Blockchains

• Centralized Systems - a single person (party/node) controls who can read, write, and delete data. If the person dies or is dishonest, the system crashes

• Controlled-Access Distributed Systems - Nodes collectively control the system. If only few nodes are faulty, the system remains operational. Controlled participation means only authorized parties

• Open-Access Distributed Systems - anyone can participate, join or leave as they please

• A blockchain is a distributed database that satisfies a unique set of safety and liveness properties

• Distributed ledgers use a blockchain as one possible means of implementation.

  • Consistency: everyone sees the same history
  • Liveness: everyone can add new transactions

The Never-Ending-Book Parable

A Book of Data

• Anyone can be a scribe and produce a page
• New pages are produced indefinitely, as long as scribes are interested in doing so
• Each new page requires some effort to produce

The Importance of Consensus

• If multiple conflicting books exist, which one is the right one?
• The correct book to work on and refer to is the book with the most pages. If multiple books exist, just pick one at random

Assembling the Current Book

• Each page refers to the previous one

• Assembled by stringing together the longest sequence of pages

  

Rules for Adding Pages to (Extending) the Book

• The first scribe that discovers a page announces it to everyone else