1. Bitcoin: A Peer-to-Peer Electronic Cash Systemhttps://bitcoin.org/bitcoin.pdf
2. Ethereum: A secure decentralised generalised transaction ledger;Wood;Ethereum Proj. Yellow Pap.,2014
3. Ring Confidential Transactionshttp://ledger.pitt.edu/ojs/ledger/article/view/34
4. Pricing Via Processing or Combatting Junk Mail;Dwork,1992