1. Majority is not Enough: Bitcoin Mining is Vulnerable
Ittay Eyal and Emin Gün Sirer
Department of Computer Science,
Cornell University
Presented By
Ovia Seshadri, CSE IITD

2. The original version of this paper was Published in Financial Cryptography and Data Security (FC 2014).
Lecture Notes in Computer Science 8437, Springer; chapter/ / _28
Laid foundations for the well known Selfish Mining Attack
Cited by 896 and counting
Gained popularity in all Financial markets and news

3. Preliminaries Blockchain, Bitcoin, PoW, Hashing Power, Mining, Pools
Forks
Longest chain Rule, Majority, 51% attack
Block Rewards, Difficulty

4. Discussion An Honest majority is an important requirement!!
Miners are independent and self motivated
Best strategy must be to play honest
A Blockchain must be fair! Incentive – compatibility
Are pools a problem??

5. Miner controls 25% he gets 1 block every 4 blocks

6. Paper Contributions Bitcoin Mining is not incentive Compatible
Incentive to form pools and strategy to benefit pools
Possibility of system collapse above a threshold
A possible solution to increase threshold.

8. Selfish Mining Selfish Mining outperforms honest mining
GOAL: Get more that fair share
HOW: Maintain secret blocks, publish judiciously
INTUITION: Risk some work, Others waste a lot more.

9. Attacker tries to create as long a
secret chain as possible
Publish secret branch just
before losing lead
(assuming no latency)

10. Also Publish when the lead is lost!! Intentional public fork - RACE
Risk - RACE
Also Publish when the lead is lost!! Intentional public fork - RACE

13. Markov Chain model

14. Fraction of Attacker’s hash power - α

15. System is partitioned at every arrival.
The system grows at the same rate left to right or right to left.
Pi – is the probability of being at ith state.

16. Where 0<=α<=1/2

19. Solution
Discussion
System Collapse – Even attackers are invested in the coin
Altruistic Agents – moral nodes
Naïve Lines of Defense – police infiltration into selfish pools
Imminent Danger

20. Thank You