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Altcoins

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Lecture on alternate designs for cryptocurrency

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Altcoins

  1. 1. Altcoins: Alternate Designs for Cryptocurrency CS4501 Fall 2015 David Evans and Samee Zahur University of Virginia
  2. 2. Elevator Pitch: Today • Blockchain Voting, Sugat Poudel, Austin J. Varshneya, Xhama Vyas • Bitcoin at Point of Sale, Elizabeth Kukla • Vending on Dark Net Markets, Collin Berman • Distributed Bitcoin Mixing with Interest, Carter Hall, Reid Bixler • Analyzing the Feasibility of a Donation Accountability System in Bitcoin, Kienan Adams
  3. 3. What’s wrong with it? • Confirmations are slow • Not completely anonymous • Not quite decentralized • Volatile price
  4. 4. Alternate designs • Litecoin: different proof of work • Ripple: no proof of work • Ethereum: distributed programs
  5. 5. coinmarketcap.com
  6. 6. Litecoin • Faster confirmations: 2.5 minutes per block on average • Proof of work: scrypt • Less valuable
  7. 7. • http://www.cryptocoincharts.info www.cryptocoincharts.info
  8. 8. Ripple Faster transactions by eliminating proof of work
  9. 9. “Rippling” Consensus
  10. 10. Byzantine Generals Problem All generals propose either “attack” or “retreat” as the next step. They all must reach consensus. Some generals might be corrupted
  11. 11. Byzantine Limit No unconditionally secure algorithm exists if 3𝑓 ≥ 𝑛
  12. 12. Ripple Uses a variation of “Fast Byzantine Paxos”, which can tolerate 𝑓 ≤ 𝑛−1 5 Assumes a “well connected” graph.
  13. 13. Algorithm 1. Each server makes its own “candidate list” 2. They check validity 3. Vote on which transactions to keep 4. Any transaction with too few votes are discarded Repeat Finally, transactions over 80% vote among neighbors are kept
  14. 14. Bitcoin vs Ripple
  15. 15. Bitcoin vs Ripple No proof of work • Anybody can join, more decentralized • Anybody can claim to be many people • Extremely fast: transactions confirmed in a few seconds
  16. 16. Deployment
  17. 17. coinmarketcap.com
  18. 18. Ethereum • Proof of work hash: Ethash (custom) • Mean block mining period: 12 seconds • Block reward: … complicated … • Scripting language: Turing complete
  19. 19. cryptorps.com
  20. 20. “Smart Contracts” Careful of security pitfalls!
  21. 21. Gas!
  22. 22. Transaction • Recipient • Gas price • Gas limit • Value • Signature
  23. 23. Mining Reward •A static block reward for the 'winning' block, consisting of exactly 5.0 Ether •All of the gas expended within the block […]. •An extra reward for including 1/32 Uncles as part of the block
  24. 24. Contracts Snippets of code floating around in the network. They can send messages/money/gas to each other. Each transaction triggers at least one message. Contracts have their own: • Account balance • Stack • Memory (integer-indexed) • Storage (key-value)
  25. 25. Common Pitfalls
  26. 26. Common Pitfalls • Everything is public • Race conditions • Limited stack
  27. 27. Bitcoin the ultimate • There are ways to enrich it • Make it faster • More decentralized
  28. 28. The end: elevator pitches
  29. 29. Elevator Pitch: Today • Blockchain Voting, Sugat Poudel, Austin J. Varshneya, Xhama Vyas • Bitcoin at Point of Sale, Elizabeth Kukla • Vending on Dark Net Markets, Collin Berman • Distributed Bitcoin Mixing with Interest, Carter Hall, Reid Bixler • Analyzing the Feasibility of a Donation Accountability System in Bitcoin, Kienan Adams

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