BSV-ex is a general purpose library for building Bitcoin SV applications in Elixir. Under the hood, Curvy is used for all secp256k1 flavoured crypto, making BSV-ex the first pure Elixir Bitcoin library.

Features

Currently supported features:

• Keypair generation and address encoding and decoding
• BIP-39 mnemonic phrase generation and BIP-32 hierarchical deterministic keys
• Script and smart contract builder with built in Script simulator
• Transaction builder, signing and verification
• Block and block header parsing and serialization
• Merkle proof parsing, serialization and verification
• Bitcoin Signed Messages and ECIES encryption (Electrum compatible)

Installation

The package can be installed by adding bsv to your list of dependencies in mix.exs:

def deps do
  [
    {:bsv, "~> 2.1.0"}
  ]
end

Upgrading

Version 2.x of this library is so signifcantly different to version 0.x that we skipped an entire version. This is a rewrite from top to bottom, with an entirely new API, and makes no attempt to maintain backwards compatibility.

If upgrading from a previous version then be prepared to update your code where it interfaces with this library. If this library is depended on by other third party dependencies, then check each dependency and make sure it has been upgraded to support version 2.x.

Main changes:

• Many modules have been renamed to follow the conventions established in Money Button's bsv JavaScript library.
• from_binary/2 and to_binary/2 functions replace the old parse/2 and serialize/2 functions.
• The old Crypto namespace and modules have been removed. Crypto code unrelated to Bitcoin is no longer maintained. Hash functions can be found in the BSV.Hash module, and ECDSA functions are provided by Curvy.
• An entirely new script and smart contract building API has been created.

Configuration

Optionally, BSV can be configured for testnet network by editing your application's configuration:

config :bsv,
  network: :test  # defaults to :main

Usage

BSV-ex is a comprehensive Bitcoin library. Many examples can be found through the documentation. See the following for some quick-start examples:

Keypairs, Addresses, BIP-32

Generate a new random keypair and derive its address.

iex> keypair = BSV.KeyPair.new()
%BSV.KeyPair{
  privkey: %BSV.PrivKey{
    compressed: true,
    d: <<119, 134, 104, 227, 196, 255, 3, 163, 39, 9, 0, 43, 84, 137, 55, 218, 146, 182, 246, 3, 18, 64, 159, 108, 46, 24, 108, 111, 239, 180, 74, 161>>
  },
  pubkey: %BSV.PubKey{
    compressed: true,
    point: %Curvy.Point{
      x: 80675204119348790085831157628459085855227400073327708725575496785606354176436,
      y: 9270420727654506759611377999115473532064051910093243567168505762017618809348
    }
  }
}

iex> address = BSV.Address.from_pubkey(keypair.pubkey)
iex> BSV.Address.to_string(address)
"19D5DoRKchdZbsP3fXYhopbFDdCJCPaLjr"

Generate a BIP-32 HD wallet, derive and child and its address.

iex> mnemonic = BSV.Mnemonic.new()
"taste canvas eternal brain rent cement fat dilemma duty fame floor defy"

iex> seed = BSV.Mnemonic.to_seed(mnemonic)
iex> extkey = BSV.ExtKey.from_seed!(seed)
%BSV.ExtKey{
  chain_code: <<110, 26, 215, 117, 61, 123, 141, 33, 144, 225, 219, 244, 190, 61, 102, 123, 48, 131, 110, 209, 3, 193, 247, 57, 46, 72, 196, 13, 33, 189, 61, 6>>,
  child_index: 0,
  depth: 0,
  fingerprint: <<0, 0, 0, 0>>,
  privkey: %BSV.PrivKey{
    compressed: true,
    d: <<177, 226, 248, 91, 203, 59, 219, 9, 27, 117, 171, 67, 62, 138, 86, 122, 9, 215, 241, 4, 118, 97, 110, 174, 141, 2, 86, 116, 186, 32, 155, 133>>
  },
  pubkey: %BSV.PubKey{
    compressed: true,
    point: %Curvy.Point{
      x: 13957581247370416663735268664956755789623055115850818561656783044351458532461,
      y: 13811705978617564383043442008879108616838570537839984416253146804416417872149
    }
  },
  version: <<4, 136, 173, 228>>
}

# Derive child key and address
iex> child = BSV.ExtKey.derive(extkey, "m/0/1")
iex> address = BSV.Address.from_pubkey(child.pubkey)
iex> BSV.Address.to_string(address)
"1Cax2dCtapJZtwzYXCdLuTkZ1egG8JSugA"

Building transactions

The TxBuilder module provides a simple declarative way to build any type of transaction.

iex> alias BSV.Contract.{P2PKH, OpReturn}

iex> utxo = BSV.UTXO.from_params(utxo_params)
iex> builder = %BSV.TxBuilder{
...>   inputs: [
...>     P2PKH.unlock(utxo, %{keypair: keypair})
...>   ],
...>   outputs: [
...>     P2PKH.lock(10000, %{address: address}),
...>     OpReturn.lock(0, %{data: ["hello", "world"]})
...>   ]
...> }

iex> tx = BSV.TxBuilder.to_tx(builder)
iex> rawtx = BSV.Tx.to_binary(tx, encoding: :hex)
"0100000001121a9ac1e0..."

Creating custom contracts

The BSV.Contract module provides a way to define a locking script and unlocking script in a pure Elixir function.

# Define a module that implements the `Contract` behaviour
defmodule P2PKH do
  use BSV.Contract

  def locking_script(ctx, %{address: address}) do
    ctx
    |> op_dup
    |> op_hash160
    |> push(address.pubkey_hash)
    |> op_equalverify
    |> op_checksig
  end

  def unlocking_script(ctx, %{keypair: keypair}) do
    ctx
    |> sig(keypair.privkey)
    |> push(BSV.PubKey.to_binary(keypair.pubkey))
  end
end

Contracts can be tested using the built-in simulator.

iex> keypair = BSV.KeyPair.new()
iex> lock_params = %{address: BSV.Address.from_pubkey(keypair.pubkey)}
iex> unlock_params = %{keypair: keypair}
iex> {:ok, vm} = BSV.Contract.simulate(P2PKH, lock_params, unlock_params)
iex> BSV.VM.valid?(vm)
true