Dr. Elaine Shi presents at Consensus 2019 and describes the ThunderCore Blockchain approach to consensus. She explains the Thunderella Protocol and the move to Pala and going open source.

1. Elaine Shi
Joint work with Hubert Chan and Rafael Pass
@Thunder Research
Consensus Protocols for
ThunderCore’s Mainnet

2. State-machine replication
(a.k.a. blockchain, consensus)

3. State-machine replication
(a.k.a. blockchain, consensus)
Consistency:
honest nodes agree on log
Liveness:
TXs are incorporated soon

4. Challenges in large-scale consensus
Incentives
and
economicsScalability,
Scalability,
Scalability
!
Rethink
mathematical
modeling

5. Ethereum Transaction Fees

6. ThunderCore v1:
The Thunderella Paradigm
This Talk
ThunderCore v2:
Fast-path Accelerator Rotation

8. Proposer proposes block
(seq, )

9. Vote

10. Confirm onupon ¾ n votes

11. Confirm on upon ⅔ n votes¾ n votes: notarization

12. VoteHonest nodes vote uniquely at each seq #

13. ¾ n
“X”
¾ n
“Y”
Must intersect at an honest node
Assume: < ½ n corrupt

14. ¾ n
“X”
¾ n
“Y”
Must intersect at an honest node
quorum quorum
Thus =

15. Consistency
Liveness
Honest majority
• ¾ honest
• honest
Liveness

16. Consistency
Liveness
Honest majority
Liveness
How to achieve liveness w/ honest maj?

17. How to achieve liveness w/ honest maj?

18. Vote
Slow chain
Thunderella: fall back to slow chain to
switch proposer
Slow chain
Fast path
Consistency+liveness
under honest majority

19. Vote
Slow chain
Thunderella: fall back to slow chain to
switch proposer
Decentralization
Performance

20. Fallback
Detect fast-path failure

21. Post periodic to slowchain
Notarized hash
of fast path log

22. k blocks withoutddd
k blocks

23. Need: agree on log before fallback completes

24. Post notarized, uncheckpointedTXs to slowchain

25. Consistency
+ liveness
Liveness
Honest majority
• ¾ honest
• honest
Fast
“Optimistic Responsiveness”

26. Recap: Thunderella in 2 sentences
Use slowchain
for fallback
Single round of
voting
When things go badWhen things are good

27. Proposer switch takes ~10min
Lessons Learned from
Implementing Thunderella

28. ● Agile proposer rotation on fast path
● A full-fledged consensus protocol
Pili/Pala: ThunderCore’s
new fast-path consensus

29. 1 3 4 5 6 7 8
Every epoch:
● Proposer proposes a block extending
freshest notarized chain
● Vote if proposal is “nice”
● A block with majority votes is notarized
Finalization:
● 6 consecutive at the end, chop off 5

30. Optimistic
Responsiveness
Best-possible
partition
tolerance
https://eprint.iacr.org/2018/981
https://eprint.iacr.org/2018/980
https://eprint.iacr.org/2019/179

31. Do we still need a slowchain?
● Decentralized monitoring of fast path
● Reconciliation under extraordinary
circumstances
e.g., entire committee corrupt

32. Pili/Pala Consensus
Open Source Release:
github.com/thundercore/pala
May / 2019
By Chia-Hao Lo and Thunder Research

33. Thank you!elaine@thundercore.com
elaine@cs.cornell.edu