README.md

Ruby Quiz - Challenge #2 - Calculate the Bitcoin Genesis Block Hash (SHA-256)

Let's calculate the classic bitcoin (crypto) block hash from scratch (zero). Let's start with the genesis block, that is block #0 with the unique block hash id 000000000019d6689c085ae165831e934ff763ae46a2a6c172b3f1b60a8ce26f.

Note: You can search and browse bitcoin blocks using (online) block explorers. Example:

• blockchain.info/block/000000000019d6689c085ae165831e934ff763ae46a2a6c172b3f1b60a8ce26f
• blockexplorer.com/block/000000000019d6689c085ae165831e934ff763ae46a2a6c172b3f1b60a8ce26f
• and others.

The classic bitcoin (crypto) block hash gets calculated from the 80-byte block header:

Field	Size (Bytes)	Comments
version	4 byte	Block version number
prev	32 byte	256-bit hash of the previous block header
merkleroot	32 byte	256-bit hash of all transactions in the block
time	4 bytes	Current timestamp as seconds since 1970-01-01 00:00
bits	4 bytes	Current difficulty target in compact binary format
nonce	4 bytes	32-bit number of the (mined) lucky lottery number used once

Note: 32 byte x 8 bit = 256 bit

Tip: Find out more about the Bitcoin Block hashing algorithm in the wiki page.

Using the data for the genesis block the setup is:

version    = 1
prev       = "0000000000000000000000000000000000000000000000000000000000000000"
merkleroot = "4a5e1e4baab89f3a32518a88c31bc87f618f76673e2cc77ab2127b7afdeda33b"
time       = 1231006505
bits       = "1d00ffff"
nonce      = 2083236893

The challenge: Code a calculate method that returns the Bitcoin hash. Start from scratch or, yes, use any library / gem you can find.

def calculate( version, prev, merkleroot, time, bits, nonce )
  # ...
end

To qualify for solving the code challenge / puzzle you must pass the test:

require 'minitest/autorun'


class RubyQuizTest < MiniTest::Test

  def test_calculate

    hash = "000000000019d6689c085ae165831e934ff763ae46a2a6c172b3f1b60a8ce26f"

    version    = 1
    prev       = "0000000000000000000000000000000000000000000000000000000000000000"
    merkleroot = "4a5e1e4baab89f3a32518a88c31bc87f618f76673e2cc77ab2127b7afdeda33b"
    time       = 1231006505
    bits       = "1d00ffff"
    nonce      = 2083236893
    
    assert_equal hash, calculate( version, prev, merkleroot, time, bits, nonce )

  end # method test_calculate
end # class RubyQuizTest

Post your code snippets on the "official" Ruby Quiz Channel, that is, the ruby-talk mailing list.

Happy hacking and crypto mining with Ruby.