03 - Tokens, revisions


  • Description:: revisions on general concepts, tokens!


  • double spending let users spend twice a currency
  • the ledger is ordered: transactions are sequentially stored
  • PoW in Bitcoin forces node to prove computational effort to publish new blocks


  • the minimum transaction to activate pieces of code is 1
  • The blockchain is NOT a database: it doesn’t store every single account, it only stores transactions


  • tokens are not cryptofuel, nor anything conceptually new, after all!
    • it is like flying miles
  • private vs public
  • permission means private? NO
  • permissionless means private? NO

The different kinds of web

  • web 1.0 is just client-server architecture
    • I ask things, I receive things
  • web 2.0 always client-server but both of them perform requests and responses
  • web 3.0 the front is always the same, the backend has interesting features (like smart contracts)

Do i need blockchain?

  • not everything, not for everywhere


  1. Birch model → no
    1. steem → social media for example, if I get enough upvotes I get token, that I convert in cryptos that I can convert in money
  2. …



  • graphs are structures consisting of
    • nodes
    • arcs connecting nodes
      • directed graphs has directed arcs → we always assume graphs to be directed, unless specified otherwise
  • two nodes are adjacent if at least an arc exists that is incident on them
  • a node is a successor of another node if an arc exists that is directed from the former to the latter
  • a path is a walk such that arcs are never traversed twice
  • a cycle is a loop (first node = last node)

Unicycle graphs: chain

Bits nibbles and boring stuff

  • nibble is a sequence of 4 bits
  • byte is a sequence of 8 bits


hashing is a function that associates k to values.

Token vs crypto

  • crypto is the euro
  • token is the bubbles, flowers, whatever

We can resell tokens in terms of money. I can buy some flowers coins in euros

The blockchain IS NOT a software, is NOT a computer, is NOT a software system

This is why different blockchains exist.

General definitions

  • ledger is a collation of transactions
  • mining nodes are the subset of nodes that maintain the blockchain by publishing new blocks
  • transaction are added to the blockchain when a mining node publishes a block
  • a block collates transactions
    • transactions are stored and sorted in block
  • validity is ensured by checking that
    • input accounts have signed the transaction
    • input accounts have sufficient funds on their account
    • the block timestamp (needs deep revision)
  • the other mining nodes WILL NOT accept a block if it contains any invalid transactions!