Blockene is a blockchain system that enables high-throughput and large-scale participation while remaining lightweight enough to run on resource-constrained mobile devices like smartphones. It achieves this by having resource-constrained citizen nodes perform consensus voting through gossip with resource-heavy politician nodes that handle transaction execution and storage. The system was tested with 2000 citizen nodes achieving over 1000 transactions per second while using only megabytes of storage and data per day on citizen devices.

1. Blockene: A High-throughput Blockchain
Over Mobile Devices
Sambhav Satija and Apurv Mehra, Microsoft Research India; S
udheesh Singanamalla, University of Washington; Karan Grov
er, Muthian Sivathanu, Nishanth Chandran, Divya Gupta, and
Satya Lokam, Microsoft Research India
14th USENIX Symposium on Operating Systems Design and Implementation
November 4–6, 2020

2. Blockchain is fundamentally heavyweight
Storage cost
terabytes of replicated
storage in high throughput
blockchain (e.g., 1000TPS)
Ledger Ledger
Ledger Ledger
Network cost
45 GB/day of network
communication cost
Compute cost
intensive crypto

3. Blockchain can be lightweight?
Practically impossible !

4. Blockchain can be lightweight?
Existing solution: Offloads to resource-heavy node
Practically possible, but
not a true blockchain

5. Blockene: A (ultra) Lightweight Blockchain
Consensus made by resource-constrained node
Execution & storage by resource-heavy node

6. Blockene: A (ultra) Lightweight Blockchain
Consensus made by resource-constrained node
Execution & storage by resource-heavy node
Detect malicious behavior
(Audit)

7. ⚫ High performance: 1045 transactions / sec
• Good enough of real-world applications
⚫ Large-scale
• Millions of participants
⚫ Ultra-Lightweight: Need only a smartphone
• ~60MB/day data usage (cellular-data friendly)
• MBs of storage
• ~3% battery cost per day
Blockene

8. Contributions

9. No Incentive? A target use-case

10. No Incentive? A target use-case
Citizens want to audit
without any incentive

11. ⚫ Citizens
• Resource constrained (i.e., run on smartphones)
• Large-scale participation (millions)
• Run (committee-based) consensus without incentives
• 66% majority honest (2/3)
• Detect maliciousness of Politicians (80%) & Citizens (33%)
⚫ Politicians
• Resource powerful (i.e., run server)
• Small-scale participation (low hundreds)
• Only execute decisions taken by Citizens
• 80% of the politicians can be malicious
• Including collusions among themselves and 1/3 citizens
Blockene: Split-Trust Architecture

12. ⚫ Citizen’s attack vector
• Bribing attack on Citizens
• Sybil attack by Citizens
⚫ Policitian’s attack vector
• Staleness attack
• Split-View attack (i.e., fork)
• Drop attack
• Denial-of-Service attack
• Sybil attack
Threat Model

13. ⚫ Bribing attack on Citizens
• Politicians can offer bribes to sufficient number of
committee members
• Exclude this attack by two reasons:
• Carrier-grade NAT:
• IP address of Citizen not exposed
• Push notifications in smartphones:
• Blockene app on the Citizen will ignore any spurious traffic
⚫ Sybil attack by Citizens
• Blockene exploits TEE available in smartphones of
Citizens and ensures a smartphone can have at most
one identity on the blockchain
Threat Model: Citizen’s attack vector

14. ⚫ Staleness attack
• Return non-latest state
⚫ Split-View attack (i.e., fork)
• Respond with two different values to different subsets of
Citizens
⚫ Drop attack
• Ignore Citizen’s request
⚫ Sybil attack
• Assumes out-of-band registration mechanism (identity
known in real-world)
⚫ DoS attack
• Assumes all nodes employ standard DoS protection
Threat Model: Policitian’s attack vector

15. Blockene Architecture

16. ⚫ Citizen
• Run on a smartphone
• Network bandwidth: 1 MB/s
• Block size of 9MB, containing about 90k transactions
• 1 transaction: 100 bytes
⚫ Politician
• Network bandwidth of 40 MB/s
• 200 nodes
Design: System Configuration

