# BSV
BSV-ex is a general purpose library for building Bitcoin SV applications in Elixir. Under the hood, [Curvy](https://hexdocs.pm/curvy) is used for all `secp256k1` flavoured crypto, making BSV-ex the only 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`:
```elixir
def deps do
[
{:bsv, "~> 2.1"}
]
end
```
## Upgrading
Version `2.x` of this library is so significantly 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](https://github.com/moneybutton/bsv).
* `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 Crypto code unrelated to Bitcoin is no longer maintained.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:
```elixir
config :bsv,
network: :test # defaults to :main
```
## Usage
BSV-ex is a comprehensive Bitcoin library. Many examples can be found through [the documentation](https://hexdocs.pm/bsv). See the following for some quick-start examples:
### Keypairs, Addresses, BIP-32
Generate a new random keypair and derive its address.
```elixir
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.
```elixir
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.
```elixir
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.
```elixir
# 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.
```elixir
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
```
## License
BSV-ex is open source and released under the [Apache-2 License](https://github.com/libitx/bsv-elixir/blob/master/LICENSE).
© Copyright 2019-2021 Chronos Labs Ltd.
