hd_wallet.rb

require 'money-tree'
require 'digest'

#
# Every key in the HD wallet is derived from this root seed
# If you have a backup of this root seed, you can re-create the entire wallet.
# The root seed is mostly represented by a “mnemonic word sequence”
# to make it easier for people to store.
#
# Use can generate master private key by using libbitcoin explore:
#   - Set configuration file path for libbitcoin explore
#     export BX_CONFIG="/usr/local/etc/libbitcoin/testnet.cfg" to .bash_profile or .zshrc
#   - $ bx seed | bx hd-new
#   - @master_node = MoneyTree::Node.from_bip32(master_private_key)

# Or getting seed EC-HEX 64 hexadecimal digits
seed = Digest::SHA256.digest('happy sad love password haha hihi').unpack("H*")[0]
puts seed

# Import the seed for creating a new master node.
@master = MoneyTree::Master.new seed_hex: seed

p @master.to_serialized_address(:private) # DEPRECATED.
p @master.to_bip32(:private) # new

# xprv9s21ZrQH143K37WQTsCNcUjyLv4Qmz8G8Q4R3817euzJ7iEuiA8HUpYut6VtCKEQpiTywzhEKnJbhSdE9sUfbvqqDdgtNBC7PGMQAxf524p

# generate the m/0
@node = @master.node_for_path "m/0"

# generate the m/0 extended public key
p @node.to_serialized_address # old
p @node.to_bip32 # new

# generate the m/0 extended private key
p @node.to_serialized_address :private
# xprv9tvWjMnzKSw4RLufcHyQqjpsLXm8thZ33WthMFrabLcWZnmHC3xGokAEzgX8dTSKgX5KtJJsKwL8R96dBcMm2JsrnJjLnJ5YVmiAvDKR98J

# show the private key of m/0 as a WIF
p @node.private_key.to_wif
# Ky1jAmxVjXSXiHSdbE2NWKxzwCrQpZCZmcFv3c4kM3Xi1ad9Rd4G

# show the bitcoin address of M/0
p @node.to_address
# 1NsLs3trs7Y5aHjuLysXCVSovx7EUs8j6g

# generate m/0/1'/2
@node = @master.node_for_path "m/0/1'/2"
p @node.private_key.to_wif
p @node.to_address
# L4rxY47cbMM7exZ3adKXB4STPoLKMktmQZRwM84dU45bBiAvUXzM
# 1P2ioDZfrAeLB7CdkN9ho7pFBJQmESJkBC

# Bitcoin addresses can be generated by a public wallet key.
# but  private keys for spending bitcoins can only be generated using a private wallet key.

@node = @master.node_for_path("M/0/3") # or "m/0/3.pub" or "M/0/3.pub"...these are equivalent

p @node.to_bip32
# xpub6BXtqq512LSJtV843RSHoxkJevNk8AwFZQR4WLvr751vSneePouH4Gt2bPPGU6QdzvqYPKc8ed2KW6KWk8aaZhZ28R8ydUpFWW7HrminPwK

@node.to_serialized_address(:private)
# raises MoneyTree::Node::PrivatePublicMismatch error

# Now the “extended public key” can be installed on a web server
# and can generate bitcoin addresses as much as we want.
# The web server will not have any private keys that would be vulnerable to theft.
# Without HD wallets, the only way to do this is generating a plenty of addresses on a secure server
# and then load them on the web server.

# BIP0044 Multi-Account Hierarchy for Deterministic Wallets
# https://github.com/bitcoin/bips/blob/master/bip-0044.mediawiki#path-levels
# m / 44' / coin_type' / account' / change / address_index