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README.md
solution.rb
test.rb

README.md

Ruby Quiz - Challenge #5 -Crypto Mining - Find the Winning Lucky Number - Nonce (=Number used ONCE) for the Proof-of-Work (PoW) Hash (SHA-256)

Let's find the the winning lucky lumber, that is, nonce (=Number used ONCE) for the proof-of-work (PoW) hash using SHA-256.


Aside: What's a (Crypto) Hash?

Classic Bitcoin uses the SHA256 hash algorithm. Let's try

require 'digest'

Digest::SHA256.hexdigest( 'Hello, Cryptos!' )

resulting in

#=> "33eedea60b0662c66c289ceba71863a864cf84b00e10002ca1069bf58f9362d5"

Try some more

Digest::SHA256.hexdigest( 'Hello, Cryptos! - Hello, Cryptos! - Hello, Cryptos!' )
#=> "c4b5e2b9685062ecca5d0f6f6ba605b3f99eafed3a3729d2ae1ccaa2b440b1cc"
Digest::SHA256.hexdigest( 'Your Name Here' )
#=> "39459289c09c33a7b516bef926c1873c6ecd2e6db09218b065d7465b6736f801"
Digest::SHA256.hexdigest( 'Data Data Data Data' )
#=> "a7bbfc531b2ecf641b9abcd7ad8e50267e1c873e5a396d1919f504973090565a"

Note: The resulting hash is always 256-bit in size or 64 hex(adecimal) chars (0-9,a-f) in length even if the input is less than 256-bit or much bigger than 256-bit.

Trivia Quiz: What's SHA256?

  • (A) Still Hacking Anyway
  • (B) Secure Hash Algorithm
  • (C) Sweet Home Austria
  • (D) Super High Aperture

B: SHA256 == Secure Hash Algorithms 256 Bits

SHA256 is a (secure) hashing algorithm designed by the National Security Agency (NSA) of the United States of America (USA).

Find out more @ Secure Hash Algorithms (SHA) @ Wikipedia.


The challenge: Code a compute_nonce method that passes the RubyQuizTest :-), that is, the hash for the nonce plus the data must start with four leading zeros (0000), that is, the "hard-coded" proof-of-work difficulty in the test:

hash = Digest::SHA256.hexdigest( "#{nonce}#{data}" )
## e.g. hash = "000000000019d6689c085ae165831e934ff763ae46a2a6c172b3f1b60a8ce26f"
assert hash.start_with?( "0000" )

Note: data is a (random) string e.g. "Hello, Crypto! The epoch time is now >1541927781<." and compute_nonce is expected to return the nonce (=Number used ONCE) as an integer number e.g. 26762 or 68419 etc.

def compute_nonce( data )
  # ...
end

Start from scratch or, yes, use any library / gem you can find.

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

require 'minitest/autorun'
require 'digest'

class RubyQuizTest < MiniTest::Test

  def test_hash_with_proof_of_work
    data  = "Hello, Crypto! The epoch time is now >#{Time.now.to_i}<."

    nonce = compute_nonce( data )
    hash = Digest::SHA256.hexdigest( "#{nonce}#{data}" )

    ## difficulty '0000' - four leading zeros (minimum) in hash
    assert_equal '0000', hash[0..3]
    assert hash.start_with?( '0000' )
  end # method hash_with_proof_of_work
end # class RubyQuizTest

Note: The test data for compute_nonce is "random", that is, always changes with every test run (e.g. includes Epoch time that is, seconds since January 1st, 1970).


Aside: What's the mining / proof-of-work difficulty? What's 0000?

In classic bitcoin you have to compute a hash that starts with leading zeros (00). The more leading zeros the harder (more difficult) to compute. Let's keep it easy to compute and let's start with two leading zeros (00), that is, 16^2 = 256 possibilities (^1,2). Three leading zeros (000) would be 16^3 = 4 096 possibilities and four zeros (0000) would be 16^4 = 65 536 and so on.

(1): 16 possibilities because it's a hex or hexadecimal or base 16 number, that is, 0 1 2 3 4 5 6 7 8 9 a (10) b (11) c (12) d (13) e (14) f (15).

(2): A random secure hash algorithm needs on average 256 tries (might be lets say 305 tries, for example, because it's NOT a perfect statistic distribution of possibilities).


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

Happy crypto mining and hashing with Ruby.