Skip to content

Latest commit

 

History

History
236 lines (187 loc) · 7.59 KB

03_blockchain.md

File metadata and controls

236 lines (187 loc) · 7.59 KB
Raw

Blockchain

Blockchain! Blockchain! Blockchain!

Let's link the (crypto) blocks together into a chain of blocks, that is, blockchain, to revolutionize the world one block at a time.

Trivia Quiz: What's the unique id(entifier) of a block?

  • (A) (Secure) Hash
  • (B) Block Hash
  • (C) Digital (Crypto) Digest

A: All of the above :-). (Secure) hash == block hash == digital (crypto) digest.

Thus, add the (secure) hash of the prev(ious) block to the new block and the hash calculation e.g.:

Digest::SHA256.hexdigest( "#{nonce}#{prev}#{data}" )

Bingo! Blockchain! Blockchain! Blockchain! All together now:

require 'digest'
require 'pp'      ## pp = pretty print


class Block
  attr_reader :data
  attr_reader :prev   # prev(ious) (block) hash
  attr_reader :hash
  attr_reader :nonce  # number used once - lucky (mining) lottery number

  def initialize(data, prev)
    @data          = data
    @prev          = prev
    @nonce, @hash  = compute_hash_with_proof_of_work
  end

  def compute_hash_with_proof_of_work( difficulty='0000' )
    nonce = 0
    loop do
      hash = Digest::SHA256.hexdigest( "#{nonce}#{prev}#{data}" )
      if hash.start_with?( difficulty )
        return [nonce,hash]    ## bingo! proof of work if hash starts with leading zeros (00)
      else
        nonce += 1             ## keep trying (and trying and trying)
      end
    end # loop
  end # method compute_hash_with_proof_of_work

end # class Block

Note: For the first block, that is, the genesis block, there's no prev(ious) block. What (block) hash to use? Let's follow the classic bitcoin convention and lets use all zeros eg. 0000000000000000000000000000000000000000000000000000000000000000.

Genesis. A new blockchain is born!

b0 = Block.new( 'Hello, Cryptos!', '0000000000000000000000000000000000000000000000000000000000000000' )
#=> #<Block:0x4d11ce0
#       @data="Hello, Cryptos!",
#       @hash="000047954e7d5877b6dea6915c48e84579b5c64fb58d5b6488863c241f1ce2af",
#       @nonce=24287,
#       @prev="0000000000000000000000000000000000000000000000000000000000000000">

Let's mine (build) some more blocks linked (chained) together with crypto hashes:

b1 = Block.new( 'Hello, Cryptos! - Hello, Cryptos!',
                '000047954e7d5877b6dea6915c48e84579b5c64fb58d5b6488863c241f1ce2af' )
# -or-
b1 = Block.new( 'Hello, Cryptos! - Hello, Cryptos!', b0.hash )
#=> #<Block:0x4dce620
#      @data="Hello, Cryptos! - Hello, Cryptos!",
#      @hash="00002acb41e00fb252b8fedeed7d4a629dafb28517bcf6235b90367ee6f63a7f",
#      @nonce=191453,
#      @prev="000047954e7d5877b6dea6915c48e84579b5c64fb58d5b6488863c241f1ce2af">

b2 = Block.new( 'Your Name Here', b1.hash )
#=> #<Block:0x4d9d798
#       @data="Your Name Here",
#       @hash="0000d85423bc8d3ccda0e83ddd6e7e9d6a30f393b73705409b481be57eeaad37",
#       @nonce=109213,
#       @prev="00002acb41e00fb252b8fedeed7d4a629dafb28517bcf6235b90367ee6f63a7f">

b3 = Block.new( 'Data Data Data Data', b2.hash )
#=> #<Block:0x46cfc80
#       @data="Data Data Data Data",
#       @hash="000000c652265dcf44f0b18911435100f4677bdc468f8f1dd85910d581b3542d",
#       @nonce=129257,
#       @prev="0000d85423bc8d3ccda0e83ddd6e7e9d6a30f393b73705409b481be57eeaad37">

