830b73ba

Step4. broadcast it through any Ethereum node, or third-party services ( like infura )

curl https://mainnet.infura.io/v3/<YOUR-PROJECT-ID>
  -X POST
  -H "Content-Type: application/json"
  -d '{
        "jsonrpc":"2.0",
        "method":"eth_sendRawTransaction",
        "params":[
          "0xf86c82039585174876e800825208943ae7a18407b17037b2ecc4901c1b77db98367cda866d23ad5f80008026a085b81f23b7e80c65f6e8d97f2c6482c0cc7d660fc538f566c47c22e57c841726a07351fe455188b160c726d3032d03ddcdf1929716bb1c5aa06274fdf2830b73ba"
        ],
        "id":1
      }'

you will get result like:

{
  "jsonrpc":"2.0",
  "id":1,
  "result":"0x371c92a5815a734c6cd4c6e890e4b9216aa9eeee482b6a8279bea1bdeebc0d2d"
}

Or, just get the TXID with tx.hash.

Utils

Validate an EIP55 checksummed address:

Eth::Utils.valid_address? address

Or add a checksum to an existing address:

Eth::Utils.format_address "0x4bc787699093f11316e819b5692be04a712c4e69" # => "0x4bc787699093f11316e819B5692be04A712C4E69"

Personal Signatures

You can recover public keys and generate web3/metamask-compatible signatures:

# Generate signature
key.personal_sign('hello world')

# Recover signature
message = 'test'
signature = '0x3eb24bd327df8c2b614c3f652ec86efe13aa721daf203820241c44861a26d37f2bffc6e03e68fc4c3d8d967054c9cb230ed34339b12ef89d512b42ae5bf8c2ae1c'
Eth::Key.personal_recover(message, signature) # => 043e5b33f0080491e21f9f5f7566de59a08faabf53edbc3c32aaacc438552b25fdde531f8d1053ced090e9879cbf2b0d1c054e4b25941dab9254d2070f39418afc

Configure

In order to prevent replay attacks, you must specify which Ethereum chain your transactions are created for. See EIP 155 for more detail.

Eth.configure do |config|
  config.chain_id = 1 # nil by default, meaning valid on any chain
end

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/se3000/ethereum-tx. Tests are encouraged.

Tests

First install the Ethereum common tests:

git submodule update --init

Then run the associated tests:

rspec

License

The gem is available as open source under the terms of the MIT License.

TODO

• Better test suite.
• Expose API for HD keys.
• Support signing with libsecp256k1.