CS 251 Blockchain and Cryptocurrency Technologies #

This course #

Consensus layer: public append-only data structure
- Persistence: can never remove added data
- Safety: all honest participants have same data
- Liveness: honest participants can add new transactions
- Open: anyone can add data (no authentication)
  - Not strict requirement
- How are blocks added to chains?
  - End users A, B, C with secret keys SKA, SKB, SKC
  - Transactions sent to miners (validators) that operate blockchains
  - One validator randomly selected to create the next block
  - Next block sent to distributed other validators, validator gets “block reward” for work done in creating the block
  - Other validators verify transactions, lead validator only gets reward if transaction is verified
- Why is consensus hard?
  - Good case: all copies are the same and valid
  - Problems:
    - Network delays: can affect transaction order
    - Network partition (severing connections between two parts of the world): how to merge lists after partition is resolved?
    - Crashes
    - Malicious participants
Blockchain computer
- Decentralized applications (DAPPs)
  - Run on blockchain: code and state written on chain
  - Accept transactions from users: state transitions recorded on chain
User-facing servers
- Cloud frontend that interact with DAPPs on change
- End-users issue transactions via these servers

See CS255 notes.