Artur Skrzeta

Modeling Blockchain with Python

Intro

• Chain of blocks that contain information.


• Each block contains data, hash and hash of previous block.
  - data stored inside a block depends on type of blockchain
  - hash, as a fingerprint, is unique and identifies a block with all of its content - it's being calculated once block created
  - changing something inside the block causes the block's hash to change (that detects any atttempts of changes to block)
  - hash of the previous block actually creates a chain
  - having blocks chained in that way, it ensures security of the blockchain
  - changing one block would make all of the following blocks in the chain invalid because of invalid 'has of previous block' - changing one block way back in the chain it would affect all of the hashes of blocks going forward


• Additional security mechanism is the proof-of-work:
  - recalculating new hashes can be performed very fast so it's not enough to keep blockchain secure
  - proof-of-work mechanism slows down the creation of new blocks
  - f.e. for bitcoin proof-of-work consumes 10 minutes to add new block to the chain
  - because of proof-of-work, changes to one block would require recalculating the proof-of-work for all of the following block within the chain
  


• It's distributed which increases security level
  - is uses peer-to-peer network
  - when someone joins network he gets full copy of the blockchain - the node
  - if there is an attempt to change the block it will be rejected by the rest of the nodes in the network
  - the changes would be possible when affecting more than 50% of the network nodes at once which is very hard
  


• To make change to block you would need to change all of the blocks in the chain, recalculate the proof-of-work for each block and take control of min 50% of peer-to-peer network nodes. That sounds like impossible mission.


• Blockchain with security mechanizms stays stable and steady.