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ETH Zurich – Distributed Computing Group
Roger Wattenhofer
What Should We Learn From Nakamoto's Blockchain? Roger Wattenhofer - - PowerPoint PPT Presentation
What Should We Learn From Nakamoto's Blockchain? Roger Wattenhofer - - PowerPoint PPT Presentation
What Should We Learn From Nakamoto's Blockchain? Roger Wattenhofer ETH Zurich Distributed Computing Group Not Me! Blockchain: The Biggest Story in Distributed Systems Since the Internet?!? Cryptocurrencies Blockchain So What
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Blockchain: The Biggest Story in Distributed Systems Since …
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… the Internet?!?
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Cryptocurrencies
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Blockchain
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So What Is a Blockchain?
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Distributed Systems & Cryptography (1982) (1976)
Blockchain
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Blockchain
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Transaction
4 1 5
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Why the Hype?
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Let’s Dig Deeper!
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Persistence NIL Provable NIL Byzantine Fault-Tolerance
Blockchain
Immutable Crash
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Eventual Strong Speed
Blockchain
10 tx/s 10m tx/s Throughput Immediate 10k tx/s
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10 nodes 100 nodes Scalability
Blockchain
1000 nodes
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Energy Consumption
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Hashrate
- Energy/Hash ≈ 1.3 GW
13 109 GH/s 0.1 J/GH
Proof of Work
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Market / Energy Value ≈ 19 GW $20k/BTC 12.5 BTC $0.08/kWh 6/h
Economic Incentives
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Upper Bound 19 GW Reality? Well… Lower Bound 1,3 GW
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Maybe Around 5 GW
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10 nodes 100 nodes Scalability
Blockchain
Country Server Room Energy 1000 nodes Village
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What About Privacy?
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It’s Complicated.
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Operator Open PoW
Privacy
World
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The Seven Blockchain Dimensions
Persistence Speed Privacy
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The Seven Blockchain Dimensions
Persistence Speed Privacy
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Plenty of Research Dimensions
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piChain
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piChain: When a Blockchain Meets Paxos
= +
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piChain: When a Blockchain Meets Paxos
= + +
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Transaction
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Block
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depth parent
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medium quick slow
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quick slow medium time wait wait New Transaction: Reaction Time
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quick medium slow seen : either deeper or by State Transitions
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Self-Healing healthy
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Self-Healing
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committed
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time ack Truncated Paxos *and next propose
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Normal Paxos
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A Typical Example
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similar essentially same goals simple e.g., no explicit leader election silent no msg when no tx, no heartbeat scalable O(1) msgs per node per tx
piChain vs. Raft
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Persistence NIL Provable NIL Byzantine Fault-Tolerance
Blockchain
Immutable Crash
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Eventual Strong Speed
Blockchain
10 tx/s 10m tx/s Throughput Immediate 10k tx/s
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10 nodes 100 nodes Scalability
Blockchain
Country Server Room Energy 1000 nodes Village
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Fundamental Problem Every Node Sees Every Transaction
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Payment Networks
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Payment Network
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Hashed Timelocked Contract (HTLC)
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HTLC Example ( sells to )
- 1. Generate
random secret r
- 2. Send
hash(r) to
- 3. “Send
money if r is known at time 4”
- 4. “Send
money if r is known at time 3”
- 5. “Send
money if r is known at time 2”
- 6. “Send
money if r is known at time 1”
- 7. Use
secret r to access good
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Single Hop in Network
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Duplex Micropayment Channels (Example for Smart Contract)
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5 5
10
Duplex Micropayment Channel
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5 5
10
T=100
5 5
Duplex Micropayment Channel
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5 5
10
5 5
Blockchain
T=100
Duplex Micropayment Channel
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5 5
10
5 5
Blockchain
T=100
Duplex Micropayment Channel
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5 5
10
5 5
Blockchain
T=99
6
4
T=100
Duplex Micropayment Channel
[Decker,W,2015]
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5 5
10
5 5
Blockchain
T=99
6
4
T=100
Duplex Micropayment Channel
Channel must be renewed often?
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10
5 5
ΔT=99
6
4
ΔT=100
5 5
Blockchain
Duplex Micropayment Channel
Relative timelocks to keep channel alive forever! But only 99 transactions?
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ΔT=20 ΔT=19 ΔT=20 ΔT=19 ΔT=20 ΔT=19 ΔT=20 ΔT=19 ΔT=19 ΔT=20 ΔT=20 ΔT=19 ΔT=20 ΔT=19
Duplex Micropayment Channel
[Decker,W,2015]
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5 5
10
5 5
Blockchain
T=99
4 5
T=100
HTLC Revisited
1
can be spent by blue with secret r or by green after 3 days
- 4. “Send
money if r is known at time 3”
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5 5
10
5 5
Blockchain
T=99
4 5
T=100
HTLC Revisited
1 4 6
T=98
can be spent by blue with secret r or by green after 3 days
- 4. Send
money if r is known at time 3
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Solved?
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Still Too Many Channels!?
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… needs two transactions on blockchain … has locked-in funds by both parties
Each and Every Channel
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… needs two transactions on blockchain 200-800M channels only … has locked-in funds by both parties all my bitcoins are locked-in… sad.
Each and Every Channel
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Blockchain Space
so far 4 signatures for every channel
Blockchain Space ~ Number of Signatures
Settlement Funding
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Locked Funds
? ?
A node wants to make connections… Where does it lock the funds?
? ?
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5 5 5 5
T=99
6
4
T=100
5 5 5
T=100 T=99
... ... ... ... ... ... ... ... ... Channel funding layer Payment network layer
Multi Layer Networks
[Burchert, Decker, W 2017]
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5 5 5 5 5
ΔT=100 ΔT=99
... ... ... ... ... ... ... ... ...
Multi Layer Networks
...
[Burchert, Decker, W 2017]
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5 5 5 5 5
... ... ... ... ... ... ... ... ...
Multi Layer Networks
...
5 5 5 5 5
Settlement Transaction
ΔT=100 ΔT=99 [Burchert, Decker, W 2017]
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5 5 5 5 5
... ... ... ... ... ... ... ... ...
Multi Layer Networks
...
5 5 5 5 5
Settlement Transaction Actual channels never reach the blockchain!
ΔT=100 ΔT=99 [Burchert, Decker, W 2017]
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5 5 5 5 5 5 5 5 5 5
2 signatures per user independent of channels 4 signatures per channel
Blockchain Transactions
- ld
new
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Are We Finally Done?!?
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Yes, unless you have Bitcoin Cash…
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Persistence NIL Provable NIL Byzantine Fault-Tolerance
Blockchain
Immutable Crash
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Eventual Strong Speed
Blockchain
10 tx/s 10m tx/s Throughput Immediate 10k tx/s
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10 nodes 100 nodes Scalability
Blockchain
Country Server Room Energy 1000 nodes Village
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Summary
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Thank You!
Questions & Comments?
www.disco.ethz.ch
Thanks to my co-authors Conrad Burchert Christian Decker