Table of Contents


double spend
attach where the given set of coins is spent in more than one transaction

Solution to double-spending

  • P2P network
  • Network timestamps transactions by hashing them into an ongoing chain of hash-based proof-of-work
  • Forms a record that cannot be changed without redoing the proof-of-work
  • Longest chain not only serves as proof of the sequence of events witnessed, but proof that i came from the largest pool of CPU power
  • Thus, as long as pool of majority of CPU power is controlled by nodes that are not cooperating to attack the network, they'll generate the longest chain and outpace attackers


  • Electronic coin defined as a chain of digital signatures
  • Each owner transfers the coin to the next by digitally signing a hash of the previous transaction and the public key of the next owner, adding those to the end of the coin