Neutrino 輕客戶端

Lightning Node Requirements

Full Node Mode:
• Storage: ~600 GB (and growing)
• Initial sync: hours to days
• Memory: at least 2-4 GB
• Network: continuous block downloads

Problems:
• Cannot run on mobile
• Cannot run on low-end devices
• High barrier to entry

Neutrino Light Client:
• Storage: ~100 MB (filters) + channel data
• Initial sync: minutes
• Memory: few hundred MB
• Network: on-demand downloads

Advantages:
• Runs on mobile
• Fast startup
• Maintains non-custodial nature

BIP 157/158 How It Works

Block Filter:
• Each block generates a small filter (~20KB)
• Filters use Golomb-Rice encoding compression
• Contains all output scripts and input outpoints in the block
• Filter corresponds to block height
• Filters are deterministically generated
• Any full node can generate identical filters

Light Client Flow:
1. Download block headers (80 bytes each)
2. Download corresponding block filters
3. Query filters with local addresses/scripts
4. If filter matches, download full block
5. Verify relevant transactions in block

Privacy Advantages (vs SPV/Bloom):

Bloom Filter (old method):
• Client tells server which addresses it cares about
• Server knows client's addresses
• Serious privacy leak

Compact Block Filter (Neutrino):
• Client downloads all filters
• Local queries, server doesn't know what client cares about
• Good privacy protection

Lightning Node Using Neutrino

Events to Monitor:
1. Channel funding transaction confirmation
   - Monitor if funding_txid enters a block

2. Channel close transactions
   - Monitor commitment or closing transactions

3. HTLC on-chain settlement
   - Monitor HTLC-Success/Timeout transactions

4. Counterparty fraud detection
   - Monitor if old commitment transactions are published

5. Penalty transaction confirmation
   - Ensure penalty transaction succeeds

Workflow:
1. Lightning node starts
2. Neutrino syncs block headers and filters
3. Query scripts related to channels
4. Download full block when match is found
5. Verify transactions and update channel state
6. Continue monitoring new blocks

LND Neutrino 配置：

lnd.conf：
[Bitcoin]
bitcoin.active=true
bitcoin.mainnet=true

# 使用 Neutrino 模式
bitcoin.node=neutrino

[Neutrino]
# 連接的 Neutrino 服務節點
neutrino.addpeer=btcd-mainnet.lightning.computer
neutrino.addpeer=mainnet1-btcd.zaphq.io
neutrino.addpeer=mainnet2-btcd.zaphq.io

# 費率估算來源
neutrino.feeurl=https://nodes.lightning.computer/fees/v1/btc-fee-estimates.json

# 同步模式
neutrino.validatechannels=true

啟動命令：
lnd --bitcoin.node=neutrino

查看同步狀態：
lncli getinfo
# recovery_mode: false
# synced_to_chain: true
# synced_to_graph: true

Neutrino-Enabled Lightning Wallets

Mobile Wallets:

Blixt Wallet
• Platform: Android, iOS
• Type: Full LND node + Neutrino
• Feature: True non-custodial mobile Lightning wallet
• Initial sync: ~5-10 minutes

Breez
• Platform: Android, iOS
• Type: Neutrino backend
• Feature: User-friendly interface

Zeus
• Platform: Android, iOS
• Type: Supports built-in LND + Neutrino
• Feature: Can also connect to remote nodes

Desktop Apps:

Zap Desktop
• Optional Neutrino mode
• Fast startup without full node

Neutrino Limitations

Functional Limitations:
1. Cannot verify all transactions
   - Can only verify transactions related to yourself

2. Historical transaction queries
   - Need to download and scan old blocks
   - Wallet recovery may be slower

3. Fee estimation
   - Requires external sources
   - Full nodes can estimate locally

4. Network dependency
   - Requires connection to Neutrino service nodes
   - Node availability affects wallet functionality

Trade-off Considerations:

Use Neutrino when:
• Mobile devices
• Limited storage space
• Need fast startup
• Managing small amounts

Use Full Node when:
• Large amounts
• Running routing node
• Maximum security requirements
• Supporting Bitcoin network