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data consumers data producers company
(icons by parkjisun from noun project)
Distributed ledgers: how, why, and why not? Sarah Meiklejohn - - PowerPoint PPT Presentation
Distributed ledgers: how, why, and why not? Sarah Meiklejohn - - PowerPoint PPT Presentation
Distributed ledgers: how, why, and why not? Sarah Meiklejohn (University College London) company company data consumers data producers company company 2 (icons by parkjisun from noun project) data consumers data producers 3 (icons by
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data consumers data producers
(icons by parkjisun from noun project)
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10 usability 9 governance 8 comparisons 7 key management 6 agility 5 interoperability 4 scalability 3 cost-effectiveness 2 privacy 1 scalability top ten obstacles for blockchains
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1 scalability 10 usability 9 governance 8 comparisons 7 key management 6 agility 5 interoperability 4 scalability 3 cost-effectiveness 2 privacy
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Bitcoin / blockchains / distributed ledgers “mining”
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- ver 4 EH/s (4 × 1018 H/s) to achieve 7 tx/s!
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full state replication
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120 GB and (always) rising
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full state replication ↑ computational power ⇒ ↓ throughput
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monetary supply ledger
central distribute decentral decentral central central
transparent?
y y (or n) n
pseudonyms?
y y (or n) n
computation
high! low low RSCoin
RSCoin [DM NDSS’16]
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mintette mintette mintette mintette bank user mintettes already reach consensus before sending info to bank mintettes store info only within a given shard
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RSCoin consensus
mintette1 mintette1 user
1 2 tx:
✓
3 4
service mintette1
✓
1 2
1
mintette2 mintette2 mintette2
1 tx
✓ ✓
2
tx tx
simple adaptation of Two-Phase Commit (2PC)
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user
1 2 tx:
service
1 2
1
t r a n s a c t i o n s
mintette mintette mintette mintette mintette mintette mintette mintette mintette mintette mintette mintette mintette mintette mintette mintette mintette mintette
1 : 2 :
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mintette1 mintette1 user
1 2 tx:
mintette1
1
service
1 2
1
mintettes check for double spending… …using lists of unspent transaction outputs (utxo)
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mintette1 mintette1 user
1 2 tx:
✓
mintette1
✓
1
2
service
1 2
1
signed ‘yes’ vote
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mintette1 mintette1 user
1 2 tx:
✓
3
service mintette1
✓
1 2
1
mintette2 mintette2 mintette2
1 tx
✓ ✓
2
“bundle of evidence” contains ‘yes’ votes from majority of mintettes in shard mintettes check validity of bundle by checking for signatures from authorized mintettes…
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mintette1 mintette1 user
1 2 tx:
✓
3 4
service mintette1
✓
1 2
1
mintette2 mintette2 mintette2
1 tx
✓ ✓
2
tx tx
…and if satisfied they add transaction to be committed and send back receipt
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security properties
no double spending (if honest majority per shard) non-repudiation auditability (if mintettes log their behavior)
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consensus features
conceptually simple no broadcast mintettes communicate only with users no expensive hashing! scalable
↑ computational power ⇒ ↑ throughput
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T = set of txs generated per second Q = # mintettes per shard M = # mintettes
- comm. per mintette per sec =
∑tx∈T 2(mtx+1)Q
scales infinitely as more mintettes are added!
M consensus features
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each new mintette adds ≈ 75 tx/sec compared to Bitcoin’s 7
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mintette mintette mintette mintette bank user
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Elastico [LNZBGS CCS’16]
committee member consensus committee directory committee committee member committee member committee member run PBFT run PBFT
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Elastico [LNZBGS CCS’16]
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1 scalability 10 usability 9 governance 8 comparisons 7 key management 6 agility 5 interoperability 4 scalability 3 cost-effectiveness 2 privacy
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8 comparisons 1 scalability 10 usability 9 governance 7 key management 6 agility 5 interoperability 4 scalability 3 cost-effectiveness 2 privacy
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mintette mintette mintette mintette bank
RSCoin [DM NDSS’16]
user
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mintette mintette mintette mintette user
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user log server
log
log server
log
log server
log
log server
log
no unified log ⇒ no need for consensus can (retroactively) detect inconsistencies between logs
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system Log CheckEntry GenEventSet Inspect Gossip evidence log server
log
monitor
snap BE E
auditor snap CheckEvidence
transparency overlays [CM CCS’16]
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system Log GenEventSet GenEventSet log server
log
log server
log
log server
log
log server
log
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auditors (efficiently) determine if events are in the log
system Log CheckEntry GenEventSet (meaning |snap| ≪ |log|) auditor snap log server
log
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monitors (inefficiently) detect bad events in the log
system Log CheckEntry GenEventSet Inspect log server
log
auditor snap monitor
snap BE E
(meaning |E| ≈ |log|)
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auditors and monitors ensure consistent view of log
system Log CheckEntry GenEventSet Inspect Gossip evidence log server
log
monitor
snap BE E
auditor snap CheckEvidence (can output evidence of inconsistencies)
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security properties
consistency: log server can’t offer different views of log non-frameability: auditor and monitor can’t frame the log accountability: log server is held to its promises
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log server
log
monitor
snap BE E
auditor snap prover verifier ? ?
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log server
log
monitor
snap BE E
auditor snap prover verifier ? ?
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Log CheckEntry Inspect Gossip evidence log server
log
monitor
snap BE E
auditor snap CheckEvidence
Bitcoin
sender receiver miner blockchain
sender and receiver don’t need to store blockchain gives rise to hybrid system (≈RSCoin) with no mining
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Log CheckEntry Inspect Gossip evidence log server
log
monitor
snap BE E
auditor snap CheckEvidence
Certificate Transparency [LL13]
CA client website
bad certificate issuance is exposed ⇒ clients are less likely to accept bad certificates
(icon by parkjisun from noun project)
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Log CheckEntry id provider
log
auditor snap
CONIKS [MBBFF USENIX Sec’16]
client client
(icon by parkjisun from noun project)
Inspect
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Log CheckEntry ILS log validator
snap
ARPKI [BCKPSS CCS’13]
CA client website
(icon by parkjisun from noun project)
ILS log
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RSCoin
- paque
centralized transparent decentralized
what is this distance?
CONIKS ARPKI
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security properties
consistency non-frameability accountability no double spending non-repudiation auditability
⇔ ⇔ ⇔
privacy (of what)? privacy (of what)?
(transparency overlays) (RSCoin)
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RSCoin
- paque
centralized transparent decentralized
what is this distance? what security properties to look for?
CONIKS ARPKI
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8 comparisons 1 scalability 10 usability 9 governance 7 key management 6 agility 5 interoperability 4 scalability 3 cost-effectiveness 2 privacy
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