17. ⚫ Using VRF to select a committee (inspired from Algorand)
⚫ Lightweighting Algorand
• In Algorand, each participant wake up every round whether
it is chosen in the committee
• However, Citizen on a mobile phone cannot afford to do
such frequent checks due to significant battery drain
--> Citizens wake up every 10 blocks
⚫ Probabilistic security guarantee
• Recommends 2000 of committee size, assuming 2/3
Citizens are honest
Design: Selecting Committee of Citizens
= 11010110111…000000
Last k bits are all zero,
→ Be a committee

18. ⚫ Citizen periodically verifies the structural integrity of the
blockchain to enforce that the chain of hashes
⚫ Track local state
• Each citizen locally remembers latest 10 blocks
⚫ Chained ID sub-blocks
• Records valid identity of Citizens
⚫ Incremental Validation
• Every 10 blocks, each Citizen queries a safe sample of
Politicians for the latest block number
• Checks signatures of committee of the latest block
Design: Fork-proof Structural Validation

19. ⚫ Citizens validates
• Signatures of the transaction
• Nonce to detect replay attacks
• Semantic correctness (e.g., double spending)
• Referenced values using Merkle path from leaf to root
• Citizens ask challenge path of Merkle tree
Design: Transaction Validation

20. Design: Block Proposal
Proposer
(by VRF)
Committee
Citizens
1. Pick a safe sample and send Tx to them
Politicians
Gossip
Tx
Tx
Tx
Tx
Tx
Update merkle tree

21. Design: Block Proposal
Proposer
(by VRF)
Committee
Citizens
2. Pick a safe sample and proposes a new block
Politicians
Gossip
2.1 Freezes the exact set of
transactions: tx_pool ( 2000 txes)
2.2 Generates a commitment with
signed hash of the tx_pool and block#
2.3 Return the commitment to Citizen
tx_pool

22. Design: Block Proposal
Proposer
(by VRF)
Committee
Citizens
3. Proposer uploads a new block only with commitment
so that other citizens can reconstruct that block by downl
oading the tx_pools
Politicians
Gossip

23. Design: Block Commit Protocol
Citizens
1. Committee members downloads tx_pools & commitment
Politicians
Gossip

24. Design: Block Commit Protocol
Citizens
2. Uploads a signed witness list with the commitments
Politicians
Gossip

25. Design: Block Commit Protocol
Citizens
3. Each proposer downloads all witness lists from a safe sample
and picks commitments with at least a threshold
Politicians
Gossip

26. Design: Block Commit Protocol
Citizens
4. Committee members run consensus on the commitments
with gossip through Politicians
Politicians
Gossip
(Byzantine Agreement)

27. Design: Block Commit Protocol
Citizens
5. Each committee member downloads challenge paths for all keys
on the agreed transactions & validates them
Politicians
Gossip

28. Design: Block Commit Protocol
Citizens
6. If validation is successful, each committee member creates
a block, computes the new Merkle root of the updated values
& uploads them with signature
Politicians
Gossip

29. Design: Block Commit Protocol
Citizens
7. The proposed block is committed when more than a threshold number
of signatures have accumulated for the block
Politicians
Gossip

30. ⚫ Citizen nodes
• Android app on SDK v23, 10k LoC
• Battery-optimized build and runs as a background app
• Multi-threaded event-driven model on top of EventBus to
parallelize and pipeline network and compute intensive
task
⚫ Politician nodes
• C++, 11K LoC
• State-machine based architecture
• C-Actor-Framework
Implementation

31. ⚫ 2000 Citizen nodes and 200 Politician nodes
⚫ Citizen nodes
• 1-core VMs on Azure with a Xeon E5-2673,
• 2GB of RAM,
• Spread across three geographic regions across WAN
• Runs an Android 7.1 image
• 1MB/s network upload and download
• 2000 committee size
⚫ Politician nodes
• 8-core Azure VMs with a Xeon E5-2673, 32 GB of RAM
• 40MB/s network bandwidth
Experimental Setup

32. Evaluation: TPS under varying malicious nodes
(Politician/Citizens)

33. Evaluation: Commit Latency

34. ⚫ Blockene enables a high-throughput lightweight
blockchain where members (with smartphone) perform
block validation and consensus
⚫ Blockene provide three conflicting properties
• Large scale of participation
• High transaction throughput
• Low resource usage at member nodes
Conclusion

35. Blockene is a lightweight version of Algorand
SOSP’17
Blockene
OSDI’20
Lightweight
Stake-based consensus
(proof-of-stake)
Voting-based consensus
(majority voting)
Gossip through all members Gossip through politicians