Zero-Conf Channels 零確認通道

標準通道開設流程：

時間線：
T0      T1             T2              T3
│       │              │               │
▼       ▼              ▼               ▼
開始    Funding TX     等待確認        通道可用
協商    廣播           (3-6 區塊)
        │              │               │
        └──────────────┴───────────────┘
              約 30-60 分鐘

────────────────────────────────────────────

零確認通道流程：

時間線：
T0      T1
│       │
▼       ▼
開始    Funding TX 廣播 + 通道立即可用!
協商
        │
        └─────> 立即可以發送/接收支付

優勢：從開始到可用只需幾秒鐘

Short Channel ID (SCID) Structure:

Standard SCID (after confirmation):
┌──────────────┬──────────────┬──────────────┐
│ Block Height │ TX Index     │ Output Index │
│ (3 bytes)    │ (3 bytes)    │ (2 bytes)    │
└──────────────┴──────────────┴──────────────┘
Example: 700000x1234x0

Zero-conf issue:
• Unconfirmed tx has no block height
• Cannot calculate real SCID

SCID Alias solution:
• Use temporary alias SCID
• Format: randomly generated 8-byte identifier
• Feature bit: option_scid_alias (bit 46/47)

After channel confirmation:
• Can still use alias to reference channel
• Can also use real SCID
• For private channels, alias hides block info

option_zeroconf negotiation:

Feature bit: option_zeroconf (bit 50/51)

Flow:
1. Both parties announce option_zeroconf in init message
2. Opener requests zero-conf in open_channel/open_channel2
3. Acceptor agrees in accept_channel/accept_channel2

Message structure changes:
open_channel2:
  ...
  channel_type:
    - option_zeroconf
    - option_scid_alias
    - option_anchors_zero_fee_htlc_tx
  ...

Conditions for accepting zero-conf:
• Acceptor trusts opener not to double-spend
• Usually only with known LSP or partners
• Can set node whitelist

LSP Instant Channel Opening:

1. User's first incoming payment
   ┌──────────┐         ┌──────────┐         ┌──────────┐
   │  Sender  │ ──────> │   LSP    │ ──────> │   User   │
   └──────────┘         └────┬─────┘         └──────────┘
                             │
                             │ User has no channel!
                             │ LSP opens zero-conf channel
                             ▼
   Process:
   1. LSP creates funding tx (LSP funds)
   2. LSP broadcasts funding tx
   3. Channel created immediately (zero-conf)
   4. Payment routed to user via new channel
   5. User receives payment instantly!

Security:
• LSP provides funding, won't double-spend itself
• User can trust the LSP
• Even if LSP double-spends, user only loses recent payment

2. JIT (Just-In-Time) Channels
   • Only open channel when needed
   • Saves block space
   • Improves user experience