09 - Consensus

Wooclap

• Which of the following units is in use for Bitcoin payments?

  • Satoshi

• In Bitcoin the block (mining) reward

  • WRONG is halved every 105.000 transactions
  • is right-shifted every 210.000

• Transaction fee is

  • the difference between input and output

  • input is always higher than output

• An account address is

  • a b58 encoding of pk hash with checksum and version

PoW and hash

• PoW: solve a hard puzzle
  • this hard puzzle it is made by a nonce + hash + difficulty
  • you must find a value (nonce), a random value that if found must leads to a number beginning with {difficulty}rest_of_the_hash
• how can we optimize finding a good nonce?
  • we can’t store the results that starts with 00000 for example if diff=5 because the block header changes everytime
  • … but we can if we use a divide et impera approach
    • by splitting workload on blocks
• retarget is the action to keep the difficulty more of than equal distributed by blocks, by changing the difficulty once every two weeks (it should takes 20160 minutes)
• ASICS are computers without disks, just memory to evaluates these kind of calculations. They are way less inexpensive for this reason. They need computational power.
• Stale blocks are created when two miners found the solution at the same time
  • longest chains are confirmed
  • if they have the same chains, then who arrives before

---