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PERUN: Virtual Payment Hubs over
Cryptocurrencies StefanDziembowski
LisaEckey
SebastianFaust
DanielMalinowski
Goal: Microtransactions
Blockchain Scalability
Problem:Blockchaintransactionsareslowandexpensive
TransactionFees
Alice Bob
SendtoBob
Cheap Fast Offline Secure 2
Smart Contracts
SmartContract
Storeandsendcoins
Executecode
StoredataLock Interact
Gas
Alice Bob
3 Guaranteedbytheunderlyingcryptocurrency
PERUN in a Nutshell
Newcryptographicprotocolthatallowsmicrotransactionsovercryptocurrencies
• Basedonsmartcontracts• InaHub-network
2Typesofpaymentchannels• Ledgerchannels:buildovertheblockchain• Virtualchannels:buildoverledgerchannels
Ledger Payment Channels
Virtual Payment Channels
Cheap Fast Offline Secure
Outline
o Motivation
o LedgerPaymentChannels
o VirtualPaymentChannels
o Security&Performance
o Summary&Outlook5
1. Create 2. Update 3. Close
(Ledger) Payment Channels*
Alice Bob
LockcA LockcBChannel Contract (cA + cB coins)
* Lightning,Spilman,Duplex,Sprites,Raiden,Counterfactual,L2….
6 1. Create 2. Update 3. Close
Off-chainchannelstate:sv=(xA,xB,v)
Alice Bob
cA cB
s1=(cA+5,cB-5,1)
s0=(cA,cB,0) s1=(cA+5,cB-5,1)
s0=(cA,cB,0)Cheap Fast Offline Secure
updates1
updates1
+5 -5
7
chanAB
(Ledger) Payment Channels
1. Create 2. Update 3. Close
(Ledger) Payment Channels
Alice Bob
…
Channel Contract
snisvalidifq xA+xB=cA+cBq AprovedbyAandB...Waitformessage
fromBob...
sn=(xA,xB,n) sm=(xA,xB,m)
8
Sendsn Sendsm
UnlockxA UnlockxBSelectmorerecentstate
forpayout
1. Create 2. Update 3. Close
Outline
o Motivation
o LedgerPaymentChannels
o VirtualPaymentChannels
o Security&Performance
o Summary&Outlook9
Hashed Time Locked Contracts (HTLC)*
Idea:Routeeverytransactionviaintermediary
chanIB
* J.Poon,T.Dryja:Thebitcoinlightningnetwork:Scalableoff-chaininstantpayments.(2016)
Alice Bob
Ingrid
Fee
chanAI
ZZ
IngridpaysAliceifBobpaysIngrid
Ingridpays
Bobif
AlicepaysIn
grid
10
PERUN Virtual Channels
chanIB
Alice
Ingrid
chanAIBob
Cheap Fast Offline Secure
11
chanAB
PERUN Virtual Channels
Alice Bob
cI-1
cA-1cB-1
cI-1
openvirtualchanAB
openvirtualchanAB
openvirtualchanAB
Ingrid
12
chanIBchanAI2
2chanIBchanAI
1. Create 2. Update 3. Close
PERUN Virtual Channels
Alice
Ingrid
cI-1
cA-1 cB-1
cI-1
22
chanIBchanAI
1 1
vs0=(1,1,0)
Bob
1. Create 2. Update 3. Close
sm=(cA-1,cI-1,m)
vs0=(1,1,0)
sn=(cI-1,cB-1,n)
2 0
updatevs1
vs1=(2,0,1) vs1=(2,0,1) 13
chanAB
PERUN Virtual Channels
Alice
Ingrid
Bob
cI-1
cA-1cB-1
cI-1
laststate:vsn laststate:vsm
14
chanIBchanAI
1. Create 2. Update 3. Close
22
PERUN Virtual Channels
Alice
Ingrid
Bob
cI-1
cA+1cB-1
cI+1
updatechanAI
updatechanIB
updatechanIB
22
chanIBchanAI
Ingrid stays financially neutral
cA+1cI+1
15
updatechanAI
1. Create 2. Update 3. Close
cA-1cI-1
Outline
o Motivation
o LedgerPaymentChannels
o VirtualPaymentChannels
o Security&Performance
o Summary&Outlook16
(Informal) PERUN Security
• Balanceneutralityforintermediary
• Consensusonchannelcreationandupdate
• GuaranteedbalancepayoutforAlice&Bob
• Guaranteedchannelclosing
ThismustholdevenifALLotherplayerscollude
Validity=t
2 2
17
PERUN Performance Virtual
Channel HTLC
Network Ledger
Channel
ChannelOpening
Update
Agreement
DisagreementClosing
on-chain off-chain/viaIngridoff-chain/direct
off-chain/viaIngrid
off-chain/direct
on-chain off-chain/viaIngrid
on-chain on-chain on-chain
12ct.
55ct.
50ct.
84ct.84ct.
Fee/Payment
Fee/Validity
18
Outline
o Motivation
o LedgerPaymentChannels
o VirtualPaymentChannels
o Security&Performance
o Summary&Outlook19
Summary
• Newformalismforpaymentchannels
• Virtualpaymentchannels• Canbeopenedandclosedoff-chain• Canbeupdatedwithoutintermediary
• Provablesecureprotocol• NewmodelofDLandSmartContracts• RigoroussecurityproofinUCmodel
Extensions
GeneralStateChannelNetworks
Multi-partyVirtualStateChannels
@CCS2018
@Eurocrypt20
19
Formoreinformationvisit:
www.perun.network
Thank you for your attention!
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