Let's store all blocks together (in an array):

blockchain = [b0, b1, b2, b3]

pp blockchain      ## pretty print (pp) blockchain

#=> [#<Block:0x4d010a8
#        @data="Hello, Cryptos!",
#        @hash="000047954e7d5877b6dea6915c48e84579b5c64fb58d5b6488863c241f1ce2af",
#        @nonce=24287,
#        @prev="0000000000000000000000000000000000000000000000000000000000000000">,
#    #<Block:0x4685388
#        @data="Hello, Cryptos! - Hello, Cryptos!",
#        @hash="00002acb41e00fb252b8fedeed7d4a629dafb28517bcf6235b90367ee6f63a7f",
#        @nonce=191453,
#        @prev="000047954e7d5877b6dea6915c48e84579b5c64fb58d5b6488863c241f1ce2af">,
#    #<Block:0x4d6d120
#        @data="Your Name Here",
#        @hash="0000d85423bc8d3ccda0e83ddd6e7e9d6a30f393b73705409b481be57eeaad37",
#        @nonce=109213,
#        @prev="00002acb41e00fb252b8fedeed7d4a629dafb28517bcf6235b90367ee6f63a7f">,
#    #<Block:0x469ec30
#        @data="Data Data Data Data",
#        @hash="000000c652265dcf44f0b18911435100f4677bdc468f8f1dd85910d581b3542d",
#        @nonce=129257,
#        @prev="0000d85423bc8d3ccda0e83ddd6e7e9d6a30f393b73705409b481be57eeaad37">]

Note: If you want to change the data in block b1, for examples, you have to change all the blocks on top (that is, b2 and b3) too and update their hashes too! With every block added breaking the chain gets harder and harder and harder (not to say practically impossible!). That's the magic of the blockchain - it's (almost) unbreakable if you have many shared / cloned copies. The data gets more secure with every block added (on top), ...

Blockchain Broken?

How do you know if anyone changed (broke) the (almost) unbreakable blockchain and changed some data in blocks? Let's run tests checking up on the chained / linked (crypto) hashes:

b0.prev == '0000000000000000000000000000000000000000000000000000000000000000'
#=> true
b1.prev == b0.hash
#=> true
b2.prev == b1.hash
#=> true
b3.prev == b2.hash
#=> true

All true, true, true, true. All in order? What if someone changes the data but keeps the original (now fake non-matching) hash? Let's run more tests checking up on the (crypto) hashes by recalculating (using nonce+prev+data) right on the spot plus checking up on the proof-of-work difficulty (hash must start with 0000):

## shortcut convenience helper
def sha256( data )
  Digest::SHA256.hexdigest( data )
end

b0.hash == sha256( "#{b0.nonce}#{b0.prev}#{b0.data}" )
# => true
b1.hash == sha256( "#{b1.nonce}#{b1.prev}#{b1.data}" )
# => true
b2.hash == sha256( "#{b2.nonce}#{b2.prev}#{b2.data}" )
# => true
b3.hash == sha256( "#{b3.nonce}#{b3.prev}#{b3.data}" )
# => true

b0.hash.start_with?( '0000' )
# => true
b1.hash.start_with?( '0000' )
# => true
b2.hash.start_with?( '0000' )
# => true
b3.hash.start_with?( '0000' )
# => true

All true, true, true, true, true, true, true, true. All in order? Yes. The blockchain is (almost) unbreakable.

Let's try to break the unbreakable. Let's change the block b1 from 'Hello, Cryptos!' to 'Hello, Koruptos!':

b1 = Block.new( 'Hello, Koruptos! - Hello, Koruptos!', b0.hash )
#=> #<Block:0x4daa9f8
#       @data="Hello, Koruptos! - Hello, Koruptos!",
#       @hash="00000c915e240a2b386fc86ef6170261a19292b9fdebebce049c621da1ab7e8f",
#       @nonce=27889,
#       @prev="000047954e7d5877b6dea6915c48e84579b5c64fb58d5b6488863c241f1ce2af">

Now if you check:

b0.prev == '0000000000000000000000000000000000000000000000000000000000000000'
#=> true
b1.prev == b0.hash
#=> true
b2.prev == b1.hash
#=> false
b3.prev == b2.hash
#=> true

Fail! False! No longer all true. The chain is now broken. The chained / linked (crypto) hashes

  • b1.hash => 00002acb41e00fb252b8fedeed7d4a629dafb28517bcf6235b90367ee6f63a7f
  • b2.prev => 00000c915e240a2b386fc86ef6170261a19292b9fdebebce049c621da1ab7e8f

do no longer match. The only way to get the chained / linked (crypto) hashes back in order to true, true, true, true is to rebuild (remine) all blocks on top.