区块链长延时协议技术研究
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caused easily!
“bad” asynchronous networks, equipment failure,… malicious attacks
eclipse attacks [HKZG15], which allow an adversary to control 32 IP addresses to monopolize all connections to and from a target bitcoin node with 85% probability
Blockchain
Basic security requirement All the miners maintain the same record Achieve consensus in the permissionless setting
B1 B2 B3
B1 B2 B3
B1 B’2 B’3
Analysis of the Blockchain Protocol with Long Delays
区块链长延时协议技术研究
1
Nakamoto’s blockchain
Bitcoin Decentralized payment system
Ledger maintained by the public in a decentralized manner Attractive properties
Slowdown the generation of blocks Longest chain rule
H(h | " ? < %
5
Nakamoto’s blockchain
Common prefix
Chain growth
Chain quality
Security
Garay, Kiayias and Leonardos [GKL15] provide a rigorous analysis
4
Fra Baidu bibliotek
Nakamoto’s blockchain
Proof of work (PoW)
Integrity:More difficult for the adversary to modify the chain Synchronism:help the distributed miners to synchronize
Why consider the delay? 6
Blockchain protocol with delays
Bitcoin P2P network
Delays are inevitable
New block
The propagation delay in the network is the primary cause for blockchain forks [DW13]
Decentralization, Pseudonymity, Robustness …
Blockchain
Chain-structured ledger maintained by all the participants (miners)
2
Nakamoto’s blockchain
*: the number of miners +:the probability that a miner succeeds
in mining a block at a round
! silence ! silence
unique success Convergence opportunity
8
In the real world, long delays, say ∆ ≥ 1/np, could be
Block 1
h0 m1 r1
Block 2
h1 m2 r2
Bitcoin Backbone Protocol [GKL15] blockchain C=(!", ! $ , … , !&) block ! ( = (ℎ(,$, - ( , .( , ℎ() ℎ( = / ( ℎ ( , $ | | - ( | .( , s. t. ℎ( <D
permissionless anyone can join (or leave) the protocol execution
3
Nakamoto’s blockchain
Proof of work (PoW) Solve a “cryptographic puzzle”
H(h | - ? < 6
Decker and Wattenhofer
Information propagation in the bitcoin network (2013)
7
Blockchain protocol with delays
Results [PSS17]
• Chain growth: ( , - . ) / , w h e r e 2 ≈ *+
of blockchain protocol
Synchronous model
Pass, Seeman and shelat [PSS17] analyze the security in an
asynchronous network with a-priori bounded delay
Asynchronous model
, 0/1
• Consistency: 4 with probability 1 − *789(4)
•
Chain quality:1 − (1 + ; )
<=(,0/1) /
•Limitation: ! ≪ #(%/'() The
proof holds for a relatively small delay only
Eclipse attacks [HKZG15] 9
Blockchain protocol with delays
. Is the blockchain protocol based on POW still secure in the asynchronous network, where long delay, say Δ ≥1/np, is allowed?
“bad” asynchronous networks, equipment failure,… malicious attacks
eclipse attacks [HKZG15], which allow an adversary to control 32 IP addresses to monopolize all connections to and from a target bitcoin node with 85% probability
Blockchain
Basic security requirement All the miners maintain the same record Achieve consensus in the permissionless setting
B1 B2 B3
B1 B2 B3
B1 B’2 B’3
Analysis of the Blockchain Protocol with Long Delays
区块链长延时协议技术研究
1
Nakamoto’s blockchain
Bitcoin Decentralized payment system
Ledger maintained by the public in a decentralized manner Attractive properties
Slowdown the generation of blocks Longest chain rule
H(h | " ? < %
5
Nakamoto’s blockchain
Common prefix
Chain growth
Chain quality
Security
Garay, Kiayias and Leonardos [GKL15] provide a rigorous analysis
4
Fra Baidu bibliotek
Nakamoto’s blockchain
Proof of work (PoW)
Integrity:More difficult for the adversary to modify the chain Synchronism:help the distributed miners to synchronize
Why consider the delay? 6
Blockchain protocol with delays
Bitcoin P2P network
Delays are inevitable
New block
The propagation delay in the network is the primary cause for blockchain forks [DW13]
Decentralization, Pseudonymity, Robustness …
Blockchain
Chain-structured ledger maintained by all the participants (miners)
2
Nakamoto’s blockchain
*: the number of miners +:the probability that a miner succeeds
in mining a block at a round
! silence ! silence
unique success Convergence opportunity
8
In the real world, long delays, say ∆ ≥ 1/np, could be
Block 1
h0 m1 r1
Block 2
h1 m2 r2
Bitcoin Backbone Protocol [GKL15] blockchain C=(!", ! $ , … , !&) block ! ( = (ℎ(,$, - ( , .( , ℎ() ℎ( = / ( ℎ ( , $ | | - ( | .( , s. t. ℎ( <D
permissionless anyone can join (or leave) the protocol execution
3
Nakamoto’s blockchain
Proof of work (PoW) Solve a “cryptographic puzzle”
H(h | - ? < 6
Decker and Wattenhofer
Information propagation in the bitcoin network (2013)
7
Blockchain protocol with delays
Results [PSS17]
• Chain growth: ( , - . ) / , w h e r e 2 ≈ *+
of blockchain protocol
Synchronous model
Pass, Seeman and shelat [PSS17] analyze the security in an
asynchronous network with a-priori bounded delay
Asynchronous model
, 0/1
• Consistency: 4 with probability 1 − *789(4)
•
Chain quality:1 − (1 + ; )
<=(,0/1) /
•Limitation: ! ≪ #(%/'() The
proof holds for a relatively small delay only
Eclipse attacks [HKZG15] 9
Blockchain protocol with delays
. Is the blockchain protocol based on POW still secure in the asynchronous network, where long delay, say Δ ≥1/np, is allowed?