Payment Channel Introduction
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Payment channels allow for off-chain transactions between two parties to enable trustless, high-volume, low-cost micropayments on the Bitcoin blockchain. The key aspects are: (1) a multi-signature wallet is set up and funded, (2) off-chain balance updates occur via time-locked transactions, (3) the final on-chain transaction closes the channel by broadcasting the final signed state. Hashed Timelock Contracts (HTLCs) extend this to enable payments across multiple channels by using hash preimages and timelocks to guarantee delivery or refunds. Bidirectional channels allow payments in both directions through commitment transactions signed by both parties.
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P2SH Redeem script: OP_2 [A's pubkey] [B's pubkey] OP_2 OP_CHECKMULTISIG](https://image.slidesharecdn.com/blockchain-171003120237/85/Payment-Channel-Introduction-10-320.jpg)
Payment Channel Introduction
- 1. Payment Channel Introduction 2017/10/03 blockchain.tokyo #1 @mosa_siru
- 2. @mosa_siru ( ) • • TV • Gunosy PO
- 3. @mosa_siru as engineer • • (DeNA) • (Gunosy) • (Gunosy)
- 4. 1. Payment channel 2. HTLCs
- 5. bitcoin micro payment • • (API ) • bitcoin 1 1 • 2017/10 150 • ( ) 10 • 3.47
- 6. • platform user • platform user
- 7. • platform BTC user 10 platform BTC • user platform • • platform
- 8. Payment channel • trustless ( ) • off-chain transaction( broadcast ) • off-chain
- 10. Multisig • ( ) of ( ) • 2 of 3 ( 3 2 • 1 of 2 ( ) • 2 of 2 ( ) P2SH Redeem script: OP_2 [A's pubkey] [B's pubkey] OP_2 OP_CHECKMULTISIG
- 11. CLTV(CheckLockTimeVerify) • BIP65 (Final) (OP_CHECKLOCKTIMEVERIFY) • unspentable ( BTC ) ※ nLockTime ( UTXO )
- 12. CSV(CheckSequenceVerify) • BIP112 (Final) (OP_CHECKSEQUENCEVERIFY) • ( ) unspentable BTC (3 ) • • CLTV CSV TimeLock
- 13. Payment Channel
- 14. Payment Channel • trustless(A, B ) • trustless 2 of 2 multisig(A, B ) • fund • off-chain (100 )
- 15. Payment Channel (1) A → B micro payment 1. A 2 of 2(multisig) fund 1BTC deposite broadcast 2. 1 txid 1 1BTC A refund transaction B CSV CLTV 3. 1 broadcast (channel open
- 16. Payment Channel (2) 4. deposite address A, B A B (off-chain) deposite address => B(0.01BTC), A(0.99BTC) deposite address => B(0.02BTC), A(0.98BTC) … 5. B broadcast (channel close)
- 18. Trustless (1) • B • refund transaction( ) broadcast 1 (CSV or CLTV) A • refund transaction B B fund deposite • B 1 A
- 19. Trustless (2) • A • B broadcast
- 20. Time Lock • refund CLTV( ) channel close (B ) CSV( ) • CLTV nLockTime( ) • deposite txid refund transaction segwit
- 22. HTLC
- 23. HTLC (Hashed TimeLock Contracts) • CSV, CTLV TimeLock HashLock • A => B => C • channel • B A • Lightning Network
- 24. HTLC (1) A => C micro payment 1. A => B , B => C payment channel 2. C A r hash(r) generate rOpen channel Open channel
- 25. HTLC (2) 3. A => B 1BTC tx1 (off-chain) IF 1. B r 2. 10 A (CLTV) ※refund . 4. Tx1 B => C 1BTC tx2 (off-chain) 1. C r 2. 5 B (CTLV) ← tx1 5. C r tx2 broadcast 1BTC r B tx1 broadcast 1BTC
- 26. HTLC (1) • trustless A => B => C • • tx2 tx1 refund B CSV CLTV tx2
- 27. HTLC (2) • Tx1 (A => B) tx2 segwit id • r pre-image
- 29. Payment Channel (Bidirectional) • payment channel • channel 2 fund • Time Lock, Hash Lock
- 30. Payment Channel (Bidirectional) 1. A, B 5BTC 2 of 2 fund opening transaction (off-chain) 2. A secret1, B secret2( ) hash
- 31. Payment Channel (Bidirectional) 3. A commitment transaction tx2 B (off-chain) 4. B commitment transaction tx1 A (off-chain) 100block secret opening transaction broadcast.
- 32. Payment Channel (Bidirectional) A => B 1BTC 5. tx3, tx4 secret 6. Secret 1, 2 hash tx1, tx2
- 33. transaction • A => B 1BTC A tx1, tx2 secret • A tx1 broadcast A 5BTC 100block B 5BTC secret1 10BTC
- 34. Payment Channel (Bidirectional) 7. transaction broadcast
- 37. @mosa_siru