Blockchain: day 3

November 19, 2021

2 mins

Solidity course


start: 1hr 1min

stop: 1hr 31min


Welcome to blockchain

Signing transactions and private keys

  • Private key is only known to the holder, its used to sign transactions
  • Transactions can be verified with the public key
  • Your acount address is derived from a hash of your public key
  • Often when the prviate key is needed it will be required in hexidecimal format. Just prepend 0x to the start of it
  • Traditional apps are run on a centralised system, even if they are run on multiple servers, those servers are owned by the same people.
  • A blockchain is run on lots of independant nodes
  • A "node" is a single instance in a decentralized network
  • Anyone can join the network
  • Blockchain is resiliant. They are run by the network of nodes not a single entity.


  • Consensus is mechanism used to agree on the state of the blockchain.
  • proof-of-work alogrythm (mining) is a sybil resistance mechanism. This is a mechanism to protect against someone making a load of fake nodes to game the system
  • proof-of-work and proof-of-stake are both Sybil resistance mechanisms
  • Blocktime (time between blocks being published) can be changed by changing how difficult the problem is
  • Proof of work needs to be combined with a chain selection rule.
  • Chain selection algorithm helps to choose which is the correct/real chain to choose.
  • The "Nakomoto consensus". Basically this is the longest chain
  • Proof of work is a piece of the consensus protocol that bitcoin and etherium v1 use
  • Who gets paid?
  • In proof of work they are called miners
  • In proof of stake they are called validators
  • Proof of works uses lots of energy
  • Nodes compete against each other to complete the riddles so that they get the reward
  • Gas fees are paid by the user making the transaction


Sybil attack

  • bad actor creates loads of sudo anonymous accoutns to try and influence the blockchain
  • This is really trick

51% attack

  • Proof of stack nodes put up some collateral as a sybil resistance mechanism.
  • If they misbehve they loose there money
  • Nodes are randomly chosen to validate the transaction. This means there is no race and so it uses less electricity.
  • Layer 1: BAse layer blockchain implementation
  • Layer 2: Anything built on a layer 1
  • Shading and roll ups are solutions to scalability on the blockchain