1. Bitcoins Transaction Processing Yonatan Sompolinsky joint work with Aviv Zohar

2. Bitcoin hard to get easy to pass no authority, no money printing pseudonymous relatively secure ?high transaction volume decentralized cryptocurrency current protocol: conflict ghost protocol: in accord

3. Transactions in Bitcoin tx Bob Calvin ?irreversible tx

4. txs: block #81block #82 block #83 The Blockchain txs: ~ 10 min consistent grows in time kept locally at each node Time

5. A B2 B1 maintain one main chain only blocks discarded & txs cancelled Conflicting blockchains the longest chain rule delays => forks Time

6. Block tree vs Block chain 1 3 2 5 4 6 λ:= block creation rate = 6 per hour β:= growth rate of main chain = 4 per hour efficiency:= β/λ=4/6<1 Time delays => forks => inefficiency

7. Block size, Delay & Efficiency analysis of data provided to us by Decker and Wattenhofer λ = block creation rate β = growth rate of main chain 0.95 Block Propagation Time

8. Throughput (TPS) Transactions Processed per Second = (block size) X (growth rate of the main chain) 2000 1/600 TPS ~ 1736 TPS < 3.3 why?

9. Security - double spend attack tx Bob Calvin tx secret tx main chain publish !

10. Success of attack

11. Effect of increasing throughput efficiency security TPS delay

12. Security limitation on TPS attacker computational power (fraction) TPS Bitcoin today: secure but low throughput high TPS: more bandwidth needed secure TPS vulnerable TPS

13. Greedy Heaviest Observed Sub-Tree longest chain efficiency security

14. Greedy Heaviest Observed Sub-Tree B C1 A C2 C3 D1 D2 D3 E1 tx B tx main chain according to longest rule 10 4 5 1 1 1 2 6 main chain according to ghost Time

15. GHOST throughput no security constraint hardware constraints, e.g., network congestion, limit the feasible TPS 8.5-fold increase of current bandwidth can withstand TPS = 2000 in pipeline: improvement of ghost, same bandwidth more TPS … security high transaction volume

16. https://eprint.iacr.org/2013/881.pdf